Ecology and Management of Breeding Waterfowl [1 ed.] 9780816684083, 9780816620012

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Ecology and Management of Breeding Waterfowl

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Ecology and Management of Breeding Waterfowl Bruce D. J. Batt, Alan D. Afton, Michael G. Anderson, C. Davison Ankney, Douglas H. Johnson, John A. Kadlec, and Gary L. Krapu, editors

University of Minnesota Press Minneapolis and London

Copyright 1992 by the Regents of the University of Minnesota The North American Wildlife Foundation and Richard A. N. Bonnycastle provided assistance in the publication of this volume, for which the University of Minnesota Press is grateful. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Published by the University of Minnesota Press 2037 University Avenue Southeast, Minneapolis MN 55414 Printed in the United States of America on acid-free paper Library of Congress Cataloging-in-Publication Data Ecology and management of breeding waterfowl / Bruce D.J. Batt . . . [et al.], editors, p. cm. Includes bibliographical references and index. ISBN 0-8166-2001-6 (alk. paper) 1. Waterfowl—Breeding—Congresses. 2. Waterfowl management— Congresses. 3. Waterfowl—Ecology—Congresses. I. Batt, Bruce D. J. QL696.A52E34 1992 639.9'7841-dc20 92-22813 CIP The University of Minnesota is an equal-opportunity educator and employer.

We dedicate this book to the pioneers of North American waterfowl conservation. These leaders — educators, waterfowlers, scientists, naturalists, and managers—through their tireless and enlightened efforts, have left a solid foundation for the present generation of waterfowl researchers.

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Contributors Preface Introduction: The Waterfowl Bruce D. J. Batt 1. Foraging Ecology and Nutrition Gary L. Krapu and Kenneth J. Reinecke 2. The Cost of Egg Laying and Its Relationship to Nutrient Reserves in Waterfowl Ray T. Alisauskas and C. Davison Ankney 3. Incubation and Brood Care Alan D. Afton and Stuart L. Paulus 4. Ecology of Prefledging Waterfowl James S. Sedinger 5. Ecology and Management of Postbreeding Waterfowl William L. Hohman, C. Davison Ankney, and David H. Gordon 6. The Mating Systems of Waterfowl Lewis W. Oring and Rodney D. Sayler 7. Courtship, Pair Formation, and Signal Systems Frank McKinney 8. Spacing Patterns Michael G. Anderson and Roger D. Titman 9. Ecology and Evolution of Brood Parasitism in Waterfowl Rodney D. Sayler 10. Environmental and Endocrine Control of Waterfowl Reproduction Cynthia K. Bluhm 11. Philopatry, Dispersal, and the Genetic Structure of Waterfowl Populations Michael G. Anderson, Judith M. Rhymer, and Frank C. Rohwer 12. Mortality During the Breeding Season Alan B. Sargeant and Dennis G. Raveling

ix xi xiii 1 30 62 109 128 190 214 251 290 323 365 396

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CONTENTS

13. Breeding Population Inventories and Measures of Recruitment Lewis M. Cowardin and Robert J. Blohm 14. Population Dynamics of Breeding Waterfowl Douglas H. Johnson, James D. Nichols, and Michael D. Schwartz 15. The Evolution of Reproductive Patterns in Waterfowl Frank C. Rohwer 16. Patterns in Breeding Duck Communities Thomas D. Nudds 17. Breeding Habitats of Nearctic Waterfowl Richard M. Kaminski and Milton W. Weller 18. Habitat Management for Breeding Areas John A. Kadlec and Loren M. Smith Notes on Contributors Index

423 446 486 540 568 590 611 615

Contributors

Alan D. Afton1, Wetland Wildlife Populations and Research Group, Minnesota Department of Natural Resources, 102 23rd Street, Bemidgi, Minnesota 56601

Cynthia K. Bluhm, Delta Waterfowl and Wetlands Research Station, Rural Route 1, Portage la Prairie, Manitoba R1N 3A1

Ray T. Alisauskas2, Delta Waterfowl and Wetlands Research Station, Rural Route 1, Portage la Prairie, Manitoba R1N 3A1

Lewis W Cowardin, U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Route 1, Box 96C, Jamestown, North Dakota 58401

Michael G. Anderson3, Delta Waterfowl and Wetlands Research Station, Rural Route 1, Portage la Prairie, Manitoba R1N 3A1

David H. Gordon6, Delta Waterfowl and Wetlands Research Station, Star Route 1, Box 226, Georgetown, South Carolina 29440

C. Davison Ankney, Department of Zoology, University of Western Ontario, London, Ontario N6A 5B7

William L. Hohman, U.S. Fish and Wildlife Service, National Wetlands Research Center, 700 Cajun Dome Boulevard, LaFayette, Louisiana 70506

Bruce D. J. Batt4, Delta Waterfowl and Wetlands Research Station, Rural Route 1, Portage la Prairie, Manitoba R1N 3A1

Douglas H. Johnson, U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Route 1, Box 96C, Jamestown, North Dakota 058401

Robert J. Blohm5, Office of Migratory Bird Management, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, Maryland 20811

John A. Kadlec, College of Natural Resources, Department of Fisheries and Wildlife, Utah State University, Logan, Utah 84322 Richard M. Kaminiski, Department of Wildlife and Fisheries, P.O. Drawer LW, Mississippi State University, Mississippi State, Mississippi 39762

1. Present address: U.S. Fish and Wildlife Service, Louisiana Cooperative Fish and Wildlife Research Unit, Louisiana State University, Baton Rouge, Louisiana 70803 2. Present address: Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, Saskatchewan S7N 0X4 3. Present address: Institute for Wetland and Waterfowl Research, c/o Ducks Unlimited Canada, Box 1160, Oak Hammock Marsh, Stonewall, Manitoba, ROC 2ZO 4. Present address: Institute for Wetland and Waterfowl Research, c/o Ducks Unlimited, Inc., One Waterfowl Way, Memphis, Tennessee 38120 5. Present address: Office of Migratory Bird Management, U.S. Fish and Wildlife Service, 4401 N. Fairfax Drive, Room 634, Arlington Square, Arlington, Virginia 22203

Gary L. Krapu, U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Route 1, Box 96C, Jamestown, North Dakota 58401 Frank McKinney, James Ford Bell Museum of Natural

6. Present address: Institute for Wetland and Waterfowl Research, c/o Ducks Unlimited, Inc., Star Route 1, Box 226, Georgetown, South Carolina 29440

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History, 10 Church Street S.E., University of Minnesota, Minneapolis, Minnesota 55455 James D. Nichols, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, Maryland 20708 Thomas D. Nudds, Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1 Lewis W. Oring7, Department of Biology, University of North Dakota, Grand Forks, North Dakota 58202 Stuart L. Paulus8, Rockefeller Wildlife Refuge, Louisiana Department of Wildlife and Fisheries, Route 1, Box 20-B, Grand Chenier, Louisiana 70643 Dennis G. Raveling9, Division of Wildlife and Fisheries Biology, University of California, Davis, California 95616 Kenneth J. Reinecke, U.S. Fish and Wildlife Service, Migratory Bird Habitat Research Lab, Wes-Environmental Laboratory, P.O. Box 631, Vicksburg, Mississippi 39180 10

Judith M. Rhymer , Laboratory of Molecular Systematics, National Museum of Natural History, Smithsonian Institute, Museum Support Center, Washington, D.C. 20560

7. Present address: Department of Range, Wildlife and Forestry, University of Nevada Reno, 1000 Valley Road, Reno, Nevada 89512 8. Present address: Raedeke Associates Scientific Consulting, Inc., 5711 Northeast 63rd Street, Seattle, Washington 98115 9. Deceased 10. Present address: Department of Zoological Research, Genetics Lab, Smithsonian Institute, Washington, D.C. 20008

Frank C. Rohwer11, Appalachian Environmental Lab, University of Maryland, Gunter Hall, Frostburg, Maryland 21532 Alan B. Sargeant, U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Route 1, Box 96C, Jamestown, North Dakota 58401 Rodney D. Sayler12, Institute for Ecological Studies, Box 8278, University Station, Grand Forks, North Dakota 58202 Michael D. Schwartz, U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Route 1, Box 96C, Jamestown, North Dakota 58401 James S. Sedinger, Department of Biology, Fisheries and Wildlife, 211 Irving Building, University of Alaska, Fairbanks, Alaska 99775-1780 Loren M. Smith, Department of Range Management, Box 4169, Texas Tech University, Lubbock, Texas 79409 Rodger D. Titman, Department of Renewable Resources, MacDonald College, Ste. Anne de Bellevue, Quebec H9X 3M1 Milton W. Weller, Department of Wildlife and Fisheries Science, Texas A&M University, College Station, Texas 77843

11. Present address: Department of Forestry, Wildlife and Fisheries, Louisiana State University, Baton Rouge, Louisiana 70803-6200 12. Present address: Department of Natural Resource Sciences, 115 Johnson Hall, Washington State University, Pullman, Washington 99164-6410

Preface

In August of 1987, the International Symposium on the Ecology and Management of Breeding Waterfowl was held in Winnipeg, Manitoba, Canada. It was organized by the staff of the Delta Waterfowl and Wetlands Research Station in recognition of that institution's fiftieth anniversary in 1988. A major goal of the symposium was to review progress made during the previous five decades of research on the ecology of breeding waterfowl. This volume brings together the final versions of the nineteen plenary papers presented at that meeting. Each of the chapters has since been updated by the authors, reviewed by one of the symposium editors along with two other specialists, and revised in consideration of advice received. The authors were asked to review and synthesize the complete published information on their topics and, where possible, to relate the importance of what has been learned to contemporary research priorities and waterfowl management. Because of the rich theoretical framework that has developed for the field of ecology in recent years, these challenges have been most stimulating and, we hope, successfully met. As authors and editors we hope we have developed a comprehensive treatise that will be helpful to the scientists, students, managers, and waterfowl enthusiasts who will use this book. The production of a volume such as this is possible only because of the generous contributions and sacrifices of many individuals and organizations. Prominent among these are the employers of the authors for allowing them the time required to complete their chapters. We also extend our thanks to the many individuals who served as peer reviewers: Dr. James C. Bartonek, U.S. Fish and Wildlife Service; Dr. William R. Clark, Iowa State University; Dr. Fred Cooke, Queen's University; Dr. Ronald D. Drobney, University of Missouri; Dr. David C. Duncan, Saskatchewan Wetlands Conservation Corporation; Dr. John Eadie, University of Toronto; the

late Dr. Donald S. Earner, University of Washington; Dr. Giles Gauthier, Universite Laval; Dr. George S. Hochbaum, Canadian Wildlife Service; Dr. Janet Kear, The Wildfowl Trust; the late Dr. James R. King, Washington State University; Dr. C.M. Lessells, University of Sheffield; Dr. James R. Lovvorn, University of Wyoming; Dr. Frank McKinney, University of Minnesota; Dr. Henry R. Murkin, Institute for Wetland and Waterfowl Research, Winnipeg; Dr. Gary L. Nuechterlein, North Dakota State University; Dr. Raymond J. O'Connor, University of Maine; Dr. Myrfyn Owen, The Wildfowl Trust; Dr. Hanu PÖys, Finnish Game and Fisheries Research Institute; Dr. Anne E. Pusey, University of Minnesota; Dr. Hermann Rahn, State University of New York, Buffalo; Dr. John T. Ratti, University of Idaho; the late Dr. Dennis G. Raveling, University of California, Davis; Dr. James K. Ringelman, Colorado Division of Wildlife; Dr. Donald H. Rusch, U.S. Fish and Wildlife Service; Dr. John P. Ryder, Lakehead University; Dr. John Sauer, U.S. Fish and Wildlife Service; Dr. Peter J. Sharp, Edinburgh Research Station; Dr. Thomas W. Schoener, University of California, Davis; Dr. Michael Sorensen, University of Minnesota; Dr. W. John Smith, University of Pennsylvania; Dr. Hilary Swain, Florida Institute of Technology; Dr. Michael W. Tome, U.S. Fish and Wildlife Service; Dr. Patrick J. Weatherhead, Carleton University; Dr. W. Alan Wentz, Kansas Department of Wildlife and Parks; and Dr. Richard A. Wishart, Ducks Unlimited Canada. We also appreciate the assistance of the staff of the University of Minnesota Press who helped guide this project through its many stages. The cost of publication was subsidized by proceeds from the symposium, the success of which was a credit to the many individuals who attended the event. The Delta Station especially committed a great deal of staff time to organizing the symposium and thus to the production of this book. Delta staff and students most xi

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deeply involved included Jeb Barzen, Laura Gretsinger, Sharon Gurney, Brenda Hales, Pat Hope, Sandy Kennedy, Lisette Ross, Elaine Murkin, Henry Murkin, and Ken Risi. The North American Wildlife Foundation, Delta's parent organization, took the initial chance of sponsoring this ambitious meeting. The editors extend special thanks to Mr. Richard A.N. Bonnycastle, who

personally provided funds to further offset the production costs. Bruce D.J. Batt Alan D. Afton Michael G. Anderson C. Davison Ankney Douglas H. Johnson John A. Kadlec Gary L. Krapu

Introduction The Waterfowl Bruce D. J. Batt

I. Introduction

II. The Diversity of Waterfowl

The ducks, geese, and swans of the world are the best understood of all groups of wild birds because of the historical importance of waterfowl for hunting, domestication, and aviculture (Livezey 1986). Waterfowl have a nearly cosmopolitan distribution, with Antarctica being the only continent without its own anatids. Many are large and most are easily observed. Bright plumages and spectacular displays are commonly associated with breeding, and many species live in close proximity to human beings. Even those among us most detached from the natural world would be hard-pressed to give no notice to massive gatherings of migrating Snow Geese along major countryside thoroughfares, to a female Mallard leading her downy brood through busy city traffic, or to Mute Swans engaged in their elaborate preand postcopulatory displays. (Only common names of waterfowl are cited throughout the volume. Scientific names are provided in Table 1 of this chapter.) In the eyes of many people, the world is a more interesting place because of its waterfowl. Waterfowl appeared first during the early Cenozoic period, about 50 million years ago (e.g., Johnsgard 1975). Species occupy virtually every habitat associated with water. The approximately 150 species alive today include forms ranging from those occupying specialized island niches (Weller 1980) to the Mallard, which, aided by artificial introductions, thrives on every occupied continent. To occupy this wide range of available environments, waterfowl are diverse in their anatomy, behavior, and physiology. Nowhere is diversity more strikingly expressed than in traits associated with reproduction.

Most waterfowl are well adapted for aquatic environments, either fresh water or marine, and they generally have webbed feet to aid in swimming. Some species are almost completely terrestrial, however. The Hawaiian Goose and the Magpie Goose, for example, have only partially webbed feet. Some forms, including most of the geese, may be considered to be semiterrestrial as they feed almost exclusively on uplands. At the other end of the spectrum are the eiders, which rarely come to land other than to seek a suitable substrate for nesting. Waterfowl have a dorsoventrally flattened bill with a distinct, hooked nail at the tip, which differentiates the group from other birds. Bill characteristics are highly adaptable though (Goodman and Fisher 1962), and have little taxonomic value (Woolfenden 1961). The edges of the mandibles have rows of lamellae, which are highly developed in filter-feeding types such as the Northern Shoveler, and only residual in mollusk feeders like the scoters. The bills of most geese are adapted for grazing on individual stems of vegetation, while those of the swans are more suited to digging in the bottom of wetlands. Plumage types are diverse in waterfowl. The swans, geese, and whistling ducks are sexually monomorphic, whereas most species of ducks show extreme dimorphism between the sexes with the male always more brightly colored than the female in these cases. Plumage characteristics are related to mating systems and patterns of parental care (chapters 4 and 7). A few species, particularly the Snow Goose, show plumage polymorphisms with simple Mendelian inheritance patterns, allowing much greater sophistication of research on xiii

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difficult problems related to gene flow and mate choice (see Cooke et al. 1982 for review). Plumage molt in waterfowl generally consists of an annual replacement of all feathers (swans and geese) or a double replacement of all feathers except the primaries and secondaries (most ducks). The latter is presumably a response to the higher survival value of cryptic coloration, by the otherwise brightly colored male, during the postbreeding period. Both the male and female have double annual molts of body feathers. Waterfowl share with a few other groups of waterbirds the trait of annual simultaneous flightless primary wing feather molt following breeding and preceding migration. Among the stiff-tail group, however, there is growing evidence that a double flightless wing feather molt takes place (Siegfried 1970), once during the winter and once during the summer. The loss of flight capability is often preceded by a molt migration, particularly by postbreeding males and nonbreeding birds of either sex, to areas with presumably more reliable food supplies and safety from predation (e.g., Salomonsen 1968, Dubowy 1980, Bailey 1981). The postbreeding period has recently been of greater ecological interest following expanded research on its relationships to reproductive success, nutritional requirements, and migration (chapter 5). Parental care in waterfowl is manifested in many ways (Kear 1970). Generally, for the monomorphic types, pair bonds are "permanent" and both sexes cooperate in brood rearing, families often staying together until the beginning of the next nesting season. In a few cases (e.g., the Fulvous Whistling Duck), the male even assists in incubation of the eggs. More commonly, as in most ducks, pair bonds are formed anew each year, and the male deserts the incubating female, leaving her to hatch and tend the brood on her own. Among those species that employ nest parasitism, the rearing of the young from parasitically laid eggs is left to the host female (chapter 9). In the extreme case of the obligately parasitic Black-headed Duck, the newly hatched duckling apparently leaves the nest after hatching and fends for itself (Rees and Hilgarth 1984). Newly hatched waterfowl are precocial and nidifugous. Well insulated with thick down, the young are able to swim soon after hatching. The eggs in individual nests normally hatch more or less simultaneously, and broods are led from the nest by the female or both parents when present. The Magpie Goose, however, hatches asynchronously because incubation is started before all the eggs are laid. In this case, different parts of the brood are raised by each of the sexes. The young are self-feeding right from the start in most species, although the Magpie Goose and some whistling ducks do feed their downy young (chapter 4).

The elaborate and variable behavior of courting and breeding waterfowl has been extensively studied, and behavioral traits are integral to modern taxonomic systems (e.g., Johnsgard 196la). While traits of several uncommon species are poorly known, comprehensive syntheses of breeding behavior patterns are now possible (chapter 8). Reproduction is markedly seasonal in most waterfowl, particularly for migratory types breeding in the Northern Hemisphere. In extreme cases, such as for the arctic-nesting geese, nest initiation must take place over a span of only a couple of weeks, or else nesting is forgone until subsequent breeding seasons (e.g., Barry 1962). In tropical and subtropical regions, "seasons" may be protracted with nests being initiated over a period of 6-8 months. Some groups, most notably many of the Australian waterfowl, are virtually aseasonal and can nest at any time of the year in response to the availability of suitable habitat (Frith 1982). Nest sites are generally near water, and most species nest solitarily on the ground or in emergent vegetation. Some types are cavity nesters, however, most commonly in tree cavities (e.g., the Wood Duck), but also in cavities in the ground (e.g., the Ruddy Shelduck). The success of local populations of cavity nesters can often be enhanced by the provision of artificial nest boxes. Limited availability of cavities often leads to multiple females using the same cavity, resulting in "dump" nests (Rohwer and Freeman 1989). Many waterfowl are not highly specific when choosing nest sites, and records exist for almost every conceivable location: abandoned raptor nests, haystacks, eave troughs, under tombstones, on cliff edges, in the crotch of desert cactus plants, and so on. A few types are colonial nesters, either as a basic characteristic of the species (e.g., Black Swan) or as a consequence of greatly increased nest success in predator-free environments such as on islands (e.g., Lokemoen et al. 1984). The high waterfowl nest success occurring on islands in comparison to surrounding lands has been simulated in certain situations as a deliberate management practice (chapter 18) where artificial islands have been constructed. Monogamy is the basic mating system for waterfowl (chapter 7), although, here too, there are numerous departures. "Permanent" monogamy occurs in most geese and swans, although "divorce" has been observed. Most ducks are monogamous until the female begins incubation of the nest, after which males of many species seek out new females for subsequent breeding opportunities—a form of serial polygyny. Some of the monogamous species try to take advantage of extra mating opportunities when they employ a forced copulation strategy—usually in consort with other males of the same species. One species, the Magpie Goose, demonstrates an unusual polygamous re-

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lationship with trios of one male and two females using a single nest and all three birds sharing brood-rearing responsibilities.

this information is sometimes difficult, but new computerized information-retrieval systems are simplifying these problems.

III. Sources of Technical Information

IV. The Organization of This Book

Numerous compilations of information on waterfowl have been undertaken in the popular, semitechnical, and scientific literature. The most sought after natural history reference is John C. Phillips's (1922-26) fourvolume A Natural History of the Ducks. Now stored in the rare books section of libraries, its popularity is attested to by its recent reprinting (Phillips 1986), 60 years after the original release. Other collections of natural history and scientific information have been done for the whole family by Delacour (1954-64) and Johnsgard (1965, 1968, 1978). There have been extensive monographic treatises of individual species, but others have focused on the waterfowl fauna of broad geographic areas, particularly of North America (Kortright 1943, Bellrose 1976, Palmer 1976), Europe (Scott and Boyd 1957, Ogilvie 1967, Owen 1977), and Australia (Frith 1982). Other authors have reviewed the available information on single taxonomic groups, for example, swans (Wilmore 1974) and geese (Ogilvie 1978). Weller (1980), in The Island Waterfowl, has compiled information on that specialized, but diverse, group of waterfowl. Taxonomic and natural history accounts of the avifauna of provinces, states, countries, or geographic regions abound, and these contain information about the local ducks, geese, and swans. The most significant of these for waterfowl are Dementiev and Gladkov's (1967) volumes, The Birds of the Soviet Union; Cramp and Simmons's (1977) Birds of Europe, the Middle East, and North Africa; and Brown et al.'s (1982) Birds of Africa. The reader will be led to an extensive literature on waterfowl distributions, physical descriptions, food habits, field identification, social behavior, reproductive biology, population status, conservation problems, and seasonal movements through these works and their bibliographies. Contrary to what might be expected, there is only one scientific journal dedicated to waterfowl. Wildfowl has been published once a year since 1947 by the Wildfowl Trust in Great Britain. The most readily retrievable information from waterfowl research is published in standard ornithological, ecological, and wildlife management journals of learned societies in countries all over the world. Because many waterfowl are game species, a great deal of work is conducted on waterfowl management problems under the sponsorship of public agencies. While some of this material is published in the readily available scientific literature, much of it remains in internal reports and poorly circulated bulletins. Access to

Much of science is dedicated to discovering general patterns in nature. Thus, the initial field studies that result in natural history species accounts are essential for the assembly of information on topics such as the patterns of parental care by Kear (1970) and the several reviews of the determinants of clutch size in waterfowl (Lack 1967, 1968, Johnsgard 1973, Rohwer 1986). This comparative approach to science is seen to be the most useful in exposing general patterns in nature. Typical ornithological texts are organized this way (e.g., Welty 1979, Pettingill 1985). A mammoth review of topics in ornithology has been assembled in the Avian Biology series (Farner and King 1971-75, and Farner et al. 198385). Given the extensive literature on waterfowl, it is surprising that there is only one reference text on the general ecology of waterfowl (Johnsgard 1968), and nothing in the last 20 years. It is the intent of this book to fill part of this void by undertaking reviews of specific aspects of the ecology of breeding waterfowl. More of the baseline work on breeding waterfowl has been done in North America than elsewhere. The extensive work by Europeans has been concentrated outside the breeding season because most of their waterfowl breed in inaccessible places in Northern Europe and Russia. While there is an inevitable emphasis on North American species and viewpoints for several topics, most chapters are enriched by the extensive literature from other areas. Studies of waterfowl ecology have focused on the reproductive period, as has been the case for most species of birds (Anderson and Batt 1983). Particularly in North America, however, there is a much expanded interest in examining the influence of events or factors throughout the annual cycle with a view toward possible crossseasonal influences (e.g., Raveling 1979, Heitmeyer and Fredrickson 1981, Weller and Batt 1987). While focusing on breeding ecology, numerous topics in this volume are not isolated from the wintering, migration, and postbreeding periods, as they should not be.

V. The Classification of Waterfowl The family Anatidae has a worldwide distribution. The taxonomy of the family has been extensively studied, with most modern classification schemes having their origins in the system proposed by Delacour and Mayr (1945). The affinities and classification of most species have been pretty well established, but there are still considerable debate and inquiry about the relationships of some species, and even of several of the higher taxo-

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nomic levels. Numerous types of data have been used in addressing the classification of waterfowl, including behavior characteristics, syringeal anatomy, cytogenetics, serology, osteology, feather lice, eggshell structure, eggwhite proteins, feather proteins, lipids from the uropygeal gland, myology, and mitochondrial DNA (see Livezey 1986 for review). For the purposes of this book, we have adopted the classification system outlined by Johnsgard (1978). The reader should note, though, that the recent paper by Livezey (1986) and references contained therein present compelling questions that must be answered before taxonomists of this group reach a final consensus. Characteristics of the major groups follow: Family Anatidae (ducks, geese and swans) Subfamily Anseranatinae Tribe Anseranatini: Magpie Goose (1 genus and species) Subfamily Anserinae Tribe Dendrocygnini: Whistling or tree ducks (2 genera, 9 species) Tribe Anserini: Swans and true geese (4 genera, 21 species) Tribe Cereopsini: Cape Barren Goose (1 genus and species) Tribe Stictonettini: Freckled Duck ( 1 genus and species) Subfamily Anatinae Tribe Tadornini: Sheldgeese and Shelducks (5 genera, 15 species) Tribe Tachyerini: Steamer ducks (1 genus, 3 species) Tribe Cairinini: Perching ducks (9 genera, 13 species) Tribe Merganettini: Torrent Duck (1 genus and species) Tribe Anatini: Dabbling or surface-feeding ducks (4 genera, 39 species) Tribe Aythyini: Pochards (3 genera, 16 species) Tribe Mergini: Sea Ducks (8 genera, 20 species) Tribe Oxyurini: Stiff-tailed ducks (3 genera, 8 species)

A. Subfamily Anseranatinae 1. Tribe Anseranatini (Magpie Goose) This subfamily consists of a single unique species, the Magpie Goose, and is found only in northern Australia and southern New Guinea. It is semiterrestrial with only slightly webbed feet and a strong hooked bill used for feeding by digging in hard substrates. It is the only member of the family that has a gradual, sequential primary feather molt and does not undergo a flightless period. It is also the only waterfowl known to form trios of one

male and two females for breeding (Johnsgard 1961) and one of the few actually to feed the young.

B. Subfamily Anserinae 1. Tribe Dendrocygnini (Whistling Ducks) Although they are often referred to as tree ducks, whistling ducks do not commonly perch in trees, and most species do not nest in tree cavities. Whistling ducks are gooselike in appearance and have a specialized tracheal structure that emits a high whistle. Representatives are found on all continents in tropical and subtropical regions. Plumages are monomorphic between the sexes, and pair bonds appear to be permanent. Males in this group regularly share in incubation and both sexes cooperate in brood rearing.

2. Tribe Anserini (Swans and Geese) These are the largest of the waterfowl and have long necks and noniridescent coloration. All species are sexually monomorphic in plumage, size, and voice, and all species form long-term, year-round pair bonds. Both sexes cooperate in defending nest sites and rearing the young, but only the female incubates. Many species are colonial nesters, such as the Snow Goose and the Black Swan, but most are solitary, generally nesting in open areas with good visibility. This mostly Northern Hemisphere group is migratory, although the Hawaiian Goose is nonmigratory — a trait adopted by many species of island-nesting waterfowl (Weller 1980), and the Black Swan of Australia wanders widely throughout that continent but not in a true migratory pattern. Migratory types use traditional stopover locations, which can be protected from development for other purposes, where harvest can be controlled and food provided. They are, therefore, among the more easily managed groups of waterfowl, and in North America some species are more abundant today than they were during the early years of settlement. Swans and geese are herbivorous — the geese generally feeding primarily on terrestrial vegetation and the swans on submerged aquatic vegetation. In recent times, several species of swans and the more typically marine brants have switched to upland feeding on spilled agricultural products —a trait that has enhanced their success in today's heavily farmed landscape.

3. Tribe Cereopsini (Cape Barren Goose) This tribe consists of a single species and resides on a few small islands off the southern coast of Australia. It has mostly gooselike characteristics but also shares anatomical features with the shelgeese and shelducks. The Cape Barren Goose is almost completely terrestrial in habits, and nests are often found in trees up to 5 m above the ground.

THE WATERFOWL

4. Tribe Stictonettini (Freckled Duck) This tribe also consists of a single species and is distributed locally in southern and western Australia. Although ducklike in appearance, it has many primitive anatomical characteristics that link it to true geese and swans. This species and the Cape Barren Goose are of great interest taxonomically and pose difficult conservation problems (Frith 1982).

C. Subfamily Anatinae These are the typical ducks with scutelated tarsi in front. Most have marked sexual dimorphism, and sexual displays by males are usually elaborate. The syrinx structure of males has an asymmetrical, bony bulla structure, resulting in differences in voice and calls between the sexes—the females generally making the typical "quacking" sounds, males making a variety of "rabs," "peeps," "purrs," and "whistles." Both sexes go through a double annual plumage molt. According to the terminology of Humphrey and Parkes (1959), the "alternate" is the typical breeding, or nuptial, plumage and is usually bright and elaborate in the males and more dull (usually browns, blacks, and tans) and cryptic in the females; the "basic" is a nonbreeding plumage, often called "eclipse" in the males. The basic plumage of both males and females is similar to the female breeding plumage.

1. Tribe Tadornini (Sheldgeese and Shelducks) The gooselike sheldgeese and the ducklike shelducks have many intermediate characteristics between the Anserini and other tribes in the Anatinae. Members are present on every continent except North America and Antarctica and reside mostly in low-latitude, warmer areas. Many are cavity nesters. The sexes have boldly colored monomorphic plumages in all except two of the fourteen species. There are no distinct basic and alternate plumages. All are nonmigratory. They have longterm monogamous pair bonds. Only the female incubates, but both sexes attend the young, often for up to 6 months after hatching.

2. Tribe Tachyerini (Steamer Ducks) The one genus, Tachyeres, has three species that all live off the coasts of southern South America and the Falkland Islands. Two species, the Magellanic Flightless Steamer Duck and the Falkland Flightless Steamer Duck, rarely fly (as their names indicate). All may move to inland areas for breeding and to consume fresh water. They primarily feed on mollusks, crustaceans, and small fish. The sexes are essentially monomorphic, and the males are larger than the females and very aggressive. 3. Tribe Cairinini (Perching Ducks) While there is considerable evidence supporting the

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merging of this tribe with Anatini, the dabbling ducks (Livezey 1986), Johnsgard (1978) felt that the differences between the two groups warranted tribal segregation. The perching ducks freely perch in trees and usually nest in tree cavities. Among wood ducks, a scarcity of tree cavities often results in the use of a nest site by several females (e.g., Haramis and Thompson 1985). The plumage is often bright and iridescent. Plumage is sexually dimorphic in some, such as in the genus Aix, but others are essentially monomorphic. Members of the tribe are found on all continents, although most are tropical or subtropical.

4. Tribe Merganettini (Torrent Duck) The single species has three subspecies, all found in the Andean Mountain range of eastern South America. These birds occupy feeding and breeding territories along fast-flowing, clearwater mountain streams and are rarely found in groups larger than family size. They are monomorphic and probably have permanent pair bonds. The nests are near the streams, usually in cavities or under ledges. The breeding period is extended over several months and both sexes attend the brood.

5. Tribe Anatini (Dabbling Ducks) The dabbling ducks are poor divers and obtain their food by foraging on the surface or by tipping up in shallow water to seek food on the bottom. The sexes are usually sexually dimorphic, with the male having a bright alternate plumage during the breeding season. Some monomorphic species exist, especially in the Mallard group (Johnsgard 1961b). Pair formation begins, for most species, during the fall, and pair bonds are apparently maintained until incubation is initiated, after which the male departs, leaving the female to rear the young on her own. Other than during breeding, individuals and pairs are usually gregarious and flocked throughout most of the year. They are mostly omnivorous, eating invertebrates, plants, and seeds. A few species, particularly the Mallard and Pintail, have adapted to field feeding on waste agricultural grains, but this is an exception to the general pattern. Species in this tribe occur on all continents. Most are migratory with a few species even going between hemispheres in their annual movements.

6. Tribe Aythyini (Pochards) Species in this tribe of diving ducks occur on all continents except Antarctica. They are sexually dimorphic, but are generally not as brightly colored as other groups. Only the female incubates the eggs in a nest that is always near, and usually over, water. The pochards are gregarious and can form huge flocks at all times of the year except when breeding. All forms are strictly freshwater during breeding, but several are found in saline or

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brackish coastal waters during the wintering period. The pochards typically dive for their food, and they are herbivorous or omnivorous.

7. Tribe Mergini (Sea Ducks) This diverse group includes the eiders, scoters, mergansers, goldeneyes, buffleheads, and the Harlequin Duck. They are sexually dimorphic except for two Southern Hemisphere mergansers. Broods are often raised in creches where many families merge and usually are left under the care of a few (or single) females. Some, like the buffleheads and the goldeneyes, nest in tree cavities. Most others nest on the ground in dense, often brushy, vegetation, but the eiders typically nest in the open on islands or tundra vegetation. They are generally carnivorous or omnivorous, but the eiders feed exclusively on mollusks and other marine organisms while the mergansers specialize in catching fish. The Harlequin Duck occurs in rapidly flowing, freshwater stream habitats, but most others are associated with rivers, ponds, and lakes.

8. Tribe Oxyurini (Stiff-tailed

Ducks)

This group is named for the characteristic long, stiffened tail feathers used in displays and underwater swimming. Sexual displays are elaborate, and all species, except the Musk Duck of Australia, are markedly sexually dimorphic. The Macoa Duck is known to be polygamous, often having several females nesting in the area defended for breeding. One of the most specialized species, the Black-headed Duck, is distinguished by its being the only obligate parasite from among the waterfowl. Table 1. Taxonomic classification of the family Anatidae (after Johnsgard 1978) SUBFAMILY ANSERANATINAE TRIBE ANSERANATINI Magpie Goose Anseranas semipalmata Magpie Goose SUBFAMILY ANSERINAE TRIBE DENDROCYGNINI Whistling or Tree Ducks Dendrocygna guttata Spotted Whistling Duck Dendrocygna eytoni Plumed Whistling Duck Dendrocygna bicolor Fulvous Whistling Duck Dendrocygna arcuata Wandering Whistling Duck (Subspecies: arcuata, East Indian Wandering Whistling Duck; australis, Australian Wandering Whistling Duck; and pygmaea, Lesser Wandering Whistling Duck) Dendrocygna javanica Lesser Whistling Duck Dendrocygna viduata White-faced Whistling Duck Dendrocygna arborea Cuban Whistling Duck Dendrocygna autumnalis Black-bellied Whistling Duck (Subspecies: autumnalis, Northern Black-bellied Whistling Duck; and discolor, Southern Black-bellied Whistling Duck) Thalassornis leuconotus White-backed Duck (Subspecies: leuconotus, African White-backed Duck; and insularis, Madagascan White-backed Duck) TRIBE ANSERINI Swans and True Geese Cygnus olor Mute Swan

Cygnus atratus Black Swan Cygnus melancoryphus Black-necked Swan Cygnus buccinator Trumpeter Swan Cygnus cygnus Whooper Swan Cygnus columbianus Whistling Swan Cygnus bewickii Bewick Swan Coscoroba coscoroba Coscoroba Swan Anser cygnoides Swan Goose Anser fabalis Bean Goose (Subspecies: fabalis, Western Bean Goose; johanseni, Johansen Bean Goose; middendorfi, Middendorf Bean Goose; rossicus, Russian Bean Goose; serrirostris, Thick-billed Bean Goose; and brachyrhynchus, Pink-footed Bean Goose) Anser albifrons White-fronted Goose (Subspecies: albiforns, European White-fronted Goose; flavirostris, Greenland White-fronted Goose; frontalis, Pacific White-fronted Goose; gambelli, Gambel White-fronted Goose; and elgasi, Tule White-fronted Goose) Anser erythropus Lesser White-fronted Goose Anser anser Graylag Goose (Subspecies: anser, Western Graylag Goose; and rubrirostris, Eastern Graylag Goose) Anser indicus Bar-headed Goose Anser caerulescens Snow Goose (Subspecies: caerulescens, Lesser Snow and Blue Goose; and atlanticus, Greater Snow Goose) Anser rossi Ross' Goose Anser canagicus Emperor Goose Branta sandvicensis Hawaiian Goose Branta canadensis Canada Goose (Subspecies: canadensis, Atlantic Canada Goose; interior, Hudson Bay Canada Goose; maxima, Giant Canada Goose; moffitti, Moffitt (Great Basin) Canada Goose parvipes, Lesser Canada Goose; taverneri, Taverner (Alaska) Canada Goose; fulva, Vancouver Canada Goose; occidentalis, Dusky Canada Goose; leucopareia, Aleutian Canada Goose; asiatica, Bering Canada Goose; minima, Cackling Canada Goose; and hutchinsii, Baffin Island (Richardson) Canada Goose) Branta leucopsis Barnacle Goose Branta bemicla Brant (Subspecies: bernicla, Dark-bellied (Russian) Brant; orientalis, Pacific Brant; nigricans, Black Brant; and hrota, Light-bellied (Atlantic) Brant) Branta ruficollis Red-breasted Goose TRIBE CEREOPSINI Cape Barren Goose Cereopsis novaehollandiae Cape Barren Goose TRIBE STICTONETTINI Freckled Duck Stictonetta naevosa Freckled Duck SUBFAMILY ANATINAE TRIBE TADORNINI Sheldgeese and Shelducks Cyanochen cyanopterus Blue-winged Goose Chloephaga melanoptera Andean Goose Chloephaga picta Magellan Goose (Subspecies: picta, Lesser Magellan Goose; and leucoptera, Greater Magellan Goose) Chloephaga hybrida Kelp Goose (Subspecies: hybrida, Patagonian Kelp Goose; and malvinarum, Falkland Kelp Goose) Chloephaga poliocephala Ashy-headed Sheldgoose Chloephaga rubidiceps Ruddy-headed Sheldgoose Neochen jubata Orinoco Goose Alopochen aegyptiacus Egyptian Goose Tadorna ferruginea Ruddy Shelduck

THE WATERFOWL Tadorna cana Cape Shelduck Tadorna tadomoides Australian Shelduck Tadorna variegata New Zealand Shelduck Crested Shelduck Tadorna cristata Northern (Common) Shelduck Tadorna tadorna Radjah Shelduck Tadorna radjah (Subspecies: radjah, Black-backed Radjah Shelduck; and rufitergum, Red-backed Radjah Shelduck) TRIBE TACHYERINI Steamer Ducks Tacbyeres patachonicus Flying Steamer Duck Tachyeres pteneres Magellanic Flightless Steamer Duck Tachyeres brachypterus Falkland Flightless Steamer Duck TRIBE CAIRININI Perching Ducks Plectropterus gambensis Spur-winged Goose (Subspecies: gambensis, Gambian Spur-winged Goose; and niger, Black Spur-winged Goose) Cairina moschata Muscovy Duck Cairina scutulata White-winged Wood Duck Sarkidiornis melanotos Comb Duck (Subspecies: melanotos, Old World Comb Ducks; and sylvicola, South American Comb Duck) Pteronetta hartlaubi Hartlaub Duck Nettapus pulchellus Green Pygmy Goose Nettapus coromandelianus Cotton Pygmy Goose (Subspecies: coromandelianus, Indian Pygmy Goose; and albipennis, Australian Pygmy Goose) Nettapus auritus African Pygmy Goose Callonetta leucophrys Ringed Teal Aix sponsa North American Wood Duck Aix galericulata Mandarin Duck Chenonetta jubata Australian Wood Duck Amazonetta brasiliensis Brazilian Teal (Subspecies: brasiliensis, Lesser Brazilian Teal; and ipecutiri, Greater Brazilian Teal) TRIBE MERGANETTINI Torrent Duck Merganetta armata Torrent Duck (Subspecies: colombiana, Colombian Torrent Duck; leucogenis, Peruvian Torrent Duck; and armata, Argentin Torrent Duck) TRIBE ANATINI Dabbling or Surface-feeding Ducks Hymenolaimus malacorhynBlue Duck chos Anas waigiuensis Salvadori Duck Anas sparsa African Black Duck (Subspecies: sparsa, South African Black Duck; maclatchyi, Western African Black Duck; and leucostigma, Ethiopian Black Duck) Anas penelope Eurasian Wigeon Anas americana American Wigeon Anas sibilatrix Chiloe Wigeon Anas falcata Falcated Duck Anas strepera Gadwall (Subspecies: strepera, Common Gadwall; and couesi, Coues Gadwall [extinct]) Anas formosa Baikal Teal Anas crecca Green-winged Teal (Subspecies: crecca, Eurasian Green-winged Teal; nimia, Aleutian Green-winged Teal; and carolinensis, North American Greenwinged Teal) Anas flavirostris Speckled Teal (Subspecies: flavirostris, Chilean Speckled Teal; oxyptera, Sharpwinged Speckled Teal; andium, Andean Speckled Teal; and altipetans, Merida Speckled Teal) Anas capensis

Cape Teal

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Anas bernieri Madagascan Teal Anas gibberifrons Gray Teal (Subspecies: gibberifrons, East Indian Gray Teal; remissa, Rennell Island Gray Teal; gracilis, Australian Gray Teal; and albogularis, Andaman Gray Teal) Anas castanea Chestnut Teal Anas aucklandica Brown Teal (Subspecies: chlorotis, New Zealand Brown Teal; aucklandica, Auckland Island Teal; and nesiotis, Campbell Island Teal) Anas platyrhynchos Mallard (Subspecies: platyrhynchos, Common Mallard; conboschas, Greenland Mallard; fulvigula, Florida Mallard; maculosa, Mottled Mallard; diazi, Mexican Mallard; wyvilliana, Hawaiian Mallard; and laysanensis, Laysan Mallard) Anas rubripes North American Black Duck Anas melleri Meller Duck Anas undulata Yellow-billed Duck (Subspecies: ruppelli, Abyssinian Yellow-billed Duck; and undulata, South African Yellow-billed Duck) Anas poecilorhyncha Gray Duck (Subspecies: poecilorhyncha, Spot-billed Gray Duck; haringtoni, Burmese Gray Duck; zonorhyncha, Chinese Gray Duck; superciliosa, New Zealand Gray Duck; pelewensis, Lesser Gray Duck; and rogersi, Australian Gray Duck) Anas luzonica Philipine Duck Anas specularis Bronze-winged Duck Anas specularioides Crested Duck (Subspecies: alticola, Andean Crested Duck; and specularioides, Patagonian Crested Duck) Anas acuta Pintail (Subspecies: acuta, Northern Pintail; eatoni, Kerguelen Pintail; and drygalskii, Crozet Pintail) Anas georgica Brown Pintail (Subspecies: georgica, South Georgian Brown Pintail; spinicauda, Chilean Brown Pintail; and niceforoi, Niceforo Brown Pintail) Anas bahamensis White-cheeked Pintail (Subspecies: bahamensis, Lesser White-cheeked Pintail; rubrirostris, Greater White-cheeked Pintail; and galapagensis, Galapagos White-cheeked Pintail) Anas erythrorhyncha Red-billed Pintail Anas versicolor Silver Teal (Subspecies: puna, Puna Silver Teal; versicolor, Northern Silver Teal; and fretensis, Southern Silver Teal) Anas hottentota Hottentot Teal Anas querquedula Garganey Anas discors Blue-winged Teal Anas cyanoptera Cinnamon Teal (Subspecies: cyanoptera, Southern Cinnamon Teal; orinomus, Andean Cinnamon Teal; borreroi, Borrero Cinnamon Teal; tropica, Tropical Cinnamon Teal; and septentrionalium, Northern Cinnamon Teal) Anas platalea Red Shoveler Anas smithii Cape Shoveler Anas rhynchotis Australasian Shoveler (Subspecies: rhynchotis, Australian Shoveler; and variegata, New Zealand Shoveler) Anas clypeata Malacorhynchus membranaceous Marmaronetta angustirostris TRIBE AYTHYINA Pochards Rhodonessa caryophyllacea

Northern Shoveler Pink-eared Duck Marbled Teal Pink-headed Duck

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Netta rufina Red-crested Pochard Netta erythropthalma Southern Pochard (Subspecies: erythropthalma, South American Southern Pochard; and brunnea, African Southern Pochard) Netta peposaca Rosybill Aythya valisineria Canvasback Aythya ferina Eurasian Pochard Aythya americana Redhead Aythya collaris Ring-necked Duck Aythya australis Australasian White-eye (Subspecies: australis, Australian White-eye; and extima, Banks Island White-eye) Aythya baeri Siberian White-eye Aythya nyroca Ferruginous White-eye Aythya innotata Madagascan White-eye Aythya fuligula Tufted Duck Aythya novae-seelandiae New Zealand Scaup Aythya marila Greater Scaup (Subspecies: marila, European Greater Scaup; and mariloides, Pacific Greater Scaup) Aythya affinis Lesser Scaup TRIBE MERGINI Sea Ducks Somateria mollissima Eider (Common Eider) (Subspecies: mollisima, European Eider; faeroeensis, Faeroe Eider; dresseri, American Eider; sedentaria, Hudson Bay Eider; borealis, Northern Eider; and v-nigra, Pacific Eider) Somateria spectabilis King Eider Somateria fischeri Spectacled Eider Polysticta stelleri Steller Eider Camptorhynchus labradorius Labrador Duck (extinct) Histrionicus histrionicus Harlequin Duck Clangula hyemalis Long-tailed Duck Melanitta nigra Black Scoter (Subspecies: nigra, European Black Scoter; and americana, Pacific Black Scoter) Melanitta perspicillata Surf Scoter Melanitta fusca White-winged Scoter (Subspecies: fusca, European White-winged Scoter; stejnegeri, Asiatic White-winged Scoter; and deglandi, Pacific White-winged Scoter) Bucephala albeola Bufflehead Bucephala islandica Barrow Goldeneye Bucephala clangula Goldeneye (Common Goldeneye) (Subspecies: Clangula, European Goldeneye; and americana, American Goldeneye) Mergus cucullatus Hooded Merganser Mergus albellus Smew Mergus octosetaceus Brazilian Merganser Mergus senator Red-breasted Merganser (Subspecies: senator, Common Red-breasted Merganser; and schioleri, Greenland Red-breasted Merganser) Mergus squamatus Chinese Merganser Mergus merganser Goosander (Common Merganser) (Subspecies: merganser, Eurasian Goosander; comatus, Oriental Goosander; and americanus, American Goosander) Mergus australis Auckland Island Merganser TRIBE OXYURINI Stiff-tailed Ducks Heteronetta atricapilla Black-headed Duck Oxyura dominica Masked Duck

Oxyura famaicensis Ruddy Duck (Subspecies: jamaicensis, North American Ruddy Duck; andina, Colombian Ruddy Duck; and ferruginea, Peruvian Ruddy Duck) Oxyura leucocephala White-headed Duck Oxyura maccoa Maccoa Duck Oxyura vittata Argentine Blue-billed Duck Oxyura australis Australian Blue-billed Duck Biziura lobata Musk Duck

References Anderson, M. G., and B. D. J. Batt. 1983. Workshop on the ecology of wintering waterfowl. Wildl. Soc. Bull. 11:22-24. Bailey, R. O. 1981. Post-breeding ecology of the Redhead Duck. Ph.D. thesis, Macdonald College, Montreal, Canada. Barry, T. W. 1962. Effect of late seasons on Atlantic Brant reproduction. J. Wildl. Manage. 26:19-26. Bellrose, F. C. 1976. Ducks, Geese and Swans of North America. Stackpole Books, Harrisburg, Pa. Brown, L. H., E. K. Urban, and K. Newman. 1982. The birds of Africa. Vol. 1. Academic Press, London. Cooke, F. C., K. F. Abraham, J. C. Davies, C. S. Findlay, R. F. Healey, A. Sadura, and R. J. Seguin. 1982. The La Perouse Bay Snow Goose project—a thirteen year report. Unpubl. report on file with Canadian Wildlife Service, Ottawa. Cramp, S., and K. E. L. Simmons. 1977. Handbook of the birds of Europe, the Middle East, and North Africa. Vol. 1. Oxford University Press, Oxford. Delacour, J. 1954-64. The waterfowl of the world. Vols. 1-4. Country Life, London. Delacour, J., and E. Mayr. 1945. The family Anatidae. Wilson Bull. 57:4-54. Dementiev, G. P., and N. A. Gladkov. (eds.) 1967. Birds of the Soviet Union. Vol. 2. Israel Program for Scientific Translations, U.S. Dept. of the Interior and National Science Fndn., Washington, D.C. Dubowy, P. J. 1980. Optimal foraging and adaptive strategies of postbreeding male Blue-winged Teal and shovelers. M.S. thesis, University of North Dakota, Grand Forks. Earner, D. S., and J. R. King. 1971-75. Avian biology. Vols. 1-5. Academic Press, New York. Farner, D. S., J. R. King, and K. C. Parkes. 1983-85. Avian biology. Vols. 6-7. Academic Press, New York. Frith, H. J. 1982. Waterfowl in Australia. 2nd ed. Angus and Robertson, Sydney. Goodman, D. C., and H. I. Fisher. 1962. Functional anatomy of the feeding apparatus in waterfowl (Aves: Anatidae). Southern Illinois University Press, Carbondale. Haramis, G. M., and D. Q. Thompson. 1985. Density-production characteristics of box-nesting Wood Ducks in a northern greentree impoundment. J. Wildl. Manage. 49:429-436. Heitmeyer, M. E., and L. H. Fredrickson. 1981. Do wetlands in the Mississippi delta hardwoods influence Mallard recruitment? N. American Wildl. and Nat. Res. Conf. 46:44-57. Humphrey, P. S., and K. C. Parkes. 1959. An approach to the study of molts and plumages. Auk 76:1-31. Johnsgard, P. A. 1961a. The taxonomy of the Anatidae—a behavioral analysis. Ibis 103:71-85. Johnsgard, P. A. 1961b. Evolutionary relationships among North American Mallards. Auk 78:1-43. Johnsgard, P. A. 1965. Handbook of waterfowl behavior. Cornell University Press, Ithaca, N.Y. Johnsgard, P. A. 1968. Waterfowl: their biology and natural history. University of Nebraska Press, Lincoln. Johnsgard, P. A. 1975. Waterfowl of North America. Indiana University Press, Bloomington.

THE WATERFOWL Johnsgard, P. A. 1978. Ducks, geese, and swans of the world. University of Nebraska Press, Lincoln. Kear, J. 1970. The adaptive radiation of parental care in waterfowl. Pp. 357-392 in Social behavior in birds and mammals (J. H. Crook, ed.). Academic Press, London. Kortright, F. H. 1942. The ducks, geese and swans of North America. Stackpole, Harrisburg, Pa., and Wildl. Manage. Inst. Washington, D.C. Lack, D. 1967. The significance of clutch-size in waterfowl. Wildfowl 18:125-128. Lack, D. 1968. The proportion of yolk in the eggs of waterfowl. Wildfowl 19:67-69. Livezey, B. C. 1986. A phytogenetic analysis of recent anseriform genera using morphological characters. Auk 103:737-754. Lokemoen, J. T., H. F. Duebbert, and D. E. Sharp. 1984. Nest spacing, habitat selection and behavior of waterfowl on Miller Lake Island, North Dakota. J. Wildl. Manage. 48:309-321. Ogilvie, M. A. 1967. Ducks of Britain and Europe. T. and A. D. Payser, Berkhamsted, U.K. Ogilvie, M. A. 1978. Wild geese. Buteo Books, Vermillion, S.D. Owen, M. 1977. Wildfowl of Europe. Macmillan, London. Palmer, R. S. (ed.) 1976. Handbook of North American birds. Vols. 2 and 3. Yale University Press, New Haven, Conn. Pettingill, Jr., O. S. 1985. Ornithology in laboratory and field. Academic Press, New York. Phillips, J. C. 1986. A natural history of the ducks. Vols. 1 and 2. Dover, Mineola, N.Y.

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Raveling, D. G. 1979. The annual cycle of body composition of Canada Geese with special reference to control of reproduction. Auk 96:234-252. Rees, E. C., and N. Hilgarth. 1984. The breeding biology of captive Black-headed Ducks and the behavior of their young. Condor 86:242-250. Rohwer, F. C. 1986. Interspecific and intraspecific relationships between egg size and clutch size in waterfowl. In The adaptive significance of clutch size in waterfowl. Ph.D. Dissertation, University of Pennsylvania, Pittsburgh. Rohwer, F. C., and S. Freeman. 1989. The distribution of conspecific nest parasitism in birds. Can. J. Zool. 67:239-253. Salomonsen, F. 1968. The moult migration. Wildfowl 19:5-24. Scott, P., and H. Boyd. 1957. Wildfowl of the British Isles. Country Life, London. Siegfried, W. R. 1970. Double wing-moult in the Maccoa Duck. Wildfowl 21:122. Weller, M. W. 1980. The island waterfowl. Iowa State University Press, Ames. Weller, M. W, and Batt, B. D. J. 1987. Introduction. Pp. 3-8 in Waterfowl in winter (M. W. Weller, ed.). University of Minnesota Press, Minneapolis. Welty, J. C. 1979. The life of birds. Saunders, Philadelphia. Wilmore, S. B. 1974. Swans of the world. Taplinger, New York. Woolfenden, G. E. 1961. Postcranial osteology of the waterfowl. Florida State Mus. Bull. 6:1-129.

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R CHAPTER

11

Foraging Ecology and Nutrition Gary L. Krapu and Kenneth J. Reinecke

I. Introduction

America (e.g., McAfee, 1918; Cottam, 1939; Martin and Uhler, 1939).

Reproduction in birds is generally timed so that the breeding cycle coincides with maximum availability of food for nesting adults or developing young (Immelmann, 1971). Food availability to birds can vary widely within and between years, however, with major implications to reproductive success (Pitelka et al., 1955; Kahl, 1964; Simmons et al., 1986). Recruitment among waterfowl may be particularly sensitive to the quantity and quality of food resources available, because the energy and nutrient requirements of egg-laying females are large relative to those of other bird species (see chapter 2 of this volume). In this chapter, we describe adaptive strategies of waterfowl for meeting nutrient requirements for reproduction and assess the significance of food in regulating reproductive performance. Our primary focus is on waterfowl occurring in the United States, Canada, and western Europe because most of the literature on waterfowl feeding ecology is from research conducted on Northern Hemisphere species.

A. The Feeding Ecology of Breeding Ducks The strengths of early studies of the food habits of ducks were their continental scope, large sample sizes, and long-term data. The weaknesses were limitations resulting from the use of food samples from gizzards or combined gizzards and esophagi of nonbreeding birds, and from the lack of supplemental data needed to assess variation in diet associated with sex or reproductive status. Studies conducted prior to 1960 mistakenly concluded that most species of Anatini and Aythyini depended primarily on plant foods during the breeding season. The years from 1960 to 1970 were a transition period. For the first time, substantial samples of breeding ducks were collected specifically for research on food use. Comparison of foods from the esophagi and gizzards of these birds indicated that data from the latter were biased toward foods with slower rates of digestion, especially seeds and other plant parts (Perret, 1962; Bartonek and Hickey, 1969). These studies clearly demonstrated that aquatic macroinvertebrates were the most important source of food during the breeding season for species such as the Mallard, Redhead, and Canvasback. Although the occurrence of macroinvertebrates in the diet was initially attributed to increased availability during summer (Perret, 1962), the emphasis later shifted to a nutritional interpretation (Bartonek and Hickey, 1969). Differential use of macroinvertebrates by males and females was recognized during the 1960s, but temporal differences in diet were interpreted with reference to calendar rather than physiological events. The experimental work of Swanson and Bartonek (1970), which confirmed the results of field studies regarding the need

II. Historical Perspective The history of research on the feeding ecology of North American waterfowl can be traced back to 1885, when the U.S. Congress established the Section of Economic Ornithology in the Department of Agriculture (Sterling, 1974). Objectives of the new program were to continue research on bird migration initiated by the American Ornithologists' Union, and to study the behavior and food habits of birds, especially in relation to agriculture. This early commitment to study the food relationships of waterfowl and other birds continued through several reorganizations of the Section of Economic Ornithology, which later became the U.S. Fish and Wildlife Service, and resulted in the publication of comprehensive studies of the food habits of many popular game ducks in North 1

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GARY L. KRAPU AND KENNETH J. REINECKE

for esophageal food samples, separated the period of the 1960s, wherein new research methods and concepts were developed, from the subsequent period during which they were widely applied. Research on the feeding ecology of breeding ducks expanded further in the 1970s and 1980s. It was discovered that the proportion of macroinvertebrates in the diet of females varied with reproductive status (Krapu, 1974a, b; Serie and Swanson, 1976; Drobney and Fredrickson, 1979), and food use also was related to changes in nutrient reserves (Drobney, 1980; Krapu, 1981; Noyes and Jar vis, 1985). Cumulatively, these studies resulted in an integrated approach to feeding ecology research, wherein esophageal samples were used to interpret food use relative to sex, reproductive status, nutrient dynamics, and site-specific food abundance.

B. The Feeding Ecology of Prebreeding and Breeding Swans and Geese Feeding-ecology data for prebreeding and breeding swans are limited because biologists have been reluctant to collect swans for food habits research. Food habits of geese also received little attention until recently, probably because of limited perceived competition with agriculture and the remote and relatively undisturbed locations of the breeding grounds of most populations. Although the history of research on the feeding ecology of geese differs from that of the ducks, events during the 1960s had a strong influence on both. Important observations made during studies of the breeding biology of geese in the 1960s were that dramatic changes in body weight and carcass composition, and low rates of feeding, were characteristic of nesting adults (Barry, 1962; Hanson, 1962). The research stimulated by these observations initially emphasized the size, composition, and use of nutrient reserves by breeding geese (chapter 2) rather than the foraging behavior associated with nutrient acquisition. However, more recent studies of prebreeding geese (McLandress and Raveling, 198la, b; Gauthier et al., 1984a, b; Teunissen et al., 1985) have considered food use during periods of lipid and protein deposition, and the effects of sex, age, and social behavior on patterns of nutrient acquisition. Thus, differences in history and emphasis exist, but current approaches to studying the feeding ecology of prebreeding geese and breeding ducks have much in common.

III. Research Methods The first part of this section considers methods of data collection and analysis that are common to most studies of feeding ecology. In the second part, we note some special problems and opportunities regarding the study of geese and other herbivorous waterfowl.

A. Methods Common to Most Studies of Feeding Ecology Analysis of esophageal food samples is currently the preferred method of studying the diets of prebreeding and breeding waterfowl. The advantages of esophageal samples have been demonstrated with field (Bartonek and Hickey, 1969; Sedinger, 1986) and experimental (Swanson and Bartonek, 1970) studies. Alternatively, analysis of fecal samples can provide valuable data on diets of grazing species when the collection of specimens is not possible (Owen, 1975a). Once food samples have been obtained, most researchers record the frequency of occurrence and weight or volume of each type of food in each sample. Dry weight is preferred for the latter measurement because wet weight and volumetric data complicate the interpretation of nutrient and energy intake (Sugden, 1973; Reinecke and Owen, 1980). Frequency data from food samples generally are used to analyze food selection, and weight or volumetric data are used to estimate diet composition and interpret nutritional relationships. Frequency data can be used to assess food selection only if food resources are sampled when birds are collected. If this is done, food selection can be inferred from differences in the frequencies of occurrence of various food types between samples from the birds and samples from the feeding sites. Readers should consult Thomas and Taylor (1990 and references therein) for guidance on experimental design. It is probably best to interpret the results of these tests conservatively, because strong evidence for food selection requires unbiased samples of the food available to foraging birds. Obtaining unbiased samples is difficult, especially in studies where ducks feed on active organisms in complex aquatic habitats. Two methods currently are used to estimate diet composition (Swanson et al., 1974). In the aggregate weight or volume method, the percentage of each food type in the diet is estimated as the cumulative weight or volume of that food in all samples expressed as a percentage of the cumulative weight or volume of all foods in all samples. In the aggregate percent method, the percentage of each food in the diet is estimated as the average over all birds of the weight or volume of that food in each sample expressed as a percentage of the total weight or volume of the corresponding sample. If the aggregate percent method is used and each bird represents an independent observation, then standard parametric (e.g., Reinecke and Owen, 1980) and nonparametric (e.g., Drobney and Fredrickson, 1979) statistics can be used to test for differences in diet between sexes or among groups differing in reproductive status. The aggregate percent method of estimating diet composition has several advantages: (1) it prevents large

FORAGING ECOLOGY AND NUTRITION food samples with rare food types from unduly influencing estimates of diet composition (Swanson et al., 1974); (2) it avoids the restrictive assumption that all foods are digested at similar rates (Swanson and Bartonek, 1970); and (3) it facilitates statistical testing. However, the aggregate percent method also makes an assumption: that composition of the diet is unrelated to the size distribution of food samples. Generally, the aggregate percent method seems more appropriate when food-processing rates limit food intake, and the aggregate weight or volume method seems more appropriate when time spent searching for prey limits food intake.

B. Methods Specific to Studies of Geese and Other Herbivorous Waterfowl Researchers studying the feeding ecology of geese and other herbivorous waterfowl encounter special problems but also have unique opportunities. One problem concerns the interpretation of laboratory analyses of the protein content of plant tissues. Traditional proximate analyses estimate the percentage of crude protein in a sample as the percentage of nitrogen multiplied by 6.25 to account for the average nitrogen content of protein (Robbins, 1983). Crude protein overestimates the potential availability of plant protein to geese and other herbivores, however, because stems and leaves of herbaceous plants contain significant quantities of nonprotein nitrogen, mostly in refractory structural compounds. Sedinger (1984) made independent estimates of nitrogen and protein in foods of the Cackling Canada Goose and found that crude protein overestimated true protein by 22-52%. Future studies should adopt similar procedures or at least consider the implications of biased estimates when crude protein data are used to assess the availability of protein in plant tissues. Another problem involving the chemical characterization of plant foods is the analysis of cell structural compounds. Traditional proximate analyses provide an estimate of crude or acid detergent fiber, which consists of cellulose and lignin (Robbins, 1983). In the past, most researchers (e.g., Reinecke and Owen, 1980) accepted the conclusion (Mattocks, 1971) that cellulose is indigestible, and assumed that the energy in crude fiber was unavailable to waterfowl. However, recent studies have shown that herbivorous waterfowl can metabolize 25-74% of the hemicellulose in plant foods (Buchsbaum et al., 1986; Dawson et al., 1989; Sedinger et al., 1989). In contrast, data regarding digestibility of cellulose or acid detergent fiber are inconclusive (cf. Buchsbaum et al., 1986; Sedinger et al., 1989). Clearly, the ability of geese to utilize cell structural compounds appears to be an important area for future research. Although cell structural compounds present problems, they also provide a unique opportunity to study

3

the nutrition of free-living geese. If it is assumed that crude fiber, lignin, or another indigestible substance can be used as a tracer in the food and feces, traditional methods of estimating nutrient retention rates for captive birds can be used in the field. This approach, which has been explored more by European (Ebbinge et al., 1975) than by North American researchers, requires that the birds being studied: (1) feed on land and produce feces that are easily collected; (2) eat one or only a few plant species; and (3) forage in a uniform habitat patch long enough to produce feces representing the local food source. If these conditions are met, food and feces can be collected and analyzed, and digestibility estimated, with standard methods (Robbins, 1983). Using this approach, Madsen (1985a) estimated that Pinkfooted Geese in Denmark were able to digest 24-29% and 53-64% of the dry matter in pasture grasses and barley grain, respectively.

IV. Timing of Nutrient Acquisition Waterfowl employ numerous strategies to meet their nutritional needs for breeding. Some species acquire most of their nutrients for reproduction while on wintering and/or staging areas, and others depend primarily on daily intake of nutrients during the nesting season (Owen and Reinecke, 1979).

A. Swans and Geese North American swans probably derive a significant part of their nutrient requirements for reproduction from wintering grounds and/or spring staging areas. Tundra Swans of the eastern population leave midAtlantic wintering grounds relatively lean, but stop at intermediate staging areas where nutrient reserves important to reproduction are thought to be acquired (Bortner, 1985, p. 32). Information is lacking on patterns of nutrient acquisition by Trumpeter Swans. Most North American goose populations depend on nutrients imported to the breeding grounds to provide a significant part of their requirements for reproduction (Table 1-1). Canada Geese breeding in interior regions have adapted to harsh climatic conditions on their temperate, subarctic, and arctic breeding grounds prior to, and during nesting, by acquiring nutrient reserves before leaving temperate wintering and staging areas. Giant Canada Geese deposit sufficient nutrient reserves to satisfy protein and lipid requirements for egg production before leaving their wintering grounds in southern Minnesota (McLandress and Raveling, 198la). Midcontinent populations of Interior Canada Geese and Lesser Snow Geese acquire most of their nutrients for reproduction during migratory stopovers in temperate and subarctic regions (Hanson, 1962; Raveling and Lumsden, 1977; Wypkema and Ankney, 1979; Thomas and

GARY L. KRAPU AND KENNETH J. REINECKE

4

Table 1-1. The contribution of endogenous protein, fat, and calcium to egg production in selected North American waterfowl3 Protein Fat Calcium Tribe and species Reference Subfamily Anserinae Tribe Anserini Lesser Snow Goose Cackling Canada Goose Dusky Canada Goose Brant Subfamily Anatinae Tribe Cairinini Wood Duck Tribe Anatini Mallard Northern Shoveler Tribe Aythyini Canvasback

Primary fc

Primary

Primary Secondary (ca. 34%) Primary (ca. 71%)

Primary Secondary Primary

Secondary Tertiary (17%) Tertiary (ca. 13%)

Tertiary

Primary

Tertiary

Drobney (1980)

Tertiary Tertiary

Primary Primary

Tertiary

Krapu (1981) Ankney and Afton (1988)

Tertiary (ca. 1 egg) Secondary (ca. 2 eggs) Tertiary (ca. 1 egg) Tertiary

Secondary Primary Primary Primary

Tertiary (ca. 1 egg) -

Ankney and Maclnnes (1978) Campbell and Leatherland (1983) Raveling (1979b) Bromley (1984) Ankney (1984)

Noyes and Jarvis (1985) Barzen and Serie (1990) Noyes and Jarvis (1985) Hohman (1986)

Redhead Ring-necked Duck Tribe Mergini Primary Primary Korschgen (1977) Common Eider Tertiary Tertiary Tertiary White-winged Scoter Dobush (1986) Tribe Oxyurini Tertiary Secondary (ca. 35%) Tertiary Ruddy Duck Tome (1984) a lnitial nesting attempt only. b Primary = ^ 50% of the nutrient requirement for the clutch; secondary = < 50% of the nutrient requirement for the clutch and ^ the nutrient requirement for 1 egg; tertiary = < the nutrient requirement for 1 egg.

Prevett, 1982a; Alisauskas, 1988). Among Lesser Snow Geese, most fat reserves are deposited in the northern prairie region, whereas protein storage occurs early in spring migration and after geese arrive on staging areas along southern Hudson Bay (Alisauskas, 1988). Some arctic-nesting geese with widely spaced spring staging and nesting areas feed intensively after arrival on their breeding grounds, presumably to replenish depleted energy reserves. Greater Snow Geese acquire fat reserves principally on staging areas in the St. Lawrence River estuary (Gauthier et al., 1984a), but females still forage 75% of the time during the extended prelaying period (Table 1-2). Brant that follow an inland route to their breeding grounds in the arctic northwest of Hudson Bay deposit large fat reserves prior to departure from their coastal wintering grounds on Long Island, New York (VanGilder et al., 1986). However, Brant also feed intensively on the breeding grounds and derive part of their nutrient requirements for reproduction there (Ankney, 1984). Greater White-fronted Geese of the Pacific Flyway population deposit fat reserves during their annual spring stopover in the Klamath Basin. Spring weight gains of western White-fronts are somewhat less than those of most other species of arctic-nesting geese (Ely and Raveling, 1989), and the population breeding on the Yukon-Kuskokwim Delta, Alaska, acquires part of the energy and nutrient reserves necessary for reproduction after arrival on the breeding grounds (Budeau, 1989). Some species or populations of geese derive a major

part of the nutrients required for egg production from foods obtained on the breeding grounds (Tables 1-1, 1-2). Female Dusky Canada Geese nesting in a relatively mild climate on the Copper River Delta in southeastern Alaska feed intensively prior to and during egg laying (Table 1-2), and acquire an estimated 66% of their protein requirements for egg production from foods available on the nesting grounds (Bromley, 1984, p. 57). For smaller species such as Cackling Canada Geese and Brant, nutrient reserves are the primary source of lipid and protein for egg production (Table 1-1). However, daily food intake is important as a secondary source of protein for egg production and as a primary source of energy for maintenance, providing an estimated 60% of the requirements of female Cackling Canada Geese (exclusive of the energy content of eggs) between arrival and initiation of incubation (Raveling, 1979a). The extent of foraging by female geese during incubation also varies among species and populations. Female Lesser Snow Geese, Ross' Geese, Emperor Geese (Table 1-2), and Interior Canada Geese feed little during incubation and experience marked losses of body weight (Ryder, 1967; Harvey, 1971; Raveling and Lumsden, 1977; Thompson and Raveling, 1987). In contrast, female Brant feed regularly during incubation (Table 1-2), and obtain an estimated 78% of their energy requirements from foods available on coastal marshes near the nesting site (Ankney, 1984). Feeding during incubation is necessary for Barnacle Geese nesting in Spitzbergen; females that fall below median food intake rates gener-

5

FORAGING ECOLOGY AND NUTRITION Table 1-2. Foraging effort by female geese during the breeding season Reproductive status Species Anser albifrons

Anser albifrons flavirostris Anser caerulescens atlantica Anser caerulescens caerulescens Anser rossi Anser canagicus

Location

Prenesting

Laying

Incubation

Brood-rearing

Y-K Delta,3 Alaska Y-K Delta,3 Alaska Col-R Delta,b Alaska

58% 60% 68%

-

-

Greenland

68%

-

-

Bylot Island, N.W.T.

75%

-

-

"little"

85%d

"short" limited

"most"

McConnell River, N.W.T. Arlone Lake, N.W.T. Y-K Delta, Alaska

Marshy Point, Manitoba Branta canadensis maxima Y-K Delta, Alaska Branta canadensis minima Cop-R Delta,0 Alaska Branta canadensis occidentalis Branta bernicla Southampton Island, N.W.T. a Yukon-Kuskokwim River Delta. b Colville River Delta. c Copper River Delta. d Of daylight hours.

'occasionally" -

( 82% of the time. Intruders left the area > 80% of the time. Established residents were almost never displaced by intruders at the same stage of their breeding cycle. The same was true for territorial American Wigeon (Wishart 1983). Similarly, male Canvasbacks nearly always won aggressive encounters that they initiated (Anderson 1985a). Why should this be? Surely all resident birds are not that superior to intruders. Are the birds playing a simple strategy of "retreat if a pond is occupied," or are asymmetries in resource value or RHP responsible for these lopsided outcomes? Should this

275

SPACING PATTERNS convention change predictably with time, resource abundance, or population density? A related issue is the way that territory ownership is established. How do dispersion patterns develop each spring in migratory species? Female experience must be a major factor (chapter 11), but males do most of the chasing of other pairs. How do males choose where and when to chase conspecifics and how to respond to individual competitors? For most prairie ducks, settling is highly asynchronous (Humburg et al. 1978; Ohde et al. 1983; Anderson 1985a). Is this simply a matter of inability on the part of some birds to arrive early or to compete successfully, or are some individuals making what for them is the best of a difficult situation by settling later, avoiding much competition, but incurring the costs of delayed breeding in a seasonal environment? Pursuit flights in the genus Anas have caused long debates over apparently conflicting motivational tendencies and probable multiple functions. Tactics of interlopers, chasers, and defending mates should be explored using objective predictions of behavior from a priori ESS modeling in order to shed new light on this intriguing behavior pattern. ESS thinking has led to many new ideas concerning the evolution of signaling behavior. Much early thinking about displays focused on selection for unambiguous transfer of information between animals (Bastock 1967; Sebeok 1977; Smith 1977). Ethologists are now looking at displays with new questions in mind—considering bluffing versus honest signaling, salesmanship, manipulation, mind reading, exploitation, and deception (Trivers 1971; Dawkins and Krebs 1978; Rohwer 1977; Zahavi 1979; Dawkins 1982; Krebs and Dawkins 1984). These views are beginning to affect the analysis of waterfowl courtship (chapter 7) and should be extended to threat displays and other aspects of spacing behavior.

VI. A Critique of Waterfowl Spacing Studies and Recommendations for Future Research During our review of the literature on spacing behavior, we were disappointed to note that there are virtually no references to waterfowl studies in recent general reviews of spacing. Why should this be, if waterfowl are as well studied as we claim (see Introduction) ? We suspect there are at least two reasons. First, waterfowl studies are usually logistically difficult and expensive. This means that members of the family do not lend themselves well to quick experimental studies of new concepts. On the other hand, the diverse radiation of waterfowl offers great opportunity for comparative analyses of social behavior (McKinney 1978,1986), and it is in this way that waterfowl studies now contribute most to general ideas about social evolution. The second possibility is that those of us interested in waterfowl spacing behavior

have lost step with theoretical progress in this rapidly changing field and are rarely pursuing questions of general interest to behavioral ecologists. In the following section we try to identify the main gaps in our knowledge of waterfowl spacing behavior and some collective shortcomings in our approaches to studying it.

A. Empirical Needs and Comparative Studies An obvious conclusion from this survey is that numerous gaps remain in our understanding of the basic life histories of many species. Simple descriptive observations concerning aggressive behavior and breeding dispersion would be of value, especially for various whistling ducks (Dendrocygnini); several shelducks and sheldgeese (Tadornini); 17 species of tropical, Asian, Australian, and South American dabbling ducks (Anatini); the white-eyes and narrow-billed pochards (Aythyini); many Cairinini and Oxyurini; and several arctic sea ducks (Mergini). Even for the better-known species there are only meager data concerning details of agonistic behavior. Careful field studies of individually marked birds of most species are still needed. It is important to learn exactly who chases whom, where, and when (Goodburn 1984; Anderson 1985a). We still know very little about how spacing behavior changes with age, sex, and reproductive status, and how interactions vary in different contexts or between different individual competitors. Until such data are available, quantitative comparative studies will not be possible (cf. Clutton-Brock and Harvey 1977; Harvey and Mace 1982), and these are needed if we are to develop and critically test general hypotheses concerning the evolution of spacing behavior in waterfowl. Future descriptive studies of waterfowl spacing behavior should: (1) document male and female roles in agonistic interactions with conspecifics in relation to individual characteristics (e.g., sex, pairing status) and behavior of the participants, context, and the location of important resources; (2) report temporal changes in behavior, especially in relation to breeding status; and (3) describe the resulting pattern of dispersion among birds, both spatially and temporally. These suggestions are similar to McKinney's (1965a) of many years ago.

B. Resources There is a serious lack of information about the distribution and abundance of key resources that waterfowl appear to be defending. Few studies (Patterson 1982; Gauthier 1987b) have attempted to quantify the distribution of important resources, and no one has attempted to manipulate resources and look for behavioral responses. Only preliminary attempts have been made to discover and understand variation in ag-

276

MICHAEL G. ANDERSON AND ROGER D. TITMAN

gressive behavior and home ranges within species (Nudds and Ankney 1982; Amat 1983). Until measurements of resource characteristics and associated behavior are made for a variety of species or populations, we can do little else but speculate about the ecological bases of the patterns we observe. We regard this as perhaps the greatest single deficiency in waterfowl spacing studies to date.

C. Tests of General Models Although most waterfowl systems present formidable logistical difficulties for testing economic models of spacing behavior, a few situations, such as where species maintain permanent river territories, may be amenable to such studies. Regardless, cost/benefit thinking has been influential and should continue to guide the selection of specific research questions on spacing behavior for the foreseeable future. Similarly, studies of settling behavior in migratory breeding waterfowl and the dynamics of home range establishment will be difficult, but perhaps feasible, in relatively isolated study areas with small populations of marked birds. These should be pursued, because many questions remain unanswered concerning the biology of "floaters," the costs and benefits of breeding site philopatry, and the causes and consequences of "overflight" of traditional breeding grounds when environmental conditions change (see Johnson 1986; chapters 11 and 14). With the exception of pursuit flights in the genus Anas, chasing behavior and threat displays in waterfowl have received little detailed study in the context of spacing. There is undoubtedly much interesting, unexplored variation waiting to be discovered. Insights from game theory thinking and tests of specifically constructed ESS models should be employed in future studies of agonistic behavior. Several specific suggestions along these lines were made above. Observations of captive breeding birds might be particularly useful for such studies, because details of display exchanges, including subtle differences in orientation or intensity, can be recorded more easily; long-term relationships between known individuals can be studied more reliably; and experimental manipulations should be more feasible than with wild birds.

D. Long-term Field Studies Long-term studies of known individuals are needed to assess changes in agonistic behavior with age or experience and to study the fitness payoffs of different spacing strategies under variable environmental and social circumstances. Only long-term studies in natural environments can provide such data. Studies by Cooke et al.

(1982), Patterson (1982), Newton (1986), Woolfenden and Fitzpatrick (1977, 1978, 1984), Watson (1977), Watson and Moss (1972), Watson et al (1984a, b), Moss and Watson (1985), Nolan (1978), Coulson (1966, 1972, 1984), Glutton-Brock et al. (1982), and Goodall (1986) provide good models for long-term single-species research.

E. Social Relationships Rubenstein and Wrangham (1986) have emphasized the need for studies of long-term relationships among individuals who know each other and have histories of interaction. Long-term relationships may influence the costs and benefits of interactions in ways that make no sense to one observing interacting individuals for the first time. For instance, a vigorous fight over some trivial item may be inexplicable without knowing that a longterm dominance relationship between the two contestants is at stake. We agree there is a need for such analyses, particularly among individuals in sedentary populations or among tightly philopatric individuals in migratory populations, including but not limited to close kin, where the opportunity for development of long-term social relationships is greatest.

F. Density-Dependent Changes in Behavior Few studies have examined the effects of population density on the breeding behavior of waterfowl (Titman and Lowther 1975; Titman 1983), but these suggest that substantial disruption of normal patterns may occur at high densities. Further studies are needed to measure the impact of changing population density on spacing behavior and dispersion, and ultimately on reproductive success and survival. Such studies should be conducted over sufficient years to assess variability in natural populations. The long-term studies of Northern Shelducks by Patterson and his colleagues (Patterson 1982; Patterson et al. 1983) are exemplary but unique. Field experiments might be used to modify population density while also monitoring appropriate control populations. Such an approach has the additional advantage of removing possible confounding effects of year and density. The small-unit management study under way in North Dakota and Minnesota by the United States Fish and Wildlife Service is such an experiment, designed in part to determine the effects of increased density on Mallard behavior and reproduction. If management of breeding waterfowl becomes more intensive in the future, it is critically important that we gain a clearer understanding of the long-term effects of population density on spacing and reproductive success in breeding birds.

277

SPACING PATTERNS

VII. Discussion for Management A. Ethology and Waterfowl Management Unlike investigators working with many animals, waterfowl biologists frequently ask questions for three fundamentally different reasons: (1) to solve specific wildlife management problems; (2) to answer questions about the basic biology of waterfowl; and (3) to test theoretical hypotheses. Unfortunately, investigators employing these different approaches frequently contribute little to solving each others' problems. This should not be so with the study of spacing behavior. Intensive management of breeding waterfowl demands a clear understanding of spatial relationships among breeding birds and possible behavioral limits to habitat carrying capacity. We believe this continues to be a promising area for productive cooperation between ethologists and waterfowl managers.

B. Spacing and Population "Regulation" The publication of Wynne-Edwards's classic Animal Dispersion in Relation to Social Behaviour (1962) ushered in a period when much attention was given to territorial behavior as a factor in limiting animal numbers. Literature on this subject is filled with arguments, often vague, about levels of selection and whether social behavior in general, and territoriality in particular, may have evolved to limit population growth and prevent overexploitation of resources. For the great majority of animal species, that view has been refuted (II.B. above). Nevertheless, the possibility of populations being limited as a consequence of territorial behavior or other forms of spacing behavior remains an interesting question for population biologists and wildlife managers. The scale at which such limitation might occur is an important consideration. Local populations might be limited by spacing behavior, but this does not necessarily imply that whole species' populations are limited in a similar manner. Several studies with a variety of birds have shown that spacing behavior can indeed limit the number of individuals breeding in a finite study area (Orians 1961; Krebs 1971; Watson 1977; see Davies 1978 for review). Limitation of a local waterfowl population by social behavior has been demonstrated only for Northern Shelducks (Patterson 1980; Patterson et al 1983) and perhaps Buffleheads (Gauthier and Smith 1987) and Long-tailed Ducks (Alison 1975), although such limitation seems likely for at least several other species with restricted habitats (e.g., African Black Ducks,

Ball et al 1978; McKinney et al 1978) or for isolated populations in limited habitat (e.g., Mallards, Humburg etal 1978; Ohde et al 1983). The distinction between local and overall population limitation by social behavior is important for population managers to understand. Speculations about behavioral causes of population limitation in geographically widespread species (e.g., Mallards, Aldrich 1973; Pospahala et al 1974) are likely to be misleading, although local limitation might occur in some years and in certain habitats. In contrast, geographically restricted species, with specialized habitat requirements that ultimately constrain population size, may well be candidates for proximal behavioral limitation, and this possibility should not be ignored by conservationists. The extent to which local populations might be restricted by social behavior in a variety of species deserves further study. For intensively managed populations, local densities might well exceed the limits beyond which birds will not crowd further (or some other density-dependent constraint may become effective). In such cases, these limits should be identified so that additional innovative techniques to increase pair densities might be attempted, or conversely, so that useless efforts to further increase populations might be avoided. Intensively managed plots of dense nesting cover or island refuges are examples of the kinds of management practices that might be so affected. In such cases, it will also be important to understand longerterm effects of crowding, including impacts on resources, brood survival, philopatry, and reproduction in surrounding areas.

Acknowledgments For support while writing this paper we thank the North American Wildlife Foundation through the Delta Waterfowl and Wetlands Research Station (Anderson), the Institute for Wetland and Waterfowl Research (Anderson), and McGill University (Titman). We are grateful to several persons cited in the text who provided access to unpublished data and observations, and to Bruce Batt, John Ryder, Frank McKinney, Doug Johnson, and Gilles Gauthier for helpful comments on the entire manuscript. Diane Chronister, Leigh Fredrickson, and Dennis Raveling offered useful comments on specific tribal accounts. Rodger Titman is also grateful to Harry Beach of Kouchibouguac National Park for providing office space during the preparation of this paper.

MICHAEL G. ANDERSON AND ROGER D. TITMAN

278

Appendix 8-1. Spacing patterns and other characteristics of breeding waterfowl Tribe Anseranatini

Species

Anseranas setnipalmata Dendrocygnini Dendrocygna guttata D. eytoni D. bicolor D. arcuata D. javanica D. viduata D. arborea D. autumnalis Thalassornis leuconotus Anserini Cygnus olor C. atratus C. melancoryphus C. buccinator C. cygnus C. columbianus C. bewickii Coscoroba coscoroba Anser cygnoides A. fabalis A. albifrons A. erythropus A. anser A. indicus A. caerulescens A. rossii A. canagicus Branta sandvicensis B. canadensis B. leucopsis B. bernicla B. ruficollis A. brachyrhynchus Cereopsini Cereopsis novaehollandiae Stictonettini Stictonetta naevosa Cyanochen Tadornini cyanopterus Chloephaga melanoptera C. picta C. hybrida C. poliocephala C. rubidiceps Neochen jubata Alopochen aegyptiacus Tadorna ferruginea T. cana T. tadornoides T. variegata T. cristata T. tadorna T. radjah Tachyerini Tachyeres patachonicus T. pteneres T. brachypterus

Spacing system3

Pair bondb

Habitat stability0 Dietd

Home range (ha)e

Female weight (g)

Plumage dimorphismf

References8

6

1.5

1

1

2070

0

44,59,61

U

U-l

4

1

800

0

61

U 5,6 U U U U-6 5,6 U

U-l 1 1 U-l 1 U-l 1 U-l

T 4 4 4 3 4 4 3

1 1 1 3 3 1 1 2

790 690 732 525 662 1150 840 690

0 0 0 0 0 0 0 0

44,61 61,90,103,141 44,61 61 61 17,61 17,61,103 26,61

1 6 U 2 2 2 2 U

1 U-l U 1 1 1 1 U-l

3 2 3 3 4 5 5 4

1 1 2 2 1 1 1 U-3

8750 5100 4000 9400 8750 5700 5000 3800

0 0 0 0 0 0 0 0

31,62,94 61,52 61 7,54,90 31 31,62 61,62 61,62

U U-5 5 5 5,6 6 6 6 5 U-4 5 6 6 6 6 U-2

U-l 1 1 1 1 U-l 1 1 1 1 1 1 1 U-l 1 1

3 4 4 4 4 4 5 3 4 T 2 1 5 2 5 1

1 1 1 1 1 U-2 1 1 2 1 1 1 1 1 1 1

3150 2850 2275 1400 3100 2500 2510 1225 2765 1925 3000 1625 1245 1090 2340 3770

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

34,61,89 31,74 8,10,31,90 31,61 31,85,88,89,136 34,61,89 8,10,29,65,90,102 10,90,101 38,61,89 61 10,20,30,43,81 31,61,88 31,81,88,90 31,61,89 31,66 44,52,61

U U

U U

3.5 3

2 2

840 1520

0 0

18,44,61 61

U

U-l

3

U-l

3000

0

61

2 U-3 U U U-l 2

1 U-l U U-l 2

4 1 4 1 1 3

1 1 U-l 1 2 1

2800 2041 2200 2000 1250 2040

3 3 0 0 0 0

61 50,61,95 61 61 61 31

U-3 U 3 2 U 3 2 2

U-2 1 1 1 U 2 3 1

3 4 3 2 U 2 2 4

2 2 3 3 U 3 4 5

1088 1417 1291 1300 U 1025 840 2616

1 2 1 3 2 0 0 1

31 61 44,61,99 61,138 61 31,58,93,96,135 44,61 61,71,86

U-l 1

1 1

1 1

5 5

4111 3400

1 1

61,131 61,71,95,131

1

4.5 30 130

120 0.01 0.0007 0.001 0.001 1.7

0.03 0.001

1

1 1.7

279

SPACING PATTERNS Appendix 8-1. (Continued) Tribe Cairinini

Species

Plectropterus gambensis Cairina moschata C. scutulata Sarkidiornis melanotos Pteronetta hartlaubi Nettapus pulchellus N. coromandelianus N. auritus Callonetta leucophrys Aix sponsa A. galericulata Chenonetta jubata Amazonetta brasiliensis Merganettini Merganetta armata Anatini Hymenolaimus malacorhychos Anas waigiuensis A. sparsa A. penelope A. americana A. sibilatrix A. falcata A. strepera A. formosa A. crecca A. flavirostris A. capensis A. bernieri A. gibberifrons A. castanea A. aucklandica A. platyrhynchos A. laysanensis A. rubripes A. metier i A. undulata A. poecilorhyncha A. luzonica A. specularis A. specularoides A. acuta A. georgica A. bahamensis A. erythrorhyncha A. versicolor A. hottentota A. querquedula A. discors A. cyanoptera A. platalea A. smithii A. rhynchotis A. clypeata Malacorhynchus membranaceous Marmaronetta angustirostris Aythyini Netta rufina

Spacing system3

Pair bondb

Habitat stability0 Dietd

Home range (ha) e

Female weight (g)

Plumage dimorphism*

References8

U

U

4

2

4700

1

61

U U 2,3

6 2 4

1 1 3

3 3 2

1300 2485 1780

1 1 1

61 61,72 61,140

1 U-l U-3 U U

1 1 2 U-2 U-l

2 1 1 3 1

4 1 1 1 U-2

825 290 380 285 255

2 2 3 3 3

61 44,61 44,61 61 61

5 U 5 U

3 3 1 U-l

3 3 T 1

2 2 1 U

540 475 800 370

3 3 2 1

3,10,51,90 3,23,34,61 44,61,139 61

1 1

1 1

2 2

5 4

330 750

3 0

40,60,83 39,61,62,64

1 1 4 3 U U 4 U 5 U-6 U U U U 3 4 5,6 3 4 4 U U U-l 3 5 U U U U 5 3 3 3 U 3 U 3 5

1 2 3 3 2 2 3 3 4 5 5 U 3 3 2 3 3,1 3 3 3 3 U 2 2 4 U 5 4 U U 2 3 3 U 2 U 2 U

1 2 4 3 3 3 4 2 2 2 2 5 5 2 1 4 1 3 1 2 2 1 2 2 5 4 2 4 3 4 5 4 5 4 5 4 4 5

5 5 2 1 1 2 1 3 3 4 4 U 3 U 5 3 5 3 U 2 2 U 3 5 2 4 2 2 2 2 4 3 3 5 5 4 5 5

470 1000 640 680 830 585 950 430 350 395 400 U 475 540 600 1000 460 1160 U 817 1000 1025 950 900 800 535 525 565 375 250 400 330 360 525 595 665 590 345

0 0 2 3 1 3 2 3 3 0 0 0 1 2 1 3 1 1 0 0 0 0 0 3 1 1 1 1 2 2 2 2 1 1 2 3 0

61,63 6,79,61 9,13,31,55 90,133 61,125 31,61 10,36,45,90 61 31,55,90 61,127 61,119,132 61,109 44,61,67 44,61 35,61,128,129 10,31,37,49,90,120 137 10,90,111,121 61 2,61,100 2,44,61 61 61 61,127 10,78,90,116,117 61,130 61 61 61 27,61 31 10,15,90,118 10,28,77,90 61 61,77,112 44,61 10,76,90,97,110 44,61

5

3

4

2

490

0

9,31,34

5

4

4

2

1110

3

31,34,68,69

1 7.8

16 2

0.69

0.9

1

MICHAEL G. ANDERSON AND ROGER D. TITMAN

280

Appendix 8-1. (Continued) Tribe

Species

Spacing system3

Pair bondb

Habitat stability0

Dietd

Home range (ha) e

Female weight (g)

Plumage dimorphismf

References8

4 U-4 U-3 770 U N. erythropthalma 21,25,33,61,82 2 5 U-2 U 1000 U N. peposaca 61,124,125 3 4 2 5 40 1160 A. valisineria 5 4,5,10,56 3 4 4 3 930 A. ferina 5 3,16,31 3 4 3 3 970 A. americana 5 10,90,107,123 3 4 3 4 670 10,57,80 3 5 A. collaris 4 44 U-3 U-3 840 2 U-5 A. australis U 3 U 61 A. baeri 680 U 3 4 U-2 31,34 U-3 A. nyroca 520 2 U-5 4 U U 61 U 2 A. innotata U 4 5 3 31,48 710 A. fuligula 5 3 U 4 U-5 61,87 610 2 U A. novaeseelandiae 3 3 U-5 10,31,90 975 3 A. marila U-5 4 3 5 1,10,53,122 750 3 A. af finis 5 1 U-3 5 10,61,90 1900 3 Mergini Somateria 6 mollissima 2 U-3 5 10,90,91 1750 S. spectabilis 5 3 2 U-3 4 31,32,90 1625 S. fischeri 5 3 2 U-3 31,34,90 875 5 3 Polysticta stelleri 5 2 530 U-3 5 11,14,31,90 3 Histrionicus 3 histrionicus 1 U-3 5 3,31,90 690 3 3 Clangula hyemalis 3 4 2 12,90 950 5 Melanitta nigra 5 4 2 61,90 900 3 5 M. perspicillata 5 2 4 2 22,31,90 1500 5 M. fusca 5,6 3 2 0.4 330 5 3 41,46,47,90 Bucephala albeola 3 3 2 4 0.7 785 3 90,104,105,106 B. islandica 3 2 800 3 4 3 90,105 B. clangula 3 2 4 5 3 10,84,90 540 Mergus cucullatus 5 9,31,34 4 U-3 5 3 600 6 M. albellus 1 61,92 U U 5 0 M. octosetaceus U 1 44,90,134 5 5 M. serrator 3 925 5,6 2 U 5 2 34,61 U M. squamatus U 2 4 1200 5 M. merganser 3 10,31,42,90 4 2 2 61 U 5 0 M. australis U 4 U-4 1 61,123 565 U Oxyurini Heteronetta U atricapilla 2 2 61,90 340 3 U Oxyura dominica U 4 500 3 3 3 10,90,114,115 O. jamaicensis 5 U 3 4 600 31,62,77 O. leucocephala 3 U-5 4 24,61,73,114 5 4 2 575 O. maccoa 3 U 3 3 560 2 61 O. vittata U 3 5 3 2 44,61 850 3 O. australis 4 6 5 0 19,44,61 1550 Biziura lobata 3 "Spacing system classified as detailed in the text: 1—year-round strong territoriality; 2—full breeding season territoriality; 3—early breeding season territoriality; 4—territoriality with overlap; 5 —dispersion with mate guarding; 6—coloniality; U—unknown. b Pair bonds ranked according to strength and stability: 1—perennial monogamy; 2 —seasonal monogamy, strong bond of long tenure (brood rearing); forced copulation not recorded or very rare; 3 —seasonal monogamy, bond of medium tenure (midincubation), low frequency of forced copulation; 4 —seasonal monogamy, bond of short tenure, relatively frequent forced copulation; 5—monogamy with occasional bigamy; 6—no bond; U—unknown. 'Habitat ranked according to stability: 1—tropical rivers, coastal waters; 2—temperate rivers, deep waters, inland coastal areas; 3 —lakes, permanent waters, ditches, potholes; 4—very shallow productive ephemeral waters; 5 — drought-vulnerable habitats, tundra ponds; T (not included in correlations)—terrestrial habitats. d Diet classified according to plant or animal content: 1—plant diet (> 90%); 2 — 75% plant; 3—50% plant, 50% animal; 4 — 75% animal; 5 —animal diet (> 90%); U—unknown. e Area occupied during the breeding season in ha (territory or home range). f Plumage color dimorphism: 0—none; 1—slight; 2—moderate; 3 —strong or pronounced. References: 1) Afton 1985; 2) Ali and Ripley 1968; 3) Alison 1975; 4) Anderson 1984; 5) Anderson 1985a; 6) Ball etal. 1978; 7) Banko 1960; 8) Barry 1966; 9) Bauer and Glutz von Blotzheim 1968; 10) Bellrose 1976; 11) Bengtson 1966; 12) Bengtson 1970; 13) Bengtson 1971; 14) Bengtson 1972; 15) Bennett 1938; 16) Bezzel 1969; 17) Bolen 1967; 18) Braithwaite 1976; 19) Braithwaite and Frith 1969; 20) Brakhage 1965; 21) Brown et al. 1982; 22) Brown and Brown 1981; 23) Bruggers 1979; 24) Clark 1964; 25) Clark 1966; 26) Clark 1969; 27) Clark 1971; 28) Connelly and Ball 1984; 29) Cooch 1958; 30) Cooper 1978; 31) Cramp and Simmons 1977; 32) Dau and Kistchinski 1977; 33) Dean and Skead

SPACING PATTERNS

281

1977; 34) Dement'ev and Gladkov 1952; 35) Dumbell 1986; 36) Dwyer 1974; 37) Dzubin 1969; 38) Eisenhauer and Kirkpatrick 1977; 39) Eldridge 1986a; 40) Eldridge 1986b; 41) Erskine 1972a; 42) Erskine 1972b; 43) Ewaschuk and Boag 1972; 44) Frith 1967; 45) Gates 1962; 46) Gauthier 1987a, b; 47) Gauthier and Smith 1987; 48) Gillham 1987; 49) Gilmer et al. 1975; 50) Gladstone and Martell 1968; 51) Grice and Rogers 1965; 52) Guiler 1967; 53) Hammell 1973; 54) Hansen etal. 1971; 55) Hilden 1964; 56) Hochbaum 1944; 57) Hohman 1984; 58) Hori 1969; 59) Johnsgard 1961; 60) Johnsgard 1966b; 61) Johnsgard 1978; 62) Kear 1972; 63) Kear 1975; 64) Kear and Steel 1971; 65) Kerbes 1975; 66) Kerbes etal. 1971; 67) Lavery 1972; 68) Lind 1958; 69) Lind 1962; 71) Livezey and Humphrey 1985a; 72) MacKenzie and Kear 1976; 73) MacNae 1959; 74) Mathiasson 1963; 75) Matthews and Evans 1974; 76) McKinney 1967; 77) McKinney 1970; 78) McKinney 1973; 79) McKinney etal. 1978; 80) Mendall 1958; 81) Mickelson 1975; 82) Middlemiss 1958; 83) Moffett 1970; 84) Morse etal. 1969; 85) Newton and Campbell 1975; 86) Nuechterlein and Storer 1985a; 87) Oliver 1955; 88) Ogilvie 1978; 89) Owen 1980; 90) Palmer 1976; 91) Parmelee etal. 1967; 92) Partridge 1956; 93) Patterson 1982; 94) Perrins and Reynolds 1967; 95) Pettingill 1965; 96) Pienkowski and Evans 1982; 97) Poston 1974; 98) Reid and Roderick 1973; 99) Riggert 1977; 100) Rowan 1962; 101) Ryder 1967; 102) Ryder 1971; 103) Rylander and Bolen 1970; 104) Savard 1982; 105) Savard 1984; 106) Savard 1986; 107) Sayler 1985; 108) Scott 1984; 109) Scott and Lubbock 1974; 110) Seymour 1974b; 111) Seymour and Titman 1978; 112) Siegfried 1965; 113) Siegfried 1968; 114) Siegfried 1976a; 115) Siegfried 1976b; 116) R. Smith 1968; 117) Sowls 1955; 118) Stewart and Titman 1980; 119) Stolen and McKinney 1983; 120) Titman 1983; 121) Titman and Seymour 1981; 122) Trauger 1971; 123) Weller 1959; 124) Weller 1967; 125) Weller 1968a; 126) Weller 1968b; 127) Weller 1972; 128) Weller 1974; 129) Weller 1975a; 130) Weller 1975b; 131) Weller 1976; 132) Winterbottom 1974; 133) Wishart 1983; 134) Young and Titman 1986; 135) Young 1970; 136) Young 1972; 137) Moulton and Weller 1984; 138) Williams 1979; 139) Kingsford 1986; 140) Siegfried 1978; 141) Bolen and Rylander 1983.

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Weller, M. W. (1972). Ecological studies of Falkland Islands' waterfowl. Wildfowl 23, 25-44. Weller, M. W. (1974). Habitat selection and feeding patterns of Brown Teal (Anas castanea chlorotis) on Great Barrier Island. Notornis 21, 25-35. Weller, M. W. (1975a). Ecological studies of the Auckland Islands flightless teal. Auk 92, 280-297. Weller, M. W. (1975b). Ecology and behaviour of the South Georgia Pintail Anas g. georgica. Ibis 117, 217-231. Weller, M. W. (1976). Ecology and behavior of steamer ducks. Wildfowl 27,45-53. Welty, J. C. (1982). "The life of birds." 3rd edition. W.B. Saunders, Philadelphia. Wetmore, A. (1920). Observations on the habits of birds at Lake Burford, New Mexico. Auk 37, 221-247. Wiens, J. A. (1966). Group selection and Wynne-Edwards' hypothesis. Am. Sci. 54, 273-287. Wiens, J. A. (1976). Population responses to patchy environments. Ann. Rev. Ecol. Syst. 7, 81-120. Williams, G. C. (1966). "Adaptation and natural selection." Princeton Univ. Press, Princeton, New Jersey. Williams, M. (1979). The social structure, breeding and population dynamics of Paradise Shelducks in the Gisborne-East Coast District. Notornis 26, 213-272. Williams, M. J. (1973). "Dispersionary behaviour and breeding of Shelduck Tadorna tadorna on the River Ythan Estuary." Ph.D. Dissertation. Aberdeen Univ., Aberdeen, U.K. Wilson, E. O. (1975). "Sociobiology: the new synthesis." Belknap Press, Cambridge, Massachusetts. Winterbottom, J. M. (1974). The Cape Teal. Ostrich 45, 110-132. Wishart, R. A. (1983). "The behavioral ecology of the American wigeon (Anas americana) over its annual cycle." Ph.D. Dissertation. Univ. of Manitoba, Winnipeg. Wittenberger, J. E, and Hunt, G. L., Jr. (1985). The adaptive significance of coloniality in birds. In "Avian biology." Vol. 8. (D. S. Farner, J. R. King, and K. C. Parkes, eds.), pp. 1-78. Academic Press, New York. Wittenberger, J. E, and Tilson, R. L. (1980). The evolution of monogamy: hypotheses and evidence. Ann. Rev. Ecol. Syst. 11, 197-232. Wolf, L. L., and Hainsworth, F. R. (1971). Time and energy budgets of territorial hummingbirds. Ecology 52, 980-988. Wolf, L. L., Hainsworth, F. R., and Gill, F. B. (1975). Foraging efficiencies and time budgets in nectar-feeding birds. Ecology 56, 117128. Woolfenden, G. E., and Fitzpatrick, J. W. (1977). Dominance in the Florida Scrub Jay. Condor 79, 1-12. Woolfenden, G. E., and Fitzpatrick, J. W. (1978). The inheritance of territory in group-breeding birds. Bioscience 28, 104-108. Woolfenden, G. E., and Fitzpatrick, J. W. (1984). "The Florida Scrub Jay: demography of a cooperative-breeding bird." Princeton Monogr. Pop. Biol. 20. Princeton Univ. Press, Princeton, New Jersey. Wrangham, R. W, and Rubenstein, D. I. (1986). Social evolution in birds and mammals. In "Ecological aspects of social evolution." (D. I. Rubenstein and R. W. Wrangham, eds.), pp. 452-470. Princeton Univ. Press, Princeton, New Jersey. Wust, W. (1960). Das Problem des Reihens der Enten, besonders vom Anas strepera. Proc. Int. Ornithol. Congr. 12, 795-800. Wynne-Edwards, V. C. (1962). "Animal dispersion in relation to social behaviour." Oliver and Boyd, Edinburgh, U.K. Ydenberg, R. C., and Prins, H. H.Th. (1981). Spring grazing and the manipulation of food quality by barnacle geese. /. Applied Ecol. 18, 443-453. Ydenberg, R. C., and Prins, H. H.Th. (1984). Why do birds roost communally? In "Coastal waders and wildfowl in winter." (P. R. Evans,

SPACING PATTERNS J. D. Goss-Custard, and W. G. Hale, eds.), pp. 123-139. Cambridge Univ. Press, Cambridge. Ydenberg, R. C., Prins, H. H.Th., and van Dijk, J. (1983). Post-roost gatherings of barnacle geese: information centres? Ardea 71, 125-132. Young, A. D., and Titman, R. D. (1986). Costs and benefits to Redbreasted Mergansers nesting in tern and gull colonies. Can. J. Zoo/. 64, 2339-2343. Young, C. M. (1964). "An ecological study of the Common Shelduck

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(Tadorna tadorna) with special reference to the regulation of the Ythan population." Ph.D. Dissertation. Aberdeen Univ., Aberdeen, U.K. Young, C. M. (1970). Territoriality in the common shelduck (Tadorna tadorna}. Ibis 112, 330-335. Young, J. G. (1972). Breeding biology of feral Greylag Geese in southwest Scotland. Wildfowl 23, 83-87. Zahavi, A. (1979). Ritualisation and the evolution of movement signals. Behaviour 72, 77-81.

CHAPTER

9

Ecology and Evolution of Brood Parasitism in Waterfowl Rodney D. Sayler

I. Introduction

Are waterfowl merely inefficient parasites at the beginning evolutionary stages of BP? Or does the unique biology of waterfowl influence the manner in which BP is used during reproduction? In this paper, I review the hypotheses surrounding BP in waterfowl, examine potential adaptive values of parasitism, and explore evolutionary dichotomies between altricial and precocial birds.

Brood parasitism (BP) occurs when a female purposely lays eggs in a nest to be raised by an individual that is not her mate or close relative. Waterfowl (Anatidae) have long been noted for their relatively high frequency of conspecific brood parasitism (CBP) and, to a lesser extent, interspecific brood parasitism (IBP) (Weller 1959, Yom-Tov 1980). By ecological definition (Pianka 1983), BP benefits the parasite but is detrimental to the host. Among altricial birds, the consequences of being parasitized and raising nonrelated offspring are typically quite severe (Payne 1977). Parasitized altricial hosts normally incur high reproductive costs associated with loss of eggs and increased mortality of young. As a result, elaborate coevolutionary arms races between parasites and hosts are evident among some altricial birds (Lack 1968, Payne 1977, Davies and Brooke 1989a, b). It is not obvious why parasitism should be so common among precocial birds. Waterfowl are generally able to incubate, hatch, and fledge more young than normal clutch sizes indicate (Rohwer 1985). Therefore, the costs of raising parasitic young are not self-evident. Furthermore, waterfowl brood parasites do not exhibit the finely tuned adaptations for parasitism apparent in some other avian groups (Lack 1968, Payne 1977). Many parasitic waterfowl eggs fail to hatch simply because they are deposited too late during the host's incubation period to allow adequate development (Weller 1959). Waterfowl hosts seemingly lack elaborate defense mechanisms against brood parasitism, or superficially appear to "accept" parasitic eggs. It has even been suggested that, under some circumstances, waterfowl hosts may realize posthatch benefits in brood survival because of being parasitized (Nudds 1980, Andersson 1984, Eadie and Lumsden 1985, but see Eadie 1989).

II. Evolutionary Predictions: Why Parasitize? Within a given set of life history constraints, individuals leaving more surviving offspring will tend to have an evolutionary advantage. An individual that succeeds in getting another individual to raise its young may realize a number of such advantages. It may avoid high energetic costs and risks of parental care and subsequently may devote more effort toward increasing fecundity (Lack 1968). Alternatively, it may have little choice but to leave offspring with substitute parents if it is unable to adequately care for its own young or if it is more economically feasible to leave them with others than to take care of them itself. Thus, there appear to be at least two basic situations in the evolution of avian brood parasitism: (1) when parasitism is advantageous because it is a reproductive tactic more successful than typical nesting, and (2) when parasitism is a second-choice or best-alternative option for rearing some young. There is no good reason to expect that both tactics should not occur simultaneously within a given species, i.e., to nest "normally" except when forced to parasitize because of breeding impairments or parasitize when there are exceptionally good opportunities to increase fecundity or reproductive success. The best substitute parent (i.e., host) should normally be a conspecific that has the same diet, habitat selection, and behavior as the deserting parent. A strategy of leav290

ECOLOGY AND EVOLUTION OF BROOD PARASITISM ing young with conspecifics may work well when few individuals in the population are doing it. However, if parasitic behavior succeeds and such individuals become more common in the population, host parental care may be less effective when overwhelmed by many parasites, and hosts may then be selected to avoid or deter parasitism. As a result, fewer conspecific hosts will be available or the cost of parasitizing them will increase. Thus, parasitism as an alternative reproductive strategy should be affected by frequency-dependent selection. The specialist that parasitizes only conspecifics can never be so successful that it completely dominates the population numerically, or it will run out of hosts! Indeed, there are no pure parasites of conspecifics known among birds (Emlen and Wrege 1986), which suggests that it is difficult to specialize in only parasitizing conspecifics as hosts. Parasitism of other species (i.e., IBP), or even facultative parasitism (i.e., IBP or CBP), should not place quite the same restraints on the evolution of parasitism, since host availability may tend to be greater. However, for any one-host, one-parasite system, we expect to see the same general conditions apply. Species that have specialized completely in parasitizing others rather than rearing their own young are obligate brood parasites and are rare (Lack 1968). Many factors may influence the evolution of BP. If suitable hosts are not readily available, the cost of trying to parasitize others might not be worthwhile, except occasionally when good opportunities arise (e.g., densenesting situations). Thus, some species or individuals may be expected to use parasitism primarily facultatively. Hosts also must be capable of rearing extra young to make parasitism a successful option. In many instances, parasitic young might generally have lower survival than nonparasitic young, due to the difficulties of timing egg-laying with the host's laying period, competition among brood mates, and similar factors. If BP is to be used as an alternate breeding strategy with success equivalent to normal nesting (just one of several possible options), then additional eggs must be laid to compensate for the lower production. Besides the numerical challenge of greater egg production, the competitive abilities of parasitic young may need to be increased to offset lower survival in host broods. Thus, there may be a strong general numerical component or evolutionary cost to successfully evolving brood parasitism as a tactic with offspring production greater than typical nesting birds. If BP is a second-choice, best-alternative tactic of females that would normally rear their own young but cannot because of reproductive constraints, then low survival of parasitic young does not affect the occurrence of BP. Under these conditions, particularly when it costs little to parasitize, even a low return on parasitic young may be better than no return at all. Thus low suc-

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cess of parasitic young should not necessarily preclude the evolution of BP as a conditional, if then reproductive tactic (e.g., if reproduction is impaired, then parasitize). Based upon these general considerations, I make the following predictions or general observations prior to reviewing empirical data on waterfowl brood parasitism: (1) Obligate brood parasitism is rare among birds in general, probably because of constraints on host availability, lower survival of parasitic young (i.e., compared to eggs and young produced by "normal" nesting), host antiparasitism adaptations, and the evolutionary cost of offsetting these factors to achieve higher reproductive performance. If there are severe constraints to producing additional eggs beyond the normal clutch size, these will also tend to preclude obligate parasitism. (2) Brood parasitism may be adaptive and readily evolve as a salvage strategy, even if success rates and survival of parasitic young are relatively low. Consequently, either latent or facultative parasitic behavior should be widespread among female birds. (3) Dichotomies in the developmental mode of young should have strong repercussions on evolution of brood parasitism. Parasitism should be more common among species for which posthatching parental care does not strongly limit the number of fledging young. When posthatching parental care does not strongly affect the number of fledging young, there are no major disadvantages to individuals placing parasitic young in conspecific host broods, and evolutionary pressures on hosts to defend against parasitism may be relatively weak. When posthatching parental care strongly limits survival to fledging, it should also tend to limit the survival of extra parasitic young in host broods, increase the possibility of strong counterresponses by hosts, and increase the cost of evolving parasitism. Partly because there are few evolutionary hurdles to clear initially, brood parasitism may be relatively common among precocial as compared to altricial birds (also see Rohwer and Freeman 1989). (4) Precocial species should frequently benefit from parasitism used to salvage reproductive attempts due to the high, up-front costs of producing large clutches of energy-dense eggs requiring long incubation periods. (5) Altricial species should have more specialized adaptations for brood parasitism than precocial birds to offset the parental care limitations affecting brood survival, as well as to counter strong host antiparasite adaptations.

III. Occurrence of Brood Parasitism in Waterfowl A. Distribution within the Anatidae BP is common among waterfowl, being found in most

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Table 9-1. Summary of the Known Occurrence of Brood Parasitism in Waterfowl of the World3 Number of species Probable Not reported Infrequent Occurs 1 Anseranatini Dendrocygnini 6 3 Anserini 11 4 3 4 1 Cereopsini 1 Stictonettini 7 4 Tadornini 3 1 Tachyerini 3 3 10 Cairinini 1 Merganettini 24 7 6 2 Anatini 1 10 4 Aythyini 1 7 7 Mergini 3 8 Oxyurini 21 (14%) 48 (33%) 29 (20%) Total 48 (33%) a See Appendix for the occurrence of brood parasitism by species. Tribal classification follows Johnsgard (1978). Tribe

groups and in all major biogeographic regions (Table 9-1). Many species are only poorly studied, but BP probably occurs to at least some degree in the majority of all waterfowl. Nonetheless, there is considerable variation in the extent to which parasitism is used during normal breeding activities. Parasitism occurs in about 33% (N = 146) of all waterfowl species (Table 9-1). Based upon records of unusually large clutch sizes, colonial nesting, or cavity nest sites, parasitism is either possible or probable for another 20% of all waterfowl. In the remainder, BP is either infrequent (14%) or not reported or unlikely (33%). This classification of parasitic breeding is highly subjective, since the overwhelming majority of species have not been studied well enough to quantitatively determine the frequency of either CBP or IBP. BP has proven to be relatively common in whistling ducks (Dendrocygnini), some true geese (Anserini), shelducks (Tadornini), the dissimilar species commonly grouped together in the perching ducks (Cairinini) (see Livezey 1986), some dabbling ducks (Anatini), pochards (Aythyini), sea ducks (Mergini), and stiff-tailed ducks (Oxyurini) (e.g., Weller 1959, Frith 1967, Cramp and Simmons 1977, Johnsgard 1978, Yom-Tov 1980, Eadie et al. 1988, Eadie 1989, Rohwer and Freeman 1989). Parasitic breeding is found in taxa that exhibit supposed primitive features of waterfowl (e.g., whistling ducks) and derived or specialized characteristics (e.g., stifftailed ducks) (Livezey 1986). Thus, on a superficial level, there are no distinctive phylogenetic restrictions that limit the appearance of brood parasitism in waterfowl (Table 9-1).

B. Notable Brood Parasites 1. Whistling Ducks Most of the whistling ducks have not been studied to

any extent, but for those that have, parasitism seems to be common. The Black-bellied Whistling Duck is the best known, due to its distribution and use of natural cavity nest sites and artificial nest boxes. At least 70% of all clutches were parasitized in a 12-year study of nest box use in Texas, based upon clutches too large to have originated from one female (McCamant and Bolen 1979). Clutches in 778 nests averaged about 30 eggs/ nest, with as many as 101 eggs being found in a single nest! However, only 20% of 21,982 eggs hatched, and about 60% of the clutches were never incubated. In 210 successful nests, an average of 32 eggs hatched/nest. In a recent study of Black-bellied Whistling Ducks using individually marked birds and time-lapse photography, Chronister (1985) found that 18 of 20 nests (90%) were parasitized. These nests contained an average clutch size of 29 eggs in incubated clutches. Parasitism also occurs among other whistling ducks that typically nest on the ground, having been recorded for Fulvous Whistling Ducks nesting in emergent cover, rice fields, and uplands (Barnhart 1901, Meanley and Meanley 1959). Although BP is suspected of occurring regularly among probably all species of whistling ducks, detailed studies are not available (Johnsgard 1978). 2. Swans and Geese BP has not been recorded or only occurs infrequently among most swans and true geese (Table 9-1). The most significant parasitism is found among geese that regularly or occasionally nest in dense colonies. Recently, Lank et al. (1989) reported that parasitism affected about 22% of Lesser Snow Goose nests at La Perouse Bay, based on genetic analysis of color morphs. Substantially higher parasitism rates have been recorded in years of poor habitat conditions at other goose colonies (see Influence of Habitat Conditions and Demography in this chapter). For other well-studied geese, such as the Graylag Goose and Canada Goose, BP is relatively infrequent and mainly occurs under semicaptive, colonial, or other dense-nesting conditions (see Appendix). 3. Shelducks BP is well known for the Northern Shelduck, which has a breeding biology fairly typical of the rest of the shelduck group. Under natural conditions, Northern Shelducks nest in ground cavities, such as rabbit burrows. However, they will also use haystacks, artificial nest boxes buried in the ground, buildings, tree stumps, and similar sites for nests (Hori 1964). In an area with a relatively dense breeding population, Pienkowski and Evans (1982) reported that about 33% of Northern Shelduck clutches were affected by parasitism. BP occurred despite a surplus of natural and artificial nest sites. In other studies, parasitism was identified in 28% of 153 nests (Patterson 1982) and 11-48% of 130 nests

ECOLOGY AND EVOLUTION OF BROOD PARASITISM over 7 years (Hori 1969). Parasitism occurs among other shelducks (e.g., Australian and New Zealand Shelduck); however, the frequency of parasitism is difficult to estimate given the limited number of studies and difficulty of observing nests in natural ground cavities (Riggert 1977, Williams 1979).

4. Wood Ducks CBP occurs frequently among Wood Duck populations nesting in natural and artificial nest cavities. Using conservative indicators of parasitism (i.e., large clutches, laying rates > 1 egg/day, and eggs laid during the incubation period), about 46-59% of Wood Duck nests are regularly parasitized in artificial structures (Morse and Wight 1969, Clawson et al. 1979, Semel et al. 1988). In one study, 20 of 21 nests (95%) checked daily had 2 or more eggs deposited during a single day (Semel and Sherman 1986). Thus, the actual percentage of artificial nest sites affected by parasitism may be substantially greater than indicated in most nesting studies. Clutches of 20-40 eggs are commonly found, far greater than the presumed normal clutch size of 11-15 eggs in unparasitized clutches (e.g., Grice and Rogers 1965, Morse and Wight 1969, Clawson et al. 1979).

5. Dabbling Ducks—Anatini Parasitism is relatively uncommon among dabbling ducks, except for those species that utilize cavity nest sites or when birds crowd together on nesting islands. In the Chestnut Teal, about 45% of complete clutches (N = 55) and a minimum of 21% of all clutches (N = 118) had laying rates > 2 eggs/day, indicating intraspecific parasitism (Norman 1982). Parasitism is known or suspected to occur mainly among other cavity nesters (e.g., Gray Teal, Gray Duck) (see Appendix). The Gadwall illustrates the general influence of nesting conditions on parasitism for many Anas spp. Gadwall nests widely scattered in upland habitats are seldom parasitized (Rohwer and Freeman 1989, Sayler unpubl.). However, at least 9% (N = 355) of completed Gadwall clutches were parasitized intraspecifically when nests were located on islands or ditch banks (Mines and Mitchell 1984). Similarly, parasitism for other Anas spp. occurs most frequently in crowded or semicaptive nesting conditions (e.g., Titman and Lowther 1975).

6. Pochards—Ay thy ini BP is relatively common among all pochards, except perhaps the Ring-necked Duck (see Appendix). Both CBP and, to a lesser extent, IBP are common among Redcrested Pochards, Eurasian Pochards, Tufted Ducks, Redheads, Canvasbacks, and Greater and Lesser Scaup. Parasitism probably occurs among most other pochards, but in many cases, information is inadequate to document this supposition.

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In the Marismas of Spain, Red-crested Pochards parasitized about 31-67% of the Eurasian Pochard nests. At least 17% of the Red-crested Pochard nests were parasitized intraspecifically (Amat 1982, 1985). Unlike the Redhead (Weller 1959), parasitism by Red-crested Pochards tended to occur after the normal peak of nesting by this species, suggesting parasitism by young females or failed nesters (Amat 1985). At least 10% of Tufted Duck nests may be affected by IBP when dense nesting occurs on islands (Newton and Campbell 1975), although this is a highly conservative measure based on large clutch size. Similarly, parasitism by Greater and Lesser Scaup tends to be more common when birds nest closely on islands (e.g., Hines and Mitchell 1984) than when nests are dispersed in uplands. Perhaps the most widely known waterfowl brood parasite is the Redhead (e.g., Low 1940, 1945; Erickson 1948; Weller 1959; Joyner 1976, 1983; Sugden 1980; Sayler 1985). Although Redheads use many waterfowl species as hosts (Weller 1959, Joyner 1976), they clearly exploit congeners quite heavily when available (Hochbaum 1944, Weller 1959, Sugden 1980, Bouffard 1983a, Sayler 1985). On the large Delta Marsh, where Redhead numbers tend to exceed those of Canvasbacks by about 5:1, over 90-95% of the Canvasback nests may be parasitized in some years (Olson 1964, Sayler 1985). Under these conditions, Redhead eggs may comprise an average of 27-53% of all the eggs in Canvasback nests. In some heavily parasitized nests, where many eggs have been displaced into the water, Canvasbacks may incubate clutches composed entirely of Redhead eggs (Erickson 1948, Sayler 1985). In other prairie and parkland areas, about 25-70% or more of all Canvasback nests commonly may be parasitized by Redheads (Olson 1964, Sugden 1980, 1982). In Alberta, Redheads parasitized more Mallard nests (32%, N = 130) than Lesser Scaup nests (19%, N = 157), probably because of earlier nesting dates. However, Lesser Scaup nests contained significantly more Redhead eggs (Giroux 1981). CBP is more difficult to detect than IBP with general observational techniques because of similarities in egg size, shape, and coloring. However, by using a variety of criteria, at least 36-42% of the Redhead clutches in several studies have been determined to be affected by intraspecific parasitism (Lokemoen 1966, Sayler 1985). Although Canvasbacks are generally less likely to parasitize than Redheads (e.g., Erickson 1948, Sayler 1985), in a detailed nesting study in the Minnedosa pothole region, about 15% of the Canvasback eggs were deposited intraspecifically (M. Anderson, pers. comm.). Again, the actual incidence of CBP among Redheads and many other waterfowl is apt to be quite high when fully known through the use of better detection techniques (e.g., see Fleischer 1985).

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7. Mergini Parasitism among the sea ducks is most common in species that nest in tree cavities (e.g., Bufflehead, Common Goldeneye, Barrow's Goldeneye, Hooded Merganser, Smew, Common Merganser) (Table 9-1). Based on large clutch size only, 7-20% of Barrow's Goldeneye nests in boxes (N = 409) in British Columbia were parasitized annually over 5 years (Savard 1988). However, daily observations of a smaller sample of 30 boxes suggested that 40% were parasitized. Eadie (1989) reported that 38% (N = 371) of Barrow's and Common Goldeneye nests were parasitized. Similarly, CBP among Common Goldeneyes has ranged from 34-38% (Eriksson and Andersson 1982, Dow and Fredga 1984). Even though Red-breasted Mergansers typically nest on the ground, Young and Titman (1988) found that at least 64% of the nests in dense, tunnel-like vegetation on nesting islands were parasitized.

8. Oxyurini

CBP and IBP are known to occur among virtually all of the stiff-tailed ducks, although there is surprisingly little information about breeding behavior for the group. In Utah, only about 8% of the waterfowl nests were parasitized by Ruddy Ducks, and about 7% of the Ruddy Ducks hatched through IBP (Joyner 1983). However, the incidence of CBP was unknown. In the Minnedosa area, Siegfried (1976) felt that at least 8% of Ruddy Duck clutches were affected by CBP. IBP was low, occurring in less than 4% of 57 Canvasback and Redhead nests examined. At least 13% of the Maccoa Duck nests were parasitized intraspecifically, according to one study (Siegfried et al. 1976). Again, detailed information is lacking, but BP may be common in all of the other stifftails (see Appendix). The Oxyura contains the only waterfowl species believed to be an obligate brood parasite, the Black-headed Duck (Weller 1968a). Unlike other waterfowl brood parasites, the Black-headed Duck commonly parasitizes a wide range of birds, with eggs having been found in nests of at least 14 different species, including birds of prey, gulls, and coots (Weller 1968a, Johnsgard 1978). Three species of coots, especially the Red-fronted Coot (Fulica rufifrons), and another duck, the Rosy bill, are frequently parasitized. The incubation period of the Black-headed Duck is short, perhaps as little as 21 days (Johnsgard 1978), which facilitates hatching before or during hatching of the host's clutch. Observations of nests in the wild and in captivity suggests that 1 or 2 eggs are commonly laid in each nest during the host's laying period (Weller 1968a, Johnsgard 1978). In the wild hatching success of eggs in coot nests was only about 20%, indicating that not all parasitic laying is well synchronized with the host, or that many eggs receive inadequate incubation, sometimes due to being

buried in the bottom of the nest (Weller 1968a). Young Black-headed Ducks are perhaps the most precocial and independent of all waterfowl, typically leaving the host just 1 or 2 days after hatching, then rearing themselves (Rees and Hillgarth 1984). The stiff-tails possess several characteristics that may be related to BP. The group produces a relatively large egg and a large clutch mass relative to the female's body weight (Lack 1968, Johnsgard 1978). Females of some species (e.g., Ruddy Ducks) must feed quite intensively during incubation (Tome 1981). Consequently, stifftailed females encounter high energetic demands during breeding. Except for the Musk Duck (Johnsgard 1978), stiff-tail ducklings are highly precocial, self-feeding, and seem to receive relatively little parental care compared to other waterfowl. Females often desert broods at young ages. Incubation periods for the group are not well documented, but Ruddy Duck eggs may hatch in 21 days in an incubator (Johnsgard 1978), suggesting that under intensive incubation eggs will hatch in a short time period —an obvious advantage to a parasitic species. When abundant suitable hosts are available, as appears to be the case for Black-headed Ducks (Weller 1968a), these features may certainly enhance the evolution of brood parasitism.

C. Success of Parasitism Relatively few studies have reported parasitism rates for large samples of nests over several years, making it difficult to estimate true average parasitism rates for many populations or species (Table 9-2). Since CBP is more difficult to detect, most information on parasitism results from studies of IBP. Perhaps better information exists for Canvasbacks and Redheads than most other common host/parasite combinations. Redheads often parasitize anywhere from 50 to 85% or more of Canvasback nests (Table 9-2). Where parasitism is common, nests may average 3-7 parasitic eggs/ nest, sometimes greatly affecting host nest success (Erickson 1948, Weller 1959, Sayler 1985, but see Bouffard 1983a). For Redheads breeding on the variable habitats of the prairies, 20-50% of the young produced on a given area have been attributed to parasitic laying (Table 9-2). On breeding habitat with stable water levels on Lake St. Francis, Quebec, an average of about 8% of other waterfowl nests were parasitized, and only 1.6% of 1467 Redhead ducklings resulted from IBP (Alliston 1979). The success or percentage of young produced via BP is not known accurately for most waterfowl species. Parasitism produced about 5.3% (range 1.8-9.3%) of the goslings hatched annually at the La Perouse Bay Snow Goose colony near Churchill, Manitoba (Lank et al. 1989). However, the success of parasitism from an evo-

ECOLOGY AND EVOLUTION OF BROOD PARASITISM lutionary perspective cannot always be evaluated from the percentage of young raised parasitically. Certainly a heavy dependence on parasitic laying indicates that it is an important reproductive strategy. But, as previously suggested, even limited production of parasitic young may be advantageous to individuals. Let us explore potential adaptive values of parasitism in waterfowl.

IV. Brood Parasitism: A Review of Hypotheses A. Nonadaptive Explanations 1. Reproductive Error Hypothesis Some of the earlier explanations for BP in waterfowl stress autogenic origins (e.g., breakdown of nesting instincts, abnormal physiology, endocrine imbalances, breakdown of mating systems) or focus much attention on how the first eggs might have been deposited parasitically (e.g., accidental laying in the wrong nest) (see reviews in Weller 1959, Hamilton and Orians 1965) (Table 9-3). Undoubtedly, some apparent BP occurs because of reproductive mistakes by laying females. However, the high frequency of BP in some species and the apparent "purposeful" behavior of individually marked birds (Clawson et al. 1979, Semel and Sherman 1986, Sayler 1985) argue strongly against this general explanation. Hamilton and Orians (1965) stressed that frequent and repeated BP is undoubtedly an adaptive process. Reproductive error in its simplest form is not a particularly satisfactory explanation to account for the widespread occurrence of parasitism in many waterfowl species.

2. Accidental Parasitism Hypothesis Some apparent parasitism may occur "accidentally" when females select the same nest site, particularly among cavity nesters (Grenquist 1963, Erskine 1972a, Yom-Tov 1980). According to this argument, two females may begin laying, each unaware that another female is using the same nest. One female completes laying a clutch, begins incubation, and subsequently forces the other female to abandon the nest. In this situation, BP would actually be an inadvertent consequence of nest site selection and competition. However, since one female will always encounter an egg in the nest on her first laying visit, it is debatable whether two individuals can lay in a nest and not be aware that another is attempting to use the same site. Little direct evidence is available to evaluate this hypothesis, even for cavity nesters. It does not explain BP for many overwater and terrestrial-nesting waterfowl very well, since the possibility of two females accidentally selecting the exact same nest site is low. Uplandnesting ducks typically scatter nests in large blocks of vegetation, and the abundance of emergent vegetation

295

seldom limits nest placement in overwater nesters, except in drought situations (pers. observ.). Observations of marked Wood Ducks (Clawson et al. 1979) indicate that parasitic females did not attempt to begin incubation in nests in which they laid eggs. Parasitic females spent less time laying eggs than other females, spent less time around nest box areas, and actively followed other females to nest boxes that were then parasitized. Similarly, Eadie (1989) conducted bird removal experiments demonstrating that goldeneye females would not incubate nests they parasitized, even if given the opportunity. Although some truly "accidental" joint laying may occur in cavity nesters, the best empirical data suggest that inadvertent competition for nests is certainly not the primary explanation for BP in waterfowl.

B. Conditional Strategy Hypotheses Brood parasitism may be a "salvage" or "conditional" strategy used by females attempting to achieve some reproductive success when faced with obstacles preventing typical nesting (Sayler 1985). Limitations of resources critical to reproduction (e.g., nest sites, food) or other factors such as nest loss may commonly prevent many females from nesting in the normal fashion. As a result, some females may lay parasitically rather than not nest at all.

1, Poor Body Condition/Nest Loss Hypothesis Waterfowl commonly use a portion of prelaying endogenous reserves for clutch formation and use the remainder (an amount varying widely among species) to support fasting during relatively long incubation periods (e.g., Ankney and Maclnnes 1978, Raveling 1979). For example, Laughlin (1975) found that endogenous reserves in the Tufted Duck provided all lipids and about half the calcium needed for egg production. A similar amount of lipid reserves was retained for the incubation period. Laughlin (1975) suggested that Tufted Ducks might lay parasitically when lacking sufficient endogenous reserves to fast and maintain high nest attentiveness during incubation — a factor critical to reducing egg predation. Similarly, Pienkowski and Evans (1982) speculated that insufficient body reserves might explain some parasitism by Northern Shelducks, which spend about 87% of the day on the nest (Hori 1964). Relationships between brood parasitism and energy/ nutrient levels of breeding females have received little attention. Parasitic laying by Redheads increased in frequency during drought years when average female body weights declined about 20% (Sayler 1985). Some Redhead females, captured in decoy traps using other Canvasback and Redhead females as bait (Anderson et al. 1980), laid eggs at body weights more typical of females in late incubation (Sayler 1985). Therefore, some

RODNEY D.SAYLER

296

Table 9-2. Parasitism Rates and Success in Selected Waterfowl Nesting Studies Parasitic species

Host

Conspecific Conspecific Conspecific Greylag Goose Conspecific Conspecific Lesser Snow Goose Conspecific Conspecific Conspecific Emperor Goose Conspecific Canada Goose Conspecific Northern Shelduck Conspecific Conspecific Conspecific Wood Duck Conspecific Conspecific Conspecific Conspecific Conspecific Conspecific Conspecific Conspecific Conspecific Conspecific Eurasian Wigeon Mixed species Conspecific Gadwall Conspecific Conspecific Conspecific Mallard Mixed species Green-winged Teal Mixed species Conspecific Chestnut Teal Conspecific Mallard Conspecific Conspecific Conspecific Gadwall Mixed species Red-crested Pochard Conspecific Conspecific Common Pochard Redhead Canvasback Conspecific Redhead Conspecific Conspecific Conspecific Cinnamon Teal Cinnamon Teal Cinnamon Teal Cinnamon Teal Pintail Mallard Mallard Mallard Mixed species Mixed species Mixed species Mixed species Black-bellied Whistling Duck

Mixed species Mixed species Mixed species

Nest site Cavity Cavity Cavity Upland Upland: island Upland: colony Upland: colony Upland: colony Upland: dense Upland Cavity Cavity Cavity Cavity Cavity Cavity Cavity Cavity Cavity Cavity Cavity Cavity Upland:island Upland: island Upland: island Upland: island Upland: island Upland: island Upland:island Upland: island Upland: island Cavity Upland: island Upland:island Upland & boxes Upland:island Upland:island Upland:island Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent Emergent

Nests parasitized3

91 74e 90 4

(78) (778) (20)

3 6 80 12-31 (13148) 5e (341) 1 27 (130) 33-50 32 (63) 57 (274) 53 (86) 59 (202) 65 (168) 50 (1058) (31) 32e 14-43 (66) 95 (21) 30-50 (245) 1 (1012) 11 4e (140) 2 (272) 9 (161) 9 (355) 4 (281) 13 1 45 (55) (67) 10 1 (301) 21 (267) 11 (280) 8 (161) 6 48 17 33e (199) 1 (77) 36 (59) 29 (38) 20 (188) 17 (51) 53 48 (474) 79 25 44 (48) 70 (5.5) 68 (4) 31 (29) 6-30(>5000) 69 37 (716) 6 (5000) 39 7

Parasitic eggs Young Eggsb Hatchedc producedd

2.5(63)

193 271 62 44 15 16 52 33 21 28 200 184 58 136 16 89 19 20 116 520 679 252 68 82 10 3 5 74 23 92 21 341 410

N N C B N W N N N N N B B B B C N/R C A N N N N N C N N B C N N B B B N N B B B B/N N N N N N

Location

Manitoba Iowa Saskatchewan Latvia Poland Finland Manitoba North Dakota Manitoba Utah Manitoba North Dakota Manitoba North Dakota Manitoba Maine & Vermont Manitoba Saskatchewan Latvia Latvia Minnesota Maine & Vermont Maine New York Manitoba North Dakota Manitoba

6 7 8 1 4 2 4 2 3 3 3 6 6 4 6 2 7 4 3 7 7 3 3 2 7 2 2 2 2 8

but this may vary with habitat conditions and population density (e.g., Dane 1965, Blohm 1979, Krapu and Doty 1979, Krapu et al. 1983, Afton 1984, Anderson 1985a and unpubl., Hepp et al. 1989; see also chapter 14). For species with delayed breeding, such as geese and swans, environmental variation can also affect age of first breeding (e.g., Finney and Cooke 1978, Davies and Cooke 1983, Aldrich and Raveling 1983, Laurila 1988; see also chapter 15). Delayed breeding is also common in sea ducks (tribe Mergini) (chapters 14 and 15) and little is known about what these subadults do before entering the breeding population (but see Alison 1975, 1977, Eadie and Gauthier 1985). Thus, the behavior

% Returned

44.4 33.3 13.3 41.7 46.0 5.0 33.3 28.8 50.0 57.9 14.3 43.0 14.5 30.0 56.5C 38.6 27 37.5 28.8 45.5 33.3 7.1 48.5 8.7 13.8 4.4 0 24.7 42.1 15.0 3.4 7.7 1.2 10.3 14.7 9.8 30 _d

_d

53.0° 69.6 12.0 14.3 74.5 26.8

Source R. Wishart (pers. comm.) Sowls (1955) Coulter and Miller (1968) Doty and Lee (1974) Lokemoen et al. 1990 Titman (1983) Bishop etal (1978) Gollop (1959) Mihelsons et al. (1986) Majewski and Beszterda (1990) Valikangas (1933) Sowls (1955) Derrickson (1977) Sowls (1955) Gates (1962) Blohm (1979) Lokemoen etal. (1990) Sowls (1955) Lokemoen et al. (1990) McHenry (1971) Coulter and Miller (1968) Sowls (1955) Poston (1974) Mihelsons et al. (1986) Mihelsons et al. (1986) W. Hohman (pers. comm.) Coulter and Miller (1968) Mendall (1958) Alliston (1979) Johnson (1978) Jobes (1980) Anderson (1985a); Serie (pers. comm.)

and detectability of homing birds may vary greatly from time to time and place to place. In most cases, adult males returned at lower rates than did adult females (Table 11-3). This sample of males marked on the breeding grounds as adults includes both paired (mostly) and unpaired birds. Nearly all males that returned to breeding areas used in a previous year returned unpaired, and very few returned for more than one season (but see Blums et al. 1990). The only major exceptions to this are found among the sea ducks (tribe Mergini) (see below). The few reports of homing by males marked as juveniles are also of unpaired birds. Therefore, effective dispersal by males, especially in sea-

369

PHILOPATRY, DISPERSAL, AND GENETIC STRUCTURE Table 11-1. Evidence for natal and breeding philopatry by female ducks (continued) Species A. af finis

A. fuligula A. ferina Aix sponsa

Clangula hyemalis Somateria mollissima

Histrionicus histrionicus Melanitta fusca Bucephala clangula

B. icelandica B. albeola Lophodytes cucullatus

Age at return3 A Y A Y Y A Y Y A Y A Y Y A/SU A A A Y A A A A A Y A Y A A/Y A A A

Location N.W.T.

Years studied 3

Manitoba

3

Alaska Latvia

2 12 7 7 12 7 7 3 6 4 22 9 1 15 9 3

Latvia Illinois Massachusetts South Carolina N. Manitoba Britain Maine N. Canada Baltic Sea Quebec Iceland Finland Saskatchewan Sweden N. Finland British Columbia British Columbia Oregon Missouri

Banded birds in sample 330 626 58 76 490' 880 1854 479 440 248 536 250 2945 p ca. 900 650 26 5607 643 40

8 19 21 17 6 3 3 3 2 p

Marker typeb N N N N B B B B B W B/W W W N/B B B B B B C

% Returned 20.0 12.0 65.5 48.7 6.5 66.0 5.6 1.9 49.1 6.5 43.0 23.2 5.2e _f 89.0g 71.0h 88.5 1.1 22.6 50.0

83.9 B B 67.3 B >65.0 _a I 19 B 57.9 114' B 0.0 184 N 69.6 _ j _ j B ("high" in Gauthier 1987) 21 B 61.9k 75 B 62.71 _d 94 B/I/A

118 1105 410

Source Trauger (1971) Afton (pers. comm.) McKnight and Buss (1962) Mihelsons et al. (1986) Mihelsons et al. (1986) Bellrose et al. (1964) Grice and Rogers (1965) Heppetal. (1989) Alison (1975, 1977) Coulson (1984) Wakeley and Mendall (1976) Cooch (1965) Franzmann (1983) Reed (1975) Bengtson (1972) Koskimies (1957) Kehoeetal. (1989) Dow and Fredga (1983) Rajala and Ormio (1970) Savard (1985, pers. comm.) Erskine (1961, 1972) Gauthier (1985) Morse et al. (1969) Uansenetal. (1969)

California 2 A Gray (1980) Oxyura jamaicensis A = AHY = birds > 1 year old; Y = HY = birds < 1 year old; SU = nonbreeding subadults; S = SY = birds 2 years old. b B = metal leg band only; C = colored leg bands; N = colored nasal markers; W = web tags; A = nape tags; I = wing tags; K = colored neck collars; R = radios. c Minimum estimate, high rate of saddle loss between years. d lnsufficient data given to calculate % return, but some birds did home. e Recruitment rate for young female ducklings. f !3 females and 2 males returned, number marked not reported; "few" male and "many" female subadults returned. g Survival estimate calculated from mark/recapture data on breeding females. h Estimated return rate (36.8% were recaptured on same island as banded; 2.5% on different islands; but only ca. 30% of homing females were recaptured in each year). 'Both sexes; we assume ca. 1/2 were females. '23 of 35 females returned to the same nest hole; 12 returned to other nest sites. 9 females marked as ducklings returned to breed. Number of birds banded was not reported. k 64% of returning females utilized the same set of nest boxes that they used the previous year. '21 banded birds of both sexes were recaptured; color tags were inadequate for unbiased sample; sex split not given. a

sonally monogamous migratory ducks, may be even greater than the data in Tables 11-2 and 11-3 indicate. Homing by unpaired males may partly reflect the significantly male-skewed sex ratios in most waterfowl (Bellrose et al. 1961) that result in many males not breeding each year. For example, if we assume that a population is composed of 65% males, then there are 1.86 males/female and < 54% of all males can pair each year. If pairing two years in a row for males is random with respect to pairing status the previous year, and if we

further assume an adult survival rate of 70%, then by chance alone about 38% of males alive and paired in year (t) will be alive and unpaired in year (t + 1). This percentage would be lower, perhaps much lower, if previous pairing experience helped an individual in competition to pair again. Nevertheless, we should expect a substantial proportion of previously paired males to be unsuccessful each year. The return rates reported for adult males (Table 11-3) (most of which are unpaired) are lower than this "random" rate, however, suggesting

MICHAEL G. ANDERSON ET AL.

370

Table 11-2. Comparative natal philopatry of male and female waterfowl % Return (Number banded)

Species

Age at return3

Location

1-4

N. Manitoba

1-4

Years Marker studied typeb

Males

Females

(n)

X2 P value0

16.3

(10356)

1) values of adults by, say, 80%. We then obtain for an average year: An = 1.00, A12 = 0.56, A13 = 0.19, A14 = 0.05, and A15 = 0.01. These total 1.81. Clutch size is larger for older Mallards than yearlings and decreases with nesting attempt. We propose the following clutch sizes under average conditions: Cn = 10, C12 = 9, C13 = 8, C14 = 7, C15 = 6; C21 = 11, C22 = 10, C23 = 9, C24 = 8, C25 = 7. Combining these values with the {Ajj} above gives average clutch sizes in an average year of 9.38 for yearlings and 10.30 for adults. If wetland and feeding conditions are excellent, clutch sizes increase by 1; if those conditions or weather is very unfavorable, or if nest parasitism is considerable, clutch sizes decrease by 1. Nest success rates of Mallards in the Prairie Pothole Region are highly variable (Klett, Shaffer, and Johnson 1988), but we take H = 0.12 as a typical value (Greenwood et al. 1987), H = 0.40 as a typical high value, and H = 0.05 as a not-uncommon low value. Survival of eggs in successful nests is generally high; we use E = 0.91, as the average of six studies reported in Table 14-2. Variation does not seem appreciable, so we take E = 0.96 and 0.86 as extreme points. Brood survival is lower, however, and we take the average of three studies included in chapter 12 of this volume, plus the 0.68 obtained by Lokemoen, Duebbert, and Sharp (1990), or B = 0.47. Extreme values were B = 0.28 and 0.68, which we will use. To assess the influence of variation in the parameters described above, we computed equation 4 for each combination of three levels (high, typical, and low) of each of the six parameters (D, a, C, H, E, and B). We assumed a population consisting of 44% yearlings and 56% older hens; these fractions represent a population with the stable age distribution based on survival rates given in Table 14-1. We subjected the resulting 729 observations to a regression analysis (Proc REG of SAS Institute 1987). The relative influence of each parameter was assessed by comparing standardized regression coefficients. Results indicated that nest success (H) and brood survival (B) were the most influential components of production, with standardized regression coefficients of 0.76 and 0.40, respectively (Table 14-4). Breeding incidence (D) was the next most influential, followed by nesting intensity (a), clutch size (C), and survival of individual eggs (E). For Mallards in the Prairie Pothole Region, nest success is determined primarily by predation, with wetland conditions or precipitation also playing a role. The determinants of brood survival are largely unknown but

471

Table 14-4. Standardized regression coefficients for three modeled populations Parameter

Mallard

Dump nesting Breeding incidence Nesting intensity Clutch size Nest success Egg survival Brood survival

0.00 0.28 0.13 0.09 0.76 0.05 0.40

Population modeled Snow Goose Wood Duck

0.00 0.35 0.00 0.50 0.47 0.28 0.57

0.14

0.38 0.20 0.19 0.53 0.35 0.54

are thought to include predation, weather, food supplies in wetlands, and possibly disease; some effects may be density-dependent. Breeding incidence in Mallards may vary according to wetland conditions early in the breeding season. Thus predation and wetland conditions likely exert the greatest influence on productivity of prairie Mallards.

4. Example—Snow Geese in the Arctic Our second example deals with the Snow Goose, which breeds in the Arctic. This is a long-lived species with substantial age-related variation in productivity, so we consider 1 = 5 age classes. Again we do not account for senescence (Ratcliffe, Rockwell, and Cooke 1988), assuming that the population contains few birds old enough to have deteriorated reproductive capacity. Also, we included parasitically laid eggs with the clutch of the host (Lank et al. 1989). Most of the information pertains to the population at La Perouse Bay, Manitoba. Because of the detailed study conducted there over a long period of time by F. Cooke and his colleagues, we were able to examine actual year-to-year variation in many of the variables. Thus, instead of considering a typical value and two extremes, we fit an empirical probability distribution to each variable and drew random deviates from those distributions to simulate the dynamics of the population. From Prevett (1972), Rockwell, Findlay, and Cooke (1983), and Cooke and Rockwell (1988), we estimated the proportion in each age class that breeds in a typical year to be Dl = 0, D2 = 0.35, D3 = 0.60, D4 = 0.90, and D5 = 0.95. Breeding incidence may be diminished by adverse weather on the breeding grounds (Uspenski 1965), drought in the prairies during spring migration (Davies and Cooke 1983), and possibly high density or a lack of nest sites (Hanson et al. 1972). We took these D values as random deviates from beta distributions with parameters p and q. Values of the parameters were D2: p = 3.5, q = 6.5; D3: p = 6, q = 4; D4: p = 18, q = 2; D5: p = 38, q = 2. These gave deviates averaging 0.35, 0.60, 0.90, and 0.95 for the respective age classes, as well as appropriate variation. Snow Geese ordinarily make but one nesting attempt in a breeding season, but limited continuation nesting

472

DOUGLAS H. JOHNSON ET AL.

may occur if the first clutch is lost early in laying (Barry 1967; F. Cooke, pers. commun.). We accordingly permit J = 2 attempts and set nesting probabilities at A41 = 1 for all i and, following the reasoning we used for Mallards, Ai2 = O.JD^l — H)2. This formulation allows slightly more continuation nesting for older geese and when breeding conditions are favorable (the inclusion of Dj), more continuation nesting when clutch destruction is likely to occur earlier (the dependence on H), but lower renesting overall than Mallards (the 0.5). Clutch size of Snow Geese is most markedly affected by seasonal decline and age of the female. In addition, clutches may be smaller in years of poor conditions along the spring migration route or when breeding densities are high (Findlay and Cooke 1983, Cooch et al. 1989). For initial clutch sizes in a typical year, we use averages from Rockwell, Findlay, and Cooke (1983: Table 1): C21 = 3.4, C31 = 3.8, C41 = 4.1, and C51 = 4.4. The standard deviation among years was 0.28, irrespective of age, and clutch sizes had an approximately normal distribution. Thus we took clutch size to be normal with mean appropriate for age and standard deviation 0.28. Clutch sizes of continuation nests average much smaller, we assume, by an average of two eggs. Nest success rates of the La Perouse Bay Snow Geese were remarkably high. From data provided by E. Cooch and F. Cooke (pers. commun.), the average was about 0.73 (standard deviation 0.04), and the yearly values were such that log(0.80 — nest success) was distributed roughly normally with mean —2.81 and standard deviation 0.62. Egg loss at La Perouse Bay was minor; egg survival averaged 0.95 (standard deviation 0.015) during 197385 (E. Cooch and F. Cooke, pers. commun.). We found that log(egg survival) was approximately normally distributed with mean —0.055 and standard deviation 0.0155. In addition, an average of 0.91 (standard deviation 0.032) of the eggs hatched. We found that log(hatch rate - 0.85) was nearly normally distributed with mean —2.98 and standard deviation 0.52. Gosling survival in the La Perouse Bay study averaged 0.75 (standard deviation 0.056) during 1973-85 (E. Cooch and F. Cooke, pers. commun.). We generated gosling survival rates from a normal distribution with those parameters. We computed equation 4 for 1,000 random sets of variates (D, C, H, E, B) independently generated from distributions described above. We assumed a population consisting of 21% yearlings, 16% two-year-olds, 13% three-year-olds, 10% four-year-olds, and 40% older hens. These values were based on a population with stable age distribution derived from survival rates of 40.7% for young-of-the-year and 79.5% for older birds (based on Richards 1986). A comparison of standardized regression coefficients indicated that brood sur-

vival, clutch size, and nest success were the most influential variables, followed by breeding incidence and egg survival (Table 14-4). For Snow Geese, brood survival is influenced by predation (Bousfield and Syroechkovskiy 1985, Cooke and Rockwell 1988) and possibly starvation (Cooke and Rockwell 1988). Clutch size is reduced in years with delayed nesting and when conditions along the migration route are poor (Cooke and Rockwell 1988). Nest success is mostly affected by predation and abandonment, the latter possibly due to high densities of birds (Owen and Wells 1979), extreme weather conditions (Harvey 1971, Cole 1979, Cooke and Rockwell 1988), and reduced nutrient reserves of females (Harvey 1971, Ankney and Maclnnes 1978). Breeding incidence is affected by weather conditions at the onset of the breeding season, drought along the spring migration path (Davies and Cooke 1983), and possibly high density or lack of nest sites (Hanson et al. 1972). Thus, productivity of the Snow Goose appears to be most markedly affected by weather and predation. Cooke and Rockwell (1988) concluded that survival, especially during the first year of life, was the major source of variation in lifetime reproductive success of Snow Geese at La Perouse Bay. Most mortality occurs during the hunting season, so their results are not directly comparable to ours, which are restricted to the breeding season.

5. Example—Southern Wood Ducks We next consider a population of Wood Ducks breeding in the southern United States. Most of the data we use are derived from studies in artificial nest structures. As with Mallards, two age classes (K = 2) seem adequate, as does a maximum of five nesting attempts (J = 5). We set D! — 0.90 and D2 — 1.00 under average breeding conditions^! = D2 = 1.00 under excellent conditions, and Dj = 0.60 and D2 = 0.80 in adverse situations. Breeding may be depressed by high densities of breeding birds relative to the number of nest sites (Grice and Rogers 1965) or by inadequate food supplies. Nesting probabilities differ from those of the Mallard in two regards: a longer nesting season and ample food supplies may encourage repeated renesting (Fredrickson and Hansen 1983), and renesting after a successful breeding effort occurs fairly regularly (Fredrickson and Hansen 1983). Because renesting rates do not decline as fast as those of the Mallard, in equation 5 we take where 0 =s (3 =s 1; small values of (3 imply greater nesting persistence (P = 1 for Mallards). We permit double brooding by letting q be positive. Since q, seems likely to vary with r)5 we simply take it to be a fraction (1 - P) of that value:

POPULATION DYNAMICS OF BREEDING WATERFOWL

Note that when (3 = 1, as for the Mallard, qj = 0. Thus the Mallard formulation is a special case of this one. Solving the resulting equations, we get

Again we can view a as a measure of nesting effort, and P essentially indicates how much greater nesting effort would be for Wood Ducks than for Mallards under similar circumstances. We take a = 1.10, 0.90, and 0.50 for excellent, average, and poor conditions, respectively, and set 3 = 0.70. Alpha is likely to vary mostly with density of breeding birds, relative to the number of available nest sites. Under average conditions (a = 0.90 and nest success H = 0.60), we get the following values: A21 = 1.00, A22 = 0.30, A23 = 0.046, A 24 = 0.0046, and A25 = 0.00035. Yearling Wood Ducks begin nesting much later than older birds (Grice and Rogers 1965, Hansen 1971), so they would be able to make fewer attempts during a season. We accommodate this difference by multiplying nesting persistence values of adults by 70%. We then obtain in a typical year: A n = 1, A12 = 0.21, A13 = 0.032, A14 = 0.0032, and A15 = 0.00024. Wood Ducks, especially in situations with artificial nest structures, are subject to considerable intra- and interspecific parasitism. This dump nesting is more common early in the breeding season (Grice and Rogers 1965), when nest sites are limited (Clawson, Hartman, and Fredrickson 1979) and possibly when nest structures are congregated and highly visible (Semel and Sherman 1986). We consider two levels of dump nesting, none and high. Yearling Wood Ducks initiate nesting later than older birds so are less likely to be parasitized. We suggest the following probabilities that a nest in the high dump nesting scenario will be parasitized: Pn = 0.70, P12 = 0.50, P13 = 0.30, P14 = 0.10, P15 = 0.00; P21 = 0.90, P22 = 0.70, P23 - 0.50, P24 = 0.30, and P25 = 0.10. Values for late clutches are inconsequential because very few such clutches are laid. Intraspecifically parasitic birds are considered members of the breeding population. Clutch sizes of Wood Ducks are confused by dump nesting. Normal clutches of Wood Ducks on average are larger than those of Mallards and probably decline more slowly with repeated nesting attempts (Clawson, Hartman, and Fredrickson 1979). We take for normal clutches: Cn = 11, C12 = 10.5, C13 = 10, C14 = 9.5, ^-*15

==

^» ^21 =

5 22 = AJ.J, v- .10). The Mallard data, which were most numerous and covered the most extensive area, showed a peak in clutch size at intermediate latitudes (Fig. 15-14). Only Lesser Scaup showed a significant decline of clutch size with increasing latitude (Fig. 15-14); this was only because of the relatively large average clutch sizes recorded in two studies in southern breeding areas (California). Interspecific and intraspecific analyses suggest that clutch sizes of waterfowl decline slightly with increasing latitude. This pattern is contrary to that observed for most birds that feed their young (Moreau 1944, Lack 1947, Skutch 1949, Klomp 1970, Ricklefs 1980). The contrast between feeders and nonfeeders has no bearing on some of the hypotheses proposed as explanations of the latitudinal patterns of clutch size variation (Table 15-9). For instance, Lack (1947, 1954, 1968) championed the hypothesis that longer day lengths allowed more time for parents to find food for their young, so clutch size increased with latitude. The day-length hypothesis, as envisioned by Lack, has no bearing on waterfowl, which do not feed their young. Other hypotheses (Table 15-9) that explain the latitudinal variation in clutch size are not so restricted.

B. Resource Abundance for Breeding Birds Ricklefs (1980) and Koenig (1984, 1986) have supported seasonal productivity ratios (i.e., Ashmole's [1963] hypothesis) as an explanation for interspecific and intraspecific increases in clutch size with latitude. They reason that large clutches are possible at northern localities because there are low densities of breeding birds in relation to resources (specifically food for nestlings). Northern localities have low breeding densities because the low winter productivity limits population size (Fig. 15-15). In contrast, tropical areas show much less difference between breeding and nonbreeding season productivity, so even if winter resources limit population size, there will still be density-dependent effects

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FRANK C. ROHWER

Figure 15-14. Clutch size vs. breeding latitude for Mallards and Lesser Scaup. Clutch sizes are means from nesting studies in North America (Rohwer unpublished). Lesser Scaup show a significant decline in clutch size at northern latitudes (r = 0.63), whereas Mallard clutch sizes peak at midlatitudes (r = 0.52).

on reproduction (i.e., smaller clutches). In essence, the ratio of breeding season to nonbreeding season productivity influences the relative abundance of resources for breeding birds because of density-dependent winter mortality. The seasonal-productivity hypothesis should apply to any organisms whose reproductive output is limited by resource levels. So why are the waterfowl contradictory? Northern waterfowl migrate to wintering areas that have relatively high winter productivity, but so do most passerines, which show clutch size patterns consistent with the seasonal-productivity hypothesis (Ricklefs 1980). Perhaps individual resource availability on the breeding grounds has little influence on waterfowl

Figure 15-15. A graphical model of how seasonal productivity ratios influence clutch size (after Ricklefs 1980). The size of the breeding population is limited by resource levels during the winter. The resources available for reproduction are therefore set by the amplitude of seasonal fluctuations. Small fluctuations (in the relatively stable tropics) mean little summer excess, so tropical birds lay small clutches. Large fluctuations (as expected at the highly seasonal poles) cause a relative abundance of resources during the breeding season, hence large clutches.

Table 15-9. Explanations for latitudinal gradients in clutch size Hypotheses related to resource abundance (1) Day length: long days at high latitudes allow more foraging time (Lack 1947, 1954; Hussell 1972). (2) Concentration of productivity: food is temporarily more abundant in northern areas because short summers concentrate productivity. (3) Relative population density (a) Seasonal productivity ratios: northern breeding populations are low in comparison to resources because winter food availability limits population size (Ashmole 1963, Ricklefs 1980). (b) r/K demographics: per capita resource abundance is high during the breeding season in northern breeding areas because of density-independent devastations of northern populations. (4) Use of stored nutrients: some birds (i.e., waterfowl) meet the energetic demands of egg laying by depending on stored reserves (Ryder 1970). The amount and/or utilization pattern of stored reserves use can vary with latitude. Hypotheses concerned with demographic optimization (5) Balancing current and future reproduction: larger clutch size reflects a shift toward current reproduction because high adult mortality (not associated with breeding) decreases the likelihood of future reproduction (Cody 1966). (6) Bet hedging: variance in adult vs. offspring survival affects optimal reproductive effort. High variance in offspring survival shifts the balance toward restraint and multiple breeding events (Murphy 1968, Schaffer 1974a). Other hypotheses (7) Predation: clutch size is inversely related to nest predation rates (Skutch 1949, Slagsvold 1982), which may vary with latitude.

EVOLUTION OF REPRODUCTIVE PATTERNS clutch sizes. Incubation ability, brood survival, and viability/predation/hatching synchrony are all independent of productivity, so we could invoke one or more of these as hypotheses to exonerate the seasonal-productivity hypothesis. The scant data for arctic waterfowl, however, do not support the incubation-ability or broodrearing hypotheses. An alternative is that clutch size of waterfowl is largely independent of breeding-area productivity because of the utilization of stored nutrients for breeding (see chapter 2 of this volume). The consequences of this idea are developed in a later section of this chapter. Elevated clutch sizes at high latitudes have been considered by some (Cody 1966, Pianka 1978) to be yet another r-type trait that results from the instability of arctic populations in comparison to tropical areas (Dobzhansky 1950). This explanation is surprisingly similar to the seasonal-productivity hypothesis in that large clutches in northern areas are seen as a result of the reduced importance of density-dependent resource limitation during the reproductive period. The abundance of resources in the r/K scheme is due to density-independent devastations periodically reducing arctic populations so that they rarely compete for breeding resources. Ricklefs's (1980) most direct test of the seasonal-productivity hypothesis was to correlate clutch size to the ratio of resource levels to the density of breeding. The resulting positive correlation, however, provides as much support for the r/K explanation as it does for the seasonal-productivity hypothesis. The r/K hypothesis, like the seasonal-resources hypothesis, offers no obvious explanation for the contrasting latitudinal patterns of waterfowl and altricial birds.

C. Reproductive Optimization and Bet Hedging Considerations of reproductive optimization (Fisher 1958, Williams 1966a, Charnov & Krebs 1974) have also influenced the way people interpret latitudinal variation in clutch size. The logic of this argument is that higher clutch sizes in the Arctic are a consequence of lower adult survival (irrespective of breeding effort), which discounts the value of future breeding attempts in favor of higher investment in the current clutch. This argument is built on the premise that increased reproductive effort (RE) also brings about increased likelihood of mortality. The logic may appear circular, because higher reproductive output at high latitudes must mean higher mortality rates in a persistent population. The higher mortality, however, could be largely due to prereproductive mortality, while survival rates of adults in northern localities could approach those of southern areas. Factors such as the perils of migration and harsh winter environments would be likely candidates to cause higher adult mortality,

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thereby shifting the optimal balance toward higher RE on each breeding attempt. Although optimization-of-effort arguments are of great theoretical importance (Fisher 1958, Williams 1966a, Murphy 1968, Charnov & Krebs 1974, Charlesworth &c Leon 1976), their relevance to variation in clutch size is not well substantiated. Three studies have failed to document lower survival of altricial parents that were overworked due to experimental increases in the number of young they had to feed (De Stevens 1980, Roskaft 1985, Boyce & Perrins 1987). On the other hand, two experimental brood manipulations have shown increased RE does reduce survival (Nur 1984) or future reproductive output (Roskaft 1985). Askenmo (1979) reported low return rates for male Pied Flycatchers (Ficedula hypoleuca) that attended enlarged broods, but this result may reflect increased dispersal in response to low reproductive success and not an increased death rate. Relationships between adult survival and nonmanipulated brood sizes can shed little light on the cost of reproduction controversy because much of the natural variation in clutch size is adaptive (Hogstedt 1980, Smith 1981, Askenmo 1982, Alerstam & Hogstedt 1984; but see Nur 1987). Clutch size and brood size enlargements in Canada Geese (Lessells 1986) and Snow Geese (Rockwell et al. 1987; brood sizes of 6 and 7 are due to intraspecific egg parasitism) produced no appreciable differences in adult survival. Of course, the more appropriate test of manipulating egg laying and looking at survival has not been done. In spite of the scarcity of data to show a trade-off between survival and RE in birds, we might still accept the basic premise (Nur 1988). If so, then optimization arguments may explain clutch size gradients, but the hypothesis can offer no a priori clue as to why waterfowl would have decreasing clutch sizes at high latitudes. The interspecific pattern could reflect longer lived species, such as geese and swans, in arctic regions, but Arnold's (1988) analyses suggest that is not the case (but see Laurila 1988). Bet-hedging arguments also have as a central assumption the notion that RE and survival are inversely related. The key factor affecting the balance between current reproduction and residual reproductive value is the variance in age-specific survival (Cohen 1966, Murphy 1968, Schaffer 1974a). If adult survival is highly variable then the balance shifts toward higher RE, whereas more variable recruitment (survival to breeding age) selects for reproductive restraint in order to increase the number of breeding attempts. The bet-hedging hypothesis would predict that arctic populations or species of waterfowl have more annual variation in reproductive success than do their temperate or equatorial counterparts. This prediction is supported by a lot of

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waterfowl lore but not much data (Cooch 1961, Barry 1962). The flip side of the bet-hedging argument is that increased clutch size of arctic passerines is due to high variance in adult survival relative to offspring survival, an argument that is much less appealing. Slagsvold (1981) and others (Kremetz & Handford 1984, Jarvinen 1986) report clutch size patterns in altricial birds that do not match predictions of either of these hypotheses concerning allocation of RE. Likewise, the importance of RE optimization arguments for birds have been discounted based on modeling (Ricklefs 1977b) and the logic and evidence of the relationship between RE and survival in birds (Alerstam & Hogstedt 1984). Bet-hedging and reproductive-optimization explanations both hold that geographic variation in clutch size is a reflection of shifting the balance between RE and residual reproductive value. As a direct test of these hypotheses one could manipulate clutch sizes of some altricial birds, such as Northern Flickers, at several different latitudes. Arguments based on RE would predict that northern populations, which lay larger clutches (Koenig 1984), are already near maximum output, so individuals with enlarged broods should be unable to increase their productivity. Southern populations, however, are presumed to show reproductive restraint, so enlarged brood sizes should be more likely to fledge more young than the control nests at that latitude. In contrast to RE hypotheses, the r/K and seasonal-productivity hypotheses, which are based on resource abundance relative to the density of nesting birds, would predict that enlarged broods would fare equally well or poorly at both high and low latitudes. Differing rates of nest predation have been a popular argument for regional variation in clutch size (Skutch 1949). Once again, the generality of the predation hypothesis is brought into question by the contrasting clutch size gradients of waterfowl and birds that feed their young. There is no reason to expect that nest predation rates would be considerably greater for arctic species or populations than for more equatorial waterfowl. In fact, reduced diversity of mammalian predators in the Arctic would argue for lower, not higher, predation (see Ricklefs 1969).

D. Egg Production and Latitudinal Variation in Clutch Size The contrasting geographic patterns of clutch size between waterfowl and altricial birds may simply show that the limitations on clutch size in ducks, geese, and swans are very different than for other birds. If egg production limits clutch size in waterfowl, then the foregoing idea would be reasonable. Declining clutch size with increasing latitude is easy to reconcile with the egg-production hypothesis. Three mechanisms seem possible.

The longer migration distance of arctic nesters (populations or species) could cause them to arrive at the nesting areas with fewer reserves because the nutrient reserves, acquired on southern staging areas, must also fuel migration (Ryder 1970, Calverley & Boag 1977, Dunn & Maclnnes 1987). A second alternative is that nutrient reserves are equivalent at arrival, but northern populations (species) have less food available at the time of laying. Consequently, a greater percentage of each egg is composed of nutrients from reserves, so females deplete their reserves at a greater rate. A third option is that the amount and rate of stored nutrient use is invariant, but northern females quit laying with greater nutrient stores in anticipation of higher dependence on reserves to fuel incubation. All three explanations assume that stored nutrients not only are necessary for egg production, but also directly limit egg production. The validity of these assumptions was discussed in section IV.D.4 of this chapter, but no conclusion was apparent. If we assume that stored nutrients are integral to egg production, then it should be possible to test the importance of these three alternatives. Mass and body condition upon arrival at nesting areas of differing latitude is one type of data that would be important to resolve the alternatives. Calverley and Boag (1977) collected Northern Pintails in the parklands of Alberta and almost 2,000 km north on the Mackenzie River Delta, Northwest Territories. The northern sample did not include birds collected at arrival, but at the start of laying the arctic birds weighed about 40 g less than parkland birds (Calverley 8c Boag 1977: Fig. 5). Migration from the parkland site to the Mackenzie Delta would require at least 70 g of lipid (Calverley & Boag, 1977), but it is likely that pintails would interrupt migration and feed at northern parkland sites, and perhaps at Great Slave Lake, N.W.T. (Bellrose 1980). The lower mass of the pintails on the Mackenzie Delta is consistent with the hypothesis that migration to far northern areas uses nutrients that could be allocated to egg production. The northern birds may, however, have used some nutrients in unsuccessful nesting at southern areas before moving to the Mackenzie Delta, or may have evolved a strategy of reduced clutch size at higher latitudes (Nudds 1978). To test the hypothesis that stored nutrients are used more rapidly in arctic regions would involve a comparison of the slopes of regressions between reproductive nutrients and body nutrients (Alisauskas &c Ankney 1985). I know of no data that would allow such a comparison. The third variant of the egg-production hypothesis suggests that females in the arctic terminate laying with greater reserves than temperate-zone breeders. Females might sacrifice egg production so they will have more reserves available for incubation. Comparative data on mass or body condition at the onset of incubation is an obvious test of this hypothesis, but such data are very scarce. Northern Pintails breeding in the Arctic appear

EVOLUTION OF REPRODUCTIVE PATTERNS

521

Table 15-10. The relationship between age/experience and breeding time, egg mass, and clutch size in waterfowl and Galliformes Species Anseriformes Red-breasted Merganser Blue-winged Teal Redhead American Black Duck Gadwall Wood Duck Canada Goose Mallard Hooded Merganser Snow Goose Mandarin Duck Hawaiian Goose Barnacle Goose Canvasback Common Eider Mute Swan Lesser Scaup Common Goldeneye Northern Pintail Galliformes Gray Partridge Ring-necked Pheasant Sage Grouse Blue Grouse Willow Ptarmigan

Nesting date

A< Y A< Y A< Y A< Y A< Y A< Y A< Y A< Y A< Y A> Y A< Y A< Y A< Y A< Y A< Y

Egg mass

Clutch size

-

A> Y A> Y A> Y -

A& Y A = Y A = Y -

A> Y A> Y A = Y A> Y A> Y

A^Y

A> A> A> A> A> A> A> A>

A> Y A = Y A = Y A = Y

A< Y A< Y A< Y A = Y

As: Y

Y Y Y Y Y Y Y Y

A< Y A> Y A = Y A> Y A> Y A> Y As; Y A> Y A = Y A=£ Y K^Y White-tailed Ptarmigan A< Y A> Y Spruce Grouse A^Y Rock Ptarmigan A< Y A> Y Note: Adult (A) birds are those with at least one year of breeding experience. Young (Y) birds are a Captive birds

to weigh less, not more, than southern birds at the beginning of incubation (Calverley & Boag 1977: Fig. 5). Obviously, more data are needed to evaluate these hypotheses. It is clear that the causes of the geographic trends in clutch size of birds in general and waterfowl in particular are not well understood. At present, the most parsimonious explanation for declining clutch sizes of highlatitude waterfowl would be related to nutrient usage for egg laying and incubation. Northern females probably arrive with fewer reserves and use those reserves at a greater rate during the prelaying and laying periods. Northern waterfowl may also allocate more stored reserves to incubation. There is probably some interaction between clutch size and laying dates. Short arctic seasons may require arrival and initiation of nesting at a phenologically early period in the spring, when maintenance requirements are high and food is not yet abundant. Thus, the benefits of earlier laying outweigh the cost in clutch size for such early nesting. If reduced clutches are a common pattern among northern populations, then it makes one wonder why waterfowl migrate north. Among passerines, the larger clutches at higher

Source(s) Wilhjelm 1938 (in Klomp 1970) Bennet 1938, Dane 1965 Low 1945 Stotts & Davis 1960, Coulter & Miller 1968 Gates 1962 Bellrose et al. 1964, Grice & Rogers 1965 Brakhage 1965, Cooper 1978, Raveling 1981 Coulter & Miller 1968, Krapu & Doty 1979 Batt & Prince 1978a Morse et al. 1969 Finney & Cooke 1978, Newell pers. comm. Bruggers 1979 Kear & Berger 1980 Owen 1980a Bluhm 1981a Baillie & Milne 1982 Birkhead et al. 1983 Afton 1984 Dow &c Fredga 1984 Duncan 1987a, b Blank &c Ash 1960 Labisky & Jackson 1969a Wallestad & Pyrah 1974 Zwickel 1975, 1977 Myrberget 1977, 1986 Hannon & Smith, 1984 Erikstad et al. 1985 Giesen et al. 1980 Keppie 1982 Steen & Unander 1985 those in their first breeding attempt.

latitudes provide an obvious benefit to offset the assumed perils of longer migrations. VII. Parental Age and Reproductive Performance One of the most pervasive patterns in avian life histories is for young birds to reproduce less than older birds. Young birds typically nest later, lay smaller clutches of smaller eggs, and raise fewer young than older birds (Tables 15-10 &c 15-11). Age effects have also been noted for other reproductive traits, such as the frequency of renesting (Strohmeyer 1967, Sopuck & Zwickel 1983, Ross 1980), interclutch intervals (Nol & Smith 1987), and even nestling sex ratios and hatching asynchrony (Blank 6c Nolan 1983). Several studies examined the performance of known-age birds over many years. The handicap of youth or inexperience is largely eliminated after one to three breeding seasons, even in long-lived seabirds (Richdale 1957, Coulson 1966, Mills 1973; but see Ollason 8c Dunnet 1978, Pugesek 1987). In many ducks, second-time breeders are nearly as proficient as more-experienced females (but see Afton 1984). Among

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FRANK C. ROHWER Table 15-11. Relationships between age/experience and hatchability, nest success, and productivity of waterfowl and Galliformes

Species

Hatchability

Nest success

Fledgling success

Number of fledglings

Anseriformes Canada Goose A> Y A = Y A> Y A> Y A = Y Snow Goose Mandarin Duck A> Y Hawaiian Goose A> Y Common Eider A = Y Mute Swans A> Y Lesser Scaup A> Y A= Y Common Goldeneye A> Y Barnacle Goose A> Y Galliformes Blue Grouse A = Y A - Y Spruce Grouse A = Y A = Y Willow Ptarmigan A = Y A = Y A> Y Rock Ptarmigan A> Y Note: Adult (A) birds are those with at least one year of breeding experience. Young (Y) birds are

geese and swans, breeding productivity seems to plateau after two to three breeding seasons (Cooper 1978, Finney & Cooke 1978, Birkhead et al. 1983, Rockwell et al. 1983). The converse of examining the effects of youth is to question what happens in old age. Relatively few studies have looked for such effects, and their results are much more variable than studies reporting on the effects of youth. Production of fledglings or, better yet, numbers of offspring that become recruits, are inherently variable measures of reproductive performance, so it is quite difficult to demonstrate significant old-age effects. In this light, the study by Perrins and Moss (1974) that revealed both decreased brood size and decreased return rates of fledglings for very old Great Tits is exceptional. Female Northern Sparrowhawks (Accipiter nisus] lay progressively earlier and produce larger clutches with increased nest success up to the age of 4 or 5, but these traits all decline after age 5 or 6 (Newton et al. 1981). Several other species show old-age declines (though usually nonsignificant) in egg size (Richdale 1957, Brooke 1978, Mills 1979, Nisbet et al. 1984, Shaw 1986), clutch size (Coulson & Horobin 1976, Nisbet et al. 1984, Shaw 1986), the earliness of laying (Richdale 1957, Davis 1975, Shaw 1986), hatching success (Richdale 1957, Perrins & Moss 1974), fledging success (Coulson &c Horobin 1976, Pugesek 1987), or recruitment (Ratcliffe et al. 1987). Contrary to these studies, the oldest age classes in several birds have shown no decrease in reproductive proficiency in terms of egg size (Coulson &c Horobin 1976, Cooper 1978, Lloyd 1979, Mills & Shaw 1980, Baillie & Milne 1982, Blank & Nolan 1983), clutch size (Richdale 1957, Mills 1973, Perrins & Moss 1974, Cooper 1978, Ratcliffe 1980, Baillie & Milne 1982, Birkhead et al. 1983, Pugesek & Diem 1983, Rockwell et al. 1983, Nisbet et al. 1984), laying date (Coulson & Horobin 1976, Lloyd 1979), or measures of success such as hatchability, nest success, or fledging success (Coulson &c Horobin 1976, Ollason &

Source(s) Brakage 1965, Cooper 1978, Raveling 1981 Finney & Cooke 1978 Bruggers 1979 Kear & Berger 1980 Baillie & Milne 1982 Birkhead et al. 1983 Afton 1984 Dow & Fredga 1984 Owen 1984 Zwickel 1975 Keppie 1982 Hannon & Smith 1984 Steen & Unander 1985 those in their first breeding attempt.

Dunnet 1978, Baillie & Milne 1982, Nisbet et al. 1984). In some species the old-aged birds showed mixed sets of effects. For instance, Common Greenshanks (Tringa nebularia) lay smaller eggs from age 2 onward, and clutch volume of Herring Gulls decreases in birds over 8 years old (Davis 1975, Thompson et al. 1986). Yet in both species old birds nest earlier than young birds, and the senior gulls maintained their productivity in spite of the changes in eggs. Productivity of Greenshanks in relation to their age could not be determined because of brood mobility. In Arctic Terns (Sterna paradisaea] clutch size peaks in middle age, yet the oldest birds had the highest productivity (Coulson & Horobin 1976).

A. Hypotheses for Age-specific Reproductive Patterns The most obvious question concerning age-specific reproductive effort is why such age-related patterns exist. There are at least three quite different hypotheses to explain why reproductive performance increases after the initial breeding attempts. The oldest and most widely accepted hypothesis is that young breeders are just poor breeders —the constraint hypothesis (Nice 1937, Lack 1968, most older references in Tables 15-10 & 15-11). A newer hypothesis is an outgrowth of Williams's (1966a) succinct statement about the trade-off between reproductive effort (RE) and residual reproductive value. The idea of the restraint hypothesis is that younger breeders hold back on RE to increase their chances of future reproduction (Pugesek 1981, Curio 1983). The third hypothesis suggests that birds of poor quality have both poorer reproductive performance and poorer survival (Potts 1969, Perrins 1979: 230, Curio 1983, Coulson & Porter 1985, Nol & Smith 1987). According to this quality-correlation hypothesis the poor breeders are also the birds least likely to survive to reproduce in subsequent seasons, so the increased performance with age is actually caused by the mortality of the ineffectual breed-

EVOLUTION OF REPRODUCTIVE PATTERNS ers that lowered the average reproductive output for the young breeders. There are two ways to test the quality-correlation hypothesis. First, we can look at individual changes in reproductive performance. Among several birds, such measures as clutch size, breeding date, and number of young fledged all increase for individuals monitored over two or more years (Aldrich & Raveling 1983, Afton 1984, Dow & Fredga 1984, Harvey et al. 1985, Hamann &c Cooke 1987), which is strong evidence that the age-related changes in productivity are not due solely to disappearance of poor-quality birds. A second approach to testing the quality-correlation hypothesis contrasts the performance in year one of birds that survived and birds that disappeared and presumably died. Song Sparrows (Melospiza melodia) that breed in two or more years produce 0.67 more young in their first year of breeding (as yearlings) than do the yearlings that are not seen in later years (Nol & Smith 1987). This suggests that the quality-correlation hypothesis at least partially accounts for age-related changes in reproductive performance (see also Potts 1969, Coulson &c Porter 1985). Nol and Smith's (1987: Table 2a) data also show that Song Sparrows that survived to breed in two or more years raised 0.84 more independent young in their second year than in their first year. Thus, the quality-correlation hypothesis is supported, but the birds are also restrained or are constrained from greater reproductive output in year one. Dow and Fredga's (1984) study of Common Goldeneye provides no support for the quality-correlation hypothesis. Breeding first-year birds that were never seen in later years laid 8.56 eggs compared to 7.68 eggs for those birds that were seen in later years. Likewise, among second-year birds the nonreturning birds laid slightly larger clutches than the second-year birds that were present in later years (Dow & Fredga 1984).

B. Are Young Birds Constrained by Their Inefficiency? The constraint hypothesis implies that young birds are less capable of laying eggs or caring for young than are older birds. Three subhypotheses have been proposed to explain the deficiencies of younger birds. Young birds, because of their age, could show less skill in any learned behaviors that are important for successful reproduction. Alternatively, young birds have had little experience with breeding, so it may be that specific experiences learned from breeding are the cause of agerelated increases in productivity. The third idea is that age and social status are correlated, so age effects are caused by increased rank in the social system (Arcese 6t Smith 1985). I will ignore the last variant, because if increased breeding success is due to rank in the social system (which could mean that birds of high rank acquire

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better territories or in some way exclude subordinate birds from prime resources) then we must explain why age affects rank. The question of whether age (and therefore general experience) or breeding experience, per se, influences success has been addressed in several studies. The general protocol is to examine breeders of some known age, such as 2-year-olds. The comparison of interest is between the birds that breed first at age 2 and the other 2-year-old nesters that also nested when they were yearlings. Three outcomes seem possible. A first, and rather unlikely, scenario is that the 2-year-olds with prior experience would have lower output than the 2-year-olds that did not attempt to breed at age 1. Such data would suggest that early nesting reduces subsequent reproductive output. The second possibility is that reproductive parameters of both groups of 2-year-olds could be equal, but greater than for the birds that breed as yearlings. This result would suggest that age and not breeding experience was the constraint on reproduction. Finally, the group of birds with prior experience might have greater success at their second breeding than sameage birds breeding for the first time. Typically that result is considered support for the hypothesis that experience with breeding contributes to increased reproductive output. The birds that postponed breeding, however, may be low-quality birds that have reduced reproductive output because of their poor quality, not because of their lack of breeding experience. Several studies have failed to find differences in reproductive performance when comparing equal-aged birds that differed in breeding experience (Richdale 1957, Ainley & Schlatter 1972, Fisher 1975, Newton et al. 1981, Loman 1984, Nol & Smith 1987). These data suggest that breeding experience plays little role in the improvement of breeding parameters with age. Breeding experience per se, however, may contribute to success in some species (Lehrman & Words 1967, Potts et al. 1980, Aldrich & Raveling 1983, Harvey et al. 1985). For instance, 2-year-old female Pied Flycatchers that had bred before did no better than those that had not, but first-time breeders of age 3 raised fewer young than same-aged birds with breeding experience (Harvey et al. 1985). Among male flycatchers, 2-year-olds with prior experience were more successful than naive males at age 2. Interpretation of these data as evidence of the effects of breeding experience is somewhat risky (Harvey et al. 1985). Increased success may have little to do with experience learned by prior nesting. Individuals that begin breeding a year earlier than others are likely to be of higher quality, and that inherent high quality may cause them to subsequently outperform similar-aged birds that abstained from nesting in their first year. To overcome this problem one could experimentally alter nest-

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ing experience so that some first-year individuals completed nesting, thereby accruing benefits of experience, but other birds were disturbed during laying, therefore gaining breeding experience only in pairing behavior and nest construction. Comparisons of the second-year reproductive output of these two groups would show the importance of breeding experience with parent quality held constant. There are other, albeit less direct, ways to distinguish between quality and experience. Female Pied Flycatchers that nested as 1-and 2-year-olds had greater survival to age 3 than did the females that first nested at age 2 (Harvey et al. 1985). This suggests that nesting experience and quality are correlated. It would also be instructive to compare reproductive success of the proposed good-and poor-quality groups after both had bred for several seasons. Differences in breeding experience should no longer be important, so remaining differences in performance would most parsimoniously be explained as inherent (though not necessarily inheritable) quality effects. In general, the breeding experience variant of the constraint hypothesis has little support. It is quite possible, however, that the general experience that comes with increased age explains why old birds breed more effectively than young birds. The constraint hypothesis is often supported by observations that young birds have lower feeding efficiency than older birds (Orians 1969, Recher & Recher 1969, Dunn 1972, Buckley & Buckley 1974, Barash et al. 1975, Verbeck 1977, Groves 1978, Ingolfsson & Estrella 1978, Morrison et al. 1978, Searcy 1978, Dekker 1980, Quinney & Smith 1980, Espin et al. 1983, Burger & Gochfeld 1986, MacLean 1986, Sutherland et al. 1986). In some species the foraging efficiency of young birds relative to old birds increased considerably over a study period of only a few months (Recher & Recher 1969, Dekker 1980), but stayed below adult level. In other species there was no apparent increase in the foraging success of young birds (Dunn 1972, Morrison et al. 1978). Glaucous-winged Gulls (Larus glaucescens) become increasingly proficient at cracking clams between their first and second years and between their second and subsequent years (Barash et al. 1975). Likewise, their fishing ability as adults is greater than as yearlings or 2-year-olds (Searcy 1978). Herring Gulls also become progressively more efficient at shell dropping and at foraging at dumps over at least their first five years of life (Ingolfsson & Estrella 1978, Greig et al. 1983). Unfortunately, all of these studies contrasted adults (birds of breeding age) with birds of nonbreeding ages. Pugesek (1984) suggests that the gradual increase in foraging efficiency shown by the nonbreeders would not continue once birds reach adulthood. There are, however, no data to support or reject that view, and it seems plausible that birds in their early

reproductive years are still learning how to forage effectively. Ainley &c Schlatter (1972) showed that breeding Adelie Penguins (Pygoscelis adelie) produce heavier chicks after they have bred several times, and they suggest this change reflects increased foraging efficiency. There is, however, no way to exclude the alternative that the older birds are expending more RE and are not any more efficient in their foraging. This idea of age-specific changes in RE will be addressed in detail in the following section.

C. Do Young Birds Show Breeding Restraint? Young birds may have low reproductive output (Tables 15-10 &c 15-11) because they are showing restraint in their breeding effort. The restraint hypothesis first assumes that there is a trade-off between the level of reproductive effort and subsequent survival. That assumption has been difficult to support (see section VLB of this chapter and reviews by Stearns 1976, Reznick 1985, Nur 1988), but seems safe on logical grounds (but see Alerstam & Hogstedt 1982). The second and more critical assumption is that birds have declining survival as they age. Theoretical predictions or simulations for stable populations that are based on these two assumptions almost uniformly predict that RE should increase as organisms grow older (Gadgil &c Bosert 1970; Schaffer 1974a, 1974b; Pianka & Parker 1975; Charles worth &c Leon 1976; Stearns 1976). The applicability of such models to organisms other than mammals is questionable, however, because of the second assumption about senescence. In mammals, senescence manifests itself in declining survival in old-age groups (Deevey 1947, Caughley 1966, Fryxell 1986, Glutton-Brock et al. 1988, Packer et al. 1988) and, in some cases, reduced reproductive performance in these old-age groups (Packer et al. 1988). Theory predicts that senescence should be widespread (Hamilton 1966), but the avian data fail to comply. I have already mentioned that old-aged birds do not consistently show declines in reproductive performance. The more controversial data are those of age-specific death rates. Early studies of avian demography suggested that after the initial period of high mortality the chance of death for birds became constant (Lack 1943a, Deevey 1947). Simply stated, a 10-year-old Mallard has the same chance of living another year as does a 3-yearold Mallard. (Mammals reading this paper should pause to consider how such a pattern of mortality would influence their lives.) If constant mortality is the rule for birds, then life history theory that predicts increased RE in older age groups is not appropriate for birds. The issue of senescence in birds is a controversial topic partially because of the difficulty of examining age-specific mortality rates. It is not yet possible to col-

EVOLUTION OF REPRODUCTIVE PATTERNS lect a batch of birds and determine the actual age of individuals in the sample. That means that age-specific fecundity and mortality schedules have to be derived from birds that were initially banded or otherwise marked as young birds. Age-specific survival estimates are therefore based on the resighting of these marked birds, the recovery of their bands or both. There are a variety of problems with estimating age-specific survival rates from such data, and there is considerable controversy about what methodology is best (cf. Cave 1977, North 8c Cormack 1981, Lakhani & Newton 1983, Dobson 1985, Fryxell 1986). The concern for us is not whether the survival estimates are biased (though this is a serious concern in its own right; cf. Brownie et al. 1978, Anderson et al. 1985); rather the concern is if there is an interaction between the bias and a bird's age. Unfortunately there are indications of such effects. Band loss is a serious problem facing reliable estimates of age-specific rates. Bands wear out (Ludwig 1967, Coulson 1976, Thomas 1979, Seguin & Cooke 1983), so the senescence that appears in some long-lived birds may only be senescence of bird bands. Another problem is that most age-specific survival data that include estimates for old-age birds are based on resightings obtained in long-term studies of breeding birds. Buckland (1982) suggests that survival estimates for old birds are often biased downward because old individuals may be as old as the study itself, so the probability of their being overlooked even though they were present is greater than for young birds. Band loss and nonsightings both bias survival estimates downward for the oldest age groups and may create the appearance of senescence when none exists. On the other hand, the large variance associated with age-specific survival estimates makes it very difficult to show statistically significant declines in survival, even if such patterns exist (cf. Richards 1986). With these caveats in mind, it is clear that the listings in Table 15-12 should be viewed with suspicion. Nevertheless, a number of studies have failed to detect declining survival in old birds. Several recent papers have suggested that the lack of documentation of senescence in avian populations is a result of the small sample of older individuals; however, many studies have marked individuals for a long period relative to life expectancy. In these studies few individuals live to extreme ages, so lack of sample size makes it impossible to show significant declines in survival values. Larger samples of ancient individuals probably would reveal senescence, yet it is doubtful that senescence at this age would have a substantial impact on the evolution of optimal patterns of age-specific investment in RE. For example, Austin and Austin's (1956) analysis of Common Terns (Sterna hirundo) was based on more than a quarter of a million banded birds and more than 40,000 returns. Yearly mor-

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Table 15-12. The effects of old age on the survival of birds Species with no apparent decline in survival with old age European Robin Lack 1943a European Starling, Common Deevey 1947 & Siler 1979 (data Blackbird, Song Thrush from Lack 1943b) Yellow-eyed Penguin Richdale 1957 Gambel's Quail Sowls 1960 California Quail Raitt & Genelly 1964 Caspian Tern Ludwig 1967 (see also Ludwig 1965) Dunlin Soikkeli 1967 Herring Gull Kadlec & Drury 1968 Osprey Henny & Wight 1969 Shag3 Potts 1969 Dominican Gull Fordham &c Cormack 1970 Blue Grouse Zwickel 8c Bendell 1967, 1972, pers. comm. Great Tit Bulmer & Perrins 1973, Dobson 1985 Buller's Mollymauk Richdale Sc Warham 1973 Arctic Tern Coulson & Horobin 1976 White-winged Scoter Brown & Houston 1982 Northern Fulmar Buckland 1982 Tawny Owl, Barn Owl Dobson 1982 Common Goldeneye Dow & Fredga 1984 Chaffinch, Pied Wagtail, Dobson 1985 Jackdaw, Jay Canada Goose Parkin & White-Robinson 1985 Cactus Ground Finch Gibb & Grant 1987 Song Sparrow Nol 8t Smith 1987 Species where survival declines in old age, but the decline is not significant Northern Lapwing Deevey 1947 (data from Lack 1943b) Red Grouse Jenkins et al. 1963 Blue Tit Dobson 1982 Hen Harrier Dobson 1982, Rothery 1985 Barnacle Goose Owen 1982 California Gull Pugesek 1983 Scrub Jay Woolfenden & Fitzpatrick 1984 Robin Dobson 1985 Snow Goose Richards 1986 Medium Ground Finch3 Gibbs & Grant 1987 Species where survival declines significantly in old age Common Tern Austin & Austin 1956 Pied Flycatcher Berndt & Sternberg 1963 Coulson & Wooler 1976 Black-legged Kittiwake Northern Fulmar Dunnet & Ollason 1978 Adelie Penguin Ainley & DeMaster 1980 Common Kestrel, Northern Dobson 1982 Sparrow hawk, Merlin, Northern Lapwing Common Eider Coulson 1984 Black-capped Chickadee Loery et al. 1987 Bradley et al. 1989 Short-tailed Shearwaters a

Only one of four cohorts shows a decline in age-specific survival. tality is constant from years 5 to 18, but increases thereafter. The Austins eliminated band-loss biases by rebanding individuals, and their study was of such long duration that there was ample opportunity to record birds much older than the record longevity (21 years). Therefore, it is clear that declining survival after 18 years is a real phenomenon, but it may be relatively un-

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important in terms of optimizing RE because considerably less than 1% of the breeding population reached this age. According to the restraint hypothesis, RE not only should be reduced in early years, but also should continue to increase throughout life. The actual pattern seems to be one of increased effort during the first few attempts, but then reproductive output appears to level off (most citations in Table 15-10; but see Pugesek & Diem 1983). This pattern is more consistent with the constraint hypothesis than the restraint hypothesis. This logic assumes that the general constancy of clutch size and other measures of reproductive intensity in middleand old-aged birds actually reflects constant RE. It is possible that a true measure of RE (Williams [1966a] defined RE in terms of the effect of breeding on the probability of survival, cf. Glutton-Brock [1984]) actually increases with age; yet this increased effort is not apparent because another potential effect of senescence is to decrease the physiological ability to have a large reproductive output. In this scenario, the physiological effects of senescence (decreased bodily function) and the evolutionary response to senescence (increased RE with age) compensate for one another so that the variables that we measure (clutch size, etc.) show no change after birds age a few years. In simple terms, a 10-year-old Mallard that lays a clutch of 12 eggs is risking much more than a 3-year-old Mallard that lays the same number of similar-sized eggs. This will be a very difficult issue to resolve.

D. Examining the Restraint and Constraint Hypotheses for Waterfowl In waterfowl, the pattern of reduced output by young birds is well documented (Tables 15-10 6c 15-11). The period of greatest female effort is the egg-laying stage. In this group it will be difficult to experimentally increase RE in younger and older breeders. Because some waterfowl use stored reserves to meet breeding requirements, we can make some inferences about the restraint and constraint hypotheses. We know that young waterfowl lay smaller clutches than adults (Table 15-10). The constraint hypothesis predicts that young females, due to their inexperience, will have smaller reserves at the start of nesting. The restraint hypothesis might make the same prediction, since accumulating or maintaining large reserve levels may entail some increased risks of mortality, such as increased predation (Pienkowski et al. 1984, Lima 1986). At the end of laying, however, the predictions of the two hypotheses are quite different. The restraint hypothesis predicts higher reserve levels in young breeders, whereas the constraint hypothesis predicts equal or lower reserves in young breeders. These

predictions assume that incubation is equally costly for both age groups. (Of course, these predictions also assume that nutrient reserves are important to breeding success and adult survival.) The available data are consistent with the constraint hypothesis and are contrary to the predictions of the restraint hypothesis: 2- and 3-year-old Common Eiders, the youngest breeders, begin incubation weighing 110 g less than birds 4-17 years of age (Baillie & Milne 1982). Moreover, the oldest breeders, those over 10 years of age, had the greatest mass at the beginning of incubation and had laid as large a clutch as any age group. These data suggest that young females are not showing restraint; their reduced clutch size is instead a result of their youth and inexperience. Eiders are an excellent species to use in such an analysis because they are presumed to be highly dependent on stored reserves for incubation (Korschgen 1977; chapter 3 of this volume). Data on female mass in relation to age are also available for breeding Canada Geese (Aldrich & Raveling 1983). This captive population was breeding in a seminatural pen that had a high density of geese. The inexperienced breeders laid smaller clutches, began incubation at a lighter weight, ended incubation at lower weight, and were less attentive than experienced breeders (Aldrich &c Raveling 1983). Finally, yearling Mallards have fewer reserves at all stages in the breeding cycle than adults (Krapu & Doty 1979). Mallards, however, show less dependence on nutrient reserves for incubation (Krapu 1981) than do geese and eiders (see chapter 3 of this volume). These patterns are all consistent with the constraint hypothesis, but not with the restraint hypothesis, which predicts that young birds will have a higher mass during incubation. Krapu and Doty (1979) suggested that clutch size of young Mallards is low because they are ineffective at acquiring nutrients for egg production. This version of the constraint hypothesis would predict that young captive birds with unlimited food would not show reduced reproductive output compared to older birds. This is just the result obtained with captive Mallards and Pintails that had separate breeding pens in order to eliminate the effects of social interactions in open flight pens (Batt & Prince 1978, Duncan 1987a). If young breeders had evolved restraint then we might have expected smaller clutches from young breeders in captivity as well as in the wild. The exceptions to the pattern of reduced reproductive effort in young birds are almost more interesting than the cases that provide further support for the pattern. For both laying date and clutch size, the exceptional species where adults and young perform quite similarly are usually small, short-lived passerines. In summary, it appears that the constraint hypothesis is the most appropriate explanation for the reduced re-

EVOLUTION OF REPRODUCTIVE PATTERNS productive output of young breeders. The restraint hypothesis may be important in some species, especially in the long-lived birds where reproductive output increases over several breeding attempts. The quality-correlation hypothesis seems quite plausible, yet the increases in individual reproductive output suggest that this hypothesis explains little of the age-related variation in productivity.

E. Age at First Breeding Several waterfowl show a dramatic form of age-related productivity — they forgo reproduction during their first potential breeding year or years. Such deferred breeding has been the subject of a great deal of theoretical interest (Cole 1954; Lack 1954, 1968; Williams 1966b; Murphy 1968; Gadgil & Bossert 1970; Pianka 1970; Wiley 1974; Stearns 1976; Wittenberger 1979). Hypotheses proposed to account for the evolution of deferred maturity suggest that delayed reproduction allows: (1) increased growth in size; (2) higher fecundity once breeding commences; (3) increased individual survival; and (4) greater population viability for declining populations. The last hypothesis is probably not important because most populations are relatively stable, and populations that are declining are prone to extinction. The hypothesis concerning growth in size is unlikely to be relevant to birds and mammals, which show determinant growth and therefore do not have marked size-fecundity relationships. In contrast, the benefits of improved survival (Stearns 1976, Reznick 1985) and reproduction (references in section VII of this chapter) seem quite appropriate for birds. Wittenberger's (1979) modeling predicts deferred maturity in birds when: (1) subadults have considerably reduced breeding success relative to adults; (2) the risks of breeding as a subadult are high; and/or (3) adult mortality rates are low. Several recent papers have stressed the importance of body size on life history traits, including age at first reproduction (Blueweiss et al. 1978, Western 1979, Western &c Ssemakula 1982, Sterns 1983, Saether 1987, Laurila 1988). In general, age at maturity in birds shows lower correlations with body mass than do other life history variables, such as egg mass, clutch mass, incubation period, and lifespan (Western & Ssemakula 1982, Saether 1987). Because theory concerning delayed breeding relates to mortality rates, it would be most informative to know how age at maturity relates to adult survival. An early analysis showed the expected correlation between lifespan and delayed breeding (Ricklefs 1973: Fig. 2). As a group, the waterfowl breed somewhat younger than would be expected for birds in general based upon their size (Saether 1987). The Galliformes, another group with precocial development, show a much greater departure from expectation in terms of early breeding,

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whereas the seabirds and raptors show longer delays than expected based on their size (Saether 1987). Within the waterfowl, large body mass also relates to age at first breeding (Laurila 1988). Swans generally do not nest until their fourth or fifth year, geese typically nest in their third year, and members of the Tadornini, Mergini, and Aythyini often do not nest until their second or third year (Johnsgard 1978, Bellrose 1980, Saether 1987, Laurila 1988). Laurila's (1988) analyses show that after adjusting for body mass, the late-maturing species of waterfowl had reduced clutch size and had reduced development times (as shown by shorter incubation and fledging periods) than early-maturing species. The greater development rates of late-maturing species are probably an artifact caused by late-maturing species' inhabiting northern breeding areas, which influences development time (Laurila 1988). The delay in breeding is often lengthened in crowded conditions of captivity (Wood 1964, Aldrich & Raveling 1983). It is unclear whether this results from lack of resources or from the greater frequency of social interactions in captive flocks (Aldrich &c Raveling 1983, Lamprecht 1986). The converse effect of decreasing age at first breeding has been seen in populations at low densities. Intensive harvest that significantly lowered densities of some mammals resulted in breeding by young age classes (reviewed in Caughley 1977). Among waterfowl it has been proposed that shortages of scarce nest sites, specifically nest cavities in trees, could cause delayed maturation (Eadie & Gautheir 1985). Cavity-nesting ducks in North America delay breeding much more often than do ground nesters (Eadie &c Gauthier 1985). This analysis inappropriately treated species as independent units (see Harvey &c Mace 1982), however, so the result is largely an effect of delayed breeding by the Mergini, many of which nest in tree cavities. Even the Mergini that do not nest in tree cavities show delayed breeding (Alison 1975, Bellrose 1980). In a later paper Gauthier and Smith (1987) concluded that cavity nest sites were not limiting for Buffleheads, which casts further doubt on the hypothesis that delayed breeding in Buffleheads and their congeners was due to their cavity nesting.

VIII. Overview The life history questions that are the central focus of this chapter have been in the forefront of research on avian reproductive biology during the last several decades. It is apparent that we still have a great deal of research to do. That is especially true for work concerning precocial species. Although we know the descriptive breeding biology of most Northern Hemisphere waterfowl, we have not made equal progress in understanding why certain reproductive patterns exist instead of others. Questions about the timing of breeding make this

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point clear. A considerable body of work suggests that individuals that breed early have the highest reproductive success, yet very few ecologists have questioned why waterfowl or any other birds do not nest earlier in the spring. There seems to be consensus that the timing of seasonal breeding of birds in general is mainly influenced by the time when food supplies begin to become abundant. There is considerable controversy, however, over whether egg production or the demands of rapidly growing chicks limit how early birds can begin nesting. It may be that both factors are important, and that food for egg production constrains laying dates only in years when food is relatively scarce (Meijer et al. 1989; but see Korpimaki 1989). Although descriptive analyses of food supplies or the energy required for breeding (Figs. 15-1 &C 15-2) may clarify or emphasize some hypotheses, it is unlikely that considerable resolution of hypotheses concerning breeding times will be possible without experimental studies. Nevertheless, there are too few waterfowl studies that relate nest and brood success to relative breeding date. Such studies are very common for altricial birds. A manipulation of hatch times for any temperate-zone or arctic-breeding waterfowl, as outlined in section II.D, would be helpful in understanding the timing of waterfowl breeding. Self-feeding young make it likely that waterfowl breed as early as they can produce eggs, which represent a major energy investment. Questions concerning clutch size have received a great deal more attention than have those associated with nesting date. In this chapter I have attempted a critical review of the prevailing hypothesis that clutch size is limited by the energetics of egg production. There is no doubt that many waterfowl use stored reserves to produce eggs. It is much less clear that those stored reserves are necessary for egg production, let alone that the quantity of nutrient stores dictates clutch size. Further descriptive accounts of the patterns of nutrient use in temperate-zone ducks will not help to clarify these questions. The egg-production hypothesis is not supported by correlations of egg size and clutch size either within or between species. Likewise, relaying birds show little dependence on stored nutrients for egg production. Finally, there are at least some cases of temperate-zone ducks laying excessively large clutches. All these data suggest that the egg-production hypothesis has been overemphasized, probably because the hypothesis is intuitively appealing and is consistent with the nutrient dynamics of laying waterfowl. The relatively recent ideas concerning the interactions of egg viability and nest predation (Arnold et al. 1987) need to be studied in greater detail. It is particularly important that the physiological constraints of changing development to insure hatching synchrony be incorpo-

rated into revised models of clutch size determination in waterfowl. In addition, more experiments involving clutch and brood manipulations would be a great benefit in getting a better assessment of the success of eggs or ducklings in relation to clutch or brood size. Such studies are particularly important in other groups of precocial birds, where clutch size studies are very scarce. The seasonal decline in clutch size among waterfowl has received scant attention. Most waterfowl ecologists presume that seasonal declines are a result of renesting or of young birds laying late and laying small clutches. Neither of these sets of observations can explain the seasonal decline in clutch size, nor can they account for the seasonal decline in clutch size (Fig. 15-9). The most likely explanations for seasonal declines in clutch size assume that egg production is costly and that large clutches require substantial stored nutrients. Delaying nesting allows time to store nutrients and increase clutch size, but the time delays mean poor chick and postfledging survival and less time for renesting. Seasonal declines may also represent a seasonal shift toward less reproductive effort and greater importance of residual reproductive value. Such a shift may come about because of lower survival of late-season young and higher risks to adults for breeding late and having to molt and migrate later than is optimal. Recent analyses of latitudinal gradients in the clutch size of waterfowl have shown inverse relationships between latitude and clutch size. This exception to the general avian pattern may simply indicate that the determinants of clutch size in precocial birds are different than those of altricial birds. Intraspecific analyses of gradients in clutch size have revealed no relationships in several temperate-zone ducks, so the interspecific analyses may be confounded by survival or body size effects. The two simplest explanations for small clutches at high latitudes are that: (1) long-distance migration usurps reserves that would otherwise be used for egg production; and (2) short breeding seasons at high latitudes provide strong selection for early breeding, so that laying occurs well before substantial food becomes available on the breeding grounds and the stored reserves are utilized more rapidly. The waterfowl are consistent with other birds and mammals in showing an age-specific fecundity wherein young females have lower productivity than older females. The hypothesis that such changes reflect differential mortality of the least productive birds is not consistent with several data sets. Likewise, the evidence for waterfowl does not suggest that young birds are showing less reproductive effort than old birds in an effort to improve their survival. The most likely explanation for diminished reproductive output of young breeders is that these birds are constrained to low reproductive output by their youth and attendant inefficiency

EVOLUTION OF REPRODUCTIVE PATTERNS at foraging. The importance of age versus breeding experience has been a continual matter of contention, though resolution of this question is not possible. I might close with a request for two sorts of studies. We need more studies designed to critically assess hypotheses concerning the patterns of variation that we see in waterfowl biology. This statement applies to all aspects of waterfowl ecology, not simply to questions concerning life history questions dealing with reproduction. The other type of studies that is sorely lacking is longterm studies of marked populations of waterfowl. The work of Fred Cooke and his colleagues has been some of the critical work in almost all of the topics I have addressed. Such long-term studies take a great deal of personal dedication, good luck, and a funding commitment that is unusual in the United States. Nevertheless, the rewards should be obvious from the wealth of information and insight provided by the Snow Goose study.

Acknowledgments I owe a great deal to the people who contributed data or unpublished information that was used in this review. That includes A. D. Afton, C. D. Ankney, R. J. Blohm, E. Cooch, F. Cooke, D. C. Duncan, R. C. Gatti, L. Gustafsson, D. A. Hill, D. B. Lank, C. M. Lessells, J. Nelson, and R. A. Wishart. Without the help of my wife, Sheila, I don't think I ever would have finished this chapter. Three people, A. D. Afton, D. C. Duncan, and C. M. Lessells, read the entire review and made extensive comments on content and style. They substantially improved the manuscript, and I greatly appreciate their help. On several points we had to agree to disagree, but isn't that what makes science interesting?

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in relation to habitats for survival and breeding. Ornis Scand. 13: 25-37. , & . 1984. How important is clutch size dependent adult mortality? Oikos 43: 253-254. Alisauskas, R. T., & C. D. Ankney. 1985. Nutrient reserves and the energetics of reproduction in American Coots. Auk 102: 133-144. Alison, R. M. 1975. Breeding biology and behavior of the Oldsquaw (Clangula by emails L.). Ornithol. Monogr. 18. Anderson, D. R., K. P. Burnham, & G. C. White. 1985. Problems in estimating age-specific survival rates from recovery data of birds ringed as young. J. Anim. Ecol. 54: 89-98. Anderson, M. G. 1985. Variations on monogamy in Canvasbacks (Aythya valisineria). Pp. 57-121 in Avian monogamy (P. A. Gowaty &c D. W. Mock, Eds.). Ornithol. Monogr. 37. Andersson, M. 1984. Brood parasitism within species. Pp. 195-227 in Producers and scroungers: strategies of exploitation and parasitism (C. J. Barnard, Ed.). Groom Helm, London. , §c M. O. G. Eriksson. 1982. Nest parasitism in Goldeneyes Bucephala clangula: some evolutionary aspects. Amer. Natur. 120: 1-16. Ankney, C. D. 1980. Egg weight, survival, and growth of Lesser Snow Goose goslings. J. Wildl. Manage. 44: 174-182. . 1984. Nutrient reserve dynamics of breeding and molting Brant. Auk 101: 361-370. ., & A. R. Bisset. 1976. An explanation of egg-weight variation in the Lesser Snow Goose. J. Wildl. Manage. 40: 729-734. ., & C. D. Maclnnes. 1978. Nutrient reserves and reproductive performance of female Lesser Snow Geese. Auk 95: 459—471. ., & D. M. Scott. 1980. Changes in nutrient reserves and diet of breeding Brown-headed Cowbirds. Auk 97: 684-696. ., & A. D. Afton. 1988. Bioenergetics of breeding Northern Shovelers: diet, nutrient reserves, clutch size, and incubation. Condor 90: 459-472. Arcese, P., 8t J. N. M. Smith. 1985. Phenotypic correlates and ecological consequences of dominance in Song Sparrows. J. Anim. Ecol. 54: 817-830. Arnold, T. W. 1988. Life histories of North American game birds: a reanalysis. Can. J. Zool. 66: 1906-1912. , F. C. Rohwer, & T. Armstrong. 1987. Egg viability, nest predation, and the adaptive significance of clutch size in prairie ducks. Amer. Natur. 130: 643-653. Ashmole, N. P. 1963. The regulation of numbers of tropical oceanic birds. Ibis 103b: 458-473. . 1968. Breeding and molt in the White Tern (Gygis alba) on Christmas Island, Pacific Ocean. Condor 70: 35-55. Askenmo, C. 1973. Nestling weight and its relation to season and brood-size in the Pied Flycatcher Ficedula hypoleuca (Pallas). Ornis Scand. 4: 25-31. . 1979. Reproductive effort and return rate of male Pied Flycatchers. Amer. Natur. 114: 748-753. .. 1982. Clutch size flexibility in the Pied Flycatcher Ficedula hypoleuca. Ardea 70: 189-196. ., & U. Unger. 1986. How to be double-brooded: trends and timing of breeding performance in the Rock Pipit. Ornis Scand. 17: 237-244. Austin, O. L., & O. L. Austin, Jr. 1956. Some demographic aspects of the Cape Cod population of Common Terns. Bird-Banding 27: 5566. Bailey, R. O. 1981. A theoretical approach to problems in waterfowl management. Trans. North Am. Wildl. & Nat. Res. Conf. 46: 5871. Baillie, S. R., & H. Milne. 1982. The influence of female age on breeding in the Eider Somateria mollissima. Bird Study 29: 55-66. Baker, J. R. 1938. The evolution of breeding seasons. Pp. 161-177 in Evolution: essays on aspects of evolutionary biology. (G. R. deBeer, Ed.). Oxford Univ. Press, London.

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Western, D. 1979. Size, life history and ecology in mammals. Afr. J. Ecol. 17: 185-204. , & J. Ssemakula. 1982. Life history patterns in birds and mammals and their evolutionary interpretation. Oecologia 54: 281290. Wiley, R. H. 1974. Evolution of social organization and life-history patterns among grouse. Q. Rev. Biol. 49: 201-227. Williams, G. C. 1966a. Natural selection, the costs of reproduction, and a refinement of Lack's principle. Am. Nat. 100: 687-690. 1966b. Adaptation and natural selection. Princeton Univ. Press, Princeton, N.J. Williams, M. 1974. Creching behaviour of the Shelduck Tadorna tadorna L. Ornis Scand. 5: 131-143. Wingfield, J. C. 1983. Environmental and endrocrine control of avian reproduction: an ecological approach. Pp. 265-288 in Avian endrocrinology: environmental and ecological perspectives (S. Mikami et al., Eds.). Springer-Verlag, Berlin. Winkler, D. W. 1985. Factors determining a clutch size reduction in California Gulls (Larus californicus): a multi-hypothesis approach. Evolution 39: 667-677. , Sc J. R. Walters. 1983. The determination of clutch size in precocial birds. Pp. 33-68 in Current ornithology vol. 1 (R. F. Johnston, Ed.). Plenum Press, New York. Wishart, R. A. 1983. The behavioral ecology of the American Wigeon (Anas americana) over its annual cycle. Unpubl. Ph.D. dissertation, Univ. of Manitoba, Winnipeg. Witkowski, J. 1983. Population studies of the Grey-lag Goose Anser anser breeding in the Baryez Valley, Poland. Acta Ornithol. 19: 179216. Wittenberger, J. F. 1979. A model for delayed reproduction in iteroparous animals. Amer. Natur. 114: 439-446. , & R. L. Tilson. 1980. The evolution of monogamy: hypotheses and evidence. Ann. Rev. Ecol. Syst. 11: 197-232. Wood, J. S. 1964. Normal development and causes of reproductive failure in Canada Geese. J. Wildl. Manage. 28: 197-208. Wooley, J. B., 8c R. B. Owen, Jr. 1978. Energy costs of activity and daily energy expenditure in the Black Duck. J. Wildl. Manage. 42: 739-745. Woolfenden, G. E., & J. W. Fitzpatrick. 1984. The Florida Scrub Jay: demography of a cooperative-breeding bird. Princeton Univ. Press, Princeton, N.J. Wypkema, R. C., & C. D. Ankney. 1979. Nutrient reserve dynamics of Lesser Snow Geese staging at James Bay, Ontario. Can. J. Zool. 57: 213-219. Yom-Tov, Y. 1974. The effect of food and predation on breeding density and success, clutch size and laying date of the Crow (Corvus corone L.). J. Anim. Ecol. 43: 479-498. . 1980. Intraspecific nest parasitism in birds. Biol. Rev. 55: 93108. Zwickel, F. C. 1975. Nesting parameters of Blue Grouse and their relevance to populations. Condor 77: 423-430. 1977. Local variations in the time of breeding of female Blue Grouse. Condor 79: 185-191. .. 1984. Factors affecting the return of young Blue Grouse to breeding range. Can. J. Zool. 61: 1128-1132. ., & J. F. Bendell. 1967. Early mortality and the regulation of numbers in Blue Grouse. Can. J. Zool. 45: 817-851. , & 1972. Blue Grouse, habitat, and populations. Proc. Int. Ornithol. Congr. 15: 150-169.

CHAPTERR

16

Patterns in Breeding Waterfowl Communities Thomas D. Nudds

I. Introduction

ciency. The data are more consistent with the idea that there has been a bias in favor of studies of waterfowl as organisms and as populations, and I focus next on the reasons for this. There are perhaps two that are important: the problems of (1) defining communities and (2) an implicit assumption about the purpose of research on game animals.

The study of biology can be conveniently partitioned where biological organization itself forms natural interfaces, for example, between cells and organisms, between organisms and populations, or between populations and communities. Biologists have not paid as much attention to the study of waterfowl communities as they have to the study of waterfowl as organisms and populations. For example, 12 of 18 chapters in this book are about waterfowl as organisms (e.g., nutrition and feeding, energetics, genetics, endocrinology, and behavior), 8 deal with waterfowl populations (inventories, recruitment, mortality, dynamics, and habitat management), and some deal with waterfowl at both levels of organization simultaneously. This chapter deals with biological organization at the level of communities. The titles of 59,840 papers published by BioAbstracts between 1970 and 1987 made reference to community ecology, and 12,662 made reference to waterfowl. The number of titles that appeared in both lists was 197. Even this figure overestimated the number of papers about waterfowl community ecology because it included many references to natural history surveys in which waterfowl were listed but were not the group of birds of principal interest. This small number of papers about waterfowl communities was lower than the number that might be expected by chance. Based on the relative contribution by papers about waterfowl to the total literature about Passeriformes, Charadriiformes and Anseriformes (chosen with the a priori knowledge that at least some published work about communities existed for each order), there should have been about 470 works about waterfowl community ecology. Instead, there were fewer than 40% of that number (X2 = 210, p < 0.0001). Happenstance wouldn't seem to be able to account for this defi-

A. The Definition of Community The concept of community is newer than those of organism or population, and with newness comes difficulty with definition. Humans tend to most easily understand levels of the biological hierarchy with which they most readily associate (Allen and Starr 1982: 30) —organisms and populations. It is more difficult to appreciate structure at levels of organization both "above" populations (at community or ecosystem levels) or "below" organisms (at the levels of cells, organelles, or genes). There are many definitions of community, but they all boil down to something like this: communities are collections of populations of species that, conceptually, lie somewhere in the hierarchy between single populations and whole ecosystems (Whittaker 1975). Though unsettling to some biologists because of its vagueness, this definition suffices for others because it is not unnecessarily restrictive. For example, the definition allows freedom to choose the kind of assemblage of species that an ecologist wishes to study. One ecologist's community may be another's guild, but then guilds also can be defined as narrowly, or as widely, as one wishes (Jaksic 1982). In one instance (Fig. 16-1A), the guilds (Root 1967) of diving and dabbling ducks can be considered parts of the duck community in the prairie-pothole ecosystem. Here, the definition of community is taxonomically based, and 540

PATTERNS IN BREEDING DUCK COMMUNITIES

541

Figure 16-1. A. The "horizontal" view of a waterfowl community. There are two "guilds" of ducks based on similarity of taxonomy, habitat use, and feeding behavior. B. The "vertical" view of a waterfowl community. In this case "guilds," or compartments, are defined on the basis of shared food resources. Carnivorous invertebrates, shorebirds, salamanders, ducks, and fish are all members of the invertebrate-feeding guild.

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guild membership is based partly on the ways species behave ecologically and partly on taxonomy. This "horizontal" view of communities (one trophic level), in which competition was thought to be a pervasive force affecting species' abundances and distributions, dominated much of community ecology (e.g., Cody and Diamond 1975). It has largely been the view adopted by waterfowl community ecologists (e.g., Poysa 1983a, b; Nudds 1983a, b). In the past decade, community ecology underwent major upheavals (see Lewin 1983a, b; Strong et al. 1984; Diamond and Case 1986). In variable environments, it was recognized that species may compete only when resources are in short supply (Wiens 1977, DeAngelis and Waterhouse 1987). Ecologists began to appreciate, too, that other factors (like predation) could be important insofar as they could affect the outcome of competition, or whether competition happened at all. The "vertical" view of communities that accompanied the de-emphasis on competition, and reemphasis of predation, sees them as collections of populations spanning more than one trophic level (Fig. 16-IB). In this view, "food web" and "community" are synonymous. The "guild" of the "horizontal" community model is akin to the "compartment" (Pimm 1982) of the "vertical" community model. The compartmentation of a food web may be based on similarities among species with respect to habitat use (Pimm 1982) or diet (Jaksic et al. 1981, Adams 1985). Thus, ducks are part of the guild of predators of aquatic invertebrates, which includes other invertebrates, amphibians, shorebirds, and fish. A food web approach to the study of waterfowl has been in evidence for a relatively short period (see Nelson and Kadlec 1984, Pederson and van der Valk 1984). Still others have suggested that there might be different ways to group species of waterfowl. Poysa (1984a) recognized "core" and "satellite" species of dabbling ducks based on similarities of local abundances and regional distributions. Similarly, Bellrose (1979) grouped species of dabbling ducks based on differences in how they varied in abundance with latitude in North America. Brandl and Schmidtke (1983) used multivariate ordination to identify subgroups of waterfowl based on species' associations in the field. Maybe the only aspect of the definitions of community about which some agreement exists is that properties that are measureable exist at the level of community (or higher) but not lower. (This doesn't necessarily mean, however, that communities are more than the sums of their parts or possess emergent properties [see Schoener 1986]). For example, populations can be characterized by abundance, biomass, density of individuals, or the magnitude and rate of change in any of those properties over time or space. Similarly, all of those things can be measured at the community level. Only at

the community level, however, can properties like species richness, evenness, diversity, food web connectance, length of food chains, and compartmentation be measured. Nudds (1983a) and Poysa (1984b) showed that some properties of duck communities (like richness and evenness) can be less variable than population-level properties (like abundance) of their constituent species. Whether this indicates that communities are entities above the level of populations that function independently of population-level processes (see Allen and Starr 1982) remains unknown.

B. Waterfowl and Single-Species Management Although the problem of defining communities is common to all biologists, community studies are particularly rare for waterfowl. Presumably, the reason is not to be found in the relative ease with which different kinds of birds lend themselves to community studies because there are many logistic reasons why waterfowl provide good study material: an abundance of coexisting species, many of which are relatively numerous, easily identified in the field, their habits easily observed and measured (Nudds 1983a). Perhaps the reason lies more in differences among biologists with respect to opinions about the purpose of research on game species. Leopold (1933) defined game management as making land produce sustained annual crops. There are notable exceptions, of course, but one widespread view is that research on waterfowl is done "to grow two where only one grew before" (Green et al. 1964: 568) and so "that we may learn to produce more and more ducks from less and less acreage" (Cook 1964: 569). This has led to a predisposition among some biologists (at least implicitly) to treat waterfowl as annual, harvestable crops. Historically, the only concept considered by biologists interested in achieving sustained yields was maximum sustainable yield theory. The idea was generated by fisheries biologists (Beverton and Holt 1957) but abandoned by them some time ago (Holt and Talbot 1978, Larkin 1977). In its simplicity, it assumed that carrying capacity was relatively constant and that the major agents of population regulation of harvested species acted in a density-dependent manner. Further, it focused on single species and ignored intratrophic- and intertrophic-level interactions among species. The breeding habitats of many waterfowl, however, are variable, and many ducks exhibit wide fluctuations in population size (e.g., Pospahala et al. 1972, Boyd 1981) and density-independent population fluctuations (Patterson 1979, Vickery and Nudds 1984). Despite early alternatives (Anderson 1975), recipes for mallard management were borrowed from the largely forsaken

543

PATTERNS IN BREEDING DUCK COMMUNITIES Table 16-1. Hypotheses about the generation and regulation of species diversity

Hypothesis 1.

Time (a) Evolutionary (b) Ecological

2. 3. 4. 5. 6.

7. 8. 9. a

a,

Predation, Compensatory Mortality Productivity

Related hypotheses with same effect

Mode of action Species evolution and niche diversification leading to saturation and high diversity with time. Dispersal to empty habitats by existing species leading to saturation and high diversity with time. Frequency or density-dependent predation alters the outcome of competition and leads to either higher or lower diversity.

Highly productive environments select for specialization and niche diversification, leading to increased diversity, or favor increase in abundance of a few species, leading to decreased diversity. Spatial Greater habitat complexity fulfills niche requirements of more Heterogeneity species, leading to increased diversity. Competition, Limited resources select for niche specialization and diversification, Niche Diversification leading to high diversity. Density-independent mortality means that resources are seldom in Climatic Instability, Rarefaction, short supply, leading to increased diversity in unsaturated environIntermediate Disturbance ments. At disturbance frequencies too high or too low, diversity decreases. Mass Effects Species can become established in areas where they cannot be selfmaintaining; symbioses and mutualisms lead to high diversity. Circular Networks Some species (A) is superior to some competititor (B) and B is superior to C but C is superior to A, leading to high diversity. Species are approximately equal in colonizing and competitive Equal Chance, ability, so diversity is a function of the species pool. Ecological Equivalency Connell and Orias 1964; b, Pianka 1966; c, Connell 1978; d, Shmida and Wilson 1985.

literature about fisheries management (e.g., Brown et al. 1976). Although a new generation of models for waterfowl management (e.g., Williams 1982; Anderson 1985; Caughley 1985; Johnson et al. 1986,1988; Cowardin et al. 1988) is emerging to deal with the variable nature of many waterfowl populations, the influence of interspecific interactions is still largely ignored. Investigation of the effects of interspecific interactions on the abundance and dynamics of populations lies in the realm of community ecology. II. Theory and Evidence About the 'Regulation' of Waterfowl Community Structure The diversity of a community can be measured as simply the number of species (species richness), the relative abundances of species (evenness), or some combination of the two. Although there has been much debate about whether some indexes of diversity are better than others, all convey much the same information (Hill 1973). Theories about the control of community diversity have changed little over 25 years (Table 16-1). This can mean either that community ecologists are "stuck," or that the field of community ecology has settled comfortably into a theoretical framework that is broad enough to account for a majority of observations about the structure and dynamics of communities. The controver-

Source3

3; 6; 7; 8; 9

a, b

3; 5; 6; 7; 8; 9

a, b

5

b, c

5

a, b

la, b; 3

b, d

la, b; 7

a, b, c, d

4; 6

a, b, c

la, b; 7; 8

d

la, b; 3; 8; 9

c

la, b; 7; 9

c, d

sies among community ecologists (Lewin 1983a, b) of the past decade were more about the relative importance of different factors that influence community diversity than about attempts to introduce any new hypotheses. For example, prevalent among community ecologists during the 1960s and 1970s was the idea that communities were in an equilibrium state determined by resource supply. Competing hypotheses (Wiens 1977; Connell 1975, 1978; Caswell 1978), however, were already entrenched in the literature (Connell and Orias 1964, Pianka 1966) but did not receive a great deal of attention until the late 1970s and early 1980s. Even the relatively new problem of scale effects (Allen and Starr 1982, Maurer 1985a, O'Neill et al. 1986, Wiens 1986), that is, the idea that the various diversity hypotheses might be differentially important, or operate in concert, at different scales of time and space, was recognized in the mid-1960s (Connell and Orias 1964, Pianka 1966, Ciller 1984: 110), particularly for temporal variation in diversity (Table 16-1). Recent literature on determinants of diversity either reemphasizes the importance of temporal scale (e.g., Connell 1980, Maurer 1985b) or more formally introduces the effects of spatial scale (e.g., Shmida and Wilson 1985). Only six hypotheses can be assessed with the existing literature about waterfowl communities, and much of this assessment consists of inferential evidence. The six hypotheses relate to the effects of: time, predation, pro-

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Figure 16-2. A model of variation in species diversity. Species' niches, or resource utilization curves, a, are arrayed along some gradient of resources (food types or habitats), b, the length of which indicates the diversity of resources available. The abundance of resources at points along the gradient is given by the resource production curve, c. Where c is higher, resources are more abundant than at other points along the gradient. Consequently, species' resource utilization curves are taller at those points, and the area under each curve is proportional to the abundance of that species. If, as the Competition Hypothesis predicts, there is a limit to how similar two species can be and still coexist, then, everything else being equal, an increase in the number of species can be accomplished only by decreasing average niche width, w (alternative A). In other words, niche separation (d/w) should increase with addition of species. If, however, niche width remained constant, and niche overlap cannot increase, then additional species can be accommodated only by increasing the kinds of resources available (alternative B). The Spatial Heterogeneity Hypothesis predicts this type of response. Changes to

niche shape and position like those in A and B are usually called niche shifts when they refer to habitat use or foods and character displacement when the shift is in morphology. Species richness can also increase if resources aren't limiting (alternative C). Here, populations of species are below densities where competition is important. Addition of species results in decreased niche separation, opposite to alternative A. Variation in productivity or predation might operate this way. To the extent that populations can track changes in c or b, the Rarefaction Hypothesis (or Climatic Instability Hypothesis) predicts that alternative A happens in constant, benign environments and alternative C happens in variable, rigorous environments. Varying resource abundance, c, at different points along the resource gradient, b, can influence the relative abundance of species (or evenness) as well as richness. Taken together, richness and evenness characterize community diversity. Though illustrated as alternatives Bl to B4, this same process can also apply to alternatives A and C.

ductivity, spatial heterogeneity, competition, and climatic instability. Although the hypotheses were originally advanced to explain large-scale, latitudinal diversity gradients, much small-scale fieldwork was conducted with the implicit assumption that the behavior of small-scale systems would provide insight to the behavior of the large-scale systems. Whether this assumption was warranted is currently the focus of a lot of research in community ecology. Figure 16-2 summarizes graphically the mechanisms offered by these hypotheses and provides a framework to organize the literature review and assess each hypothesis that might explain patterns of diversity in waterfowl communities (at any scale).

olutionary time, this is presumed to occur through speciation and niche diversification (in a variant of alternative B, Fig. 16-2) until all available kinds of resources are used and the environment is filled with all the species it can support. In shorter expanses of time, or ecological time, the mechanism is the same but existing species fill the ecological voids. There is little information available to evaluate either of the time hypotheses for waterfowl. The Evolutionary Time Hypothesis supposes that the effects of one glacial age after another on northern environments should result in fewer species at northern latitudes, reflecting the younger age of existing northern environments. Consistent with this idea, Anseriforms apparently originated in the southern hemisphere and radiated northward (Livezey 1986). Also, over a short range of latitude, lakes in southern Finland had assemblages of up to six

A. Time Hypotheses The time hypotheses (Table 16-1) have in common the idea that environments that are devoid of species, but capable of supporting them, can fill up with time. In ev-

PATTERNS IN BREEDING DUCK COMMUNITIES

Figure 16-3. Latitudinal gradients of waterfowl diversity in North America. From range maps in Johnsgard (1975).

species of dabbling ducks, whereas lakes in the north rarely had more than four (Poysa 1984a). In North America, however, the diversity of breeding waterfowl is greatest at midlatitudes, and there are regions in the extreme north where waterfowl diversity is as great as, or greater than, at low latitudes (Fig. 16-3). In extreme northern Fennoscandia, there is similarly no evidence of a simple latitudinal diversity cline (Haapanen and Nilsson 1979). Duck diversity increases with latitude in Sweden, perhaps because highly productive fens are abundant farther north and less-productive bogs predominate in the south (Bostrom and Nilsson 1983). In all of these cases, variation in waterfowl diversity seems to be dictated by landform (Haapanen and Nilsson 1979) or wetland productivity (Haapanen and Nilsson 1979, Poysa 1984a), more in accord with the Spatial Heterogeneity or Productivity Hypotheses than with the Evolutionary Time Hypothesis. It is probably too simplistic to expect a simple correlation between diversity with latitude anyway, because there existed glacial refugia at northern latitudes in which waterfowl resided and, presumably, from which they recolonized glaciated areas relatively quickly during postglacial periods (Ploeger 1968).

545

The diversity of diving ducks in North American prairies fluctuates considerably over ecological time (Nudds 1983a), due mainly to changes in species richness (Nudds 1983b). Vickery and Nudds (1984) speculated that some species, like ruddy ducks, disappeared and reappeared because they were "inappropriate" members (Wiens 1974) of the guild of prairie diving ducks and incapable of breeding in prairies unless conditions allowed. In other words, they colonized available breeding habitat during ecological time. On a broader scale, individuals of some species are distributed according to prevailing wetland conditions in different years (e.g., Hansen and McKnight 1964, Smith 1970, Henny 1973, Derksen and Eldridge 1980). "Flyover" occurs over regional and latitudinal scales and is another example of the response of waterfowl to changes in available resource space in ecological time. Mallards and bluewinged teal appear to respond numerically (Patterson 1979, Vickery and Nudds 1984) to episodic increases in habitat productivity such as the increase that follows drought on the prairies (Nudds 1983a). While it might be tempting to conclude, then, that some evidence in support of the Ecological Time Hypothesis exists, other events ultimately determine when and where resources appear or disappear. Therefore, it might be better to consider the variation in diversity that occurs in ecological time as a result of other ultimate causes of variation in diversity like Climatic Instability, Predation, or Productivity.

B. Predation Hypothesis When the Predation Hypothesis was formulated (Paine 1966), keystone predators were thought to prey disproportionately on the most abundant, and competitively superior, species of a group of competing species. By reducing the abundance of some species, keystone predation had the effect of freeing resources for use by other species and enhancing the diversity of the community (in a variant of alternative C, Fig. 16-2). Subsequently, it was demonstrated that such predators might lower community diversity, too. Whether predation enhanced or depressed diversity of coexisting species was shown to be related to complex interactions among varying efficiencies of predation in different habitats and the palatabilities, habitat preferences, and competitive abilities of prey (e.g., Caswell 1978, Lubchenco 1978). Waterfowl can potentially be keystone predators or themselves be influenced by predators in higher trophic levels (Fig. 16-1). These situations are loosely referred to as "top-down" food chain regulation (Fretwell 1977, Pimm 1982). On the other hand, food chain regulation can occur from the "bottom up." That is, species might respond more to variation in productivity of trophic levels below them than to the effects of predators (Pimm 1982).

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Figure 16-4. A. Sizes of invertebrates inside and outside of predator exclosures at depths of 30, 60, and 100 cm in a wetland in western Manitoba, where dabbling ducks were major predators of invertebrates. B. Density of invertebrates inside and outside of predator exclosures. Data pooled from samples collected over all water depths. From Barnes and Nudds (unpubl. manuscript).

The evidence about whether waterfowl regulate the structure of food webs is contradictory: two experiments using predator exclosures revealed different responses by invertebrates to cessation of waterfowl predation. On the Delta Marsh, Manitoba, Wrubleski (1987) found that chironomid density was higher in exclosures where ducks had not removed vegetation. On the other hand, Barnes and Nudds (unpubl. data) found no effects of predator exclosures on either abundance or size distributions of invertebrates on prairie wetlands in western Manitoba, suggesting that ducks are not keystone predators of invertebrate communities (Figure 164). There is little evidence to assess whether waterfowl are themselves regulated in a top-down fashion. Some predators, however, exert considerable mortality on waterfowl during the breeding season (e.g., Johnson and Sargeant 1977, Sargeant et al. 1984) and in a manner consistent with the conditions under which predation might be expected to influence diversity of coexisting ducks. For example, red fox (Vulpes vulpes} prey more frequently on more-abundant species of dabbling ducks, and there are differences among species in the degree to which hens are susceptible to predation, depending upon nesting chronology and location of nest sites (Sargeant et al. 1984). Likewise, Pehrsson (1986)

showed that avian predators switch readily from rodents to ducklings of oldsquaw as availability dictates. Nudds (1983a), however, thought that predation might be expected to be a less important determinant of duck diversity than competition because the relative importance of competition should be greater at higher trophic levels and predation should be more important at lower trophic levels (Hairston et al. 1960, Menge and Sutherland 1976, Fretwell 1977). Although some waterfowl (geese) principally consume primary production, others (many ducks) are among the consumers at high trophic levels (Fig. 16-1). A high proportion of experiments conducted in freshwater systems detected interspecific competition more frequently among consumers at higher trophic levels than among consumers at lower trophic levels (Schoener 1983). At present, it is not known what effect predation might have on waterfowl communities. Better information is needed about whether predators of ducks actually regulate population sizes of some species and, if so, whether they might have done so historically when the predators of breeding waterfowl were very different and less efficient (Johnson and Sargeant 1977, Sargeant et al. 1984). Currently, the Predation Hypothesis remains an untested, but viable, alternative to other hypotheses for which more evidence exists.

PATTERNS IN BREEDING DUCK COMMUNITIES

547

Figure 16-5. An increase in productivity can have different effects on community diversity, depending on whether the community is unsaturated and population sizes are well below carrying capacities (that is, resource supply-to-demand is greater than 1) or whether the community is saturated. In the former case, alternative C, diversity is enhanced by increased niche overlap (decreased niche separation) because resources aren't limiting and competition is weak (like alternative C in Fig. 16-2). In the latter case, on the left, either increased productivity will allow for niche specialization and enhance diversity (alternative A), or it might favor an increase in the relative abundance of a particular species causing community evenness and, hence, diversity to decrease (alternative B).

C. Productivity Hypothesis Originally the Productivity Hypothesis stated that, everything else being equal, greater productivity should result in greater diversity (Hutchinson 1959; but see Connell and Orias 1964, Pianka 1966). Community ecologists often use the term productivity in a general way to mean the rate at which resources at lower trophic levels become available to higher trophic levels. Sometimes, when highly productive environments also have high standing crops, standing crop biomass is used as a substitute for productivity. Under these circumstances, what matters more than the method of assessment is that the Productivity Hypothesis simply states that the supply of resources to consumers is a primary determinant of diversity. When ratios of resource supply-to-demand are large, resources are not limiting, there is little competition, and there are more resources available for more species to use (Fig. 16-5). This is the manner in which nonequilibrium communities might respond to changes in productivity. It is also possible to imagine saturated, equilibrium communities, in which fluctuations in production are just matched by compensatory changes in consumption, so that the ratio of resource supply-to-demand never strays far from 1.0. Under these circumstances, increased productivity might increase or decrease diversity (Fig. 16-5), depending on how different species respond to changes in resource supply. The Productivity Hypothesis makes some of the same

predictions as the Predation and Climatic Instability Hypotheses. In the former case, however, productivity per se changes (i.e., supply outpaces demand), causing changes in diversity. In the latter cases, relative production changes, not necessarily because of changes in supply, but perhaps because of changes in demand. The Productivity Hypothesis also makes a prediction similar to the Competition Hypothesis: increased niche specialization should lead to increased diversity. The difference is that niche specialization is "allowed" under the former mechanism, but "forced" under the latter. It is clear, then, that like all of the diversity hypotheses, the Productivity Hypothesis makes few unique predictions. Tests of it are therefore naturally confounded because other causes of variation in diversity may produce the same effects. 1. Small-Scale, Short-term Studies Patterson (1976) studied a community of breeding ducks on beaver (Castor canadensis) ponds of eastern Ontario, Canada. Twenty-one ponds were chosen to represent a wide range of sizes (0.7-6.6 ha) and water chemistry. Like Moyle (1956), he demonstrated that water hardness correlated with pond fertility and macrophyte productivity. Nevertheless, duck species richness was better correlated with pond size (r = 0.60, p < 0.01; Fig. 16-6A) than it was with pond fertility (r = 0.14). Though density was generally greater on morefertile ponds late in the breeding season, diversity was

548

THOMAS D. NUDDS

Figure 16-6. Some relationships of wetland productivity and size to species richness of ducks. A. Richness of dabbling and diving ducks on beaver ponds in mixed forest, Ontario, Canada (data from Patterson 1974). Productivity (water hardness in mg HCO3/1) does not explain more variation in species richness than does pond size. B. Species richness of dabbling and diving ducks on prairie potholes in western Manitoba, Canada (data from Nudds 1980). Productivity (dry weight biomass of invertebrates) does not account for more variation in richness than does pond size. Among wetlands smaller than 2 ha, however, a prairie pothole has two to three times the species richness of a beaver pond.

not. Similarly, Nudds (1980) studied breeding ducks on small wetlands (0.3-1.7 ha) in western Manitoba. Pond productivity was estimated as the standing crop of invertebrates. If anything, species richness was lower on more-productive ponds (Fig. 16-6B), but was correlated with pond size (r = 0.88, p < 0.01). The results of these two studies each accord better with the Spatial Heterogeneity Hypothesis than with the Productivity Hypothesis. In the Falkland Islands, wetlands with the greatest standing crops of invertebrates supported the greatest diversity of waterfowl; productivity, in turn, was influenced by basin structure and substrate (Weller 1972). Still other studies have shown that when wetland productivity was altered, usually as a result of habitat management, waterfowl diversity was affected in ways consistent with the Productivity Hypothesis. For example, diversity was greater on manipulated than on natural salt marshes on the east coast of North America (Burger et al. 1982). Sjoberg and Danell (1982) and Danell and Sjoberg (1982a, b) studied changes in foraging behavior and habitat use by ducks in relation to annual, seasonal, and diel availability of foods in northern Sweden. Normally, tufted ducks, pintail, mallard, Eurasian green-winged teal, and European wigeon spent greater to lesser amounts of time, respectively, foraging beneath the wa-

ter surface. At times of the day when chironomids were abundant on the water surface, all species foraged similarly (see Sjoberg and Danell 1982b: Fig. 4) and species overlapped in microhabitat use (Sjoberg and Danell 1981) consistent with alternative C (Fig. 16-5). Likewise, changes in the relative productivity of different foraging substrates may be why dabbling ducks sometimes dive for food (Schwede and Rutschke 1978, Kear and Johnsgard 1968, Miller 1983). Nudds (1980) measured microhabitat separation in two-, three-, and five-species assemblages of diving ducks on seven prairie wetlands. Niche separation tended to be less on more-productive ponds, regardless of species richness. On productive ponds, assemblages tended to be dominated by one species; other species used these ponds rarely. In this case, the effect of productivity appears to be best illustrated by alternative B (Fig. 16-5). Based on Sjoberg's and DanelPs data about the relative productivity of different strata in the water column, Poysa (1985, 1986a) inferred that some species of dabbling ducks in Finland shift foraging activity vertically in the water column in response to changing food availability and the presence of other species of waterfowl. Generally, when there was evidence of interaction between pairs of species, such as northern shoveler and

PATTERNS IN BREEDING DUCK COMMUNITIES Eurasian teal, they were more similar in foraging behavior when resources were abundant and diverged when resources declined (alternative C, Fig. 16-5). 2. Large-Scale, Long-term Studies Eutrophic lakes in Finland always supported assemblages of three to six species of dabbling ducks, but dystrophic lakes never had more than three (Poysa 1984a). Waterfowl diversity increased over time with lake eutrophication in the Baltic region (Helminen and Eriksson 1978). Further, using morphological data to infer differences in resource use among species (an assumption largely validated for waterfowl; e.g., Poysa 1983a, b; Nudds and Bowlby 1984; Crome 1985), Poysa (1984a) found that species most similar morphologically coexisted more frequently on productive lakes than on unproductive lakes. Similarly, Nudds et al. (1981) reported that, in terms of morphology, dabbling duck guilds were packed more tightly on productive wetlands of North American prairies than on less-productive bogs and peatlands in Finland. Together, these data suggest that increased productivity enhances waterfowl diversity (alternative C, Fig. 16-5). Fretwell (1975) thought that wetland productivity altered the outcome of competition between species, but that the competitive advantage shifted to species of different body sizes in different guilds. For example, he thought that among dabbling ducks, impoverished marshes supported just the largest and smallest species, but rich marshes added many middle-sized species. On the other hand, he thought that unproductive deep-water habitats tended to favor middle-sized species of diving ducks and that richer habitats supported also the larger and smaller species of the group. His hypothesis remains to be examined more fully. Haapanen and Nilsson (1979) reported regional differences in wetland productivity and waterfowl diversity across northern Fennoscandia. Eutrophic wetlands were rare and simple productivity-diversity relationships were hard to discern at that scale. Oligotrophic wetlands of coastal and mountain regions of Norway were least diverse. Mountainous areas in northern Finland and southern Sweden were most diverse, though these regions were also characterized mainly by dystrophic and oligotrophic lakes. These generally weak associations of diversity with productivity in northern Fennoscandia contrast sharply with the marked latitudinal and regional differences in waterfowl diversity in North America (Fig. 16-3) that are often attributed to differences in wetland productivity among different biomes (e.g., prairies vs. boreal forest; Bellrose 1976, 1979) and regions within biomes (e.g., Stewart and Kantrud 1973,1974). In North America, the abundance of some waterfowl species fluctuates considerably, contributing to wide fluctuations in com-

549

munity diversity (Nudds 1983a, b) in relation to the abundance of intermittent water bodies on the prairies. These wetlands are considered the most productive in terms of invertebrate foods (e.g., Krapu 1974, Swanson and Meyer 1977). Similarly, duck species richness decreased from greater than seven to four over an altidudinal gradient in pond productivity in the Uinta Mountains, Utah (Peterson and Low 1977). Among waterfowl communities of 29 eutrophic Swedish lakes, diversity decreased with increasing pollution (Nilsson 1978). Also, Nudds (1983a) argued that increases in population sizes of two species (mallard and blue-winged teal) caused evenness and diversity of dabbling ducks to decrease during the productive, wet periods following drought in the mixed prairie of North America. Other studies reported positive effects of productivity on waterfowl diversity, despite increases in the abundance of just a few species (Helminen and Eriksson 1978). The literature about the effects of productivity on waterfowl diversity is characterized by contradiction. This may be due to either of two reasons. First, results appear to be scale-dependent. There are greater differences in waterfowl diversity over latitudinal, and perhaps productivity, gradients in North America than in northern Fennoscandia. In North America, however, published accounts of distribution and abundance also cover a wider range of latitude and topography. Northern Fennoscandia is principally mountainous and characterized by wetlands with lower productivity. Nilsson (1978) concluded that lake heterogeneity influenced the diversity of breeding ducks more than did productivity, like the patterns at smaller spatial scales (Fig. 16-6). Second, depending on how diversity is measured, different correlations with productivity are found. For example, Nilsson (1978) found that waterfowl diversity, indexed using the Shannon-Weaver formula (see Hill 1973), decreased with increasing eutrophication. Species richness, however, increased from 7 species on oligotrophic, lightly polluted lakes to 13 species on lakes classified as polluted, then decreased to 5 species on extremely polluted lakes (see Nilsson 1978: Table 1). Taken together, these data suggested that community evenness also changed significantly over the productivity gradient. Evenness was lowest in the assemblages of the most highly polluted lakes, which were dominanted by mallards (alternative B, Fig. 16-5).

D. Spatial Heterogeneity Hypothesis Unlike the Predation and Productivity Hypotheses, the Spatial Heterogeneity Hypothesis makes a straightforward prediction: more-complex environments support more-diverse communities. Resource heterogeneity acts as an environmental template upon which the richness

THOMAS D. NUDDS

550

Table 16-2. Summary of published evidence of correlations between diversity of waterfowl communities and various indices of resource heterogeneity Measure of diversity

Index of resource heterogeneity

richness lake area lake area < 0.5 m deep richness lake area with emergents richness emergent diversity richness richness pond area dabbling duck richness pond area diving duck richness pond area pond area total richness richness pond area island size richness dabbling duck diversity11 number of ponds diving duck diversity1* number of ponds a Data reanalyzed from original source. b Simpson's index.

and evenness of ecological communities are patterned (see Fig. 16-2). Also unlike many of the other diversity hypotheses, there is a lot of published information about waterfowl consistent with the Spatial Heterogeneity Hypothesis. For instance, Table 16-2 lists a number of studies in which relationships between waterfowl diversity and some indexes of heterogeneity were reported. A number of other studies reported or inferred similar relationships between habitat or food heterogeneity and diversity (e.g., Weller and Spatcher 1965, Dobrowolski 1969, Nilsson 1978, Amat 1981). Sometimes relationships were reported for entire avifaunas of wetlands, of which

Correlation statistics r r r r r r r r r r r r

= = = = = = = = = =

0.72, 0.55, 0.47, 0.44, 0.60, 0.75, 0.66, 0.88, 0.74, 0.65, 0.75, 0.78,

p< p< P< p< p< p< p< p< p< p< p< p
2 ha in area, with goose use exceeding wetland availability most for wetlands > 25 ha. However, these larger wetlands also generally contained islands, islets, and expanses of emergent vegetation with muskrat lodges that often provided nesting sites. The combined availability of suitable nest sites and wetland habitat probably influenced use of those wetlands by nesting geese more than did wetland size. Hanson (1965) indicated that, although Canada geese exhibit wide habitat adaptability, nesting habitats should be available in large blocks and contain permanent bodies of water of moderate-to-large size with depths of ^ 75 cm. Nigus and Dinsmore (1980), however, observed that Canada geese in Iowa nest initially each year in small, shallow wetlands that became free of snow and ice early, whereas late nests were established within deep lakes, implying that time of breeding and nesting can influence selection of available wetlands. Canada geese nest frequently in wetlands containing robust emergent vegetation (e.g., Typha spp., Scirpus spp.), perhaps because such wetlands often contain muskrat lodges suitable for nesting substrates. Cooper (1978) stressed the important interrelationships between emergent vegetation, muskrats, and nesting Canada geese in a large Manitoba marsh. He demonstrated a positive correlation of Canada goose nest density with the density of nest boxes, water bodies, and islands, the area of certain emergents (Typha spp., Scolochloa festucacea), and shoreline length. These associations suggest that goose nesting density may be related to the availability of potential nest and territorial sites. Results of other studies also imply that wetland use by breeding geese is influenced by nest and territorial site availability because of positive relationships between numbers of nesting geese and islands (Sherwood 1966, Raveling and Lumsden 1977) and shoreline development (Hammond and Mann 1956).

4. Nest Sites of Geese Except for some giant Canada goose populations (Hanson 1965) and the nonmigratory Hawaiian goose and

Vancouver Canada goose (Ogilvie 1978, Ratti and Timm 1979), Nearctic geese are migratory and can be classed as either arctic- or north-temperate-nesting species. Ogilvie (1978) discussed the possible reasons for the evolution of northern latitude nesting by geese. The advantages include: (1) abundant and often nutritious forage during brood rearing and molting; (2) less foraging competition from other grazing species like mammals; (3) near-continuous daylight during nesting and brood rearing that facilitates foraging and predator detection; (4) wetland abundance; (5) abundance of favored nesting habitat (e.g., insular sites); and (6) fewer potential predators than at southern latitudes. Presumably, these advantages offset any possible disadvantages of the harsh climate, long flights between breeding and wintering areas, and the comparatively short growing and brood-rearing periods in the Arctic (Ogilvie 1978). Several factors appear to be correlated with nest-site selection and subsequent reproductive success in arcticnesting geese. Most, if not all species, establish nests on elevated sites. Raised nest sites may enhance the following (Ogilvie 1978): (1) nest vigilance, (2) water drainage and protection from floods, and (3) early availability because of accelerated loss of snow and ice. Other attributes of nest sites often are their insular nature and nearness to wetlands and feeding areas. Nesting on insular sites helps protect against arctic fox (Alopex lagopus), and proximity to wetlands and foraging areas probably increases survival of goslings and adults (Ogilvie 1978). Geese also gain protection from predators and weather by nesting amid vegetation (e.g., Barry 1962, 1966; Ryder 1972; Mickelson 1975; Bellrose 1976; Palmer 1976; Eisenhauer and Kirkpatrick 1977; Heagy and Cooke 1979; Cooke and Abraham 1980; McLandress 1983; Jackson et al 1988). Rock ledges or pinnacles provide similar protection for barnacle geese and several Palearctic species (Ogilvie 1978). Nest-site selection in some arctic-nesting geese is influenced by an attraction to conspecifics or other species, apparently for protection from predators. For example, snow geese and Ross' geese nest in pure (Ogilvie 1978) and mixed (McLandress 1983) colonies, and several species of geese nest near raptors (Ogilvie 1978, Owen 1980). Finally, the presence of nesting material may be a proximate factor correlated with site selection by some species like Ross' geese (McLandress 1983). But the presence of nest material seems least important in nestsite selection, because some arctic geese are known to nest on bare rock (McLandress 1983). Few studies have dealt specifically with nest-site selection in arctic-nesting geese. Ryder (1972) reported that Ross' geese selected nest sites next to rocks and patches of birch (Betula glandulosa) more often than expected based on availability. In 1976, McLandress (1983) revisited Ryder's area to study the mixed nesting colony of

BREEDING HABITATS OF NEARCTIC WATERFOWL Ross' geese and snow geese. Ross' geese nested preferentially and laid the largest clutches in heath (Ericaceae) habitats. Perhaps heath provided a microhabitat in 1976 similar to that provided previously during Ryder's study by rock and birch. The highest nest densities of snow geese occurred on snow-free tops of the tallest drumlins. Apparently, habitat preferences differed between the two species of geese. Mean clutch sizes of Ross' geese and snow geese were larger on island than mainland habitats, but the difference was probably due to older or earlier-nesting females of both species on the islands. Heagy and Cooke (1979), Cooke and Abraham (1980), and Jackson et al (1988) further elucidated nest-site selection in snow geese. Heagy and Cooke (1979) showed that the presence of two plants (Elymus arenarius, Chrysanthemum articum) was associated with snow goose nest sites but not with random sites. They suggested that the geese probably were not selecting for these plants but instead for elevated, welldrained sites where the plants grow. Cooke and Abraham (1980) and Jackson et al. (1988) recorded greater reproductive success in lesser snow geese that nested amid Salix bushes than among those nesting within Elymus, but the effect of nesting habitat on fecundity varied between years. Cooke and Abraham (1980) also showed that the first nests of snow geese were usually located in an area of the colony closest to the feeding area they used as immature birds. Thus, when snow geese choose their first nest site, they may be influenced not only by habitat type but also by proximity of the nest site to a familiar feeding area. Nevertheless, Cooke and Abraham (1980) noted that there were exceptions to this pattern, and they termed nonconforming geese "tradition breakers." Natural selection might favor "tradition breakers" or "tradition maintainers," at different times, especially in dynamic environs such as these geese inhabit (Cooke and Abraham 1980). Nest-site selection in geese has been studied most in Canada geese. Canada geese use the widest array of nest sites (Bellrose 1976), which may reflect the diverse subspecific composition and geographic distribution of the species. Canada geese nest on (or in) muskrat and beaver lodges, islands and other insular sites, floating and rooted emergent vegetation, ditch banks, haystacks, cliff ledges, tundra, abandoned nests of other species, trees, ground, forest interiors, and a diversity of structures made or placed especially for the species (Table 17-1). A number of factors have been proposed as possibly influencing nest-site selection in Canada geese (Table 17-2). However, few studies have attempted to identify factors of nest-site selection by analyzing differences between sites used and not used by nesting Canada geese or between sites with successful and unsuccessful nests. Kaminski and Prince (1977) and Reese et al. (1987)

571

Table 17-1. Nest substrates used by Canada geese and references documenting their use Substrate Muskrat or beaver lodges Insular sites

Emergent vegetation Ditch banks Haystacks Cliff ledges Tundra Nests of other species Trees Ground Forest interior Artificial structures

Reference(s) Williams and Sooter 1940, Miller and Collins 1953, Hammond and Mann 1956, Hanson 1965, Kaminski and Prince 1977, Cooper 1978, Nigus and Dinsmore 1980, Reese et al. 1987 Dow 1943, Craighead and Craighead 1949, Miller and Collins 1953, Naylor and Hunt 1954, Geis 1956, Steel et al. 1957, Klopman 1958, Hanson and Browning 1959, Hanson 1965, Sherwood 1968, Wiegand et al. 1968, Vermeer 1970, Culbertson et al. 1971, Hanson and Eberhardt 1971, Mickelson 1975, Raveling and Lumsden 1977, Kaminski and Prince 1977, Cooper 1978, McCabe 1979, Nigus and Dinsmore 1980, Reese et al. 1987 Williams and Marshall 1937, Dow 1943, Kaminski and Prince 1977, Nigus and Dinsmore 1980 Williams and Marshall 1937, Dow 1943, Miller and Collins 1953, Naylor and Hunt 1954, Wiegand et al. 1968 Dow 1943, Steel et al. 1957, Cooper 1978 Geis 1956, Culbertson et al. 1971, Hanson and Eberhardt 1971, Graber 1977, Ball et al. 1981 Maclnnes 1962, Mickelson 1975 Ball et al. 1981, Schmutz et al. 1988 Davison 1925, Geis 1956, Hanson 1965, Lebeda and Ratti 1983 Culbertson et al. 1971, Cooper 1978, Ball et al. 1981 Lebeda and Ratti 1983 Yocom 1952, Hammond and Mann 1956, Hanson and Browning 1959, Brakhage 1965, Dill and Lee 1970, Will and Crawford 1970, Szymczak 1975, Cooper 1978, Atkins and Fuller 1979, Brenner and Mondok 1979, Fielder 1979, Giroux 1981a, Giroux etal.1983, Mackey et al. 1988, Schmutz et al. 1988, Reese et al. 1987

compared vegetative and structural characteristics of muskrat lodges and islands used and not used by nesting Canada geese. Kaminski and Prince (1977) reported that lodges used by nesting geese had larger tops and were taller, had more emergent cover around them, and were closer to open water than unused lodges. When lodges and islands were both available, Reese et al. (1987) found that muskrat lodges generally were avoided in favor of larger, constructed islands. Islands used by nesting geese tended to be higher, farther from the mainland or closer to open water, have less cover or be in shorter vegetation, and be farther apart than islands not used by nesting geese (Kaminski and Prince 1977, Reese et al. 1987). McCabe (1979) also measured characteristics at Canada goose island nest sites and sites along transects that traversed islands. His results generally indicated that nest sites were not subject to inundation, were protected from the wind, and provided isolation from conspecifics. Finally, Giroux (1981a) and Giroux et al. (1983) studied the use of constructed

572

RICHARD M. KAMINSKI AND MILTON W. WELLER

Table 17-2. Factors correlated with nest-site selection by Canada geese and references of documentation Factor

References

Early loss of snow or ice Firm foundation Elevated site promoting early availability and vigilance

Size of site Site insularity or proximity to water

Water depth Concealment (vegetation or other structure) Waiting site for gander Isolation

Cooper 1978, Ogilvie 1978 Williams and Marshall 1937, Hanson 1965, Cooper 1978, Giroux et al. 1983 Williams and Marshall 1937, Williams and Sooter 1940, Dow 1943, Williams and Nelson 1943, Kossack 1950, Miller and Collins 1953, Naylor 1953, Hanson and Browning 1959, Hanson 1965, Brakhage 1965, Kaminski and Prince 1977, McCabe 1979, Krohn and Bizeau 1980, Reese et al. 1987, O'Neil 1988 Reinecker 1971, Raveling and Lumsden 1977, Kaminski and Prince 1977, Giroux et al. 1983, Reese et al. 1987 Williams and Sooter 1940; Williams and Nelson 1943; Kossack 1950; Brakhage 1965, 1966; Sherwood 1968; Vermeer 1970; Mickelson 1975; Kaminski and Prince 1977; Cooper 1978; Giroux 1981a; Giroux et al. 1983; Reese et al. 1987; O'Neil 1988 Giroux 1981a, Reese et al. 1987 Yocom 1952, Sherwood 1968, Raveling and Lumsden 1977, Cooper 1978, McCabe 1979, Giroux 1981a, Ball et al. 1981 Brakhage 1966, Sherwood 1968 Miller and Collins 1953, Sherwood 1968, McCabe 1979, Giroux 198 la, Reese et al. 1987 Brakhage 1965, Hanson 1965

Previous nest success at a specific location or nest substrate Familiarity with nest Kossack 1950, Craighead and Stockstad substrate or locale 1961, Brakhage 1965, Reinecker 1971, Cooper 1978, Giroux et al. 1983

earthen and rock islands and straw bales by nesting Canada geese. Earthen islands used by nesting geese and from which ^ 1 successful nests were produced had deeper water around them, were farther from the mainland, and had more cover than unused islands (Giroux 198la). Rock islands used by nesting geese were older, nearly 3 times farther offshore, had larger tops, and possessed nesting material compared to rock islands not used by Canada geese (Giroux et al. 1983). Flax-straw bales were used more often when placed upright than when on their sides, but geese experienced similar levels of nesting success on rock islands and straw bales.

C. Perching Ducks (Cairinini) 1. Wetlands of Wood Ducks There are numerous general accounts of wetland use by breeding wood ducks but few specific ones. Palmer (1976) indicated that breeding wood ducks inhabit shallow, nonturbulent, fresh-to-brackish wetlands in or near deciduous or mixed woodland. Types of wetlands used

by wood ducks include rivers, forested wetlands, lakes, emergent wetlands, and beaver ponds (Nevers 1968, Prince 1968, Beshears 1974, Bellrose 1976, Heitmeyer and Fredrickson 1990). For a wetland to be attractive to breeding wood ducks, rate of flow, water depth, habitat structure, invertebrate availability, period of availability, and proximity of nesting and brood-rearing habitats seem important (McGilvrey 1968, Heitmeyer and Fredrickson 1988). Still or slowly moving water, 8-46 cm deep, seems suitable (McGilvrey 1968). In a study of seasonal habitat use by wood ducks within Mingo Swamp in southeastern Missouri, Heitmeyer and Fredrickson (1990) demonstrated that wood ducks selected unimpounded hardwood bottomlands and green-tree reservoirs (GTRs) during spring, with pin oak (Quercus palustris) sites being preferred. Hardwood bottomlands and GTRs provide breeding wood ducks with necessary foods and cover within a complex of structurally different habitats (Heitmeyer and Fredrickson 1990). Drobney and Fredrickson (1985) have hypothesized that protein acquisition through invertebrate consumption potentially limits clutch size in wood ducks; hence, availability of invertebrates may be a cue affecting wood duck wetland use and ultimately recruitment. Wetlands should be available ^ 3 weeks before nesting occurs in the southern United States and when migrants arrive to breed in the North (McGilvrey 1968). Suitable broodrearing wetlands should be available =£ 0.8 km to nesting habitat (McGilvrey 1968). Breeding wood ducks seek aquatic cover that affords concealment along with freedom of movement. The particular ratio of water to cover is unknown, but equal proportions probably suffice (McGilvrey 1968). Robb (1986) reported that forested and wetland habitats made up an average of 60% and 44%, respectively, of the home ranges of radiotelemetered female wood ducks nesting in Indiana. Mature shrubs (e.g., Cephalanthus occidentalis) that rise approximately 0.5-1.0 m above the water and have spreading branches provide ideal cover and loafing substrates. Emergents (e.g., Typha spp., Scirpus spp., Sparganium spp.) and floating vegetation (e.g., Nelumbo spp., Nuphar spp.) also provide good cover for pairs if adequately interspersed with open water. Robinson (1958) found that nest boxes erected in wetlands choked with emergents were not used by wood ducks.

2. Nest Sites of Wood Ducks The wood duck is a cavity nester. Numerous investigators have quantified characteristics of natural cavities and trees selected as nest sites by wood ducks (Table 173). Although cavities used by nesting wood ducks vary greatly in dimensional and qualitative characteristics, the basic requirements for a suitable nesting cavity in-

573

BREEDING HABITATS OF NEARCTIC WATERFOWL Table 17-3. Characteristics of natural tree cavities and trees selected as nest sites by wood ducks Parameter Cavity Entrance (cm2)3

Basal area (cm2)a

Depth (cm)

Height above ground (m)

Directional orientation

Type

Mean, range, or other criterion 63 45 54-81 62-730 180 ^516 324-1140 531 258-316 392 23-122

8-452 30-107 12-122 15-122 2-183 55-158 25-48 48 2-8 1-3 46-132 2-15 2-15 9-11 11 Random Random =£ 90° to nearest canopy opening Random Bucket and side entrance Bucket and side entrance

Reference Dries and Hendrickson 1952 Grice and Rogers 1965 Weier 1966 McGilvrey 1968 Robb 1986 Grice and Rogers 1965 McGilvrey 1968 Prince 1968 Bellrose 1976 Robb 1986 Dries and Hendrickson 1952 Bellrose et al. 1964 Weier 1966 Grice and Rogers 1965 McGilvrey 1968 Prince 1968 Gilmer et al. 1978 Bellrose 1976 Robb 1986 Dries and Hendrickson 1952, Bellrose et al. 1964 Grice and Rogers 1965 Weier 1966 Prince 1968 McGilvrey 1968 Gilmer et al. 1978 Robb 1986 Grice and Rogers 1965 Gilmer et al. 1978 Gilmer et al. 1978 Robb 1986 Prince 1968 Gilmer et al. 1978

elude: (1) accessibility; (2) protection from weather, predators, and competitors; (3) an exit for ducklings; and (4) proximity to suitable breeding-pair and brood habitat. Although many characteristics of cavities have been measured, attempts to relate these characteristics to wood duck use and reproductive success have been few. However, Robb (1986) reported that cavities with side entrances into tree boles were used by wood ducks in greater proportion than their availability, which may reflect higher nesting success in enclosed cavities compared to open bucket-type cavities (Prince 1968). The probability of cavity use and nest success also seems to increase with increasing cavity depth and volume (Robb 1986). Additionally, Robb (1986) reported that wood duck nest success tended to increase with increasing distance of cavity trees away from water, which he sug-

Parameter

Location (%) Trunk Branch Tree Status (%) Live Dead Suitable cavities («) D.B.H. (cm)

Diameter of bole at entrance (cm) Height (m) Age (yr) Distance to water (m)

Mean, range, or other criterion Bucket, side entrance, and irregular Side entrance

Reference Robb 1986 Lowney and Hill 1989 Robb 1986

78 22

Robb 1986 81 19 1.3

Robb 1986

33-69 33-91 >30 40-91 42-58 59 41

Weier 1966 Grice and Rogers 1965 Prince 1968 McGilvrey 1968 Gilmer ef al. 1978 Robb 1986 Robb 1986

15-22 68-112 0-98 ssSOO 0-350 75 207 446

Gilmer et al. 1978 Gilmer et al. 1978 Weier 1966 Grice and Rogers 1965 Gilmer et al. 1978 Robb 1986 Robb 1986 Robb 1986

Feb. -Mar. Jul. Distance to brood habitat (m) Distance to 0-200 nearest canopy opening (m) 96 Distance to nearest forest opening > 0.1 ha (m) a Calculated assuming circularity.

Gilmer et al. 1978 Robb 1986

gested was related to reduced nest-site attraction and subsequent nest destruction by raccoon (Procyon lotor). Prince (1968), Gilmer et al. (1978), and Robb (1986) investigated characteristics of forest lands where wood ducks nested. Prince (1968) reported that mean tree density and basal area were 24% less than the mean values of these variables for the overall floodplain forest, suggesting that wood ducks nest in comparatively open forest stands. Similarly, Bellrose (1955) characterized ideal nesting habitat for wood ducks as open areas in dense hardwood bottomland with many mature trees. However, Gilmer et al. (1978) and Robb (1986) reported no differences in tree density and basal area around nest sites and random sites but found that cavity trees used by nesting wood ducks were generally closer to canopy or forest openings than random cavity trees or cavities

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RICHARD M. KAMINSKI AND MILTON W. WELLER

not used by wood ducks. Gilmer et al. (1978) also found that plots with wood duck nest cavities contain significantly more cavities per tree than do random plots. Thus, the amount of forest and canopy openness may be a proximate factor that attracts nesting wood ducks, but cavity selection and reproductive success seem influenced by the availability of suitable, protected cavities and brood-rearing habitat. Wood ducks also readily nest in artificial structures, which are primarily of 3 types: vertical wooden boxes, vertical metal or plastic cylinders, and horizontal metal or plastic cylinders (Bellrose 1976). However, wood ducks will also nest in house chimneys (R. M. Kaminski, Mississippi State Univ., pers. obs.). Although Strange et al. (1971) concluded that wood ducks prefer boxes over natural cavities, other factors (e.g., higher previous nesting success and philopatry) tend to confound this conclusion. Lacki et al. (1987) measured 8 variables related to the placement of nest boxes used and not used by wood ducks. Boxes erected higher above the water in locales of simpler emergent communities received increased use by nesting wood ducks. Heusmann and Early (1988) found that wood ducks used and nested more successfully in wooden boxes than modified plastic buckets, but Griffith and Fendley (1981) found similar use of wooden boxes and plastic buckets. Heusmann and Early (1988) recommended that if plastic buckets are used, they should be dark colored; however, Hartley and Hill (1990) cautioned against the use of plastic nest structures at southern latitudes, because temperatures inside plastic structures can reach levels lethal to embryos. Wood duck use of boxes can increase local recruitment, especially where the availability of suitable natural cavities is low and where boxes are inconspicuous, thereby reducing nest parasitism and increasing hatchability (Semel et al. 1988). In northern forests, where cavities are more abundant (Prince 1968, Haramis 1975, Gilmer et al. 1978, Soulliere 1988) than in southern hardwood bottomlands (Lowney and Hill 1989), wood duck nest box programs may be less justified from a production standpoint (Soulliere 1986, 1988) but may be an effective means for monitoring wood duck breeding population and production trends (Zicus and Hennes 1987).

3. Wetlands and Nest Sites of Muscovy Ducks Muscovy ducks use a variety of natural and irrigated wetlands in areas that were formerly semitropical or tropical forestland (Rangel and Bolen 1984). Muscovies usually nest in cavities of mature trees in riparian woodlands (Rangel and Bolen 1984). Due to extensive clearing of their natural habitat in Mexico and reduced availability of natural cavities, muscovies have readily accepted nest boxes erected close to wetlands (Rangel and Bolen 1984). Rangel and Bolen (1984) concluded

that an intensive nest box program in Mexico may reverse the continued decline in muscovy duck numbers.

D. Dabbling Ducks (Anatini) 1. Wetlands Wetland use by breeding dabbling ducks has been studied in relation to many proximate and ultimate factors. These factors can be grouped as follows: (1) landscape type; (2) wetland type; (3) habitat diversity; (4) wetland abundance, annual conditions, size, and morphometry; (5) aquatic invertebrate foods; and (6) water quality. Breeding dabbling ducks use wetlands in a variety of landscapes. Bellrose (1979) and Johnson and Grier (1988) summarized data for the periods 1955-74 and 1955-81, respectively, on the distribution of breeding dabblers in North America. Dabblers occur in 14 landscapes, but only in mixed prairie, parkland, delta, and Alaskan taiga and tundra did percent dabbler use exceed the areal percentage of landscape types (Table 17-4). Breeding dabbling duck populations exceeded (17%) landscape area most in the parkland. Dabbler use was highest in the parkland and mixed-prairie (—20%), implicating the importance of these landscapes to continental dabbler populations. Hochbaum (1983), Wishart et al. (1983), and Johnson and Grier (1988) also presented data corroborating the importance of the prairieparkland region to North American ducks. Stewart and Kantrud (1973, 1974) and Brewster et al. (1976) documented a similar pattern in breeding duck use of physiographic regions of North Dakota and South Dakota, respectively. Within landscapes, breeding dabblers use some wetland types more than others but often proportionately to their availability. In the prairie-parkland region of southern Canada and northern United States, shallowbasin wetlands represent the principal aquatic habitat used by prebreeding and breeding dabbling ducks. StewTable 17-4. Percentages of available area and breeding dabbling ducks in 14 landscapes in North America, 1955-74 (adapted from Bellrose 1979) Landscape Alaskan tundra Alaskan open taiga Canadian open taiga Alaskan closed taiga Northern closed taiga Eastern closed taiga Canadian arctic deltas Subarctic deltas Parkland Mixed prairie Shortgrass prairie Tallgrass prairie Great Lakes forest Intermountain Valley a Complete data not available.

% Area

% Ducks

2.5 0.8 9.8 0.9 22.0 28.6 0.4 1.0 4.7 7.4 7.6 4.3 10.1 - a

4.5 6.0 1.3 9.0 3.2 0.4 13.4 12.5 21.2 17.3 5.8 4.0 1.3 - a

BREEDING HABITATS OF NEARCTIC WATERFOWL art and Kantrud (1973, 1974) and Kantrud and Stewart (1977) reported that most dabbling duck pairs breeding in North Dakota were observed on seasonal and semipermanent wetlands. Although use of both wetland types by breeding dabblers only slightly exceeded their combined availability at the time of the study, these wetlands are important to breeding ducks. They are rich in invertebrate foods needed by egg-laying females (Swanson et al. 1979); their dispersion provides isolation for pairs; and loafing, roosting, and nesting sites are usually abundant within them (Kantrud and Stewart 1977). In South Dakota, Ruwaldt et al. (1979) reported high use of semipermanent wetlands by breeding dabblers, but man-made stock ponds were also a primary dabbler habitat. These 2 wetland types composed the largest percentage of available surface water in South Dakota (Flake 1978). Similarly, because breeding mallard use of structurally different wetlands in Saskatchewan was proportional to the ponds' estimated availabilities, Mulhern et al. (1985) inferred no preference by mallards for these ponds. However, Dwyer et al. (1979) reported that mallard hens breeding in North Dakota used temporary and seasonal wetlands within their home ranges more than the availability of these wetlands, implying a preference for these wetlands. Some dabbler species, such as blue-winged teal, mallard, northern shoveler, and northern pintail, select or heavily use seasonal ponds and seasonally flooded zones of large northern prairie marshes in years when these habitats are inundated (Kantrud and Stewart 1977, Swanson and Meyer 1977, Bishop et al. 1979, Weller 1979, Kaminski and Prince 1984, Mulhern et al. 1985). Moreover, breeding dabblers vary their diurnal use of wetland types by exhibiting crepuscular peaks in use of shallow emergent wetlands (Klett and Kirsch 1976) as well as differential nocturnal use (Swanson and Sargeant 1972). The spatially and temporally dynamic nature of prairie wetlands may have selected for plasticity in use of habitats and foraging strategies in dabbling ducks (Swanson and Meyer 1977, Kaminski and Prince 198la, Mulhern etal.1985, Ball and Nudds 1989). Within forested landscapes, breeding dabbling ducks exhibit some preferences for certain wetland types that presumably fulfill breeding requisites. Mallards (Gilmer et al. 1975, Kirby et al. 1985) and black ducks (Ringelman et al. 1982) selected wetland habitats in Minnesota and Maine, respectively, that contained herbaceous and deciduous wooded vegetation, which may have enhanced the availabilities of aquatic invertebrate foods and resting sites and offered protection from predators and weather. Although dabbling ducks differentially use certain wetland types within and among years, a diversity of wetlands within a complex of aquatic and terrestrial habitats seems most attractive to breeding dabbling

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ducks and appears to affect their reproductive success, especially during wet years when a variety of wetland types are available. Numerous authors have suggested the importance of a wetland complex for fulfillment of the physiological and behavioral needs of breeding dabblers (e.g., Flake 1978, Dwyer et al. 1979, Swanson 1985, Swanson et al. 1979, Weller 1981, Ringelman et al. 1982). Apparently, few individual wetlands meet the total needs of breeding ducks. In agriculturally impacted landscapes with reduced wetland availability and diversity, dabbler breeding pair densities generally have decreased, and relative abundance of blue-winged teal has increased over mallard (Dwyer 1970, Trauger and Stoudt 1978). Conversely, in relatively pristine landscapes harboring a complex of wetlands and upland habitats, these patterns have not occurred (Leitch and Kaminski 1985). These results imply the importance of diverse wetlands and upland cover in contiguity for dabbling duck recruitment. Brown and Dinsmore (1986) also reported that bird-species richness (including dabbling ducks) tends to be greater in diverse wetland complexes than in large, isolated marshes. Within wetlands, habitat structural diversity appears to play a role in dabbler habitat selection. Weller and Spatcher (1965) and Weller and Fredrickson (1973) reported that avian abundance and species richness in several Iowa marshes were highest during years when emergent vegetation and open water covered approximately equal proportions of the basins (i.e., a hemimarsh configuration). These patterns led Kaminski and Prince (1981b) and Murkin et al. (1982) to test whether dabbling ducks in the Delta Marsh, Manitoba, were equally attracted to plots manipulated to provide 1 of 3 percent ratios (30:70, 50:50, 70:30) of emergent vegetation and open water. Dabbling duck pair densities and species diversity were highest on 50:50 plots (Kaminski and Prince 198Ib, Murkin et al. 1982) that contained the greatest coverages of both structural components (i.e., emergent vegetation and open water) and edge. The higher dabbler densities and species diversity on hemimarsh configured plots may have been related to the effects that vegetation-water interspersion had on the availabilities of aquatic invertebrates (Kaminski and Prince 198Ib, Kaminski and Prince 1984, Nelson and Kadlec 1984), isolated space for breeding pairs and broods (Murkin et al. 1982, Kaminski and Prince 1984, Monda and Ratti 1988), and nesting and resting sites (Sowls 1955, Drewien and Springer 1969, Weller 1979, Krapu et al. 1979, Kaminski and Prince 1984). Thus, abundant vegetation-water interspersion, which enhances habitat structural diversity in emergent wetlands, may be a proximate cue that breeding dabbling ducks use to assess wetland suitability for the aforementioned resources. Generally, positive correlations have been demon-

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strated between numbers of breeding dabbling ducks and spring wetlands (Patterson 1979, Bellrose 1979, Bailey 1981, Krapu et al. 1983, Leitch and Kaminski 1985, Johnson and Grier 1988), although there have been exceptions for some species (e.g., mallard, gadwall, and northern shoveler) (Stewart and Kantrud 1974, Trauger and Stoudt 1978, Leitch and Kaminski 1985), and the strength of the correlation for mallard has decreased during recent years (Johnson and Shaffer 1987). Presumably, as numbers of wetlands and water levels increase, so do available wetland areas for pairs, along with resources harbored within these wetlands (Burgess 1969, Danell and Sjoberg 1978, Weller 1979, Bishop et al. 1979, Kaminski and Prince 1984). However, when numbers of wetlands and water levels decrease, breeding pair densities and occupancy rates increase (Bellrose 1979, Krapu et al. 1983), and emigration may ensue, especially during severe drought (Smith 1970, Henny 1973, Calverley and Boag 1977, Derksen and Eldridge 1980, Giroux 198Ib, Kaminski and Prince 1984). Several studies have demonstrated positive relationships between correlates of mallard fitness and indices of spring or summer wetland conditions (Mayhew 1955, Crissey 1969, Stoudt 1971, Smith 1971, Dzubin and Gollop 1972), both of which should influence habitat use. Nichols et al. (1982) presented evidence suggesting that mallard annual survival rates were positively related to breeding-ground wetland conditions, and Krapu et al. (1983), Cowardin et al. (1985), and Eldridge and Krapu (1988) suggested that mallards exhibit flexible reproductive strategies relative to food quantity and quality as affected by spring wetland conditions. Kaminski and Gluesing (1987) showed that an index of mallard recruitment rate was positively correlated more with breeding-ground wetland conditions than wintering-ground wetland conditions, but breeding population density was inversely and most strongly related to recruitment rate. Finally, Leitch and Kaminski (1985) reported that numbers of broods and an index of recruitment rate for several dabbler species were positively correlated with numbers of wetlands in August but not May. They suggested that the persistence of good wetland conditions between spring and summer was critical to dabbling duck recruitment. Breeding dabbling duck use of wetlands also appears to be related to wetland surface area. In South Dakota, Evans and Black (1956), Drewien and Springer (1969), and McEnroe (1976) found positive associations between dabbler pair use and individual wetland area. Similarly, Patterson (1976), Godin and Joyner (1981), and Ball and Nudds (1989) reported that breeding pair use of Ontario wetlands increased with increasing surface area of available wetlands, but use of individual wetlands and perhaps even breeding population density may be regulated intraspecifically by mate and space de-

fense (Dzubin 1969, Patterson 1976, Godin and Joyner 1981, Titman and Seymour 1981). Toft et al. (1982) also reported that both abundance and species richness of dabbler pairs in the Northwest Territories were positively correlated with pond area. Danell and Sjoberg (1978) and Andersson (1982) found in Sweden that use of lakes by breeding dabbling ducks increased with lake size. Two explanations for the apparent positive relationship between breeding dabbler use of wetlands and wetland size may be that large, conspicuous wetlands, like "island" habitats (MacArthur and Wilson 1967; Weller 1980; Brown and Dinsmore 1986, 1988), attract more dabblers and avian species than do small wetlands, and the availability of breeding space, isolation, and other resources for pair members and broods may increase with wetland size and water permanency. Wetland size often is correlated with length of shoreline and emergent vegetation-water interface, and sometimes with shoreline irregularity. Generally, breeding dabbling duck use increases with increasing extent and convolution of shoreline or emergent vegetation-water interface. This pattern has been shown for waterfowl using natural (McEnroe 1976, Nilsson 1978, Hines and Mitchell 1983a, Kaminski and Prince 1984) and constructed (Giron 1981) wetlands, probably for the reasons suggested above for the relationship between dabbler use and wetland size. The diets of female dabbling ducks during egg laying consist largely of aquatic invertebrates because of females' need for animal protein and calcium for egg production (Krapu 1979, Swanson 1985, Swanson et al. 1979). Recognition of the importance of aquatic invertebrate foods to breeding dabbling ducks has led researchers to test for associations between dabbling duck habitat use and invertebrate resources. Most studies report some positive relationship between breeding dabbling duck habitat use (or foraging) and resource levels of aquatic invertebrates. Murkin et al. (1982) and Murkin and Kadlec (1986) found positive correlations between densities of dabbler pairs and aquatic invertebrates in Manitoba. Joyner (1980) and Ball and Nudds (1989), both working in Ontario, indicated that breeding dabbler habitat use was positively associated with either invertebrate abundance, biomass, or taxonomic diversity. In Nova Scotia, Whitman (1976) reported concurrent increases in numbers of both dabbling duck pairs and aquatic invertebrates, and in Utah (McKnight and Low 1969, Peterson and Low 1977) and Sweden (Danell and Sjoberg 1978), parallel trends occurred between dabbler habitat use or production and aquatic invertebrate resources. Only Godin and Joyner (1981) and Kaminski and Prince (1981b) reported no discernible relationship between breeding dabbler use of habitat and aquatic invertebrate abundance or biomass. However, Godin and Joyner (1981) did demonstrate a positive association between

BREEDING HABITATS OF NEARCTIC WATERFOWL habitat use by mallard broods and invertebrate abundance, and Kaminski and Prince (198la) and Ball (1984) showed that breeding dabbling ducks appeared to allocate their foraging effort within habitat patches relative to the quantity and quality of aquatic invertebrates. Thus, because of the nutritional importance of aquatic invertebrates to breeding female dabblers and the considerable support for associations between dabbler use of wetlands and invertebrate resources, invertebrate availability may be a major factor affecting dabbling duck habitat selection, foraging, and ultimately reproductive success (Swanson et al 1979, Murkin and Kadlec 1986). Water quality and hydrology affect the structure and function of wetlands, but few studies demonstrate direct relationships between dabbling duck use of wetlands and these effects. Murphy et al. (1984) studied breeding dabbling and diving duck use of Alaskan taiga ponds either connected to or separated from a creek system. Duck use tended to be lower on hydrologically isolated ponds, which had lower nutrient levels than ponds linked to the creek. The hydrology and the plant productivity of such a system, as affected by nutrient dynamics (e.g., nitrogen, phosphorous), may have influenced waterfowl use patterns of these taiga ponds (Murphy et al. 1984) and some Swedish lakes (Nilsson and Nilsson 1978). In North Dakota, breeding dabblers used saline lakes where they fed on a variety of salt-tolerant invertebrates, vascular plants, and filamentous algae, but duckling use was closely associated with inflows of water low in salt from spring seepages or adjacent wetlands (Swanson et al. 1984). In contrast, Dwyer (1970), Patterson (1976), Nilsson (1978), and Danell and Sjoberg (1978) reported no associations between use of wetlands by breeding dabblers and various limnologic variables. Apparently, water quality and hydrology are indirect and inconsistent correlates of dabbler wetland use.

2. Nest Sites Nest sites of dabbling ducks have been studied extensively. Choice has been related to availability, density, and height of cover more than to plant species; to nestsite security from predators and inundation; to proximity of wetlands vital to breeding females and their broods; and to presence of other nesting species. Although light-to-moderate grazing and periodic burning render vegetative conditions attractive to certain species of dabblers and sometimes even increase nest density and success (e.g., Glover 1956, Burgess et al. 1965, Duebbert et al. 1986), most studies indicate that dabbler nest densities and nesting success increase with increasing availability of undisturbed, dense grass, forbs, and shrubs (e.g., Duebbert and Lokemoen 1976; Kirsch et al. 1978; Livezey 1981a, b; Duebbert 1982; Lokemoen et al. 1984; Sugden and Beyersbergen 1987).

577

Northern pintails are an exception, often nesting in sparse upland cover (Milonski 1958, Duncan 1987). Nevertheless, early nesting species such as northern pintail and mallard require residual or perennial cover for nest establishment (Kirsch et al. 1978). Cowardin et al. (1985) and Klett et al. (1988) tested for nest habitat preferences of mallards and 5 species of dabblers, respectively. Klett et al. (1988) showed that 5 dabbler species preferred herbaceous cover planted for wildlife or for erosion control, and all avoided croplands where nesting success was low. Nest success for all 5 species combined was highest in idle grasslands. Idle grassland provided greater security from predators than did cropland. Greenwood et al. (1987) also found dabbler nest success to correlate positively with the proportion of grassland in their study areas, and most nests were located in grass-brush associations. Female dabblers apparently prefer to nest in undisturbed, dense cover or odd sites (e.g., rock piles, shelterbelts, haystacks) where nest success and hen survival increase due to decreased losses from mammalian or avian predation. Several studies show that predation on eggs and dabbler hens are primary factors reducing recruitment rates (Duebbert and Lokemoen 1980, Sargeant et al. 1984, Cowardin et al. 1985, Johnson et al. 1987a), but recruitment rates can be increased through habitat management and predator control (Kantrud 1986, Duebbert and Lokemoen 1980, Klett et al. 1988). Dabblers often nest within 100 m of water (Bellrose 1976). Proximity of nests to water may be an adaptive strategy that enhances duckling survival, or, in some landscapes (e.g., prairie-pothole complexes), it may be a consequence of high wetland density and loss of upland cover. Livezey (1981b) found that dabbler nests were located nearer to water than random sites; however, successful nests were located farther from water than nests destroyed by predators. He hypothesized that high predator densities near wetlands may have influenced the increased rate of nest loss recorded near the wetlands. Contrary to the pattern found in most dabblers, northern pintail commonly nest 1-2 km from wetlands in grasslands. Duncan (1987) hypothesized that female pintails nest far from wetlands by choice to avoid nest depredation by predators that concentrate around wetlands. Dabbling ducks have been found nesting in close association with gulls, Canada geese, and shorebirds (Hilden 1964, Vermeer 1968, Bengston 1972a, Newton and Campbell 1975, Giroux 198Ic, Amat 1982). Nesting success of the ducks is generally enhanced by communal nesting, but in some cases gulls kill ducklings after nest exodus (Dwernychuk and Boag 1972). In contrast, Lokemoen et al. (1984) did not observe a nesting association between dabblers and terns, gulls, Canada geese, or shorebirds on a North Dakota island. Instead, duck nests were clustered in dense cover.

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Dabblers are primarily upland nesters, although some species also nest on natural and constructed islands, in wetland basins, and in artificial structures. Duebbert et al. (1983) and Lokemoen et al. (1984) reviewed several studies documenting island nesting by dabblers. Gadwall and mallard are the principal species that nest densely on islands (Hammond and Mann 1956; Giroux 1981a; Duebbert 1982; Hines and Mitchell 1983a, b; Duebbert et al 1983; Duncan 1987). Northern pintails nest infrequently on islands; hence, artificial islands may be less effective for increasing pintail production (Duncan 1987). As suggested in several studies (Hammond and Mann 1956, Hines and Mitchell 1983b, Duebbert et al. 1983), major factors contributing to dense nesting and relatively high nest success on islands include: (1) reduction in mammalian predators, (2) a higher rate of homing by successful than unsuccessful nesting hens, (3) innate and learned selection by hens of the safest nesting areas, (4) imprinting of newly hatched ducklings on the habitat around the nest, and (5) social attraction among nesting females. As in mainland nesting habitats, island nesting dabblers also tend to locate their nests in dense cover (Duebbert 1982; Hines and Mitchell 1983a, b; Duebbert et al 1983; Lokemoen et al 1984). Giroux (198la, b, c, d) conducted an intensive study of nesting waterfowl use of constructed earthen islands in Alberta. He reported that duck nesting density and success were positively correlated with island distance from the mainland and amount of island cover but inversely associated with island size. Additionally, greatly increased densities of nests occurred during a drought year, when drought-displaced ducks apparently used Alberta impoundments containing permanent water and islands. Several other studies have reported nesting dabbler use of constructed islands (Hammond and Mann 1956, Johnson etal 1978, Duncan 1986, Higgins 1986) and other artificial structures, including elevated baskets (Bishop and Barratt 1970, Doty etal 1975, Doty 1979), rafts (Brenner and Mondok 1979), and straw bales (Jelinski 1980, Cowardin et al 1985). Possibly due to decreased availability of upland cover and resulting increased nest destruction by predators in agriculturally impacted areas, an increasing occurrence of emergent-marsh nesting by mallards has been observed recently (e.g., Krapu et al 1979, Talent et al 1981, Burger 1985). However, marsh nesting by mallards was documented earlier (Williams and Marshall 1938, Hochbaum 1944, Wingfield and Low 1954). Krapu et al (1979) reported that 54% of the mallard nests in marsh habitat hatched, compared to 14% of the nests in uplands, but Cowardin etal (1985) were unable to corroborate this pattern.

E. Diving Ducks (Aythyini) I. Wetlands Compared to dabbling ducks, studies of wetland use by breeding diving ducks are few. Nevertheless, landscape, wetland type and diversity, aquatic foods, water chemistry, and availability and security of nesting cover have been related to habitat use by breeding diving ducks and their reproductive success. Unlike dabbling ducks, however, annual abundance of breeding diving ducks does not correlate with wetland numbers, probably because divers are more closely tied to deeper wetlands that vary less in availability among years (Johnson and Grier 1988). Highest breeding densities for Nearctic species are reported from the following areas: (1) the prairie-parkland region of the United States and Canada for canvasback and redhead, (2) the intermountain region of the western United States for redhead, (3) the closed boreal forest of the Canadian prairie provinces for ringnecked duck, (4) the tundra and boreal forest zone of arctic and subarctic northwestern Cana(da and Alaska for greater scaup, and (5) the open and closed boreal forest and delta areas of northwestern Canada and Alaska for lesser scaup (Bellrose 1976, Johnson and Grier 1988). Within these landscapes, breeding divers use a diversity of wetlands but primarily ponds, lakes, and marshes varying from acidic (e.g., ring-necked duck) to alkaline (e.g., redhead) wetlands. In the prairie-pothole region of North Dakota, breeding diving ducks seem to prefer semipermanent potholes. Kantrud and Stewart (1977) found 75% of all indicated pairs of divers on semipermanent ponds, which made up only 41% of the'available ponds. Woodin (1987) also found that canvasback, redhead, and lesser scaup used semipermanent ponds in North Dakota significantly more than their availability, and these ponds ranked first in preference for all 3 species. Although breeding divers in the pothole region of North Dakota generally prefer semipermanent potholes, canvasback, redhead, and lesser scaup breeding in this region and the southern prairie provinces of Canada also heavily use large, deep, permanent ponds (Bellrose 1976; Lokemoen 1966; Smith 1971; Stoudt 1971, 1982; Sugden 1978). Furthermore, Stoudt (1982) reported that canvasback pair densities in Manitoba were highest on permanent ponds ranging from 0.4 to 2 ha in area and having < 1/3 of their basins covered by emergent vegetation. Within potholes of this region, canvasback and lesser scaup tend to occupy central zones of ponds, while redhead and ruddy duck use areas along pond edges. Such habitat partitioning may lessen inter-

BREEDING HABITATS OF NEARCTIC WATERFOWL specific competition for food between canvasback and redhead and between scaup and ruddy duck (Siegfried 1976a). In the subarctic taiga of the Northwest Territories, lesser scaup pairs selected large permanent ponds (Tottetal. 1982). Despite the apparent preference for semipermanent wetlands by diving duck pairs, breeding diving ducks use ephemeral, temporary, and seasonal wetlands when these types are available (Bellrose 1976, Woodin 1987). Stoudt (1982) concluded that breeding canvasback pairs require a secure nesting site in a diversified wetland complex containing ponds of various size and permanency and with different cover types. Similar to dabbling ducks, a complex of diverse wetlands appears important for habitat use and perhaps reproductive success of diving ducks. Breeding diving ducks also require protein- and energy-rich foods for successful reproduction (e.g., Hohman 1985, Noyes and Jarvis 1985, Jarvis and Noyes 1986, Woodin 1987). Therefore, the availability of proteinaceous invertebrates and energy-rich plant foods may influence diver use of breeding and brood-rearing wetlands. As noted previously, water quality has been related in some cases with breeding waterfowl use of wetlands. In a study discussed earlier, Murphy et al. (1984) reported that taiga ponds hydrologically connected to a creek system received greater use by ducks and had higher levels of most nutrients and ions than ponds separated from the creek. McAuley and Longcore (1988a, b) found that invertebrate diversity and biomass decreased with increasing wetland acidity. Consequently, juvenile ringnecked ducks using low-pH (< 6.1) wetlands consumed decreased biomass and diversity of invertebrates (McAuley and Longcore 1988b). Therefore, water quality can affect aquatic food chains, wetland use by ducks, and possibly duck recruitment through differential juvenile survival (e.g., McAuley and Longcore 1988a). The availability of nesting cover near or over water probably influences wetland use by breeding divers, although some populations are known to nest in uplands and on islands (McKnight 1974, Hines 1977, Evrard et al. 1987, Prellwitz 1987). Most species of ducks use a wide variety of cover types for nesting, seeking only a growth form that provides support and concealment (Bellrose 1976). Canvasbacks and redheads, however, primarily nest in wetlands containing robust emergents such as cattail and bulrushes. These plants provide substrate for attachment of over-water nests (Bennett 1938, Hochbaum 1944, Low 1945, Lokemoen 1966, Sugden 1978, Stoudt 1982). Ring-necked ducks, both scaup species, and Palearctic tufted ducks frequently nest amid emergent vegetation in wetlands and on insular sites in aquatic and terrestrial vegetation (Brandt 1943, Goodwin 1957, Mendall 1958, Townsend 1966, Weller et al

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1969, Bengston 1970, Bellrose 1976, Hines 1977). Thus, emergent or other nesting cover interspersed and juxtaposed with permanent water may be important for wetland use by breeding divers. Perhaps breeding diving ducks use wetlands with closely associated nest cover because divers are poor overland travelers; and, when nest cover is nearby, they experience decreased egg predation and nest parasitism from conspecifics and other species, and increased brood survival (Low 1945, Bengston 1970, Sugden 1978, Sayler 1985).

2. Nest Sites Nest-site selection and nesting success of diving ducks have been shown to correlate positively with amount of vegetative concealment (Long 1970, Hines 1977). In the Delta Marsh, Manitoba, Featherstone (1975) found that successful nests of diving ducks (canvasback, redhead, and ruddy duck) were more concealed than unsuccessful nests. Similarly, diving ducks that nested in emergent vegetation of Manitoba potholes also generally chose sites more concealed than random sites, but nest-site choice within species did not always corroborate this pattern (Krasowski and Nudds 1986). Additionally, Krasowski and Nudds (1986) were unable to detect differences in microhabitat structure between successful and unsuccessful nests. They offered several possible explanations but hypothesized that predators (e.g., raccoons), efficient at searching for nests in narrow bands of emergent vegetation around potholes, may negate the selective advantage of nonrandom location of nests. Some diving duck species may be attracted by other species and their nests. Bengston (1970) reported that nesting success of greater scaup and tufted duck was significantly higher within than outside gull colonies. Also, redheads and lesser scaup, which lay eggs parasitically in the nests of other birds, may be attracted to breeding habitats by the existence or abundance of the following: (1) potential hosts, (2) other parasitically laying individuals, and (3) host nests in preferred habitat (Weller 1959; Joyner 1976, 1983; Sugden 1980; Talent et al. 1981; Giroux 1981d; Bouffard 1983; Hines and Mitchell 1984).

F. Sea Ducks (Mergini) Sea ducks are diverse taxonomically and in habitat use. Hence, we have organized the review of sea duck habitat use by congeneric groups (i.e., eiders, scoters, buffleheads and goldeneyes, and mergansers) but address oldsquaws and harlequin ducks separately because of their distinct taxonomy and habitat use within the tribe. 1. Wetlands and Nest Sites of Eiders Eiders use coastal and arctic tundra wetlands through-

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out their breeding range (Bellrose 1976, Johnsgard 1978, Nystrom and Pehrsson 1988). In Alaska's arctic coastal plain, Bergman et al. (1977) found that king and spectacled eiders preferred tundra wetlands containing pendant grass (Arctophila fulva). Wetlands with pendant grass and water sedge (Carex aquatilis) contained abundant aquatic invertebrates, which may have influenced wetland use by eiders. Nystrom and Pehrsson (1988) hypothesized that ingestion of seawater by common eiders and scoters, as a consequence of feeding on mussels (Mytilus spp.), may constrain diving ducks' use of marine wetlands. These authors advocated considering salinity in future, applicable studies of waterfowl habitat selection. Whereas the common eider often nests on islands or small islets in coastal waters, the other eiders tend to nest near freshwater tundra ponds (Choate 1967, Mickelson 1975, Bellrose 1976, Cramp et al. 1977). On nesting islands, Pacific eiders select sites that contain relatively more driftwood than available at random (Johnson et al. 1987b) and provide wind protection and sufficient elevation to avoid flooding (Schamel 1977). Females nesting at such sites tend to experience increased nesting success. Also, the common eider frequently nests colonially (Bellrose 1976) and in association with gulls on islands where nest predation rates tend to be lower than outside gulleries (Lack 1968, Gerell 1985, Gotmark and Ahlund 1988).

2. Wetlands and Nest Sites of Scoters Little is known about the breeding habitats of scoters, least of all about the surf and black scoters. The surf scoter breeds nearly exclusively in the boreal forest regions of northern Canada and Alaska (Bellrose 1976, Johnsgard 1978). The black scoter breeds commonly in northern Eurasia but is rare in North America, being found primarily in Alaska. Major breeding habitats are freshwater ponds, lakes, and rivers in tundra and boreal forest, particularly where shrubby cover is available for nesting (Bengston 1970, Johnsgard 1978). Of the scoters, the white-winged scoter has the most widespread breeding distribution and has been studied most. These scoters breed in northern Eurasia and in North America from North Dakota across Canada into Alaska (Bellrose 1976, Johnsgard 1978). White-winged scoters are usually found on large freshwater lakes and ponds, and less commonly in marshes. They nest in dense cover on mainlands and on islands (Hochbaum 1944, Brown and Brown 1981). White-winged scoters use wetlands for breeding and brood-rearing where their primary foods (e.g., amphipods) are abundant (Brown and Fredrickson 1986).

3. Wetlands and Nest Sites of Bufflehead and Goldeneyes The breeding ranges of bufflehead and Barrow's goldeneye are largely restricted to the Nearctic; the common goldeneye has a Holarctic distribution (Johnsgard 1978). Boreal and temperate lentic or slow-lotic, shallow (< 3 m) wetlands, rich in aquatic invertebrate prey and near trees, comprise prime bufflehead breeding habitat (Erskine 1971, Cramp etal. 1977, Johnsgard 1978). Wetland use by breeding Barrow's goldeneye may be related to the availability of food, which consists mostly of amphipods and other aquatic invertebrates obtained in subarctic and arctic-alpine fresh or alkaline lakes, with expansive beds of submergent plants (Bellrose 1976, Cramp et al. 1977, Johnsgard 1978). Cramp et al. (1977) and Johnsgard (1978) reported that breeding Barrow's goldeneye also use lotic habitats in North America and Iceland, respectively. Forested middle-toupper latitudes of the Nearctic and Palearctic that contain cool, open waters with abundant invertebrate fauna but little aquatic vegetation, along with nearby aboveground nesting cavities, constitute typical breeding habitat for common goldeneye (Bellrose 1976, Cramp et al. 1977, Johnsgard 1978). Buffleheads and both goldeneyes are cavity nesters (Erskine 1971, Bellrose 1976, Savard 1982, Gauthier 1985), although Barrow's goldeneye do nest on the ground in rock crevices and in holes in treeless areas (Bellrose 1976, Johnsgard 1978). All species also "prospect" for nest cavities before the breeding season (Eadie and Gauthier 1985). Buffleheads usually nest in tree cavities excavated by flickers (Colaptes spp.) in aspen (Populus spp.) and conifers (Pseudotsuga menziesii, Pinus contorta] located generally < 200 m from water (Erskine 1971, Gauthier and Smith 1987). Peterson and Gauthier (1985) and Gauthier and Smith (1987) found that either cavity volume or depth positively correlates with use of cavities by nesting buffleheads in British Columbia. Perhaps, like wood ducks (Robb 1986), bufflehead nest success increases with increasing cavity volume and depth because nest predation decreases. Buffleheads and Barrow's goldeneye readily use nest boxes, especially ones used in previous years by the same individuals or by conspecifics and from which broods were produced (Gauthier 1988, Savard 1988). Similar patterns have been observed in common goldeneye (Eriksson 1979, Dow and Fredga 1985). Buffleheads tend to select small boxes (15 X 15 x 40 cm with a 6.5 cm diameter hole) erected near water (< 15 m) and in areas dominated by conifers (Gauthier and Smith 1987, Gauthier 1988). Gauthier and Smith (1987) concluded

BREEDING HABITATS OF NEARCTIC WATERFOWL that nest sites for buffleheads were not lacking. Instead, territorial behavior seemed to limit breeding population size, because population size tended to remain stable despite surplus suitable nest sites. Common goldeneye (Savard 1984, Fredga and Dow 1984) and Barrow's goldeneye (Savard 1984) also are territorial. However, Barrow's goldeneye may be limited by nest-site availability in certain locations, because Savard (1986, 1988) found that breeding population size increased with the addition of nest boxes. Prince (1968) found that floodplain forest around natural cavities used by common goldeneye and other ducks was more open than the surrounding forest. Cavity diameter seemed important in goldeneye nest-site selection, but most cavities used by goldeneye were opentop cavities, in contrast to side-entrance holes used by wood ducks (Prince 1968). Although Eriksson (1979) did not detect relationships between nest box size and common goldeneye clutch size and incubation efficiency, Lumsden et al. (1980, 1986) reported that common goldeneye preferred boxes with blackened interiors containing wood shavings, a 13 x 10 cm entrance, a depth of ^33 cm, and an aboveground attachment height of 6 m.

4. Wetlands and Nest Sites of Mergansers Breeding ranges of the piscivorous mergansers include North America and Eurasia for the red-breasted merganser and the common merganser (M. merganser) but only North America for the hooded merganser (Johnsgard 1978). Red-breasted mergansers generally are found breeding in tundra and boreal or temperate forest zones on fresh, brackish, and saltwater wetlands with sheltered bays or similar areas having substrate for loafing (Cramp et al. 1977, Johnsgard 1978). Within these wetlands, the habitat distribution of breeding redbreasted mergansers appears closely related to the presence and abundance of fish (Bellrose 1976, Rad 1980). Despite substantial geographic overlap with redbreasted mergansers (Bellrose 1976, Cramp et al. 1977), breeding common mergansers use lakes, rivers, and ponds in temperate forested and mountainous habitats where fish are available for adults and young (Cramp et al. 1977, Johnsgard 1978, Wood 1986). On Vancouver Island, Canada, nest density of common mergansers does not appear to be limited by breeding pair density; however, brood abundance does correlate positively with abundance of juvenile Pacific salmon (Oncorhynchus spp.) (Rad 1980, Wood 1986). This correlation suggests that availability of potential prey could be a proximate factor influencing breeding habitat selection in common and red-breasted mergansers. Breeding hooded mergansers use clear rivers, lakes, and ponds in forested habitats (Bellrose 1976, Johnsgard 1978). L. H. Fredrickson (Univ. of Missouri, pers. commun.) believes that the availability of over-water nest cavities and

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crawfish (Cambarus spp.) prey influence habitat use by breeding hooded mergansers. All merganser species tend to nest in cavities, using either tree cavities, rock crevices, ground holes, or artificial structures. The red-breasted merganser is least dependent on the availability of tree cavities. Redbreasted mergansers nest on islands and along shorelines under dense cover or in ground crevices and sometimes in tern (Sterna hirundo) colonies where females experience increased nesting success (Hilden 1964, Weller et al. 1969, Bengston 1970, Bellrose 1976, Johnsgard 1978, Cramp et al. 1977, Young and Titman 1986). The common merganser generally nests in tree cavities, occupying those excavated by woodpeckers (e.g., Dryocopus martius) and having entrances about 12 cm wide and internal diameters of about 25 cm. However, when tree cavities are not available, common mergansers will nest under boulders and bushes and in wall crevices, chimneys, or nest boxes (Cramp et al. 1977, Johnsgard 1978). Hooded mergansers usually use nest cavities that are situated next to or over water. Morse et al. (1969) and L. H. Fredrickson (Univ. of Missouri, pers. commun.) suggest that proximity to water influences choice of nest boxes and cavities by female hooded mergansers. Lumsden et al. (1980,1986) studied box-nesting hooded mergansers and found that females preferred boxes with nesting material and an entrance 13 cm x 10 cm, but box color did not seem to influence nest-site choice, according to Morse et al. (1969).

5. Wetlands and Nest Sites of Harlequin and Oldsquaw Ducks In western Canada, Alaska, and Iceland, harlequin ducks use turbulent coastal wetlands in association with cold, flowing water that supports black fly larvae (Simulidae), an important food in Iceland and probably elsewhere for this species (Bengston 1972b). They nest in well-concealed hollows amid rocks and shrubs (Cramp etal 1977, Johnsgard 1978). Breeding habitat of the oldsquaw consists primarily of tundra lakes, ponds, and coastlines, wherein wetlands with pendant grass and water sedge are preferred over other types (Bergman et al. 1977). The oldsquaw has the most northern range of any duck species, with a circumpolar nesting distribution (Bellrose 1976). Oldsquaws nest along coastlines, on islands, and in pothole habitats (Bengston 1970, Alison 1975).

G. Stiff-tailed Ducks (Oxyurini) 1. Wetlands and Nest Sites of Ruddy Ducks Breeding ruddy ducks in North Dakota select intermediate (0.4-4 ha) and large (> 4 ha) semipermanent wetlands (Woodin 1987) but also use permanent marshes and ponds with emergent vegetation for nesting and ad-

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equate open water for getting airborne and alighting (Johnsgard 1978). Within prairie-parkland wetlands, solitary ruddy ducks will forage on small potholes (< 2 ha). When mingling with pochards on larger ponds, ruddy ducks tend to forage along pond edges, perhaps because their diet overlaps with lesser scaups which tend to forage centrally within ponds (Siegfried 1976a). Woodin (1987) observed that when ruddy ducks were absent from wetlands in the North Dakota Coteau, redheads used a greater diversity of wetland types, possibly suggesting that ruddy ducks somehow restrict redheads' use of wetlands. Ruddy ducks usually nest in emergent wetland vegetation (but see McKnight 1974) and construct their nests in new growth instead of residual vegetation (Low 1941, Siegfried 1976b). Siegfried (1976b) reported that in June ruddy ducks nested in whitetop grass and sedge, whereas nests established in July were built amid new cattail and bulrush, the latter plants being typical of persistent wetlands.

2. Wetlands and Nest Sites of Masked Ducks Few Nearctic breeding records exist for the masked duck (Johnsgard and Hagemeyer 1969), but throughout its range the species is associated with tropical and subtropical marshes or swamps that are densely vegetated with emergent vegetation and floating-leaf plants (Johnsgard 1978). The masked duck breeds synchronously with rising water levels and locates its nest in dense vegetation within natural wetlands and rice fields (Johnsgard 1978).

III. Concluding Synthesis and Future Needs Nearctic waterfowl, as other waterfowl of the world, use numerous and diverse wetlands and nest sites. Inasmuch as selection connotes unrestricted choice among available habitats or intrinsic resources, abundance and diversity of habitats and resources should promote selection. Despite wide temporal and spatial variation in habitat use among taxa, some species of breeding waterfowl have specific requirements and hence narrow tolerance to habitat variation. Others have evolved flexible strategies that permit use of diverse habitats that provide critical components. Nevertheless, all must have the following: (1) abundant and nutritious foods for adults; (2) wetland space, quality, and diversity; (3) nest sites protected from predators, other egg-laying females, and flooding; and (4) food-rich, brood-rearing areas with escape cover. If major Nearctic breeding regions still contained these basic components, waterfowl could more closely realize their biotic potential and would increase in numbers. Additionally, studies of nonbreeding waterfowl suggest that habitat and resource conditions outside the breeding season may affect survival and

recruitment (Heitmeyer and Fredrickson 1981, Kaminski and Gluesing 1987, Weller 1988). Therefore, we conclude that waterfowl need abundant and diverse habitats throughout their annual cycle and range to aid their selection and acquisition of quality habitats and resources that fulfill their physiological and social requirements for survival and reproduction. Although numerous questions remain unanswered, future research on waterfowl habitat selection should emphasize experimental approaches (Romesburg 1981) and be directed toward improving our understanding of the interrelationships between habitat selection, survival, and recruitment. This research is essential for effective management of waterfowl habitats and populations. The following list of topics represents some nonprioritized but nonetheless worthy research pursuits: 1. Relate habitat selection to waterfowl survival and recruitment rates. 2. Test models and determine the effects on recruitment of possible density-dependent habitat selection (e.g., Fretwell 1972; MacArthur 1972; Rosenzweig 1981, 1985; Rosenzweig and Abramsky 1985; Morris 1987). 3. Functionally integrate habitat selection, foraging, and competition theories and models. 4. Determine habitat selection by waterfowl forced to renest, inasmuch as a significant proportion of annual recruitment may result from renesting females. 5. Determine the effect of different densities and communities of predators on waterfowl habitat selection. 6. Determine the influences on habitat selection of different factors such as: wetland size, density, and productivity; pertinent habitat cues; population density; competition; predation; philopatry; time lags related to site tenacity; previous reproductive success; water quality; and temporal and spatial variation in environmental resources (e.g., Wiens 1985:245). 7. Invoke hierarchical approaches in studies of habitat selection by individuals (Wiens 1985) to obtain data on individuals' habitat use throughout their annual cycle for incorporation into population models (e.g., Cowardin et al. 1988). 8. Relate long-term changes in wetland and upland composition to corresponding changes in waterfowl recruitment. 9. Determine the effect of variation and loss in availability of intermittently, temporarily, and seasonally flooded wetlands on waterfowl habitat selection, dispersal and emigration, and recruitment.

BREEDING HABITATS OF NEARCTIC WATERFOWL 10. Determine the effect of habitat fragmentation on waterfowl habitat selection and community organization and explore opportunities for tests of island biogeography theory (e.g., Weller 1980). 11. Determine habitat selection, survival, and recruitment of breeding females in response to conservation-farming practices (e.g., Cowan 1982, Clay and Nelson 1986, Neckles et al. 1985). 12. Evaluate waterfowl habitat selection and recruitment in relation to public and private lands restoration (e.g., North American Waterfowl Management Plan). 13. Continue research on the effects of herbicides, pesticides, contaminants, and acid precipitation on wetland systems and associated flora and fauna, and determine their effects on waterfowl recruitment. 14. Determine habitat selection by important species in areas not yet modified or degraded by human activities, so that critical habitats can be identified and preserved in advance of environmental impacts. 15. Determine habitat selection by prebreeding waterfowl during migration and before nesting. 16. Determine critical habitats and understand basic habitat affinities of all major, threatened, and endangered waterfowl of the world. Efforts should be increased to preserve, enhance, and restore waterfowl habitats worldwide, ensuring that breeding habitats contain the basic components already listed. Important waterfowl habitats of the world must be identified and critical ones conserved, as is planned in North America through the North American Waterfowl Management Plan (Chandler 1988). The Plan is particularly attractive because it incorporates public and private initiatives to conserve habitat for waterfowl and other wildlife. But it still is to be funded fully, executed, and evaluated on a continental basis to fulfill its objectives and goals. Moreover, agricultural and other human-induced impacts on private lands throughout the flyways must be reduced by providing worthwhile incentives for landowners. Finally, an uncontrollable element pending success of the Plan is disappearance of drought from the prairie-pothole region of North America. Our hope is that nature and humans will complement the Plan toward a thriving and ever harvestable waterfowl resource.

Acknowledgments Our completion of this chapter was invaluably aided by several individuals. Lindy Neely Garner, Shannon Garner, and David Richardson assisted with either literature searching or proofreading. After the literature was reviewed, Bruce Batt, Douglas Johnson, John Kadlec, and

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John Ratti edited various drafts of the text. We are extremely grateful to Cindy Wasson, who expertly typed and proofread each version of the manuscript. Last but very important, R. Kaminski lovingly thanks his family members, Loretta, Shannon, and Matthew, for patiently and understandingly bearing his long weekend absences during the extended writing phase.

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Weller, M. W. (1979). Density and habitat relationships of blue-winged teal nesting in northwestern Iowa. /. Wildl. Manage. 43, 367-374. Weller, M. W. (1980). "The island waterfowl." Iowa State Univ. Press, Ames. Weller, M. W. (1981). "Freshwater marshes, ecology and wildlife management." Univ. Minn. Press, Minneapolis. Weller, M. W, ed. (1988). "Waterfowl in winter." Univ. Minn. Press, Minneapolis. Weller, M. W, and Fredrickson, L. H. (1973). Avian ecology of a managed glacial marsh. Living Bird 12, 269-291. Weller, M. W, and Spatcher, C. S. (1965). Role of habitat in the distribution and abundance of marsh birds. Iowa State Univ. Agric. and Home Econ. Exp. Stn. Rep. No. 43, 1-31. Weller, M. W, Trauger, D. L., and Krapu, G. L. (1969). Breeding birds of the West Mirage Islands, Great Slave Lake, N.W.T. Can.-Field Nat. 83, 344-360. Whitman, W. R. (1976). Impoundments for waterfowl. Can. Wildl. Serv. Occas. Paper No. 22, 1-21. Wiegand, J. P., Pollock, M. J., and Petrides, G. A. (1968). Some aspects of reproduction of captive Canada geese. /. Wildl. Manage. 32, 894905. Wiens, J. A. (1973). Patterns and process in grassland bird communities. Ecol. Monogr. 43, 237-270. Wiens, J. A. (1976). Population responses to patchy environments. Ann. Rev. Ecol. Syst. 7, 81-120. Wiens, J. A. (1977). On competition and variable environments. Am. Sci. 65, 590-597. Wiens, J. A. (1985). Habitat selection in variable environments: shrub-steppe birds. In "Habitat selection in birds" (M. L. Cody, ed.), pp. 227-251. Academic Press, Orlando, Fl. Will, G. C., and Crawford, G. L. (1970). Elevated and floating nest structure for Canada geese. /. Wildl. Manage. 34, 583-586. Williams, C. S., and Marshall, W. H. (1937). Goose nesting studies on Bear River Migratory Refuge./. Wildl. Manage. 1, 77-86. Williams, C. S., and Marshall, W. H. (1938). Evaluation of nesting cover for waterfowl on Bear River Refuge. Trans. N. Am. Wildl. Conf. 3, 640-646. Williams, C. S., and Sooter, C. A. (1940). Canada goose habitats in Utah and Oregon. Trans. N. Am. Wildl. Conf. 5, 383-387. Williams, C. S., and Nelson, M. C. (1943). Canada goose nests and eggs. Auk 60, 341-345. Wingfield, B., and Low, J. B. (1954). Waterfowl productivity in Knudson Marsh, Salt Lake Valley, Utah. Proc. Ann. Conf. Western Assn. St. Game Fish Comm. 33, 177-181. Wishart, R. A., Herzog, P. W, Caldwell, P. J., and Macaulay, A. J. (1983). Waterfowl use of Ducks Unlimited projects across Canada. In "First west, hemisphere waterfowl and waterbird symposium" (H. Boyd, ed.), pp. 24-32. Supply and Services Canada, Ottawa, Ont. Wood, C. C. (1986). Dispersion of common merganser (Mergus merganser) breeding pairs in relation to the availability of juvenile Pacific salmon in Vancouver Island streams. Can. J. Zoo/. 64, 756-765. Woodin, M. C. (1987). "Wetland selection and foraging ecology of breeding diving ducks." Univ. of Minnesota, Minneapolis. Yocom, C. F. (1952). Techniques used to increase nesting of Canada geese. /. Wildl. Manage. 16, 425-428. Young, A. D., and Titman, R. D. (1986). Costs and benefits to redbreasted mergansers nesting in tern and gull colonies. Can. J. Zoo/. 64,2339-2343. Zicus, M. C., and Hennes, S. K. (1987). Use of nest boxes to monitor cavity-nesting waterfowl populations. Wildl. Soc. Bull. 15, 525-532. Zwank, P. J., and McKenzie, P. M. (1988). Fulvous whistling-duck abundance and habitat use in southwestern Louisiana. Wilson Bull. 100, 488-494.

CHAPTER

18

Habitat Management for Breeding Areas John A. Kadlec and Loren M. Smith

I. Introduction

management and then consider methods of implementing those principles.

The habitats used by waterfowl for breeding activities are very diverse, ranging from southern coastal marshes to arctic tundra, to rocky islands off the New England coast, to desert spring marshes in the Great Basin, and to the extensive prairie pothole region. The habitat needs of waterfowl also vary widely with both species and stage of the breeding cycle. We must concern ourselves, for example, with wintering grounds, where pair formation occurs in many species. At the other end of the breeding season, the females of some species are still molting or recovering from the physiological demands of breeding in September and October. We must be cognizant of energy and nutritional needs, especially of key stress periods such as egg-laying. Nesting cover is a vital component of actual breeding habitats. What are the optimal habitat configurations for the many activities and behavioral needs, for example, spacing mechanisms such as territoriality? How can management provide these requirements ? It is not possible to cover the entire habitat spectrum in detail. Therefore, we emphasize habitat management in midcontinent North America, a major breeding area with an extensive data base. We also discuss other regions as appropriate and where particularly good studies are available. Habitat management is always site-specific; that is, no two management situations are likely to be identical. As a consequence, a general consideration of habitat management such as this cannot give "recipes" that will always work. Good habitat management requires a manager who recognizes the seasonal needs of the birds, knows the ecology of local marsh ecosystems and adjacent uplands, and then applies appropriate principles to develop methods suitable for the local situation. We will outline the important ecological principles of habitat

II. Principles A. From the Birds' Perspective Principles of habitat management for breeding waterfowl derive both from species' needs and from the ecology of their habitats. In essence, much of this volume is devoted to understanding breeding waterfowl and their habitat requirements. Here we review briefly the major ideas relevant to habitat management. Habitat selection is the behavioral mechanism by which species meet resource needs within available habitats. We use the term resource very broadly, to encompass, for example, such things as reduced predation pressure. The population densities we observe are partly the result of the habitat selection process. They also reflect many other factors, including relative availability of habitats and local, regional, or even continental population levels. Usually selection or preference is inferred by comparing use to availability. Preference is assumed to reflect habitat quality. The habitats of breeding waterfowl must provide 1) nesting sites, 2) nutritional needs, 3) behavioral requirements such as visual isolation, and 4) cover in proper configurations to avoid or reduce predation. In general, a single vegetation type is not likely to provide all these requirements. Consequently, it is important to consider the complex of open water, wetland, and upland when considering the quality of habitat for breeding waterfowl. Food quality and quantity are important elements in waterfowl breeding biology. Different groups of waterfowl differ widely in feeding behavior and diet, and individual birds shift diets within the breeding season to meet chang590

HABITAT MANAGEMENT FOR BREEDING AREAS ing nutritional needs (for details, see chapters 1 and 2 of this volume). Two periods in the breeding cycle of most ducks are noted for special nutritional needs: egg-laying and growth of newly hatched young. In both cases, diets have often been found to be predominantly high-protein animal food, such as invertebrates. Most geese (Anserini) utilize high-protein plant parts. Egg-laying females also have high energy and calcium requirements (see chapters 1 and 2). Nutritional needs may in fact control the timing and success of reproduction. The goal for habitat managers is to provide appropriate food resources at the correct time to allow waterfowl to meet their requirements. Cover resources serve several functions, including nest sites, predator avoidance, visual isolation from conspecifics, and shelter from weather. The size and arrangement of patches of cover and water are important aspects of habitat for many species of ducks. Waterfowl nest in three basic situations: on dry land, in emergent vegetation over water, and in cavities in trees or in the ground (see chapter 3 of this volume). Obviously, management techniques to provide suitable nesting cover are very different for each of these situations. Considerations of quality and quantity of nesting cover are important, especially with respect to predation on upland and over-water nesting species. Protective cover is especially important for prefledging young and for flightless adults during the postbreeding period. Again, different groups or species have different needs. Most dabbling ducks (Anatini) prefer dense emergent cover, whereas males of many species of diving ducks (Aythyini) prefer the security of large expanses of open water (Bergman 1973; see also chapter 5 of this volume). Cover as shelter from weather in general has received little attention and may not be important, except perhaps in the case of prefledging young. However, as an example of the potential effect of weather, Smith and Webster (1955) present a dramatic account of the impact of hailstorms in Alberta. Most waterfowl seek small water areas or lee shores in stormy weather, especially during high winds. Consequently, pattern of water and land or emergents again becomes important. The importance of water as a component of habitat for breeding waterfowl is obvious. In most breeding areas, however, water levels are not static, and the timing and success of reproduction sometimes depend on the time and extent of water level change. Water quality can also be important, especially in terms of salinity (e.g., Swanson et al. 1984) and pollutants such as pesticides and herbicides (e.g., Hanson 1952, Fleming et al. 1983, Grue et al. 1986). Spatial patterns of water, emergent cover, and upland are dynamic; for example, ephemeral spring ponds dry up in summer but serve an important need when present. Therefore, habitats for waterfowl are variable in space and time. Many features of waterfowl breeding

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biology are best understood in terms of this changing "big picture" of their environmental resources. Thus, we should not lose sight of the complex of habitat needs by focusing too narrowly on meeting specific requirements, such as safe nest sites, in management programs.

B. Wetland Ecology 1. Succession Succession was traditionally a basic concept of wetland ecology, extending as well to uplands (Mitsch and Gosselink 1986). It was considered a fundamental concept of ecology for waterfowl habitat management until relatively recently (e.g., Jahn and Moyle 1964). Clements (1916) observed a zonation around shallow ponds from submersed plants in the deepest parts to floating-leaf species to emergent to wet meadow to shrub to tree plant communities as the water grew shallower and finally dry land was reached. He assumed this zonation also reflected a sequence in time and called the series of plant communities the hydrosere. Many writers (e.g., Beule 1979) talk about modifying plant succession as the guiding principle in marsh management. In recent years, however, a different set of principles has emerged, which we believe is more useful because it directs attention to basic ecological processes operating on shorter time scales more compatible with management operations. The conceptual base that appears to be replacing succession in current thinking about wetland vegetation change is a modern version of Gleason's (1917) views. As updated by van der Valk (1981), this approach considers wetland vegetation species by species, relating each plant life history to patterns of change in the environment. As an example, van der Valk considered plant reproductive patterns in relation to a cyclic pattern of drought and wet years in the prairie pothole region. He termed the water level changes an "environmental sieve" that screened out plants whose life histories were not compatible with the water regime. According to this concept, viable seeds buried in the bottom sediment, the seed bank, are an important component of marsh biota. The potential of this seed bank is expressed only when the environmental sieve permits. For example, seeds of cattail (Typha latifolia; plant names follow Cronquist et al. 1977) are usually present in bottom muds, but they do not germinate in shade or in deep water. Consequently, large-scale reestablishment of cattail by seed germination usually occurs when bare mud flats are exposed by receding water levels. Van der Valk's approach focuses on specific factors controlling vegetation change, which often are those controllable by the marsh manager. It requires specific knowledge about plant life histories and local seed banks but appears to have the potential to make specific predictions about vegetation change at a given site. In

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contrast, the general concept of succession has almost no predictive ability with respect to a particular plot of ground (MacMahon 1980). Van der Valk's (1981) conceptual approach is likely to be modified as we gain more experience with it. For example, we (Smith and Kadlec 1983, 1985a) found that in Great Salt Lake marshes, the environmental sieve probably should be modified to include salinity and light as major factors controlling plant establishment.

2. Water Regime Water regime is considered the dominant factor controlling wetland ecosystem structure and function (Mitsch and Gosselink 1986). Water regime includes both the timing and amplitude of water level change as well as sources and rates of water flow through the system. For example, the vegetation patterns and low productivity of peatlands are best understood in terms of the balance between rainfall and groundwater as sources of water and nutrients (Heinselman 1970). In tidal marshes, the frequency, depth, and salinity of flooding are of key importance in understanding plant species distributions and productivity (Gosselink 1984, Zedler et al. 1986). In the prairie potholes, the pattern of drought leading to drying of pond bottoms followed by reflooding in wet years seems to be the key to understanding vegetation dynamics and productivity (van der Valk and Davis 1978). Most highly productive waterfowl habitats are characterized by fluctuating water levels or other periodic disturbances such as fire (Weller 1979). In some cases, the short-term effects may seem disastrous —for example, drought in the prairie pothole region. However, periodic disturbance is a key to long-term productivity in most marsh ecosystems (Smith and Kadlec 1986). For example, the continued existence, as well as productivity, of the prairie potholes more than 10,000 years after their formation (McAndrews et al. 1967) may be the result of the alternate wet-dry cycle. In contrast, conventional succession theory leads to the prediction that these shallow ponds should have long since been filled in and become part of the prairie. The details of timing and pattern of water level change and water flushing rates and how they relate to wetland vegetation patterns and productivity are beyond the scope of this chapter. Suffice it to say that these are, at a minimum, regionally different and often are sitespecific. We will discuss some of the major variants when we discuss water level control as a management technique.

3. Hemi-marsh A major idea relating midcontinent prairie wetlands to waterfowl breeding ecology is the hemi-marsh concept (Weller and Spatcher 1965). This idea is based on the

observation that prairie marshes have the greatest abundance and diversity of breeding birds when emergent cover and open water occur in about equal portions. The concept has been supported by experiments (Kaminski and Prince 1981, Murkin et al. 1982) showing that 50:50 cover-water ratios were more attractive than 25:75 or 75:25 for breeding pairs of some Anatini. The exact causes of this phenomenon are uncertain but may include increased production of invertebrates as a food resource (Kaminski and Prince 1981, Nelson and Kadlec 1984), increased visual isolation (Murkin et al. 1982; see also chapter 17 of this volume), or simply closer proximity of food and cover resources. Size alone of these wetlands also influences abundance and diversity of marsh birds (Brown and Dinsmore 1986). Weller (1978) reviewed evidence that edge is the factor of basic importance in the hemi-marsh concept. The idea of hemi-marsh probably is most applicable during the portion of the breeding cycle when birds are dispersed (see chapter 8 of this volume) or need food resources adjacent to emergent cover, such as during brood-rearing. It would seem less applicable during periods when waterfowl congregate in postfledging or molting flocks or for species for which emergent cover is less important, such as the geese (Anserini).

4. Invertebrates The importance of invertebrate food resources for many species of breeding waterfowl has received increasing emphasis in recent years (Swanson and Bartonek 1970). The importance of invertebrates was recognized by some early workers in spite of a lack of literature, for Kadlec (1962) incorporated invertebrate and food habits sampling of breeding birds in a study of habitat management in the late 1950s. However, our knowledge of invertebrates in many kinds of wetlands is meager (Murkin and Batt 1987), and we are just now developing a body of ideas and data that will help us understand this important part of wetland ecology and management. Nelson and Kadlec (1984) suggested that high levels of invertebrate production in prairie potholes are dependent on high levels of primary production, probably both algae and macrophytes; sheltered water, minimizing wave action and turbidity; a structured environment providing large underwater surface areas, fostering periphyton and diverse invertebrate assemblages; and warm water with adequate dissolved oxygen. Thus, dense stands of emergents are not likely to have large invertebrate populations in midsummer, as documented by Murkin (1983), because of lack of oxygen and periphyton. Similarly, large open water areas without submersed macrophytes have fewer invertebrates because of lack of structure, physical action of waves that cause shifting bottom sediments and turbidity, and low production of algae. Invertebrates are likely to be abundant

HABITAT MANAGEMENT FOR BREEDING AREAS in early spring in beds of emergents (Murkin 1983) and later in summer in beds of submersed plants (Krull 1970, Murkin 1983). Patterns of water level change may modify these relationships; for example, overwinter drawdown, either natural or deliberate, may seriously reduce the spring peak of invertebrates (Huener 1984). 5. Vertebrates and Plant Structure Vertebrates can have a significant impact on wetland vegetation dynamics (e.g., Jeffries et al. 1979, Smith and Kadlec 1985b). Geese and muskrats (Ondatra zibethicus) have been shown to affect primary production (Smith and Kadlec 1985c) and therefore ultimately plant structure, nutrient flows, and invertebrate production. Muskrats are thought to affect plant production (although this has not been quantified) and structure in prairie potholes (van der Valk and Davis 1978), helping drive the hemi-marsh cycle. The effects these vertebrates have on plant structure probably affect both wetland use by marsh birds and invertebrate production (see above). 6. Predation The interrelationships among breeding waterfowl, habitat, and predation are indeed complex (see chapter 12 of this volume). Current concerns center on the apparent importance of nest predation in reduced recruitment of some species of upland nesting ducks (e.g., Cowardin et al. 1985). Evidence from the studies of Duebbert and Kantrud (1974) and Livezey (1981) suggests that provision of dense upland nesting cover can substantially increase nest success even without predator control. Alternatively, small patches or linear strips of dense nesting cover along dikes or roads may lure ducks to nest in areas where they are more vulnerable to predation because some predators more easily search such places (e.g., Haensly et al. 1987 for pheasants [Phasianus colchicus]). Although we believe there is much yet to be learned about the interactions of predators, prey, and cover, it is clear that predation should be an important consideration in habitat management for breeding waterfowl.

C. The Management Process Before we proceed to a detailed discussion of management problems and techniques, we need to consider the management decision process. Although there are variations depending on the specific organization or landowner, certain basic elements are common to all management decision making and actions. First, and perhaps most important, the objectives for management must be specified. If the wetland or adjacent upland is privately owned, quite clearly it is the owner's prerogative to choose the objectives. In the case of publicly owned areas, objectives are usually specified broadly by legislative or administrative policy, but there may be

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some flexibility in defining goals for specific areas. The objectives should specify what goals are to be sought in managing a given area. Is the manager to attempt to maximize production of waterfowl? Is some hunting, bird-watching, or other recreational use important? Are . nonwildlife uses important —for example, hay production? Unless these and similar questions are asked, answered, and made part of the objectives, one can neither design a management plan nor evaluate its results efficiently. The second step in management usually involves inventory or assessment of the status of the habitat. This can be as simple as getting an opinion from an experienced person or can involve mapping, surveying of populations, and the use of formalized evaluation procedures (e.g., U.S. Fish and Wildlife Service 1976, Adamus and Stockwell 1983). Obviously, the particulars of ownership, size, and sociopolitical status will determine the level of effort in this step. In the end, however, there must be some judgment or measure of how well the area is meeting the objectives and what the deficiencies, if any, may be. The next step is to select the management actions that will lead to progress toward the objectives. Such decisions usually involve at least two elements: the probability of success of the proposed action, and the cost of the action. In a simple case, a landowner-manager may have enough experience to be confident that a particular technique is worth the cost. As the scale of the decision increases in dollar cost, environmental consequences, or uncertainty about results, the decision process becomes more difficult. For example, it is not easy for a private landowner to decide to borrow a substantial amount of money to pay for management with an uncertain outcome. Although little used in waterfowl management, there is an array of techniques, commonly used in business, to help make such decisions (Halter and Dean 1971). Finally, we should not exclude from these considerations situations where the appropriate remedy is some governmental action. Habitat management is basically a land-use issue. Decision making at this level is by way of the political processes of the various levels of government. Once the decision has been made to use certain habitat management techniques, two steps remain. First, the action must be implemented. Rarely are these procedures so routine that application is "cookbook." While knowledge of the fundamentals of wetland ecosystem dynamics is vital, this has to be applied on a case-bycase basis. In most situations, local experience is as important as formal training. Finally, the results of the management action must be evaluated. Has the action resulted in progress toward the objectives? What went wrong? What went right? How much did it cost? Implicit in the need for evalua-

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tion is the desirability of making the results known to aid others who might want to use —or avoid using—the technique. This in turn requires some level of formalized data acquisition, analysis, and publication to allow others to understand the evaluation. We believe this kind of evaluation "research" is widely neglected in resource management.

III. Wetland Management We consider two broad categories of wetlands, defined on the basis of management opportunity. In the first category are those wetlands where intensive management is possible and, depending on the owner, cost-benefit considerations are appropriate. Many of the techniques of wetland management we will discuss below apply primarily to such areas. However, intensively managed wetlands will probably always be a small fraction of the total breeding habitat of waterfowl. The second category is all the diverse wetlands for which most management is likely to be indirect. By indirect, we mean those general land-use controls, policies, and economic incentives that affect the quality of habitat, frequently of whole regions. In many cases these indirect management measures are actions taken by some governmental body, such as regulations or laws. An obvious example might be a law prohibiting wetland drainage. Conceivably, such a wetland "management" procedure could have more impact on breeding waterfowl than all the intensive management of all the refuges combined! The kinds of problems that management can attempt to solve are generally different in these two categories of wetlands, although there is some overlap. Intensive management is usually directed at local ecological problems: patterns of water and cover, water regime, salinity, etc. Extensive management is more likely to be concerned with issues such as preservation, major water diversions, drainage, economic development policies, and pesticides. Both may be concerned with similar issues, such as water quality, pollution, and siltation, but the methods by which they approach these problems will be quite different. In spite of the importance of indirect management, we will not treat the topic in detail. Indirect management is a product of political processes (taken broadly) that are too complex to be analyzed in detail in this chapter. Consequently, we emphasize intensive techniques in the remainder of this chapter. The problems that might confront a wetland manager concerned with intensive management are usually variations of a few themes. A common management problem is either too much or too little emergent cover, or a poor distribution. Consequently, many marsh management techniques are concerned with altering the amount

or distribution of emergents. For a variety of reasons, some wetlands apparently do not produce adequate animal or plant food and therefore do not support desired levels of waterfowl reproduction. The reasons range from low supplies of basic plant nutrients such as nitrogen and phosphorus to excessive salts in some closed inland basin ponds. Hydrology and water quality are the basic determinants of wetland type (Kadlec 1987). The control or management of water supply rates, depths, and quality is critical to wetland management. Frequently the first and most important step in marsh management is to institute some method of water control. Water quality problems include siltation and pollution, which includes both toxicants and excess nutrient inputs. Wetland water quality issues are often different from those of lakes and streams. Pristine natural wetlands often would not meet the criteria considered important in other surface waters. For example, dissolved oxygen levels in some natural wetlands frequently fall below minimal acceptable levels for lakes and streams. In general, both intensive and extensive management attempt to minimize inputs of pollutants and silt to wetlands. In some cases, however, that may not be necessary. Silt introduced by annual flooding of bottomland hardwoods may be vital to maintaining the productivity of that system. Also, silt supplies and flooding may be critical to the high levels of waterfowl production on the deltas of some large northern rivers (e.g., Dirschl 1972, Gill 1973). In nutrient-poor habitats, adding secondary sewage effluent, rich in nitrogen and phosphorus, has actually been observed to improve waterfowl habitat (R. H. Kadlec, pers. comm.). Consequently, it is probably not wise to automatically condemn all silt and pollutant inputs to wetlands. Toxicants include three general categories of compounds: pesticides, herbicides, and heavy metals. Pesticide problems occur on two levels: 1) direct application to wetlands, either deliberately (e.g., mosquito control) or by drift from agricultural field spraying, and 2) general use with widespread residues and accumulation through the food chain, as exemplified by DDT. Direct application is a problem for local management, whereas widespread use requires attack by methods appropriate for extensive management. Herbicides can be a problem if they reach wetlands in sufficient concentration to kill aquatic vegetation. Although some toxicants are immobilized in wetlands, some accumulate via the food chain and are serious problems. The bulk of the information on intensive management techniques is from North America and, more specifically, from the north-central United States. A. Water Level Control Following the great drought of the 1930s, managers

HABITAT MANAGEMENT FOR BREEDING AREAS

Figure 18-1. Alkali bulrush (Scirpus maritimus) sprouting stimulated by a drawdown.

were keenly aware of the need to manage and conserve water, and the construction of dams and dikes was an important part of early management efforts (Day 1949; see also Suring and Knighton 1985 for a review). In the United States, ill-conceived drainage projects in the Great Lake states failed during the drought, the land was acquired by state and federal agencies, and dams and dikes were built to restore former wetlands (Leopold 1931). By the late 1940s and 1950s (Uhler 1944, Hartman 1949), the concept of planned water level changes to accomplish management objectives was gaining acceptance. A common problem was the loss of productivity in impoundments after a peak in about the second or third year of flooding (MacNamara 1957). Temporary drainage, to mimic natural drawdown during dry years, was considered a potential technique for restoring productivity, and a number of studies documented the effects of drawdowns (Kadlec 1962, Harris and Marshall 1963, Burgess 1969, Meeks 1969). The technique was soon incorporated into marsh management manuals (e.g., Linde 1969). Among the postulated benefits of drawdowns were 1) nutrient release due to decomposition of bottom sediment, 2) consolidation of loose sediments due to drying, and 3) germination and establishment of marsh vegetation, especially emergents (Fig. 18-1) and wetland annuals. While all of these effects have been observed, there are also cases where some or all of these benefits have not occurred (Verry 1985, Kadlec 1989). The key for effects 1 and 2, and to some degree 3, seems to be in the physics and chemistry of the sediment and the intensity of drying. The details are beyond the scope of this paper, but in general saline (Smith and Kadlec 1983) or coarse

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sand sediments (Kadlec 1962) are not likely to respond well to drawdowns. Establishment of emergents depends on seed banks, soil moisture, salinity, and time and duration of drawdown (Meeks 1969, Smith and Kadlec 1983, van der Valk et al. 1989). Submersed plants such as sago pondweed (Potamogeton pectinatus] sometimes also grow more densely following drawdown (Bellrose and Low 1978). Relatively little is known about the response of invertebrates to drawdown. Kadlec (1962) observed a detrimental effect on benthic forms immediately following a drawdown. Most aquatic forms are drastically affected by a drawdown itself; however, to the extent that basic productivity and habitat structure for invertebrates are improved, the longer term impact of a drawdown could be more abundant macroinvertebrates (McKnight and Low 1969, Reid 1985, H. R. Murkin, pers. comm.). Drawdowns, then, can increase food and emergent cover for breeding waterfowl. During the drawdown most, if not all, waterfowl breeding is sacrificed. There has been a tendency to maintain constant water levels as deep as possible, perhaps as a holdover from early concerns about drought. Either constant levels or excessively deep water will eliminate most emergents (Uhler 1944, Mathiak 1971, Grace 1985, Murkin and Kadlec 1986, Smith and Kadlec 1986). Consequently, a common problem in early intensive habitat management was a deficiency of emergents (Griffith 1948), which may have limited nesting. More recently, Fefer (1977) suggested that excessive water depths were responsible for decreased nesting of black ducks and ring-necked ducks on wildlife impoundments in Maine. A special problem of water level control occurs in wetlands with high levels of salts in the sediments. During drawdown, evaporative concentration on moist surfaces can result in salt levels in excess of plant tolerances, eliminating germination and establishment of new emergents (Kadlec 1982, Kadlec and Smith 1984). In some cases, salt levels become high enough to kill established cattail (Nelson and Dietz 1966). To establish emergents by drawdown in such marshes, frequent or constant shallow water flushing of the salts is necessary (Nelson 1954). In summary, water level control is a very effective method of controlling the kinds and amounts of vegetation in wetlands. Specific details of techniques vary depending on management objectives, the particular problem to be solved, and the ecology of the individual marsh. Several handbooks are available for guidance (e.g., Atlantic Waterfowl Council 1963, Linde 1969, Rollins 1981). Knighton (1985) has provided detailed guidelines for the use of water level control to manage vegetation in the northern Great Lake states region. However, much remains to be learned about the appli-

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cation of this technique in other regions. If the dams and dikes are in place, it is a very inexpensive technique.

B. Burning Burning in flooded areas is usually restricted to periods of drawdown or drought. Kantrud (1985), in a recent review of the effects of fire on prairie wetlands, concluded that "burning of marsh vegetation releases nutrients, opens the canopy and detrital layer, and allows for increased insolation and resultant earlier warming of bottom soils." While these effects are common, local exceptions probably occur. For example, Smith (1983) found only slight evidence of earlier warming in shallowly flooded bottom soils following a late summer fire, probably due to shading caused by rapid regrowth of emergents. Most studies (e.g., Tester and Marshall 1962, Smith and Kadlec 1985b) find little change in species composition of perennial emergents unless the peat layer is also burned (Beule 1979). However, burning probably retards or prevents the invasion by woody species, such as willows (Salix spp.), into wetland edges. Fall, winter, and spring (prenesting) burning removes the residual cover produced by growth during the preceding summer. This benefits early-breeding ducks only if the cover was too dense for pair or nesting use prior to the fire. Regrowth may be available for later-nesting species or brood use. Earlier warming and the more open aspect of burned marshes might result in higher spring invertebrate production and/or availability (Diiro 1982) and perhaps higher pair use. Unless the fire changes plant species composition, the effects of burning are probably restricted to one growing season or less (Thompson and Shay 1985). Regrowth, probably stimulated by nutrient release or litter removal, resulted in equally or more dense stands by late summer of the season following a fall fire in a Utah marsh (Smith and Kadlec 1985c). Fire in conjunction with reflooding can control emergents. Ball (1985) found that cattail died if burned stalks were flooded to a depth that submerged the stalk stubble. Smith and Kadlec (1985b) found nearly complete mortality of salt grass (Distichlis spicata) following burning and flooding of the stubble to a depth of about 10cm.

C. Muskrats and Beaver Both muskrats and beaver (Castor canadensis) can have major impacts on the quality of habitat for some kinds of breeding waterfowl. Beaver ponds are an important component of breeding habitat for wood ducks, black ducks, and other species (Beard 1953; Coulter and Mendall 1968; Reed 1968, 1975; Renouf 1972; Hepp and Hair 1977; Ringelman and Longcore 1982). The role of

muskrats in opening up dense emergent marshes has long been recognized (Krummes 1940, Errington 1963, Bishop et al. 1979), and their role in the prairie marsh vegetation cycle has been clarified by Weller and Spatcher (1965) and van der Valk and Davis (1978). Although both muskrats and beaver are totally natural "managers" of waterfowl breeding habitat, to use them effectively in intensive management requires careful population control. Both muskrats and beaver have a tendency to overexploit their food resources (Errington 1963, Hill 1982). In the case of muskrats, high populations can lead to destruction of emergent vegetation, called "eat-outs" (Yeager 1964), and a subsequent catastrophic decline in muskrat numbers (e.g., Bishop et al. 1979). Muskrat populations at moderate levels maintain openings and good interspersion in dense emergent cover, thus improving habitat for breeding waterfowl. High numbers can be prevented by spring trapping (Clark 1987), perhaps in combination with water level management, to prolong the period of good emergent cover. The beaver is one of the success stories of wildlife management (Robinson and Bolen 1984), having been brought from very low numbers to present abundance — they are now a nuisance in some areas. In many regions, beaver ponds are again a major component of the wetland habitats available to breeding waterfowl. Beaver abandon colonies and dams when their food supply is exhausted, leading to eventual washout of the dam and loss of the pond. From the viewpoint of breeding waterfowl, high beaver populations mean many ponds and good habitat. In some cases, pond occupancy might be prolonged by carefully regulated beaver trapping (Patric and Webb 1953, Yeager and Rutherford 1957). Cycles of pond abandonment and recolonization may, in fact, maintain higher productivity of the ponds, much as in planned drawdowns and the wet-dry cycle in prairie potholes. Both muskrat (Krummes 1940) and beaver houses or lodges provide "island" nesting sites, which may be locally important. For example, at the Bear Lake National Wildlife Refuge in Idaho, muskrats are completely protected because their houses in dense hardstem bulrush (Scirpus acutus] marsh are important nest sites for Canada geese (J. Deutscher, pers. comm.). Interestingly, complete protection has not led to eat-outs in this marsh, probably due to water level fluctuations and severe winters at the high altitude (1,800 m) of the marsh. In marshes without water level control, management of beaver and, especially, muskrats may be the most important technique available to the manager.

D. Nesting Structures

The classic success story of nesting structures is the wood duck nest box program (e.g., Bellrose and Low

HABITAT MANAGEMENT FOR BREEDING AREAS 1978, McGilvrey 1968). Apparently, this was one of those instances, probably rare, where there was a limiting factor on a population that could be readily addressed by a simple management device. Nevertheless, its significance is questioned and its importance is now low in some areas (Soulliere 1986). Another example of nesting structures is nest baskets (Marcy 1986) used by mallards primarily but also by blue-winged teal, gadwall, northern pintail, redheads, and canvasbacks. Canada geese also use nest platforms (Yoakum and Dasmann 1971) if other good nest sites are scarce. Usage rates of the various kinds of nesting structures have been quite variable (e.g., see summary by Marcy 1986), probably depending on local habitat quality and populations. Common concerns are usurpation by other species, such as starlings and raccoons, and predation. Placing the structures on poles with predator guards over water reduces mammalian predation. Open nest baskets may be vulnerable to avian predation (Marcy 1986). In general, however, nest success in these structures is as high as or higher than in nests in natural sites. In some species, use of nest baskets may be a learned trait, resulting in low occupany rates until a local population accustomed to the structures is built up. For this reason, Marcy (1986) suggested that hunting may need to be curtailed locally to protect the females using the structures.

E. Mowing Mowing during drawdown or on ice is occasionally used in conjunction with water level control to manage emergents such as cattail and bulrush (Scirpus spp.) (e.g., Nelson and Dietz 1966, Beule 1979, Murkin and Ward 1980, Ball 1985, Kaminski et al. 1985, Smith and Kadlec 1985b). Regrowth of the cut plants from belowground rhizomes is usually rapid unless water levels are raised above the stubble. Water over the stubble prevents oxygen from reaching the roots and rhizomes, which then die (Sale and Wetzel 1983). Timing and methods of cutting vary with local circumstances, as do costs. A critical problem in agricultural mowing of wet meadow margins (e.g., whitetop, Scolochloa festucacea) of wetlands is the timing of mowing in relation to waterfowl nesting (Neckles et al. 1985). In areas where water level control is possible, there often is pressure from agricultural interests to lower water levels in early summer to permit substrate drying for access of mowing machinery (J. Deutscher, pers. comm.). Thus, the direct impacts of mowing on breeding waterfowl depend in part on the successful negotiation of waterfowl and agricultural interests. F. Water Quality Problems of water quality for productive breeding

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marshes are often difficult to solve. Some wetlands effectively remove silt and pollutants from surface water (e.g., Richardson and Davis 1987). The sources of the silt or chemicals are usually adjacent uplands or upstream of the affected marsh. The major exception is the direct application of insecticides on marshes, either for mosquito control or incidental to cropland spraying. Efficient management techniques should address the problems at the sources of the pollution through various laws, regulations, and economic incentives, to discourage or prohibit land uses that result in excessive erosion or to regulate pesticide use and water pollution. Persistent pesticides and heavy metals continue to be problems (Fleming et al. 1983). In the United States, the Food Security Act of 1985 contained significant provisions for reducing erosion, but no general assessment of their effectiveness is yet available. The trend toward less tillage in agriculture—for example, no-tillage farming techniques (Cowan 1982) —is encouraging in that erosion should be reduced, resulting in less siltation in marshes (National Research Council 1982). However, these farming methods place increased reliance on chemical weed control. In general, herbicides applied on uplands have not been considered a major problem in management of marshes, although they might have deleterious effects on upland nesting by either modifying the cover or directly affecting egg hatchability. Moreover, more mobile or more potent toxic herbicides developed for minimum-tillage agriculture could become a problem. Some agricultural herbicides are very toxic to submerged aquatic plants and reduce invertebrate populations (e.g., atrazine; Dewey 1986). More widespread use of such chemicals could result in loss of food supplies critical for breeding waterfowl. Toxic chemicals can be a particular problem in marshes fed by water that has been previously used for irrigating agricultural lands. In much of the arid west, water is used and reused many times as it flows from source to final discharge—which may be evaporation! In these cycles of use and reuse, more and more chemicals, both natural and manufactured, are dissolved and concentrated by evaporative water loss. This process can lead to serious problems, as dramatically illustrated by the selenium problem at the Kesterson Refuge in California (Di Silvestro 1985). Marshes, especially artificially made marshes, that rely on such much-used water in desert environments may be very attractive to breeding waterfowl (Piest and Sowls 1985) but may also be "ecological traps" in that the problems outweigh the benefits. A technique that has potential for solving silt and associated pollution problems in some limited circumstances is engineering the water supply system for the marsh to allow settling out or bypassing of silt-laden water. This is often more expensive than conventional

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marsh construction and so has been little used, but in some situations it might be cost-effective. Interestingly, some municipalities and other organizations are now considering the reverse strategy—constructing wetlands to trap silt and pollutants (e.g., Adams and Dove 1984), including polishing treatment of sewage effluent (Wolverton 1987). The value of such wetlands for waterfowl production has not been determined.

objective is to direct shallow sheet flow of water in a sinuous path over the flats, thereby producing conditions suitable for establishment of emergents (Fig. 18-2). Costs are relatively low compared to other mechanical development techniques, and the results are dramatic, converting salt flats to productive wetlands with minimal water supplies.

G. Herbicides

The common carp (Cyprinus carpio) is usually considered a nuisance in marshes managed for waterfowl (Cahoon 1953, Robel 1961, Crivelli 1983). Carp increase turbidity, and their feeding activities may uproot submersed plants. Reducing or eliminating carp (Fig. 18-3) leads to clearer water and increased submersed plant growth. Breeding ducks frequently increase, apparently attracted by increased food resources, especially invertebrates (Huener 1984). In northern regions, winter drawdown may reduce carp by limiting below-ice water volumes and creating anoxic conditions and winterkill (J. Deutscher, pers. comm.). However, this practice may have detrimental effects on invertebrates (Huener 1984). The most common technique for eliminating carp is poisoning with rotenone. Where possible, a partial drawdown to concentrate the carp and reduce water volume to be treated, and hence cost, makes the treatment more efficient. In Utah, a brief drawdown in early spring for treatment, followed by rapid reflooding, seems not to interfere with waterfowl nesting. A major deterrent to carp control is the rapidity of repopulation unless routes for reinvasion are restricted or blocked. Relatively few managed marshes are managed to prevent or restrict carp access. Carp, at least the larger mature fish, can be excluded by appropriate screens at inlets and outlets, but designs for screens that do not get plugged by debris are far from perfected (R. Perry, Bear River Migratory Bird Refuge, pers. comm.).

The use of chemicals to modify wetland habitat has not received much attention in recent years, apparently due to increasing concern about indirect effects (Linde 1985). Nevertheless, some of the common agricultural chemicals (e.g., 2,4-D, glyphosate, dalapon, simazine, atrazine, and picloram) can be used to create openings in extensive stands of dense emergents (Linde 1969, 1985; Beule 1979) and cause other vegetation changes (Rollings and Warden 1964). Chemical control is also possible for submersed plants such as milfoil (Myriophyllum spp.) (Brooker and Edwards 1973), but in general there would seem to be little benefit for breeding waterfowl in such management. Submersed plants are important as food resources, either directly or indirectly as habitat for invertebrates. While some species of submersed plants may be more desirable than others, chemical control is usually nonselective and rarely results in species change. Therefore, it is better to maintain a dense stand of any submersed plants than to have none at all.

H. Earth Moving Draglines, bulldozers, other heavy equipment, and explosives have been used to alter wetland bottom topography and thereby affect patterns of open water and cover (e.g., Scott and Dever 1940, Provost 1948, Mathiak and Linde 1956, Mathisen et al. 1964, Hopper 1978, Kadlec and Smith 1984). Commonly these take the form of level ditches and potholes with associated spoil banks. These are techniques to improve the mixture of open water and cover to increase breeding populations of waterfowl, especially dabbling ducks. The techniques are expensive, and cost-benefit analyses have frequently been reported (e.g., Mathiak and Linde 1956 for muskrats, Hopper 1972 and Lokemoen 1984 for waterfowl). Descriptions of construction techniques are available in marsh management manuals (e.g., Linde 1969). A variation of this approach has been used in very low-gradient salt flats around Great Salt Lake (Kadlec and Smith 1984). The technique, called contour furrowing, involves the use of road graders or similar equipment during drawdown to create low ridges and associated furrows following topographic contours. The

I. Carp Control

J. Seeding and Planting Artificial establishment of desired plant species was widely attempted during the early phases of habitat development (Kadlec and Wentz 1974). Many of these plantings failed, and the philosophy gradually evolved that if the proper site conditions were provided, the desired plants would invade naturally. Consequently, seeding and planting efforts were reduced or terminated. Recently, seed bank studies (Smith 1983, Kadlec and Smith 1984, Pederson and van der Valk 1984) have suggested that sources of seeds in some areas in some marshes may be limited. Thus, supplying seed may materially speed up the process of establishing desired vegetation, especially emergents, in intensively managed marshes.

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Figure 18-2. Contour furrows at the Bear River Migratory Bird Refuge, Utah. The low ridges direct the sheet flow of water, 5-10 cm deep, over extensive saline flats.

Figure 18-3. Carp control can be an important intensive management technique. The carp harvested here went to a pet food manufacturer.

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Under adverse circumstances, and where high labor costs can be justified, transplanting of blocks of sediment containing rootstocks of emergents may be necessary for establishment. These plants then spread vegetatively, if the site is suitable, to provide emergent cover where otherwise none might exist.

IV. Upland Management The uplands associated with wetlands are as diverse as the wetlands themselves; from croplands to prairie to forest to tundra. It is difficult to separate management of uplands from that of wetlands, especially given the fluctuating water levels in many types of wetlands. Therefore, we will arbitrarily discuss those plant communities having upland life history characteristics or those species living on exposed soils most of the year. We will also focus on management from arrival on nesting areas through brood-rearing. Most upland management strategies for breeding waterfowl center on nesting habitat, although a few strategies exist for upland brood sites and feeding areas for geese. Typically, upland habitat management plans are evaluated in terms of waterfowl nesting success or preference. The plant communities and their structure affect nest success and may also influence the composition of the predator community. For example, Greenwood et al. (1987) found that nest success was correlated with the amount of grass available on their study areas in prairie Canada. They noted that large contiguous blocks of native prairie were important nesting areas. These areas not only allowed waterfowl to space nests widely, reducing predator detection, but also may have had less detrimental predator communities. Once a particular habitat type is found to be successful (i.e., relatively high nest success, high waterfowl preference), a management scheme is designed to promote that particular habitat.

A. Fire One of the common upland management methods is fire. Fire was a naturally occurring disturbance on the prairie grasslands of the Great Plains (Wright and Bailey 1982). Such grassland is an important nesting substrate for the dabbling ducks in the prairie pothole region (Greenwood et al. 1987). A natural prairie fire frequency of 5-10 years has been proposed as reasonable (Wright and Bailey 1982). Most fires were caused by lightning and humans. As the Great Plains were settled and subsequently cultivated, prairie fires were suppressed and woody vegetation became more prevalent. Although fire can suppress woody vegetation, climate is thought to be a dominant factor in the maintenance of North American grasslands (Bragg and Hulbert 1976, Wright and Bailey 1982, Higgins 1986). In a management sense, however, Kirsch and

Kruse (1973:293) noted that "fire suppression and the absence of deliberate use of fire to control vegetational succession has done untold damage to prairie wildlife." Fire not only suppresses brush expansion but also prevents cool-season exotic grasses such as smooth brome (Bromus inermis] and Kentucky bluegrass (Poa pratensis) from becoming established. Where short (< 1 m) vegetation is present, the manager may want to suppress fire. Fire is used in nesting cover management to improve the structure and diversity of upland vegetation. Kirsch and Kruse (1973) found an increase in the diversity of herbaceous plant species as well as in the number of nesting avian species on previously burned sites. They also found that nest success was greater on the previously burned sites than on unburned sites and concluded that fire was an important tool for management of prairie wildlife habitat. Fire has also been found to produce desirable habitat characteristics in parkland (Wright and Bailey 1982). In addition, Linde (1969) noted that the species composition and structure of vegetation on waterfowl management areas in Wisconsin could be improved with prescribed burning, especially by controlling encroachment of tall, woody species like willow. Whether fire can be used successfully to benefit management of uplands for waterfowl depends on many factors, but two factors, previous range condition (fuel load, grazing history, etc.) and season of burning, are especially important. Fires should be timed in relation to the period in the life history of waterfowl that the manager is trying to enhance. For example, if a manager is attempting to promote nesting habitat, fires should be conducted in early spring or (the safer option) fall. In early spring, the time available between arrival of nesting waterfowl and suitable weather conditions for burning may be very narrow. In the marshes of the Great Salt Lake, Canada geese begin nesting as early as late February, making spring burns impractical. However, fall burns may not be as effective as spring burns in discouraging cool-season exotic grasses. Where cool-season grasses are a problem, it may be necessary to develop a rotation burning schedule whereby different parcels of habitat are burned in different springs. Most waterfowl species, especially early-nesting species such as mallards, prefer areas with residual cover, and therefore first-year burned sites may be used more frequently by late-nesting species such as blue-winged teal (Fritzell 1975). The length of postfire evaluation is critical in assessing fire effects on upland nesting waterfowl. Although fire on a given site may cause a short-term (1-year) decline in nest production, over longer periods of time (2-5 years) the beneficial effects of fire may become more pronounced. Most studies have evaluated nesting 1 year after fire, but future studies need to analyze nesting and cover for several years following a prescribed burn in or-

HABITAT MANAGEMENT FOR BREEDING AREAS der to realistically evaluate the impacts of fire. Fire frequency should also be taken into account. Areas burned annually are not likely to be very suitable for nesting waterfowl. Prairie fires at a frequency of 5 years are probably much more beneficial. Linde (1969) hypothesized that the nutritive quality of grasses could be improved through use of fire. Smith et al. (1984) found that protein increased in salt grass following a prescribed burn. This has important implications for the management of goose broods that feed in uplands. By providing a higher quality of vegetation for goose broods, recently burned sites might attract geese (Smith et al. 1984). Seed production of upland plant species also may increase following fire (Vogl 1964, Linde 1969). Managers wishing to initiate a prescribed burning program can find prescriptions for a range of environmental conditions in Wright and Bailey (1982).

B. Grazing Grazing and browsing by native and feral herbivores can affect wetland and upland habitat used by waterfowl. The waterfowl species themselves may also influence upland vegetation through herbivory. For example, Harwood (1977) found that snow geese affected production of upland vegetation in the Arctic and that the grazing may help maintain high protein levels in that vegetation. Jefferies et al. (1979) also found that snow geese can affect the plant species composition of arctic vegetation. A degree of controversy has surrounded the use of domestic animals in upland habitat management over the past few decades. In part, this is likely the result of a wide variety of treatments being examined with differing stock densities and grazing periods. Kirsch (1969:827) recommended, after a literature review, that grazing "be discontinued as regular land-use practice(s) on areas managed primarily for upland nesting ducks." However, other studies have found that carefully controlled grazing practices may improve nesting for some species (see review in Holechek et al. 1982). Different waterfowl species show different responses to a variety of grazing management schemes (Flake et al. 1977, Kantrud 1985). Certainly high stocking rates and continuous grazing by livestock are detrimental to nesting waterfowl. Because most waterfowl require residual vegetation for nesting (Kirsch 1969, Jarvis and Harris 1971), grazing systems that promote light stocking rates under a rotational grazing system may not be detrimental. For example, Kaiser et al. (1979) and others found that bluewinged teal nesting increased on grazed uplands. They recommended that grazing be used to reach a particular range condition favoring waterfowl nesting, and they noted that overgrazing as well as excessive rest periods

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might favor bluegrass, which was associated with lower nest densities. Domestic animal grazing of uplands can also affect waterfowl brood use of wetlands. Hudson (1983) noted that "optimum brood densities on stock ponds also are contingent upon proper grazing management and pond maintenance." Manipulating the pattern of shoreline vegetation with livestock affects the subsequent use by waterfowl broods. Rumble and Flake (1983) and Lokemoen (1973) noted that more mallard broods used vegetated than bare shorelines of stock ponds. In general, as with many other management methods, little quantitative research has been conducted on the use of domestic livestock in waterfowl habitat management. Grazing on emergents that are at least seasonally flooded can also be important. These plants include some that are very palatable, such as whitetop (Neckles et al, 1985), and some that livestock seem to avoid, such as hardstem bulrush (Tester and Marshall 1962). Susceptibility to grazing depends in part on growth stage; for example, young green growth of common reed (Pbragmites australis) may be readily grazed, whereas mature or dry stages are avoided (Denny 1985). The extent of grazing may also depend on the firmness of sediments, water depth, and distance from shore, all of which determine the ease of access by livestock (Hilliard 1974). Season and duration of grazing are important. Some Utah marshes, moderately grazed in winter, provide good habitat the following spring and summer. Conversely, even moderate grazing for a few weeks in summer can have devastating effects on some plants such as alkali bulrush (Scirpus maritimus), a preferred cover for redhead nesting in Utah. In general, the literature on grazing (see Kantrud 1985 for a review) seems to indicate that light to moderate grazing of emergents may be beneficial, or at least not harmful, to waterfowl production. Emergent cover of reduced density is apparently more attractive to breeding waterfowl than dense, ungrazed stands. Even heavily grazed areas, if not extensive, may be attractive to some species (e.g., Canada geese), especially in the prenesting stage of the breeding cycle. However, heavy grazing usually reduces emergents to undesirably low levels for nest or brood cover and may even reduce pair use. One method of controlling grazing is to fence wetland areas to exclude livestock (Berg 1956). Livestock tend to congregate around water areas, often destroying wetland vegetation even when overall stocking rates are not excessive. Under such circumstances, it may be desirable to limit the access of livestock to wetland by appropriate fencing. Sometimes the water can be piped from the wetlands to a watering tank, thus diverting livestock from the pond (Bue et al. 1952). Some grazing systems (e.g.,

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rest-rotation, Mundinger 1976) that benefit breeding waterfowl also require fencing to permit control of the livestock grazing duration, intensity, and frequency.

C. Crops and No-Till Agriculture Farming in the uplands of North America has a significant impact on nesting and brood-rearing waterfowl (e.g., Krapu 1977). Wet soils as defined by Diedrick (1981) usually would be included as upland nesting habitat adjacent to wetlands by waterfowl managers. However, wet soils are used in agricultural production and are considered productive and economically profitable (Diedrick 1981) to the agriculture industry. According to Diedrick (1981), 29% of the agricultural lands in the upper midwestern United States are tilled wet soils. Diedrick also noted that artificial drainage of these areas was profitable, in terms of crop income, and that the value of wet soil crops was important to the economy of the region. These economic considerations make it difficult to manage uplands on a regional scale for nesting and brood-rearing waterfowl versus agriculture. The impact of agricultural land modification on breeding waterfowl is generally considered to be negative. For example, Dwyer (1970) and others suggested that the lower nest density in agricultural land versus nonagricultural land was in part related to the amount of cover available to nesting ducks in Manitoba. In contrast, Trauger and Stoudt (1978) did not believe habitat alteration, including intensive agricultural practices, was the major factor responsible for the declines in waterfowl populations. However, Higgins (1977) found that vegetation loss from cultivation was limiting waterfowl production in intensively farmed areas of North Dakota. Recently, Sugden and Beyersbergen (1984) noted that the available upland habitat for nesting ducks was decreasing and that this would favor lower recruitment in local populations. Dabbling ducks commonly nest in crop stubble (e.g., Duebbert and Kantrud 1974, Higgins 1977, Cowan 1982). Most of the reported nesting occurs in cereal grain stubble (e.g., wheat and rye) rather than in row crops (e.g., corn and soybean), partly because cereal grains are currently more common at northern latitudes where ducks nest and have more residual vegetation. The amount of tillage a field receives in the summer following harvest or in the spring before planting can affect use and success of nesting ducks. Cowan (1982) found higher duck nest density and success on "zero-tillage" (seeding into stubble) farms than on farms under conventional management in Manitoba (see also Sugden and Beyersbergen 1985). He also noted that seeding wheat and rye in the fall would eliminate nest destruction that occurred during spring seeding operations. Cowan hypothesized that the higher nest success in both native and crop vegetation within zero-tillage areas ver-

sus conventionally farmed areas was due to nests being more dispersed in zero-tillage areas. Because of the potential economic and conservation-related benefits of minimum tillage to the agricultural industry, this type of farm management holds promise for future waterfowl production (Duebbert and Kantrud 1987). Although several studies on row crops (i.e., corn and soybeans) have documented minimum-tillage effects (e.g., Warburton and Klimstra 1984, Basore et al. 1986) on avian populations in the Midwest, there are few data for row crops where breeding waterfowl exist. Best (1986) recently reviewed the conservation tillage programs for avian species (not including waterfowl) in corn and soybeans and warned of the potential of these sites to serve as "ecological traps" for nesting birds. Minimum-tilled sites may provide suitable nesting cover, but nest disturbance may still be frequent enough to result in low nesting success. Potential also exists for using "lure crops" to attract waterfowl broods, especially geese. Although most "lure crops" are used for migrating and wintering birds, small-grain plantings have been used to attract goose broods, especially Canada geese (V. Bachmann, pers. comm.), as breeding populations become established in more southerly regions. Crops planted near wetlands may also affect brood use of particular wetlands. For example, Rumble and Flake (1983) noted that mallard brood use of stock ponds in western South Dakota was related to the presence of small grain on the surrounding land. However, this may have been related more to increased nesting use than to broods congregating on such ponds.

D. Herbicides Most of the research on use of herbicides in waterfowl management has been conducted on aquatic plants such as cattail. In areas with excessive woody or forb vegetation that limits nest densities and inhibits grass production, herbicides (e.g., tebuthiuron) may be used to promote grasses. Conversely, where dense grass is inhibiting forb communities, herbicides (e.g., atrazine) can be used effectively to promote forbs (Linde 1969). A great deal of information on herbicides exists in the agricultural literature. After determining the desired upland plant community species composition, a waterfowl manager must determine the proper herbicides to apply; this information can be readily obtained from local agricultural agents. Although the information in the agricultural literature on the effects of herbicides on plant communities is extensive, the effects on breeding waterfowl have received much less attention. Cowan (1982), referring to minimum tillage, noted that herbicide application in fields had little effect on waterfowl nests (Donaghy 1973).

HABITAT MANAGEMENT FOR BREEDING AREAS Also, Batt et al. (1980) found that glyphosate, a herbicide commonly used in minimum-tillage cropping in Manitoba, was not toxic to eggs. Wayland et al. (1987) also were unable to demonstrate toxicity of two postemergence herbicides to chicken eggs.

E. Cover Establishment Establishment of upland cover for nesting ducks can increase local waterfowl production through increased nest density and hatching success. On set-aside lands in South Dakota, Duebbert and Lokemoen (1976) found that, in dense nesting cover, waterfowl preferred the undisturbed cover farther from wetlands to disturbed areas that were closer. Nest density and success were much higher in the dense cover than in other areas in the prairie pothole region. The undisturbed dense vegetation was made up of intermediate wheatgrass (Agropyron intermedium), alfalfa, and smooth bromegrass. The higher nest success and egg hatchability in the dense cover were associated with lower predation rates and favorable microclimate. In Wisconsin, Livezey (1981) also found relatively low predation rates in vegetation with tall grass and alfalfa. In both studies, predators, mainly mammalian species, apparently were unable to locate nests as easily in dense cover as in surrounding farmland habitat. Also, the dense vegetation and abundant residual cover provided conditions necessary for good egg hatchability. Few studies have investigated the potential of establishing native grasses as a means of improving waterfowl nesting. In North and South Dakota, Klett et al. (1984) investigated nesting cover where native grasses were either dominant or codominant with introduced grasses and noted that nest success was not different in native prairie or tame grasses and legumes. Native grasses they investigated included switchgrass (Panicum virgatum), little bluestem (Andropogon scoparius), big bluestem (A. gerardii), western wheatgrass (Agropyron smithii), green needlegrass (Stipa viridula), and Indiangrass (Sorghastrum nutans). They noted that in areas that receive less than 50 cm of precipitation, western wheatgrass and green needlegrass could be seeded to produce good waterfowl nesting cover but that the other warmseason native grasses would be difficult to establish. Duebbert et al. (1981) provided guidelines and recommendations for site preparation and planting procedures. George et al. (1979) investigated establishment of switchgrass, Indiangrass, big bluestem, and little bluestem in relationship to upland game nesting and agricultural practices. Their seeding recommendations and management suggestions provide important considerations for waterfowl managers. Grazing of these native grasses in the warm season allowed greater nesting success of upland birds than other tame pastures and hay fields. They also provided recommendations for opti-

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mum nesting in relation to haying and seed harvest and maintenance of native prairie grass cover with prescribed burning.

F. Predator Fences Dense nesting cover has been shown to have lower predation rates than other cover types (see above), and predator control has been shown to increase waterfowl production (e.g., Duebbert and Lokemoen 1980). Recently, habitat management in the form of electric fences has also been shown to decrease predation rates (Lokemoen et al. 1982). Lokemoen et al. (1982) used sevenstrand electric fences in North Dakota and Minnesota to reduce predation on waterfowl nests by mammalian predators. Nest success and production of young were much higher in areas enclosed with electric fence versus unenclosed areas. Costs of producing ducklings using this method were lower than for ducklings produced on artificially created nesting islands.

G. Mowing Mowing or haying can have a dramatic impact on upland-nesting waterfowl depending on the frequency and season of activity. In North and South Dakota, Duebbert and Frank (1984) recommended that mowing of nesting cover be delayed until 21 July, although 1 August would be preferable. They also noted, however, that any mowing activity would affect subsequent nesting activity by affecting residual vegetation. Kirsch (1969) recommended that haying be discontinued on a regular basis on lands managed for upland-nesting ducks. Getting and Cassel (1971) investigated the effects of fall mowing of highway vegetation on subsequent nesting of waterfowl in North Dakota. They found that waterfowl preferred to nest in the unmowed vegetation in the two years following fall mowing. Nest success was also higher in unmowed vegetation. More recently, Voorhees and Cassel (1980) studied mowing in highway rights-of-way and recommended that the mowing and baling of vegetation should be conducted every 3 years on a rotational basis. They found that nest success declined in older vegetation and that mowing was required to maintain vegetative productivity. Neckles et al. (1985) noted that mowing can also be used to improve whitetop production. Removing litter permits light penetration and encourages whitetop growth. Mowing can cause the destruction of upland plant zones that are flooded periodically. For example, if saltgrass, an important upland nesting habitat in the marshes surrounding the Great Salt Lake, is inundated following mowing, the stand is virtually eliminated (Smith and Kadlec 1985b).

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H. Islands For several decades waterfowl biologists have recognized the importance of islands for a variety of waterfowl species during nesting (e.g., Hammond and Mann 1956, Choate 1967, Reed 1968, Linde 1969, McCabe 1979). Birds nesting on islands usually have higher nest density and nest success than their counterparts nesting on the mainland because of lower mammalian predation rates. The distance of the island from the mainland influences whether these predators will be present (e.g., Duebbert 1982). The species and structure of island vegetation can influence avian predators. Gulls (Lams spp.) and Corvids prey less on nests on islands with dense vegetation than on islands with sparse cover (Dietz 1967, Dwernychuk and Boag 1973, Hill 1984). In addition to avian predation problems, nest parasitism can also be high on islands (Giroux 198la), possibly because of the density of hosts. For natural islands, management may best take the form of protection from modification or simply a program to maintain upland vegetation in a productive state, through fire, for example. In general, erosion is not a problem for natural islands (Duebbert 1982), but it can be when water flow increases or the watershed has been modified (McCabe 1979). Recommendations for construction and management of artificial islands are much more extensive. Giroux (198Ib) recommended construction of rectangular islands for a greater perimeter-area ratio than circular or square islands. They also had advantages in ease of construction. He noted that islands should be approximately 0.1 ha in size and should be at least 170 m from the shore to discourage mammalian predators from swimming to them. Islands created within reservoirs were more productive than islands created by cutting off a peninsula. Duebbert (1982) recommended islands of 0.5-5.0 ha for North Dakota because those smaller than 0.5 ha did not have enough area to support high nest densities and those larger than 5.0 ha had resident mammalian predators. Most studies recommend dense vegetation, without trees, for upland cover on islands (Giroux 198la, Duebbert 1982, Duncan 1986). However, Nelson (1985) reviewed nesting island recommendations for prairie Canada and found that some of the commonly proposed guidelines, such as cover quality and distance from shore, were only weakly related to brood production. Rather, Nelson noted that areas with good spring staging populations showed the best use by island-nesting waterfowl and that islands should be placed at least 50 m from shore. Small artificial nesting islands, those just a few meters in diameter, can be established easily as an effective means of improving nesting for waterfowl (Giroux et al. 1983, Higgins 1986). Small islands can be constructed

with a bulldozer on drawn-down surfaces by pushing up old vegetation and sediment. Small islands can also be made in standing water with rock or straw bales. Those constructed from sediment and old vegetation may be short lived due to erosion from wind and wave action and muskrat burrowing activities. Small islands constructed in Great Salt Lake marshes generally persisted for 5-8 years (V. Bachmann, pers. comm.). These islands do not last as long as others; however, construction costs are very low. Higgins (1986) recently reevaluated small islands constructed in North Dakota (Johnson et al. 1978) of rock and a soil covering. After 6 years, islands still had a soil covering with vegetation (Johnson et al. 1978), but after 15 years, almost one-third of them lacked a suitable soil layer (Higgins 1986). Nest success and quality of vegetation also declined over the same period of time. The major cause of island deterioration was erosion through wave action. Small-island longevity, Higgins noted, could be increased by considering wetland size, water levels and fluctuations, watershed size, and island height. Life expectancy of these islands was about 20 years, with a fairly high cost per duckling of approximately $30. Research is needed to compare types of artificial islands (e.g., rock vs. sediment) and the relative cost-benefit ratios.

V. Research Needs Habitat management research can, for convenience, be considered in three categories: 1) the relationship between the birds and the habitat, including, for example, the behavioral mechanisms of habitat selection; 2) techniques for modifying habitats, including cost-benefit analysis; and 3) the whole range of sociopolitical factors and processes involved in preservation, land-use regulations, etc., prominently including the relationships between agriculture and waterfowl production. All of these are complex, and we believe our knowledge of the breeding biology of waterfowl, incomplete though it is, has far outstripped our understanding of the many aspects of habitat management. We are strong advocates of the planned experimental approach to questions of habitat management and marsh ecology (e.g., Batt et al. 1983), but we recognize that such research is often expensive and time-consuming. Nevertheless, experimental research is most likely to yield significant advances in knowledge on bird-habitat relationships (e.g., Murkin et al. 1982). While a similar approach is also desirable for techniques research, we believe that many opportunities for learning from ongoing management are overlooked. In general, the approach in these situations will be in the nature of before and after comparisons. Such comparisons are less powerful ways to knowledge than experi-

HABITAT MANAGEMENT FOR BREEDING AREAS ments but if repeated often enough can build up strong support for concepts and ideas. Often the incremental cost (in excess of management operations cost) of careful before-after documentation is relatively low —in a sense, this is inexpensive research. We reemphasize that to be effective, this approach requires frequent repetition—a single case history is not likely to be reliable. Research in category 3 is probably appropriately called policy and administration studies. Preservation and management of sufficient habitat to meet goals set forth by the North American waterfowl management plan (Canadian Wildlife Service and U.S. Fish and Wildlife Service 1986) will require effective efforts in the social, political, and economic arenas. Surveys and studies are needed to ensure that these efforts are soundly based. Along with a broadly based increase in research in the three categories outlined above, some specific topics have emerged as important.

A. Fire Fire as a habitat management technique is not well understood. Although there have been some good studies, they are scattered and limited in scope. A major research effort is needed to study the effects of fire in an integrated, experimental fashion. Research on fire in wetland ecosystems has lagged far behind our undestanding of fire in terrestrial systems, and a major effort is needed to fill the gap. In particular, most studies have not been sufficiently long to understand fully the responses of waterfowl to fire.

B. Increasing Invertebrate Production We know that invertebrate food supplies are important to breeding waterfowl, but we do not know if increasing invertebrates will increase duck production. If producing more invertebrates turns out to be important, more attention to techniques to increase them will be needed (Reid 1985). For example, in European pond culture of fish, organic matter was sometimes added to the ponds to increase production of invertebrate fish foods, but Andersson and Danell (1982) were unable to duplicate that effort for waterfowl. Several methods of increasing organic input to increase resources for invertebrates can be devised based on the ideas and techniques already discussed.

C. Fertilizing To our knowledge, fertilization has not been done for practical management, although greenhouse and field experiments suggest some wetlands are nutrient-limited (Moreau 1976, Wentz 1976, Cargill and Jefferies 1984). Some herbivorous birds, such as geese (Owen 1975, Owen et al. 1977, Boudewijn 1984, Sedinger and Rav-

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eling 1984), apparently are able to select vegetation higher in nitrogen and water content over vegetation with lower nitrogen and water. These lines of evidence suggest fertilization might be a useful technique. Fertilizing wetlands on a large scale could be difficult because readily soluble nutrients are easily flushed from the wetland if there is any water flow. Experience in wetland rice culture also suggests that it is difficult to increase supplies of nitrogen because of the physics and chemistry of submersed soils (Patrick and Mahapatra 1968). Excessive fertilization, as in wetland discharge of sewage effluent, often creates monocultures of cattail or duckweed (Lemnaceae) (Richardson and Davis 1987). In nutrient-limited wetlands, fertilization might be used to increase wetland productivity and hence waterfowl production. It would be expensive, and to date there are insufficient data to do a cost-benefit analysis. Basically, we have no estimate of how much it might be possible to increase waterfowl production. Carefully designed experiments, with cost data, are needed to evaluate the potential of the technique.

D. Management of Saline Habitats In semiarid and arid regions, depression wetlands often accumulate salts to high levels, not infrequently exceeding seawater in total ionic concentrations. Where fresher water is available to flush away the excess salt, very productive wetlands for breeding waterfowl can be developed (Smith and Kadlec 1986). Because fresh water is always a precious commodity in dry regions, innovative techniques are needed to maximize habitat produced with minimal use of available fresh water. Contour furrowing (Kadlec and Smith 1984) is one such technique developed in the highly productive marshes adjacent to Great Salt Lake. Other approaches are probably possible, but little work has been done to develop new ideas.

E. Waterfowl and Fish Competition for Food Although the importance of invertebrates for food for breeding waterfowl, especially ducks, is widely recognized, the untested assumption is usually that this food supply is not limiting. Yet work by Andersson et al. (1982) has shown that Swedish lakes lacking fish have higher populations of ducks and higher production of fledglings than lakes with fish. Further, Pehrsson (1979) found that ducklings guided by a domestic duck obtained significantly more food in fish-free Swedish lakes than in lakes with fish. There is also evidence of goldeneye and perch (Perca flavescens] competition for invertebrate foods (Eadie and Keast 1982). Given the very high standing crops of carp in some marshes and the low spring invertebrate densities in some cases (e.g., Huener 1984), competitive interaction between carp and breeding waterfowl seems possible, at least in some cases.

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A key problem in research involving invertebrates is the current lack of reliable methods to estimate invertebrate production when invertebrate life histories are poorly known, as is true for many marsh invertebrates.

F. Canada Geese in Urban and Rural Areas Canada geese have proved adaptable to highly humanmodified environments. Urban populations, often nonmigratory, can be nuisances (Conover and Chasko 1985). Expansion of the Great Basin Canada goose population has led to conflicts between breeding geese and local agricultural interests. In both situations, it might be possible to reduce complaints by carefully designed provision of upland grazing "lure" areas. As pointed out earlier, geese do respond to differences in food quality in grazing areas. This suggests it might be possible to manipulate goose grazing by appropriate upland management techniques.

G. Agriculture—Waterfowl Relationships For many species of waterfowl, production habitat and agriculture are inseparably intertwined over much of the breeding range. Consequently, trends in agriculture are as important as droughts in determining habitat quality and availability. In the past, waterfowl and agricultural interests have been openly antagonistic—and waterfowl often lost. However, agriculture is changing and a cooperative, reasoned approach to issues seems more possible now than in previous years. Such an approach must be based on facts — social, economic, and political as well as biological. There have been a few pioneering studies —for example, on the economics of pothole drainage (Goldstein 1971, Hammack and Brown 1974). Much more needs to be done, and the results need to be available for use in decision making at many levels.

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utilization of beaver pond habitat. Proc. Annu. Southeastern Conf. Assoc. Fish Wildl. Agencies 31, 216-225. Higgins, K. F. (1977). Duck nesting in intensively farmed areas of North Dakota. /. Wildl. Mgmt. 41, 232-242. Higgins, K. F. (1986). Further evaluation of duck nesting on small man-made islands in North Dakota. Wildl. Soc. Bull. 14, 155-157. Hill, D. A. (1984). Factors affecting nest success in the mallard and tufted duck. Ornis Scand. 15, 115-122. Hill, E. P. (1982). Beaver Castor canadensis. In "Wild Mammals of North America." (J. A. Chapman and G. A. Feldhammer, eds.) pp. 256-281. Johns Hopkins University Press, Baltimore. Hilliard, M. A. (1974). "The Effects of Regulated Livestock Grazing on Waterfowl Production." Utah Div. Wildl. Res. 747-8. Salt Lake City. Holechek, J. L., Valdez, R., Schemnitz, S. D., Pieper, R. D. and Davis, C. A. (1982). Manipulation of grazing to improve or maintain wildlife habitat. Wildl. Soc. Bull. 10, 204-210. Hopper, R. M. (1972). Waterfowl use in relation to size and cost of potholes. /. Wildl. Mgmt. 36, 459-468. Hopper, R. M. (1978). "Evaluation of Pothole Blasting for Waterfowl in Colorado." Colo. Div. Wildl. Spec. Rep. No. 44, Denver. Hudson, M. S. (1983). Waterfowl production on three age-classes of stock ponds in Montana. /. Wildl. Mgmt. 47, 112-117. Huener, J. P. (1984). A comparison of aquatic microinvertebrate responses to marsh management strategies. M.S. Thesis, Utah State University, Logan. Jahn, L. R. and Moyle, J. B. (1964). Plants on parade. In "Waterfowl Tomorrow." (J. P. Linduska, ed.) pp. 293-304. Fish Wildl. Serv., U.S. Dept. Int., Washington, D.C. Jarvis, R. L. and Harris, S. W. (1971). Land-use patterns and duck production at Malheur National Wildlife Refuge. /. Wildl. Mgmt. 35, 767-773. Jefferies, R. L., Jensen, A. and Abraham, K. F. (1979). Vegetational development and the effect of geese on vegetation at La Perouse Bay, Manitoba. Can. J. Bot. 57, 1439-1450. Johnson, R. E., Jr., Woodward, R. O. and Kirsch, L. M. (1978). Waterfowl nesting on small man-made islands in prairie wetlands. Wildl. Soc. Bull. 6, 240-243. Kadlec, J. A. (1962). Effects of a drawdown on a waterfowl impoundment. Ecology 43, 267-281. Kadlec, J. A. (1982). Mechanisms affecting salinity of Great Salt Lake marshes. Am. Midi. Nat. 107, 82-94. Kadlec, J. A. (1987). Nutrient dynamics in wetlands. In "Aquatic Plants for Water Treatment and Resource Recovery." K. R. Reddy, and W. H. Smith, eds.) pp. 393-419. Magnolia Publishing, Inc., Orlando, Fla. 1032 pp. Kadlec, J. A. (1989). Effects of deep flooding and drawdown on freshwater marsh sediments. In "Freshwater Wetlands and Wildlife." (R. R. Sharitz and J. W. Gibbons, eds.) pp. 127-143. USDOE Office of Sci. and Tech. Info., Oak Ridge, Tenn. 1265 pp. Kadlec, J. A. and Smith, L. M. (1984). Marsh plant establishment on newly flooded salt flats. Wildl. Soc. Bull. 12, 388-394. Kadlec, J. A., and Wentz, W. A. (1974). "State-of-the-Art Survey and Evaluation of Marsh Plant Establishment Techniques: Induced and Natural. Vol. I, Report of Research." U.S. Army Coastal Engineering Research Center, Final Report. 231 pp. Kaiser, P. H., Berlinger, S. S. and Fredrickson, L. H. (1979). Response of blue-winged teal to range management on waterfowl production areas in southeastern South Dakota. /. Wildl. Mgmt. 32, 295-298. Kaminski, R. M., Murkin, H. R. and Smith, C. E. (1985). Control of cattail and bulrush by cutting and flooding. In "Coastal Wetlands." (H. H. Prince and F. M. D'ltri, eds.) pp. 253-262. Lewis Publ., Inc., Chelsea, Mich. Kaminski, R. M. and Prince, H. H. (1981). Dabbling duck and aquatic microinvertebrate responses to manipulated wetland habitat. /. Wildl. Mgmt. 45, 1-15.

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Notes on Contributors

Alan D. Afton received his M.S. in wildlife ecology from the University of Minnesota in 1977 and his Ph.D. in biology from the University of North Dakota in 1983. He is a former research scientist with the Wetland Wildlife Populations and Research Group of the Minnesota Department of Natural Resources, where he studied migration and winter ecology of Lesser Scaup. Since 1988, he has been an assistant leader of the Louisiana Cooperative Fish and Wildlife Research Unit and adjunct assistant professor at Louisiana State University, where he maintains an active graduate program in waterfowl ecology and continues his long-term research on Lesser Scaup. His papers dealing with behavioral ecology and bioenergetics of waterfowl have been published in a variety of scientific journals. Ray T. Alisauskas received his B.Sc. (1980) from Macdonald College of McGill University and his M.Sc. (1982) and Ph.D. (1988) in zoology from the University of Western Ontario in London, Ontario. Since a post-doctoral fellowship (1988-89) at the University of Manitoba and the Delta Waterfowl and Wetlands Research Station, he has been employed by the Canadian Wildlife Service as a research scientist at the Prairie and Northern Wildlife Research Centre in Saskatoon, Saskatchewan, and holds an adjunct professorship with the Department of Biology at the University of Saskatchewan. Besides a continuing interest in the nutritional ecology of breeding waterfowl, he has expanded his research interests to include spring nutrition, habitat use, and brood ecology of geese in the central Canadian arctic. Michael G. Anderson graduated from North Dakota State School of Science (A.S.), Colorado State University (B.S.), Utah State University (M.S.), and the University of Minnesota, Minneapolis (Ph.D.). He studied wetland ecology and waterfowl biology through the Delta Waterfowl and

Wetlands Research Station in Manitoba, and went on to become a research scientist and then scientific director at Delta. In 1990 he became a senior research scientist with Ducks Unlimited in Winnipeg, and is currently the assistant director of Ducks Unlimited's Institute for Wetland and Waterfowl Research. His primary research interest is in avian behavioral ecology and population biology, and his long-term field studies of Canvasback ducks in southwestern Manitoba have explored factors affecting waterfowl social behavior and population dynamics. C. Davison Ankney obtained a B.S. in wildlife management from Michigan State University in 1968 and a Ph.D. from the University of Western Ontario in 1974. He has studied nutrient-reserve dynamics of Brant, Brown-headed Cowbirds, Northern Shovelers, Gadwalls, Ruddy Ducks, and American Coots. Currently he is professor of zoology at the University of Western Ontario and plans to continue research on the relationship between Mallards and Black Ducks as well as to initiate work on the bioenergetics of waterfowl breeding in boreal forest habitats. Bruce D. J. Batt is currently the Director of Ducks Unlimited's Institute for Wetland and Waterfowl Research. He received his undergraduate training at Brandon College of the University of Manitoba and his graduate degrees from the University of Florida and Michigan State University. He was previously the scientific director of the Delta Waterfowl and Wetlands Research Station, where he was employed for over 20 years. His interests are in the integration of fundamental and applied research with waterfowl conservation. Robert J. Blohm received his B.S. in fisheries and wildlife from Michigan State University, and his M.S. and Ph.D. in wildlife ecology from the University of Wisconsin. His 611

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CONTRIBUTORS

graduate work, in association with the Delta Waterfowl and Wetlands Research Station, centered on the breeding ecology of the Gadwall in southern Manitoba. Since 1979, he has worked for the U.S. Fish and Wildlife Service, Office of Migratory Bird Management, and has been involved extensively with waterfowl population survey and banding programs in North America. He is currently the Office's Chief, Branch of Operations. Cynthia K. Bluhm is a research scientist for the North American Wildlife Foundation at the Delta Waterfowl and Wetlands Research Station. Concurrently, she has been affiliated with the zoology department of the University of Manitoba as a lecturer. Her research interests center on avian environmental physiology and reproductive behavior. She holds a B.A. in biology from Carleton College, and M.S. and Ph.D. degrees in ecology and behavioral biology from the University of Minnesota. After completion of her doctoral research on environmental reproductive biology of Canvasbacks, she was awarded a postdoctoral fellowship in the Institute of Reproductive Biology in the zoology department of the University of Texas at Austin to study cellular aspects of reproductive physiology. She was later awarded an Alexander von Humboldt Postdoctoral Fellowship to study at the Max-Planck-Institute for Behavioral Physiology in Andechs, West Germany, where she conducted research on circadian rhythms, circannual rhythms, and related endocrinology in birds. Lewis M. Cowardin is a research biologist with the U.S. Fish and Wildlife Service's Northern Prairie Wildlife Research Center. He received his undergraduate degree in biology from Harvard University, his master's degree in wildlife management from the University of Massachusetts, and his doctorate in wildlife management from Cornell University. He has conducted research on the ecology of wild turkeys and several species of ducks, as well as a number of habitat inventory and classification used in the National Inventory of Wetlands in the United States. His primary interests are in waterfowl and wetland ecology, population dynamics, and remote sensing of habitat. He is currently conducting research on systems that link remotely sensed data with population models. David H. Gordon received his B.S. (1977) and Ph.D. (1985) degrees in wildlife biology from Michigan State University, and an M.S. (1981) in wildlife ecology from Oklahoma State University. He was a postdoctoral research associate at Mississippi State University from 1985 to 1988. He is currently a research scientist with the Institute of Wetland and Waterfowl Research working out of Georgetown, South Carolina, and an assistant professor at Clemson University. His research interests center on understanding ecological, physiological, and behavioral factors that influence habitat selection by waterfowl during the

nonbreeding period; patterns and processes in intensively managed wetland ecosystems; and waterfowl and wetland conservation and management, including policy and law. William L. Hohman is a wildlife research biologist for the U.S. Fish and Wildlife Service, and leader of the Baton Rouge Field Research Station, National Wetlands Research Center. He holds an M.S. in zoology from the University of North Dakota and a Ph.D. in wildlife biology from the Unversity of Minnesota. His interests are nutritional, behavioral, and containment ecology of waterfowl. Douglas H. Johnson has spent twenty years with the U.S. Fish and Wildlife Service at the Northern Prairie Wildlife Research Center, where he is currently chief of the Northern Plains Ecology Section. His research interests include population dynamics of animals, ecology of grassland birds, quantitative methods in ecology, and simulation modeling. Ongoing projects include a population model of the annual cycle of Mallards, breeding bird use of Conservation Reserve Program lands in the northern prairies, and estimation techniques for survival of clutches and broods. He has received a B.A. in mathematics and psychology from the University of Minnesota, an M.S. in statistics from the University of Wisconsin, and a Ph.D. in zoology from North Dakota State University. He holds adjunct or lecturer appointments at North Dakota State University and Jamestown College. John A. Kadlec received his Ph.D. in 1960 from the University of Michigan. He was a research biologist for the Michigan Department of Conservation for five years and also spent five years in research with the U.S. Fish and Wildlife Service. He was on the faculty at the University of Michigan and has been at Utah State University since 1974. His specialty is wetland and waterfowl ecology, and, together with his students, he has published on topics ranging from wetland hydrology to marsh invertebrates to managing marshes for waterfowl. Richard M. Kaminski is an associate professor in the Department of Wildlife and Fisheries, Mississippi State University. His special interest lies in waterfowl habitat selection and habitat management. He has conducted research on the nutrition, reproduction, molt, behavior, population-habitat relationships, and population estimation of captive and free-ranging waterfowl, as well as researching illegal waterfowl hunting and farmers' attitudes about farmland management for waterfowl. He coedited Habitat Management for Migrating and Wintering Waterfowl in North America, which was selected by The Wildlife Society for the 1991 Publication Award for an edited book. He received his doctorate and M.S. degrees from Michigan State University, and his B.S. from the University of Wisconsin-Stevens Point.

NOTES ON CONTRIBUTORS Gary L. Krapu has been a research biologist with the U.S. Fish and Wildlife Service at the Northern Prairie Wildlife Research Center since 1971. He received his doctorate degree in animal ecology from Iowa State University in 1972. The principal focus of his research has been on factors governing habitat selection and productivity in waterfowl and other migratory waterbirds that breed or stage in the midcontinent region of North America. Several of these investigations have concentrated on the role of nutrition and endogenous nutrient reserves in the life histories of ducks, geese, and cranes. He currently is studying factors affecting survival rates of pre-fledged Mallard and Gadwalls in the prairie pothole region of North Dakota. Frank McKinney was born in Northern Ireland and received his university training at Oxford and Bristol. He carried out his doctoral research at the Wildfowl Trust in England, where he developed an interest in the evolution of waterfowl behavior that became the theme of his lifelong research program. Postdoctoral work on Eiders led to a nine-year assignment at the Delta Waterfowl and Wetlands Research Station. In 1963 he joined the Bell Museum of Natural History at the University of Minnesota, where he is curator of ethology and professor of ecology, evolution and behavior. His research on waterfowl behavior has included field projects in Alaska, South Africa, New Zealand, Australia, the Bahamas, and Argentina, as well as comparative and experimental work with captives in flight pens in Minnesota. James D. Nichols earned a Ph.D. in wildlife ecology from Michigan State University. He is currently leader of the Population Estimation and Modeling Group of the Migratory Bird Research Branch, Patuxent Wildlife Research Center, U.S. Fish and Wildlife Service, in Laurel, Maryland. His research has focused on methods for estimating parameters for natural animal populations and on applications of such methods to understanding animal population dynamics, with emphasis on waterfowl populations. Thomas D. Nudds has been an associate professor of zoology at the University of Guelph, Ontario, since 1986. He received his B.Sc. (1974) and M.Sc. (1976) from the University of Windsor, and his Ph.D. (1980) from the University of Western Ontario. Competition and community structure remain the central focus of his research program, which has included physiological and behavioral ecology of ducks and geese, the effects of land use change and climate on ducks in prairie Canada, and the distribution and diversity of songbirds and mammals in real and functional ecological islands. Lewis W. Oring received his Ph.D. from the University of Oklahoma in 1966. After postdoctoral studies of Green and Solitary Sandpiper behavior at the universities of

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Copenhagen and Minnesota, he took a position at the University of North Dakota in 1968. For the next twenty-two years, he taught behavior courses there and at the University of Minnesota Forestry and Biological Station at Lake Itasca. In 1991, he accepted a position at the University of Nevada, Reno, where he has initiated a project on the effects of environmental contaminants on the population biology of Black-necked Stilts. His research has concentrated on avian mating systems. Stuart L. Paulus holds degrees from the University of California at Davis, the University of North Dakota, and Auburn University. He has studied the behavioral ecology of both wintering and breeding waterfowl in Louisiana, California, and Manitoba. He is primarily interested in learning how habitat requirements of waterfowl influence their behavior, time budgets, and mating strategies. He is currently with Raedeke Associates Scientific Consulting, Inc., in Seattle, Washington. Dennis G. Raveling (1939-1991) earned his graduate degrees in zoology from the University of Minnesota (M.S., 1963) and Southern Illinois University (Ph.D., 1967). He was a research scientist for the Canadian Wildlife Servive before joining the faculty of the University of California at Davis in 1971 as professor of wildlife biology. His research centered on investigations of the life history, behavior, and population dynamics of waterfowl, including studies on arctic breeding areas. His work has been honored by election as a fellow of the American Association for the Advancement of Science, elective membership of the American Ornithologists' Union, and receipt of a Special Recognition Service Award for leadership in wildlife education and research and a Wildlife Publication Award from The Wildlife Society. Kenneth J. Reinecke is a research biologist with the U.S. Fish and Wildlife Service and currently is leader of the Vicksburg Field Station for the Patuxent Wildlife Research Center. He earned a Ph.D. in wildlife ecology from the University of Maine in 1978, and has experience with research and management of waterfowl in Nebraska, North Dakota, and southern Canada. For the past 10 years he has been studying habitat requirements of Mallards and Wood Ducks wintering in the Mississippi Alluvial Valley. Judith M. Rhymer is a postdoctoral fellow working on the genetics of waterfowl populations at the molecular systematics laboratory affiliated with the Smithsonian Institution National Museum of Natural History in Washington, D.C. Her present work focuses on the extent of hybridization between Mallards and closely related species of waterfowl in North America and worldwide, including two endangered species in Hawaii. She received a B.Sc. and M.Sc. in zoology from the University of Manitoba and a

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NOTES ON CONTRIBUTORS

Ph.D. in waterfowl ecological genetics from Florida State University. Frank C. Rohwer is an assistant professor at Louisiana State University and is Director of the Delta Waterfowl and Wetlands Research Station, Manitoba. A major focus of his research has been to understand the limits on individual reproductive output in waterfowl. He is also interested in the timing of breeding in birds and is pursuing field experiments on that subject. Other ongoing projects include work on the ecology of Mallards wintering in Maryland and several projects on breeding waterfowl in Manitoba. He received his undergraduate training at Kansas State University and went on to graduate studies at Washington State University and the University of Pennsylvania. Alan B. Sargeant received a B.S. in wildlife management from the University of Minnesota in 1959, and continued graduate work there until joining the U.S. Fish and Wildlife Service in 1962. From 1963-67 he was part of a University of Minnesota study team using newly developed radio telemetry methods to study predators, primarily red foxes, at the Cedar Creek Natural History Area in Bethel, Minnesota. Since 1967 he has been a wildlife research biologist at the U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, where he has engaged in studies of mammalian predator ecology and behavior, predation on prairie ducks, predator distributions and abundance, and effectiveness of predator control methods. Rodney D. Sayler is an assistant professor of avian ecology at Washington State University. He formerly was director of the Institute for Ecological Studies at the University of North Dakota. He received his B.S. and M.S. in wildlife from the University of Minnesota and his Ph.D. in biology from the University of North Dakota. His research specialties include reproductive ecology of waterfowl, avian brood parasitism, behavioral ecology, and conservation biology. His recent research includes studies of spatial relationships of ground-nesting birds and predation in prairie grasslands, waterfowl brood survival, and waterfowl response to manipulated wetlands. Michael D. Schwartz received B.S. (1980) and M.S. (1981) degrees in zoology from North Dakota State University. His research emphasis has been on foraging patterns and distribution of migratory nongame birds in western North Dakota. Currently he is a biological technician for the U.S. Fish and Wildlife Service at the Northern Prairie Wildlife Research Center. James S. Sedinger is currently associate professor of wildlife ecology at the Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska,

Fairbanks. He earned a B.S. from the University of Washington (1971) and a Ph.D. from the University of California at Davis (1983). During 1984-85 he was a research wildlife biologist for the Alaska Fish and Wildlife Research Center, U.S. Fish and Wildlife Service, Anchorage. He has ten years of experience studying arctic nesting geese, primarily on tundra breeding areas in western Alaska. His current research interests include regulation of life-histories in waterfowl, population biology of waterfowl, nutritional ecology of waterfowl, and grazing ecology, and he directs studies of duck ecology in the boreal forest of Interior Alaska. Loren M. Smith received a Ph.D. in wildlife ecology from Utah State University and an M.S. degree in wildlife science from South Dakota State University. He coedited Habitat Management for Migrating and Wintering Waterfowl in North America, which received the 1991 Wildlife Publication Award for an edited book from The Wildlife Society. He was the waterfowl and wetlands associate editor for the 1990 and 1991 volumes of the Journal of Wildlife Management. He is currently an associate professor of wildlife management at Texas Tech University. Rodger D. Titman obtained a B.Sc. from McGill University, an M.Sc. from Bishop's University, and a Ph.D. from the University of New Brunswick. He was a research assistant at the Delta Waterfowl and Wetlands Research Station in Manitoba from 1966 to 1971, and has supervised graduate students conducting research there. He held a position at the University of New Brunswick in Fredericton before joining the Department of Renewable Resources on the Macdonald campus of McGill University in 1973 as a wildlife biologist. He has served as department chair and is now an associate dean of the Faculty of Agricultural and Environmental Sciences at McGill University. Milton W. Weller is currently professor, Kleberg Chair of Wildlife Ecology, in the Department of Wildlife and Fisheries Sciences at Texas A&M University. He formerly held positions in wildlife programs at the University of Minnesota, Iowa State University, and the University of Missouri, where he received his graduate education. His longterm research interests have been in waterfowl and other wetland wildlife, and habitat management associated with conservation of representative waterbird faunas. He authored much of Volume 4 of J. Delacour's Waterfowl of the World (1974), The Island Waterfowl (1980), Freshwater Marshes (2nd ed., 1987), and edited Waterfowl in Winter (1988). His recent research projects involve habitat studies of molting Black Brant in Alaska, wintering waterfowl in Texas coastal habitats, and waterbird habitat selection in saline marshes.

Index Compiled by Robert Grogan

Abraham, K. E, 571 Abrams, P. A., 556 Accidental parasitism hypothesis, 295 Acid precipitation: as contaminant, 408 Ackerman, R. A., 71 Activity: as energy cost, 4lt, 42-43 Activity Fields: spacing patterns and, 274 Adaptive radiation, 30, 558 Adelie Penguin, 524 Adomaitis, V. A., 60 Aerial chases, 264 African Black Duck, 157, 205, 238, 382; nomadism, 373; philopatry, 373; spacing, 254, 256, 263, 270, 274 African Comb Duck, 262-63 African Lion, 380 African Pygmy Goose, 157 Afton, Alan D., 62-108; on displays, 240; on incubation, 30, 64; on laying, 491, 495, 513; on nest success, 460; on nutrient reserves, 57; on pairing, 229; on philopatry, 374; on seasonal decline, 510 Age: initial breeding and, 455-56; as mate choice criterion, 232; philopatry and, 367; of reproductive maturity, 453; survival of breeding birds and, 447-49 Age/experience hypothesis, 299-300 Aggregate percent method: of diet estimation, 2 Aggregate weight (volume) method: of diet estimation, 2 Aggression: interspecific, 268-69 Aggression Fields: spacing patterns and, 274 Aggressive approach behaviors, 347 Agonistic interactions, 17; spacing and, 258-71 Agriculture: as contamination source, 407-9; farm machinery and waterfowl mortality, 405-6; fertilizer and feeding, 13; hay-cutting and waterfowl mortality,

405-6; impact on foraging, 21-22; impact on nesting, 561; no-till agriculture, 602; predator/prey alterations, 411; selenium overdose and, 15, 408, 597; waterfowl/agriculture relationships, 606 Ainley, D. G., 524 Air temperatures: brood care and, 85, 85f; laying and, 18, 341-42 Aircraft: plus telemetry, 435-36; population counts and, 425, 427-29 Aitken, R. N. C, 32 Albers, P. H., 408 Aleutian Canada Goose: predation, 406 Alfalfa, 603 Algae, 592; as calcium source, 14 Ali, R., 378, 380 Alisauskas, Ray T., 30-61; on nutrient storage, 48, 56, 504 Alison, R. M., 267 Alkali bulrush, 601 Alliston, W. G., 465 Allozyme electrophoresis, 384, 385, 386 Altruism: genetic structure and, 377-78 Altrum, Bernard, 252 Amat, J. A., 308 American Crow, 411 American Eider, 330, 346 American Goldeneye, 229, 232 American Merganser: egg production energy, 39 American Ornithologists' Union, 1, 385 American Wigeon, 147, 154, 157, 198, 227, 232; body size, 49; diet, 10, 43, 117; drought and breeding, 468; fat reserves, 5If, 53, 53t; molt, 134; pairing and dominance, 340; philopatry, 373; spacing, 264, 265, 269, 274; survival, 449 Amino acids, 45-48; availability and reproduction, 12-14, 20; balance of, 46;

615

egg composition and, 47t, 48f; feathers and, 23, 136 Amphipods, 92, 119, 580 Anas spp.: body size, 75-76; courtship displays, 222, 224, 228; endocrinology, 326; main subgroups, 238; signals, 237; spacing, 254-55 Andean Goose, 235 Andersen, O., 72 Anderson, D. R.: on band recovery, 477, 530; on population, 428, 442; on survival, 447, 449, 450, 452, 465, 467, 469 Anderson, Michael G., 251-89, 365-95; on brood parasitism, 378; on dispersal, 372; on displays, 240; on invertebrate production, 605; on molt sites, 162; on pair bonds, 225; on philopatry, 365-66, 381, 452; on spacing, 256, 270 Andersson, A., 576, 605 Andersson, M., 303, 306, 311, 498, 501; on brood parasitism, 378 Andrews, B., 511 Androgens, 327-28 Androstenedione, 327 Animal contests, 274 Animal Dispersion in Relation to Social Behaviour (Wynne-Edwards), 277 Ankney, C. Davison, 30-61, 128-89; on clutch size, 56, 501, 504; on egg mass, 459; on energy/nutrients, 48, 143, 512; on growth rates, 111; on hatching reserves, 110; on molt, 144, 150; on nutrient reserves, 57; on sex ratio, 464; on spacing, 273; on stress, 129 Anna Hummingbird, 253 Annual survival rate, 447, 4481 Antidesertion tactics, 225 Arctic fox, 6, 406, 412, 414, 570 Arctic Tern, 461, 522

616 Arctic tundra region, 396, 397map; defined, 411-12; geese mortality in, 414; mortality agents in, 411-12; population model for Snow Geese of, 471-72 Area-restricted search, 17 Armbruster, J. S., 229 Armstrong, D. P., 556 Armstrong, T., 462, 506-7, 529 Arnold, T. W., 463, 506-7, 517, 519 Arrowgrasses, 119 Artificial eggs: incubation study by, 66 Artificial nest boxes, 292, 570, 581 Ashmole, N. P., 517 Ashy-headed Sheldgoose: genetic variation, 385 Askenmo, C., 519 Aspen, 580 Aspergillosis, 409 Assenmacher, I., 328, 337 Atlantic Brant, 339 Atlantic Canada Goose, 14; corn consumption, 7 Audubon, J. J., 410 Austin, J. E., 134, 141, 154 Austin, O. L, 525 Austin, O. L., Jr., 525 Australasian Shoveler, 264 Australia Teal, 345 Australian Black Swan: endocrinology, 329 Australian Blue-billed Duck, 204 Australian Pink-eared Duck: convergent evolution, 558; food choices, 16 Australian Shelducks, 157, 161, 194; spacing, 261, 262; territoriality and mating, 206, 207 Australian Shoveler, 158 Australian White-eye, 267 Australian Wood Duck, 157; initial breeding and renesting, 456 Availability/competition for nest site hypotheses, 298-99 Avian Biology (Farner, King, and Parkes), xv

Avian botulism, 409 Avian cholera, 409 Aythyini. See Pochards Azinphosmethyl: as contaminant, 409 Bacon, P. J., 384, 455, 459 Baerends, G. P., 217 Bailey, A. W, 601 Bailey, R. E., 67 Bailey, R. O., 148, 152, 257; on activity metabolism, 141; on plumage, 132-33; on species distribution, 161, 163; on use-disuse, 144 Baker, A. J., 384, 386 Baker, J. R., 487 Baldassarre, G. A., 155 Ball, I. J., Jr., 264, 466; on habitat, 283, 286; on mortality, 409 Ball, J. P., 577 Baltin, S., 71

INDEX Band/recapture (mark/recapture): band loss, 525; fall flight estimates and, 438-39; as study method, 367 Bar-headed Goose: brood care, 93, 260; endocrinology, 328, 329, 330, 338, 347; growth rates, 111; laying frequency, 38 Barlow, G. W, 215 Barnacle Goose, 89, 156, 160, 162, 163, 224; brood care, 94; fat requirements, 14; food habits of, 7; foraging habits, 11; genetic variation, 384; growth rates, 111; incubation, 73; molt, 133, 147, 152; nest sites, 570; nutrient acquisition, timing of, 4-5; pairing, 229, 338; spacing, 256, 257, 260, 261 Barnes, G. G., 546, 554, 556 Barnett, J. T., 453, 459 Barratt, R., 430 Barrowclough, G. E, 366, 383-84, 386, 387 Barrow's Goldeneye, 194, 195, 231, 294; attack (kill) intruders, 306; brood amalgamation, 91; brood-rearing areas, 82; habitat selection, 94; interspecific territoriality and, 17; philopatry, 374, 375, 451; re-pairing, 371; spacing, 267, 268; wetlands and nest sites, 580, 581 Barry, T. W, 339, 405, 510-11 Barton, H., 387 Bartonek, J. C., 1 Bateson, P., 229-30, 377 Batt, Bruce D. J., ix-xvii; on egg size, 459; on herbicides, 603, 610; on incubation, 64; on laying dates, 455, 510 Bazely, D. R., 559 Bean Goose, 156, 259, 260; food habits of, 7; genetic variation, 385; pairs and density, 469 Beat outs, 432 Beaver, 569, 596 Bedard, J., 90, 465 Beer, C. G., 215 Bellrose, F. C., 451, 517, 542, 573-74; on age ratios, 467, 468; on brood size, 403; on clutch size, 457; on mortality, 401, 409 Belt transects, 435 Bengtson, S.-A., 344, 455-56, 458, 579 Bennett, C. L., 430 Benoit, J., 328, 331, 335 Berger, A. J., 64 Beszterda, P., 373 Bet-hedging: clutch size and, 519-20 Bewick's Swan, 259, 340, 341; brood care, 88, 90; genetic variation, 383; male and incubation, 64 Beyersbergen, G. W, 602 Bezzel, E., 229, 254, 459 Big bluestem, 603 Billard, R. S., 129 Bioenergetics (nutrition) of postbreeding waterfowl, 134-54; activity metabolism, 140-41; amino acids in plumage, 136; biosynthetic inefficiency and, 152; endogenous reserves and molt, 143-44; energy content of feathers, 136;

exogenous contributions to molt, 14647, 146t; flightlessness, duration of, 130, 13If; maintenance metabolism, 139-40; molt intensity, 138-39; muscle, compensatory changes in, 144-46, 144/", 145t; nitrogen content of plumage, 136; nutrient acquisition, timing of, 3-6; plumage mass and, 135-36; productive metabolism, 142-43; reproductive/ postbreeding interrelationships, 147-49. See also Feather(s); Nutritional stress, molt and Birch, 570 Birds of Africa (Brown, Urban, and Newman), xv Birds of Europe, the Middle East, and North Africa (Cramp and Simmons), xv The Birds of the Soviet Union (Dement'ev and Gladkov), xv Birkhead, M. E., 459, 493 Bishop, R. A., 455 Bisset, A. R., 459 Black Brant, 270, 414 Black fly, 19, 95, 581 Black, J. M., 225, 230, 248 Black, K. E., 576 Black Scoter, 240, 267, 580; clutch size, 19 Black Swan, 156, 160, 234, 341, 345; breeding, timing of, 454; carrying of young, 90; daylength and laying, 341; endocrinology, 329, 330; incubation strategies, 65-66, 72; laying frequency, 39; male and incubation, 64, 147; mortality, 410; nest success, 460; spacing, 260, 270; survival of young, 465, 466 Black Turnstone, 461 Black-bellied Whistling Duck, 65, 259, 292, 406, 496; brood patch of, 67; molt, 133; wetlands and nest site selection, 569 Black-billed Magpie, 492 Black-headed Duck, 220, 241, 268; brood care, 87; duckling self-rearing, 294; obligate brood parasitism, 201, 294 Black-necked Swan, 259, 260; carrying of young, 90 Blohm, Robert J., 423-45; on homing rates, 367; on hunting vulnerability, 480; on synchronous nesting, 455 Blomquist, S., 461 Blue Duck, 157, 158, 205, 218, 220, 239; dispersal, 382; spacing, 256, 258, 263, 268, 270 Blue-billed Duck, 158, 162, 199, 204; breeding, timing of, 19; molt, 130 Blue-winged Duck: survival, 447 Blue-winged Goose, 261 Blue-winged Teal, 158, 161, 196, 222, 301; activity metabolism, 141; agriculture and, 561; breeding, timing of, 454, 455; brood size and survival, 498; current population, 412; drought and breeding, 468; egg composition, 20, 34, 52; emigration, 373; fat reserves, 53, 53t,

INDEX 339; fire and, 600; food choices, 9, 10, 43; grazing and, 601; habitat productivity and, 545; hatching, 82; incubation, 68, 71, 75, 77; initial breeding and renesting, 455; molt, 134, 135; mortality, 413; nest baskets, 597; nesting, 388; nocturnal incubation, 63; nonbreeding, 343; nutrient reserves, 505f; philopatry, 367, 451, 452; spacing, 264, 268, 269; survival, 449; survival of young, 465, 466; temperature and nesting, 342; territoriality, 17, 253, 254, 259; thermoregulation, 40; wetlands of, 575 Bluegrass, 7, 13, 600, 601 Bluestem, 603 Bluhm, Cynthia K., 323-64; on pair displays, 227; on pairing, 229-30 Blums, P. N.: on philopatry, 375, 379, 393, 451 Blus, L. J., 407, 462 BMR. See Metabolism Boag, D. A., 457-58, 464, 467, 520; on nest abandonment, 461; on weather and reproduction, 343 Boag, P. T., 56 Body orientation: displays and, 222-24, 223f Body size: age of maturity and, 335; clutch size and, 312, 335; consequences of, 333-35; egg size and, 335; endogenous nutrients and, 43-44, 49; endurance and, 334; geese, variations in, 113; incubation and, 73-75, 76?; latitude and, 517; lifespan and, 334-35; metabolic rate and, 334; nutrient reserves and, 334; population density and, 273, 273?; predator defense and, 114; spacing patterns and, 270-71, 273, 273?; of species, 278-81?; survival and, 447; thermoregulation and, 40-41; weather and, 334 Bohren, B. B., Ill Bolen, E. C., 569 Bolen, E. G., 569, 574 Bossema, I., 229 Bouffard, S. H., 401 Boundary displays, 274 Bousfield, M. A., 458, 461 Bowden, D. C., 428 Bowlby, J. N., 18, 552, 554, 557 Bowman, G. B., 461 Bowman, T. D., 159 Boyd, H., 434, 467 Braithwaite, L. W., 65, 261, 465, 507; on incubation, 66 Brandl, R., 542, 557 Brant, 160, 163, 260, 414; activity metabolism, 141; agonistic interactions, 17; agriculture and, 21; digestion efficiency, 13; egg laying, timing of, 38; endocrinology, 329; energy/nutrients, 143; food habits of, 7; foraging habits, 11; genetic variation, 384; mixed broods, 92; molt, 133, 139, 152;

mortality, 405, 410; nesting, 342; nutrient acquisition, timing of, 4; nutrient storage, 510; pair formation, 338; pairs and density, 469; philopatry, 372; spacing, 258, 260 Breeding dispersal, 366 Breeding habitats of Nearctic waterfowl, 174-81?, 568-89; dabbling ducks, 57478, 574?; diving ducks, 578-79; habitat, defined, 568; habitat, use within tribes, 569-82; perching ducks, 572-74, 573?; sea ducks, 579-81; swans, 569; true geese, 569-72, 571?, 572?; whistling ducks, 569 Breeding pairs: breeding inventories and, 423; indicated breeding pairs, 426 Breeding philopatry, 366, 377 Breeding population inventories: breeding pairs and, 423; breeding population, defined, 423; habitat evaluation and, 424; harvest management and, 424-25; population trends and, 424; sex ratios and, 423; uses of, 424-25. See also Population estimates; Recruitment, measures of Breeding, timing of, 19, 453-55, 487-95, 489?; breeding success, versus breeding date, 487, 488?; demands of incubation, 491; food availability and, 491-93, 492?; food-supplement experiments, 492, 492?; incubation-energetics hypothesis, 489-90; laying dates, 521?; laying dates, hypotheses of, 487-89; laying-delay hypothesis, 489; manipulations of hatch dates, 493-94, 493?; nest site availability and, 494-95; optimal-rearing hypothesis, 489-91, 490f; optimal-rearing hypothesis, tests of, 491-93, 492?; periodic breeding, 487; postfledgling survival, 487-88, 488?; predators and, 494; territory for nesting, 494; territory-quality hypothesis, 508-9 Breeding-site philopatry, 366, 367-73, 377; seasonally monogamous ducks and, 36772, 368-69?, 370?, 371?, 372? Brewer, G., 229 Brewster, W. G., 435, 574 Brodsky, L. M., 229 Bronze-winged Duck, 263 Bronze-winged Teal, 208 Brood amalgamation, 89-92; adoption as, 89; characteristics favoring, 91 f; coldhardiness and, 91-92; creche (mixed brood) as, 89; frequency of, 89, 90?; gang brooding as, 89; kidnapping as, 89; predators and, 90; superbroody females and, 91; time of occurrence, 90. See also Brood parasitism Brood care of waterfowl, 83-94; age of adult and, 93; age of brood, 93; backcarrying of young, 89; brood care/parent maintenance trade-off, 83; brood size and, 93-94; brood territories, 94; brooding, 88; characteristics of, 84-86,

617 85?; competitive interactions and, 89; duckling mortality and, 86; evolution of, 84, 84?; factors influencing, 92-94; habitat selection and, 94; length of care, 86-87; males and, 85-86; parental feeding of young, 88; predators and, 83, 86, 88-89; temperature and, 85, 85?; time budgets of, 83, 87-88, 88?; time of day and, 92-93; time of year and, 92; types of care, 83. See also Brood amalgamation; Brood parasitism; Hatching and nest exodus; Prefledging waterfowl, ecology of Brood mortality/survival, 83, 116, 464-66; methods of assessing, 399; mortality rates, 402-3, 403?, 404?, 466; philopatry and, 375, 376 Brood movement, 82-83, 120-21 Brood parasitism, 201-2, 290-322; accidental parasitism hypothesis, 295; age/experience hypothesis, 299-300; antiparasitism, 291; antiparasitism, strategies of, 306-8; availability/ competition for nest site hypothesis, 298-99; clutch mass/body mass relationships, 312; clutch size and, 311; colonial nesting, 292; conditional strategy hypotheses, 295-300; conspecific brood parasitism (CBP), 290, 315-17?; density-dependent effects, 30910; determinants of, 308-12; dump nests, 308; energy-limitation hypothesis, 295, 298; environmental factors and, 308-10; evolution of, 306-7, 378; evolutionarily stable strategy (ESS), 301-3, 302f, 302?; facultative parasitism, 291; frequency dependence, 301-3; game theory and, 301; good body condition hypothesis, 298; habitat condition and, 308-9; hypotheses of, 295-303, 298?; increased longevity hypotheses, 301; indirect selection (kin parasitism) hypothesis, 304-5; interspecific brood parasitism (IBP), 290, 315-17?; laying of parasitic eggs, 307-8; life-history correlates, 311-12; locating host nests, 307; mating systems and, 201-2, 290322; nest attentiveness and, 298; nest concealment and, 306; nest density and location, 308, 315-17?; nest guarding and, 306; nest prospecting, 307; nestling removal, 306; obligate brood parasitism, 201, 291, 294; occurrence, in species, 292-94, 292?, 296-97?, 315-17?; occurrence, in tribes, 291-92, 292?; parasitic females, behavior of, 307-8; poor body condition/nest loss hypothesis, 295; population management and, 310-11; precocial young hypothesis, 303-4; precocial/ altrical dichotomy, 311-12; prelaying visits, 307; producer/scrounger model, 301; protocooperation, 304-5; reduced brood mortality hypothesis, 304; reproductive effort, 299; reproductive

618 error hypothesis, 295; residual reproductive value, 299; risk spreading (variance reduction) hypothesis, 300301; salvage strategy, 291, 295, 298; second-choice strategy, 298; success of, 294-95, 296-97*; variable reproductive effort hypothesis, 300. See also Brood amalgamation; Host, brood parasitism and Brood patch, 67, 67f Brood-limitation hypothesis, 497 Brown, G. M., 439 Brown, J. L, 252, 253, 255 Brown, L. H.: Birds of Africa, xv Brown, M., 575 Brown, P. W., 408 Brown, R. E, 399 Brown bear, 406 Brown Pintail, 265-66 Brown Teal, 208, 220, 239; spacing, 264, 265 Brown-headed Cowbird, 192, 491 Brownie, C., 447, 525 Brush Turkey, 71 Buckland, S. T, 525 Budgerigar, 347 Buechner, M., 376 Buffleheads, 162, 194, 294; brood amalgamation, 91; clutch size, 458; interspecific competition and, 17; killing of young, 465; nest abandonment, 462; philopatry, 373, 375; re-pairing, 371; spacing, 267, 268, 270, 273; survival of young, 465; wetlands and nest sites of, 580-81 Bulrush, 21, 597, 601 Burnham, K. P., 428 Burning: as wetland management, 596 Buschbaum, R. J., 13 Buss, I. O., 130, 463 Butler, G., 426 Cackling Canada Goose, 261, 414; activity metabolism, 140; crude protein and, 3; egg production energy, 39; endocrinology, 329; fat requirements, 14; foraging habits, 11; molt, 148, 149; timing of nutrient acquisition, 4-5; weight and migration, 340 Cackling Goose: duration of RFG, 35; hatching reserves, 110; mortality rates, 398 Cadwell, L. L., 463 Calcium: acquisition of, 4*, 5; femur calcium levels, 5; reproduction and, 14-15, 15*; reserves of, 48 Calder, W. A., 40 Caldwell, P. J., 72 California Gull, 407 Calverley, B. K., 343, 457, 467, 520 Campbell, C. R. G., 265, 453 Canada Goose, 90, 160, 163, 221, 234; activity metabolism, 141; age of reproductive maturity, 453; body composition studies, 128; breeding,

INDEX timing of, 453, 454, 455; brood amalgamation, 95, 292; brood size and survival, 498; bulrush and, 596; clutch size, 23, 459, 516, 519; digestion efficiency, 13; diseases, 409; duration of RFG, 35; egg loss, 462; egg size, 459; endocrinology, 328, 329, 333, 347; energy/nutrients, 143; fat requirements, 14, 44; fire and, 600; genetic variation, 382, 384, 385, 386; hatching, 81, 82; incubation, 64, 75, 77; initial breeding and renesting, 455, 456; interspecific competition and, 17; laying, 38, 347; lure areas and, 602, 606; maturing age, 335; mixed broods, 92; molt, 132, 139, 148, 149, 150, 153; molt migration, 156, 159; mortality/survival, 405, 410, 447, 448; mortality/survival of young, 465, 466; nest abandonment, 461, 462; nest counts, 433; nest platforms, 597; nest substrates of, 571*; nest success, 460, 461; nesting, 342, 495, 570-71, 572?; nutrient acquisition, timing of, 3-5; nutrient reserves, 526; pair formation, 338; philopatry, 372, 372*, 376, 384, 452; population estimate methods, 427; predation, 406; protein and reproduction, 13; renesting, 20; sex ratio of hatchlings, 464; spacing, 256, 260, 261, 271, 274; in urban areas, 606; wetlands of, 569-70. See also named subspecies Canadian Wildlife Service, 413, 423 Canvasbacks, 162, 163, 199, 220, 225, 227; breeding, timing of, 454; brood parasitism, 293; courtship, 228; current population, 412; displays, 240, 346, 347; drought and breeding, 468; endocrinology, 328, 329, 330, 336, 347; fat reserves, 53, 53*, 54, 340; food sources of, 1, 7, 43; gizzard atrophy in, 46; growth rates, 111; initial breeding and renesting, 455; molt, 134, 147, 154; mortality/survival, 447, 449; nepotistic behavior, 378; nest baskets, 597; nesting, 19, 342, 343, 344, 348, 406, 579; nutrient acquisition, timing of, 6; nutrient storage, 49, 57; pairing, 229, 230, 231; pairing and molt, 341; philopatry, 365, 367, 372, 373, 374, 375, 376, 379, 451, 452; photorefractoriness, 349; plumage, 135; population estimate methods, 426, 429; protein intakes, 45; recruitment, 387; sex ratio of hatchlings, 464; spacing, 255, 256, 257, 258, 266, 268, 269, 274; thermoregulation, 40, 41; weight cycles, 506; wetlands of, 578, 579 Cape Barren Goose, 156, 160, 235; brood care, 93; initial breeding and renesting, 456; signal systems, 235; spacing, 261 Cape Shelduck, 157, 161, 194, 385; territoriality and mating, 205-6, 207 Cape Shoveler, 158, 264

Cape Teal, 158, 208, 228, 264, 269; nomadism, 373 Capture/recapture, as study method, 448, 450 Carbohydrate: digestibility, 13 Carex rariflora, 160 Carex subspathacea, 119, 122 Carey, C., 72 Carlisle, T. R., 84, 86 Carp, 598, 599f, 605 Case, T. G., 551 Cassel, J. F., 603 Caswell, F. D., 387 Cattail, 591, 596, 597, 605 Caughley, G., 428 Cell structure compounds: analysis of, 3 Chamberlain, E. B., 434, 436 Changnon, P., 436 Charadriiformes, 303 Chattin, J. E., 429 Chen spp.: timing of egg laying, 38 Cheng, K. M., 200, 229 Chestnut Teal, 158, 208, 239, 264; brood care, 86; brood parasitism, 293; survival of young, 466 Chicken, domestic, 71; egg-production model, 32; follicle mass and RFG, 35; incubation, 72; protein utilization, 46 Chilgren, J. D., 136 Chiloe Wigeon, 208, 243, 264 Chironomids, 11, 43, 47, 119, 204, 466, 491; importance during egg formation, 7,38 Chlorinated hydrocarbons: as contaminants, 408 Chlorpyrifos: as contaminant, 409 Christoleit, E., 254 Chronister, C. D., 292, 300 Chrysanthemum articum, 571 Chu, D. S., 465 Cinnamon Teal, 264, 268, 358; egg loss, 462; laying frequency, 38 Circadian rhythms, 332 Circannual periodicities, 332, 334, 338-39 Circular fighting, 264 Clam shrimp, 11 Clancey, P. A., 517 Clark, A., 456 Clark, G. A., 129 Clark, R. G., 16, 449 Clawson, R. L., 307, 465 Clements, F. E., 591 Cliff Swallow, 71 Climatic Instability Hypothesis, 558-59 Clutch formation. See Egg production Clutch size, 19-20, 36-37*, 457-59, 496508; age and, 457-58, 521*; body size and, 312, 335, 517/"; breeding experience and, 458; brood parasitism and, 311; brood size and, 498-99; brood-limitation hypothesis, 497; costof-delay hypothesis, 511, 512-15, 5Uf, 514f; cost-of-reproduction hypothesis, 515; egg size/clutch size, 459, 502-4, 503*, 503f; energy and, 36-37*, 32-40;

INDEX evolution of, 30-31; fat reserves and, 19; food-availability hypothesis, 19-20, 50910, 51 If; hypotheses about adaptivity of, 497-98; incubation ability and, 499; interspecific parasitism, 458-59; intraspecific parasitism, 498, 499; islands and, 496-97; nutrientreallocation hypothesis, 510-12, 511f; optimum clutch size, 497; parental investment and, 499; renesting and, 51315; reproductive effort, 519; Ryder's hypothesis, 30-31. See also Clutch size, geographic variations in; Clutch size, seasonal declines in; Egg production, clutch size and Clutch size, geographic variations in, 51521, 518 f; bet-hedging, 519-20; egg production and, 520-21; explanations for, 518?; female mass and, 517f; latitudinal increases in clutch size, 51617, 516 f, 517f; r/K hypothesis, 519; reproductive optimization, 518?, 519-20; resource abundance and, 517-19, 518? Clutch size, seasonal declines in, 457, 50810, 508?, 510f; habitat-settlement hypothesis, 508-9; hatching synchrony hypothesis, 512; parent-quality hypothesis, 509; seasonal-productivity hypothesis, 517-19 Glutton-Brock, T. H., 276, 526 Cody, M. L, 258, 516, 551 Coho Salmon, 16 Coleoptera, 7, 119 Collias, E. C., 491 Collias, N. E., 491 Collisions: as mortality agents, 403-5 Coloniality: spacing patterns and, 270-71 Color-marked birds: as study method, 367 Colwell, M. A., 379, 380 Comb Duck, 195, 209, 237; forced copulation, 200; polygyny, 202-3, 204 Comins, H. N., 380 Common Eider, 22, 162, 194, 241; brood amalgamation, 89, 90; brood care, 92; clutch size, 516; creche formation, 91; diseases, 409; hatching, 82; incubation, 80, 81; mixed broods, 92; molt, 143, 342; mortality, 410; nutrient acquisition, timing of, 6; nutrient reserves, 526; philopatry, 367, 374; predation, 406; re-pairing, 371; spacing, 267; wetlands and nest sites of, 580 Common Goldeneye, 163, 196, 215, 240, 253; brood size and survival, 498; defense of territory, 91; nocturnal incubation, 64; nutrient reserves, 491; pairing and dominance, 340; philopatry, 375; RFG and laying interval, 35; spacing, 267, 268; wetlands and nest sites of, 580, 581 Common Greenshank, 522 Common Merganser, 23, 267, 294, 408; area-restricted search, 17; brood parasitism, 294; creche formation, 91; food choices, 10, 16; RFG and laying

interval, 35; survival of young, 465; wetlands and nest sites of, 581 Common Pochard, 372, 379 Common reed, 601 Common Shelduck, 371, 374, 385 Common Teal, 265 Community ecology of breeding waterfowl, 540-67; community, definitions of, 54042, 541f; density dependence and, 542; density independence and, 542; diversity and conservation, 560; diversity, indexes of, 543; Ecological Time Hypothesis, 544, 545; evolutionary convergence and, 558, 558?; Evolutionary Time Hypothesis, 544-45, 545f; flyover and ecological time, 545; future of, 561-62; game management, defined, 542; guild(s), 540-42; history of, 543-44; interclass competition and, 561; invertebrate size and, 546f; invertebrates and, 575-77; maximum sustainable yield theory, 542; management implications, 559-61; microhabitat studies, 548; population dynamics hypotheses, 56061; Predation Hypothesis, 543f, 544f, 545-46; Productivity Hypothesis, 545f, 547-49, 547f, 548f; seasonal competition and, 561; Shannon-Weaver formula, 549; single-species management and, 542-43; Spatial Heterogeneity Hypothesis, 549-51, 550f, 550?, 55If; species evenness and, 543; species introductions and, 561; species richness and, 543; theories about community regulation, 543-44, 543f; time hypotheses, 543?, 544-45, 544?. See also Competition Hypothesis, of community ecology Competition and foraging: interspecific competition, 17-18; intraspecific competition, 17 Competition Hypothesis, of community ecology, 551-58; Climatic Instability Hypothesis, 558-59; competition, kinds of, 551; differences in food and feeding, 552-53; ecomorphology and, 553-54; exploitation competition, 551; fluctuating environments and, 558; habitat use and, 554; Hutchinson's 1.3 Rule, 554, 554?; Instability Hypotheses, 544f, 558-59, 558f; interference competition, 551; Intermediate Disturbance Hypothesis, 558; kleptoparasitism as competition, 551; Mass Effects Hypothesis, 559; Niche Complementarity Hypothesis, 554-55; Niche Compression Hypothesis, 552; Niche Overlap Hypothesis, 552, 556; niche shifts, 557-58; population, size changes, 556-57; Rarefaction Hypothesis, 558; seasonal competition and, 561; territoriality as competition, 551; Type I Evidence, 551-554, 553f, 555f; Type II Evidence, 554-59, 554?,

619 556f, 558f; Type III Evidence, 557-59, 558f Conditional strategy hypotheses, 295-300 Conflicts of interest: displays and, 224-25 Connell,J. H., 558 Conroy, M. ]., 449, 450 Constraint hypothesis, 522, 523-24 Contact calls, 224, 225 Contaminants: categories of, 594; as mortality agents, 407-9 Contour furrowing, 598, 605 Cooch, F. G., 468, 472, 501 Cook, R. D., 430 Cooke, R, 529, 559, 571; on clutch size, 56, 311, 402, 421, 458, 459, 503, 534; on dispersal, 372, 373?; on follicular atresia, 511; on hatching synchrony, 512; on laying, 455; long-term data of, 471-72, 474; model for research, 276; on philopatry, 381; on population, 430; on predation, 494; on recruitment, 42324, 468; on sex of hatchlings, 464; on survival, 465, 466; on territoriality, 256, 305 Coon, N. C., 408 Cooper, J. A., 34, 38, 459, 501 Cooperative breeding ground surveys, 42728, 430, 436-39, 438f; Canadian study area, 437 Cooperative signals, 225 Coots, 294, 493, 557 Copulation: extrapair copulation, 226; as mate-choice criterion, 232-33; postcopulatory displays, 224, 234; precopulatory displays, 218, 220, 240; winter copulation, 233. See also Forced copulation (FC) Cordgrass, 7, 14 Corn, 7, 14 Cornwell, G. W., 72, 403, 410 Corophium spp., 94 Cortical bone: mineral storage and, 48 Corvids, 604 Coscoroba Swan, 259, 260, 341 Cost-of-delay hypothesis, 511, 512-15, 512f, 514f; renesting and, 513-15 Cost-of-reproduction hypothesis, 515 Cott, H. B., 410 Cotton Pygmy Goose, 157 Coulson, J. C., 276, 430, 456, 459 Coulter, M. W., 451, 457 Courtship and pair formation of waterfowl, 225-33; activity during prebreeding, 340-41; activity during winter, 337-38; age as choice criterion, 232; bond reaffirmation, 228; bond reinforcement, 225; contexts of, 227-28; copulation as choice criterion, 232-33; courtship feeding, 240; dominance rank and, 232; early experience as choice criterion, 22829, 231; extrapair copulation, 226; extrapair courtship, 228; familiarity as choice criterion, 231; filial imprinting, 229; inbreeding avoidance, 231; liaison, 226; mate choice criteria, 230-33; mate-

620 switching, 231; monogamy, 226; morphological features and, 232; nesting phase and, 346-47; pair-reinforcing signals, 240; prebreeding phase, 340-41; psychosomatic effects of, 227; reuniting, 231; sexual imprinting, 231; social courtship, 225-26; terminology of, 22526; unpaired birds and, 227. See also Mating systems of waterfowl; Social courtship Courtship feeding, 240 Cowan, W. R, 602 Cowardin, Lewis M., 423-45; CowardinJohnson model, 430-31; on egg production, 458; on habitat, 283; on mortality, 413; on nest success, 460, 607; on nesting, 456, 576, 578, 585; on population, 430, 431, 433, 435, 440 Coyote, 407, 411 Cramp, S., 62, 226, 233, 240, 265; Birds of Europe, the Middle East, and North Africa, xv Crawfish, 581 Creche (mixed brood), 89 Crested Duck, 208, 264 Crissey, W. R, 430, 438, 452, 468 Cromartie, R., 408 Cronquist, A., 591 Crook, J. H., 190, 215, 233 Crows, 411 Croxall, J. P., 77 Crude protein: analysis in diet, 3 Crustaceans, 9t, 14-15, 22 Cuban Whistling Duck, 65, 259 Culbertson, J. L., 463 Curio, E., 455-56 Cypermethrin: as contaminant, 409 Daan, S., 54, 460, 513 Dabbling ducks, 193, 238-39; aerial chases (pursuit flights), 254; age of reproductive maturity, 453; breeding, timing of, 454; brood care, 93; brood parasitism, 292, 293; competition and, 552; density of, 549; diet overlap, 552; difficulty in counting, 431-32; displays, 218, 219, 220, 221, 222; food choices, 7; foraging, 11, 117; genetic variation, 385-86; grit size differences, 552-53; guilds, 559; habitats, 161, 425, 556, 591; initial breeding and renesting, 455; mate choice, 229; nesting, 577-78, 602; pairing, 232; philopatry, 367, 451, 452; predators and, 407; signal systems, 23839; social courtship, 226; spacing, 26366; species diversity, 545; species sizes, 554?; wetlands of, 574-77, 574*. See also named species and subspecies Daily energy expenditure (DER): as cost, 40-43; estimation of, 42-43; incubation and, 81 Dane, B., 215, 217 Danell, A.: on invertebrate production, 605

INDEX Danell, K., 491, 548, 553, 576-77; on pollution, 426; on pond enhancement, 605; on population, 606 Dark-bellied Brant, 23; agriculture and, 21; food habits of, 7 Darley, J., 228-29 Darwin, Charles, 190 Davies,J. C, 311 Davies, N. B., 253, 493 Davies, S. J. J. R, 233 Davis, C. B., 596 Dawkins, R., 84, 225 Daylength: early winter phase and, 338-39; nesting phase and, 341; prebreeding phase and, 338-39 DDT and DDR: as contaminants, 408, 594 DRfi. See Daily energy expenditure Defense: mate defense, 270; of paternity, 270; timing of, 270 Delacour, J., xv, 65, 129, 214, 383; classification system, xv-xvi Delnicki, D., 449-50 Deltamethrin: as contaminant, 409 Dement'ev, G. P., 465; The Birds of the Soviet Union, xv Dennis, D. G., 435, 467 Derksen, D. V, 141, 160, 162, 452 Derrickson, S. R., 255 Dervieux, A., 229 The Descent of Man and Selection in Relation to Sex (Darwin), 190 Diamond,]. M., 551 Diedrick, R. T., 602 Diefenbach, D. R., 374 Diet of breeding waterfowl: composition estimation, aggregate percent method, 2; composition estimation, aggregate weight (volume) method, 2; food, digestibility of, 23; food-supplement experiments, 492, 492?; food tracers and, 3; nutrient reserve use and, 54; quality, seasonality, 43; specialization, 43. See also Foraging ecology and nutrition; Nutrition; Nutritional stress Dihydrotestosterone (DHT), 327 Dinsmore, J. J., 570, 575 Diptera, 7 Diseases of waterfowl, 165, 409 Dispersal: in mammals, 378-79; in other birds, 378; in passerines, 378 Dispersal of waterfowl: breeding dispersal, 366; costs of dispersal, 374-75; definitions, 366; dispersion, models of, 272-73; effective dispersal, 366; mating systems hypotheses, 379-81; natal dispersal, 366, 372?, 377, 380; nomadism, 373, 374; optimal discrepancy hypotheses, 377, 379, 380; parent/offspring competition (Oedipus) hypothesis, 380-81, 380?; patterns of, 271-72; philopatry and, 365-66; population density hypothesis, 379; resource defense versus mate defense hypothesis, 379-80; sex-biased dispersal hypotheses, 378-82; territory size and,

272-73, 272?. See also Genetic structure of waterfowl; Migration; Philopatry of waterfowl Dispersion: models of, 271-72 Displacement activities, 217 Displays of waterfowl, 215-25; actionspecific energy, 216; aerial chases (pursuit flights), 264, 354; antidesertion tactics, 225; approaches to study of, 215-25; attention-getting displays, 227; body orientation of, 222-24; boundary displays, 274; characteristics of, 221-22; circular fighting, 264; conflicts of interest and, 224-25; contact calls, 224; displacement activities, 217; display repertoires, 219, 220; display situations, 221; effects of, 224; emancipation, 217; evolution of, 217-18; fixed action patterns (FAP) approach, 215-16; as formalized interactions, 224; genetic control, 216; homologous displays, 218; imprinting and, 82, 220, 229, 231; inciting displays, 222, 230, 235, 237, 266; intention movements, 221, 222; as isolating mechanisms, 219-21; motivational conflicts approach, 216-17; pair displays, 227; postcopulatory displays, 224, 234; precopulatory displays, 218, 220, 240; preflight signals, 221, 225; ritualization, 218; selfish signalers and, 224-25; sexual selection and, 220; social courtship and, 223; as social signals, 221-24; species recognition signals, 219, 220; spontaneity, 216; stereotypy, 215-16; as taxonomic characters, 218-19; as threat signals, 222; three-bird flights, 254, 264, 265, 266, 273, 274; triumph ceremonies, 217, 223-24, 230, 234-36, 240, 243. See also Courtship and pair formation in waterfowl; Signal systems of waterfowl Diving ducks: age of reproductive maturity, 453; breeding, timing of, 454; diet of, 117; drought and nesting, 344; guilds, 559; habitat selection, 591; habitat use, 556; nest sites, 579; niche separation of, 547/, 548; philopatry, 451; predators and, 407; species diversity, 545; wetlands of, 578-79. See also named species and subspecies Dobson, R S., 378, 380 Dobush, G. R., 35, 458 Dominance rank: as mate choice criterion, 232 Doty, H. A., 451, 526 Double brooding, 201, 455 Doubly labeled water, 42 Dow, H., 307, 375, 455-56, 465, 498, 523; on invertebrate availability, 124 Dow, J. S., 406 Draulans, D., 16 Drawdown, 595, 595f

INDEX Drent, R. H., 54, 513; on incubation, 67-68, 75, 77; on nest success, 460, 461; on survival, 465, 468 Drewien, R. C, 576 Drobney, R. D., 12-13, 35, 572 Drought: drought/dry cycles, 592; reproduction and, 343-45 Dubowy, P. J., 141, 556 Duck viral enteritis (DVE), 409 Ducks: activity metabolism, 141-42; adaptations to molt, 153-54; agriculture and, 21-22; breeding-site philopatry, 367-72, 368-69?, 370?, 371*, 372?; brood care, 85-87; calcium requirements, 15; defense of territory, 91; defense of young, 89; egg-gathering as mortality factor, 410; feeding ecology of, 1-2; flightlessness, duration of, 130, 131?; food composition, 13f; food habits of, 7-10, 8?, 9?; foraging effort, 6t; genetic variation, 382; incubation constancy, 73, 76?; incubation, start of, 62; interspecific competition and, 17-18; invertebrates and, 8?; migration and social systems, 85; mixed broods, 92; molt, 133-34, 166-69?; mortality, 399?, 401?, 410; mortality, in prairie pothole region, 412-14; nutrient acquisition, timing of, 5-6; nutrient reserves, 144-45; predators and, 406-7; productivity studies of, 547-48, 548?; reproductive/ postbreeding interrelationships, 148-49; resource limitation and, 561. See also named tribes, species, and subspecies Duckweed, 605 Duebbert, H. R, 451, 453, 461, 578; on artificial islands, 604; on cover, 603, 608; on nest success, 419; on predation, 593 Ducting calls, 236, 236f, 238 Dump nests, 308, 473 Duncan, D. C., 83, 456, 466, 577; on renesting, 501, 506, 510 Dunn, E. H., 38, 455 Dunnock, 493 Dusky Canada Goose, 406, 414; clutch size, 19; nutrient acquisition, timing of, 4; protein and reproduction, 13 Dwernychuk, L. W., 464 Dwyer, T. J., 265, 456, 575, 577, 602 Dzubin, A., 265, 467; on aerial chases, 254; on philopatry, 452; on population, 426, 427, 431, 433, 440; on territoriality, 253 Eadie, J. McA., 465, 556; on brood amalgamation, 96; on brood parasitism, 294, 295, 298, 299, 300, 304, 306, 312 Early, T., 574 Early experience: as mate choice criterion, 231 Early wintering phase of reproduction, 324, 335-38, 352-53?; ambient temperature, 337; daylength, influence of, 335-37; male courtship activity during, 338;

nutrition and, 48-49, 57, 337; pair formation, 338; social factors, 338 Earthquakes: as mortality factor, 406 Earthworms, 11 Ebbinge, B. S., 469 Eberhardt, L. L., 406, 450, 463 Eberhardt, R. T., 449-50 Echinuria infestation, 409 Ecological Time Hypothesis, 544, 545 Economic defendability, 252-53 Edmond, H. D., 71 Eelgrass, 7, 21, 115-16 Effective dispersal, 366 Egg(s): air-cell temperature, 63f, 63?, 67f, 68, 69?; artificial, for incubation studies, 66; eggshell thinning from contaminants, 408; fertility and hatchability, 20, 46263?, 463; maximum daily egg energy (MDEEG), 39-40, 40/; nutrient acquisition and, 4; telemetric incubation studies, 6; turning during incubation, 72-73. See also other Egg entries Egg(s), mortality/survival of, 398-402, 402?, 462-63?; age of eggs and, 398; artificial nests to assess, 398; bias in assessing, 398; egg success, 399; embryonic death, 462-63, 462-63?; hatch rate, 398; human beings and, 461; infertility, 46263?, 463; Mayfield method of calculation, 398; methods of assessing, 398-99; mortality rates, 401?, 402, 402?; predation and, 461, 463; renesting and, 398-99; weather and, 461. See also Nest success Egg laying and nutrient reserves, 30-62, 36-37?; activity as energy cost, 41?, 42-43; adaptive radiation and, 30; body mass and, 43-44, 49; composition of eggs, 32-34; daily energy expenditure (DEE) as cost, 40-43; diet and, 54; diet quality, seasonality of, 43; diet specialization, 43; egg size and determinants, 32-34; energy density of eggs, 32, 33; energy equivalents of egg formation, 39-40, 40f; energy flow schema, 31 f; food predictability and, 49; interspecific variation and, 52-54, 55?; laying interval and, 32, 38-39; maximum daily egg energy (MDEEG), 39-40, 40f; mineral reserves, 48; morphological adaptation and, 42; nesting phenology and, 49; nutrient reserve threshold and REG, 54-55, 55f; nutrient reserve use, 56; nutrient reserve use, measurement of, 49-52, 50f, Slff; other energy costs, 40-43; sources of energy and nutrients, 43-48; temporal patterns of nutrient storage, 48-49, 57; thermoregulation as energy cost, 40-41, 41?. See also Energy requirements of egg production Egg production: calcium and, 4?, 5, 14-15, 15?; food availability and, 20; the process of, 32. See also Energy

621 requirements of egg production; Rapid follicular growth (REG) Egg production, clutch size and, 499-506; determinate laying, 502; egg addition studies, 501; egg removal studies, 501, 502; egg viability, 506-7; egg-production hypothesis, 499-500, 500f, 503, 506; egg size/clutch size, 459, 502-4, 502/", 503?; exogenous nutrients and, 503; hatching synchrony, 506-7, 507f; indeterminate layers, 501; interegg communication, 507; latitude and, 52021; laying energetics, 504-6; laying patterns and, 500-502; nest attention during laying, 506-7; nest predation, 507; renesting energetics, 505-6, 505f; stored nutrients and, 501, 504-6; weight cycles, 506 Egg size: age and, 521?; body size and, 32, 335, 502; clutch size/egg size, 459, 502-4, 502/", 503?; clutch size/egg size, genetic correlations, 503-4; as evolutionary compromise, 111; food availability and, 20; population dynamics and, 459-60; significant relationships of, 110 Egg-gathering as mortality factor, 41 Eggshell: formation of, 32; thinning from contaminants, 408 Egyptian Goose, 156-57, 161, 261, 498 Egyptian Plover, 67 Eiders: banding and, 430; breeding, timing of, 454; clutch size, 458, 459; convergent evolution, 558; diseases of young, 465; initial breeding and renesting, 455, 456; nest success, 461; population estimate methods, 426, 429; signal systems, 240-41; survival of young, 465; wetlands and nest sites of, 579-80. See also named species Eisenhauer, D. I., 459 Ekman, S., 155 Elander, M., 461 Eldridge, J. L., 33, 219, 238, 256, 576; on diet and clutch size, 458; on diet and nesting, 456; on egg size/clutch size, 459 Eldridge, W. D., 452 Elkins, W. A., 410 Elm, 14 Ely, C. R., 38, 269, 398, 405 Elymus arenarius, 571 Emancipation, 217 Emergents, 594, 595, 596, 598, 600 Emigration, 373 Emlen, S. T., 190, 379 Emperor Goose, 260, 414; agriculture and, 21; incubation, 64, 75, 76; mixed broods, 92; nutrient acquisition, timing of, 4; pair formation, 338 Emperor Penguin, 192 Endocrinology, of avian reproduction, 32430, 325f; testis, photoperiodic variations of, 332, 332f; testis, structure and function, 327; testis, stimulation by LH, 327. See also Environmental and

622 endocrine control of reproduction; Hypothalmus; Ovary and ovulatory cycle; Pituitary gland; named hormones Endogenous reserves: molt and, 143-44 Energy density of waterfowl eggs, 32, 33 Energy requirements of egg production, 32-40, 36-37?; egg laying interval and, 38-39; egg as unit of energy cost, 32-34; energy equivalents of egg formation, 39-40, 40f; energy flow schema, 3 If. See also Egg production, nutrient reserves and; Rapid follicular growth (RFC) Energy-limitation hypothesis, 295-98 Environmental and endocrine control of reproduction, 323-64, 352-56?; circadian rhythms, 332; circannual periodicities, 332, 334; hierarchical classification of information, 331-35; photoperiodic variations, 332; reproductive cycle, major phases of, 324; termination of reproduction, 348-49; ultimate environmental factors, 323, 341. See also Early wintering phase of reproduction; Endocrinology, of avian reproduction; Nesting phase of reproduction; Prebreeding phase of reproduction; Proximate environmental factors and reproduction Environmental sieve, 591 Erickson, C. J., 226 Eriksson, M. O. G., 498, 501, 581; on nest desertion, 306; on parasitism, 303, 311 Erwin, R. M., 429 Esophagus: food samples from, 1, 8?, 552 ESS. See Evolutionary stable strategy Essential fatty acids, 44 Estradiol, 328, 33 If Estrogens, 327-28, 347 Ethyl-parathione: as contaminant, 409 Eurasian Pochard, 158, 266, 293; breeding, timing of, 455; egg size, 459 Eurasian Teal: foraging behavior, 547f, 549 Eurasian Wigeon, 148, 158, 265 European Bullfinch, 156 European Eider, 231 European Shelduck, 231 European Starling: daily energy demands, 490, 490f European Wigeon. See Eurasian Wigeon Evans, C. D., 576 Evans, P. R., 295, 298, 299, 307, 465 Evolutionarily stable strategy (ESS), 274; brood parasitism and, 301-3, 302f, 302t Evolutionary Time Hypothesis, 544-45 Evolutionary trends: of brood amalgamation, 90; of brood care, 84, 84?; of brood parasitism, 306-7, 378; of clutch size, 30-31, 457; of courtship and displays, 217-18; egg size and, 111; evolutionary convergence and, 558, 558?; of growth patterns, 112-14; of habitat use, 121-22; of incubation, 62; of mating systems, 195-99; of nocturnal attentiveness, 63-64; of ritualization, 218; of signal systems, 243-44; of

INDEX spacing patterns, 251, 252, 254-56, 27475; of waterfowl, general trends, 84. See also Evolutionarily stable strategy (ESS); Reproductive patterns, evolution of Ewaschuk, E., 461 Exploitation competition, 551 Extrapair copulation (EPC), 191, 193, 194, 226 Fairy shrimp, 9, 11 Falkland Flightless Steamer Duck, 262 Falkland Upland Goose, 261 Fall age ratio, 433, 434-35 Familiarity: as mate choice criterion, 231 Farabaugh, S. M., 243 Farm machinery: as mortality agent, 405-6 Farner, D. S.: Avian Biology, xv Fat: analysis in diet, 4?; clutch size and, 19; egg lipids, 33, 33?, 50/", 51f, 55f, 110; energy and, 14, 44-45; metabolism of, 44-45; renesting energetics and, 505-6, 505f; reserves, 4, 53, 53?, 298 FC. See Forced copulation Feather(s): bioenergetics of, 135-36; chemical composition of, 136; development, 136-37; growth, efficiency of, 139; growth, rates of, 137-38, 138?; protein, 136, 142-43, 142/", 143?. See also Molt of waterfowl Feces: of geese, as fertilizer, 559; samples, in feeding research, 2, 3, 23 Feeding efficiency: philopatry and, 375-76 Fefer, S. I., 595 Femur calcium levels, 5 Fencing: predator fences, 603; upland management and, 601-2 Fendley, T. T, 574 Ferruginous White-eye, 267 Fertilizing: in wetland management, 605 Festuca rubra, 11 Fiber: nutrition and, 13 Filial imprinting, 229 Findlay, C. S., 471-72, 494, 512; on clutch size, 56, 402, 421, 459; on hatching synchrony, 465; on philopatry, 390; on predation, 466; on recruitment, 442 Fire: in habitat management, 605; upland management and, 600-601 Fischer, H., 229 Fischer, K. L., 467 Fish: as food choice, 9-10 Fitzpatrick, J. W, 276 5cc-DHT, 327 Fixed action patterns (FAP), 215-16 Flake, L. D., 427, 429, 432; on habitat, 584, 588; on pond use, 601, 602 Flicker, 580 Flight: power requirements for, 42 Flightlessness: duration of, 130, 131? Float counts, 432 Flooding: as mortality agent, 405-6 Flying Steamer Duck, 236, 262, 386; ducting call, 236, 23 6f; interspecific hostility, 236 Flyover: ecological time and, 545

Follicle stimulating hormone (FSH), 32; action on ovary, 326, 328; production, 324 Food(s) of breeding waterfowl: digestibility of, 23; food supplement experiments, 492, 492?; food tracers, as method of study, 3. See also Diet of breeding waterfowl; Foraging ecology and nutrition; Nutrition; Nutritional stress Foraging ecology and nutrition, 1-29; evolved patterns and, 10-11; fat and energy, 14; food availability and, 11-12, 12/"; food habits, 6-10; food use, factors of, 10-11; foraging efficiency, 15-17; foraging models, 15-17; historical perspective, 1-2; interspecies competition, 17-18; intraspecies competition, 17; minerals and vitamins, 14-15; nutrient sources and, 12-15, 13f; prefledglings and, 116-20, 118?; principle of lost opportunity, 16; reproduction and, 18-19; research methods of, 2-3; territoriality and, 17; timing of nutrient acquisition, 3-5; weather, impact on, 11-12. See also Food(s) of breeding waterfowl; Reproduction, food resources and Forced copulation (FC), 193-94, 200-201, 203, 254, 262, 263, 264, 265, 266; rape versus, 194; as secondary mating strategy, 193 Forster's Tern, 493? Frank, A. M., 453, 603 Freckled Duck, 160, 235, 261 Fredga, S., 307, 455-56, 465, 498, 523; on dispersal, 375 Fredrickson, L. H., 201, 572, 575, 581; on double broods, 455; on dump nests, 318, 465; on egg ratios, 468; on molt, 134; on protein and reproduction, 12-14; on range management, 608 Freeman, S., 311 Frequency dependence, 301-3 Fretwell, S. D., 549, 554, 565 Friend, M., 409 Frith, H. J., 233-34, 242, 517 Fullagar, P., 235 Fulvous Whistling Duck, 155, 259, 292, 385; incubation strategy, 65; molt, 133; wetlands and nest site selection, 569 Gadwalls, 198, 254, 340, 343; age of reproductive maturity, 453; breeding, timing of, 454; brood parasitism, 293; clutch size, 458; food choices, 9, 10, 158; incubation, 71; initial breeding and renesting, 455; molt, 147, 152; mortality, 407, 413; nest baskets, 597; nest sites of, 578; nutrient reserves, 54; philopatry, 367, 373, 375, 451, 452; plumage, 134, 135; spacing, 264, 265, 269; wetlands of, 576 Galliformes, 517, 527 Game management, defined, 542

INDEX Game theory: brood parasitism and, 301; spacing patterns and, 190, 274-75 Gammarus spp., 491 Garden Warblers, 331, 338 Garganey, 264 Gastropods, 15, 22 Gauthier, G. J., 30, 32-33, 49, 305, 310, 465, 527; on brood parasitism, 305; on clutch size, 458; on laying, 454; on nesting, 461, 580, 587; on philopatry, 375; on spacing, 269, 272, 273 Geese: activity metabolism, 140-42; adaptations to molt, 153; age of reproductive maturity, 113, 453; agriculture and, 21; body mass variations, 113; brood parasitism, 292; defense of young, 89; diet, 117; family bonds, 84; feeding ecology, 2, 3; fire and, 600, 601; food composition, 13f; food digestibility, 14*; food habits of, 7, 8*; foraging and foraging effort, 5*, 11, 117; as full-time vegetarians, 43; genetic variations, 384-85; growth, duration of, 112-13; habitats, 160, 425; incubation constancy, 73, 76*; laying frequency, 38; molt, 132, 133; mortality, 400*, 401, 402, 403*; mortality, in arctic tundra region, 414; nest sites, 570-72, 571*; nesting times, 491; nutrient reserves, 143; pair bonds, 452; philopatry, 37273, 372*, 3 731, 451; postbreeding movements, 156; predators and, 406; protein and reproduction, 12-13; reproductive/postbreeding interrelationships, 147-48; signal systems, 234; soil fertilization by, 559; spacing, 256, 260-61; timing of nutrient acquisition, 3-5; triumph ceremonies, 224; vertebrates and, 593; wetlands of, 569. See also named species and subspecies Geis, A. D., 434 Gene flow, 377, 383, 386; definition, 366; measurements of, 387 Genetic structure of waterfowl, 376-78, 382-87; allozyme electrophoresis, 384, 385, 386; altruism and, 377-78; clinal variation, 383; geographic variation, 383; hybridization, 383; inbreeding avoidance, 376-77, 379; kinship and, 377-78; measurements of, 386-87; mitochondrial DNA (mtDNA) analysis, 384, 386; monotypic species, 382; optimal discrepancy theory, 377, 379, 380; pairing and, 382; panmixia, 382, 386; polytypic species, 382; restrictionfragment length polymorphisms (RFLP), 386; sex-biased dispersal and, 379; subspecies variations, 383; variation patterns, 383-86; Wright's F statistic, 386. See also Gene flow George, J. C., 43 George, R. R., 603 Geyr von Schweppenburg, H., 254

Giant Canada Goose: corn consumption, 7, 339, 340; egg fertility, 20; egg laying sequence, 34; fat requirements, 14; foraging habits, 11; laying frequency, 39; nutrient acquisition, timing of, 3; nutrient storage, 49; thermoregulation, 40 Gilbert, A. B., 32, 35 Gillespie, J. H., 300 Gilmer, D. S., 265, 456, 458, 460, 573-74; on mortality, 417; on postbreeding movements, 157 Giroux, J.-F., 140, 308, 571, 578, 604 Gizzard: atrophy, 46; food samples from, 1 Gladkov, N. A.: The Birds of the Soviet Union, xv Glaucous-winged Gulls, 524 Gleason, H. A., 591 Gluesing, E. A., 468-69, 576 Glutz von Blotzheim, U. N., 233 GnRH. See Gonadotropin-releasing hormones Goddard, J., 428 Godin, P. R., 576 Golden Eagle, 406 Golden-winged Sunbird, 253 Goldeneye, 162; clutch size, 458, 459; hatching reserves, 110; initial breeding and renesting, 456; interspecific competition and, 17; signal systems, 240-41; survival of young, 465, 466; territoriality and, 17; timing of breeding, 454; wetlands and nest sites of, 580-81 Goldsmith, A. R., 229 Gollop, J. B., 376, 467 Gompertz equation, 111, 112 Gonadal recrudescence, 329 Gonadotropin-releasing hormones (GnRH), 324, 326 Gonadotropins, 328 Good body condition hypothesis, 298 Goodall, J., 276 Goodwin, B., 429 Gordon, David H., 30, 128-89 Gottlieb, G., 220 Grains: as fat source, 14 Grasses: as choice of ducks, 10; as principal food of geese, 7, 8* Grau, C. R., 35 Gray, B. J., 35, 120 Gray Duck, 158; brood parasitism, 293; timing of breeding, 455 Gray Teal, 158, 227, 345; brood parasitism, 293; timing of breeding, 18 Gray wolf, 406, 411 Graylag Goose, 156, 229, 234, 260; agriculture and, 21; brood parasitism, 292; foraging habits, 11; incubation, 73 Grazing and grazing management, 601-2 Great Horned Owl, 406 Great Tit, 376, 377, 379; postfledgling survival, 488 Greater Magellan Goose: molt, 130

623 Greater Scaup, 161, 293; clutch size, 19, 459; molt, 134; nest sites, 579; wetlands of, 578 Greater Snow Goose, 260, 271; activity metabolism, 140, 141; agonistic interactions of, 17; food habits of, 7; genetic variation, 384; nutrient acquisition, timing of, 4; nutrient storage, 49 Greater White-fronted Goose, 495; timing of nutrient acquisition, 4 Green, C., 215 Green Goose, 157 Green needlegrass, 603 Green Pygmy Goose, 263 Green-winged Teal, 158, 208, 222, 265, 333; endocrinology, 328, 336, 337, 338; feather growth, 138; feather-growth cost, 140; molt, 148; nocturnal incubation, 63; nonbreeding, 343; pairing and dominance, 340; philopatry, 451; photorefractoriness, 349 Greenland Mallard, 385 Greenwood, H., 449 Greenwood, P. J., 196; mating system hypothesis, 381; on philopatry, 366, 376-81 Greenwood, R. J., 460, 600 Grenquist, P., 299, 305 Grice, D., 299, 399, 515 Grier, J. W., 373, 430, 574; on philopatry, 451, 452 Grieve, R. W., 559 Griffith, M. A., 574 Griminger, P., 45 Grizzly bear, 411 Grossman, M., Ill Ground counts, 427 Group living of waterfowl: benefits of, 25658; conflict and, 258; costs of, 258 Growth and development of waterfowl, 110-14; fledging weights, 112-13*; Gompertz growth equation, 111-12; growth patterns, impact of, 112-14; growth rates, variations in, 111-12, 11213?; hatching reserves and, 110-11; nutrition and, 114-20; thermoregulation and, 110. See also Prefledging waterfowl, ecology of Guild(s), 540-42, 559 Guiler, E. R., 261 Guillemots, 410 Gulls: egg-gathering as mortality factor, 410; nesting near ducks, 571, 580; as predators, 90, 407, 412, 460, 604 Haapanen, A., 435, 549 Habitat management for breeding areas, 590-610; management process, 594-95; principles of, 590-95; saline habitats, 605; water level and, 591; water quality and, 591; waterfowl/fish competition, 605-6. See also Upland management; Wetland ecology; Wetland management Habitat-settlement hypothesis, 508-9

624 Habitats: availability and population estimates, 430; competition and, 554; evolved patterns of, 10-11, 10/"; measures of recruitment and, 425. See also Breeding habitats of Nearctic waterfowl; Habitats of postbreeding waterfowl Habitats of postbreeding waterfowl, 15563; adaptive significance of, 162-63; fidelity to areas, 159-60; movements of postbreeders, 155-58, 169-73?; patterns of use, 159-62, 174-81* Hail: as mortality agent, 405 Hailman, J. P., 215 Hair, J. D., 229 Halliday, T. R., 215 Hamann, J., 511 Hamilton, W. D., 380 Hamilton, W. J., Ill, 295 Hammack, J., 439 Hammond, M. C., 453-54, 465, 468; on population, 426, 431 Hand, C. M., 16 Handbook of Ethological Methods (Lehner), 243 Handbook of Waterfowl Behavior (Johnsgard), 214 Hansen, H. A., 452 Hansen, J. L., 201, 455 Hanson, B. J., 45 Hanson, G. A., 406 Hanson, H. C., 271, 410; on molt, 128, 139, 144, 149, 151 Hanson, W. C., 406, 463 Hansson, L., 465 Haramis, G. M., 374, 429, 449-50, 466 Hardhead, 19 Hardstem bulrush, 596, 601 Hario, M., 455, 459 Harlequin Duck, 194, 267; breeding and food supply, 19; clutch size, 458; philopatry, 371; wetlands and nest sites of, 581 Harmsen, R., 464 Harper, D. G. C., 257 Harris, L. D., 461 Hartlaub's Duck, 263 Hartley, D. R., 574 Hartman, G. W., 299, 465 Harvest management: breeding population inventories and, 424-25; recruitment measures and, 425 Harvey, P. H., 273, 366, 376 Harwood, J., 119, 601 Hatch rate of eggs. See Nest success Hatching and nest exodus: brooding habitats, 82-83; brooding of hatchlings, 81-83, 82?; duckling mortality, 83; emergence and drying, 81-82; hatching reserves, 110-11; nest departure, 82-83, 83/; pipping, 81; stages of, 81 Hatching synchrony hypothesis, 512 Hawaiian Duck, 385 Hawaiian Goose, 156, 259, 410; breeding, timing of, 454; clutch size, 458; egg size,

INDEX 459; initial breeding and renesting, 455; nest sites of, 570 Hawaiian Honeycreeper, 253 Hawkins, A. S., 426, 437 Hawks, 407 Hay-cutting: waterfowl mortality and, 405-6 Hays, H., 242 Heagy, M. I., 559, 571 Heath, 571 Heavy metals: as contaminants, 594, 597 Heinroth, O., 200, 214, 221-23, 234, 254 Heitmeyer, M. E., 139, 339, 468, 572 Helicopters, 428; nest counts by, 432 Hemi-marsh, 551, 575, 592 Hemicellulose: metabolization of, 3 Hempitera, 119 Hen success rate, 430-31. See also Nest success Henny, C. J., 452; on broods, 465, 467, 469 Hepp, G. R., 229, 449, 453, 455 Heptachlor: as contaminant, 407 Herbicides, 594, 597-98; impact on breeding, 22; upland management and, 602-3 Herring Gulls, 522, 524 Heusmann, H. W., 301, 307, 458, 574 Heyland, J. D., 429, 432 Hiding postures, 68 Hier, R. H., 374 Higgins, K. R, 602, 604 Hilden, O., 463, 465 Hill, D. A., 116,461,466 Hill, E. P., 574 Hinde, R. A., 216 Hines, J. E., 450; on survival, 477, 480, 481 Hochbaum, G. S., 387, 574; on spacing, 253 Hochbaum, H. A., 254, 305, 387, 451; on molt, 133; on molt migration, 162; on nuptial courtship, 226; sex of hatchlings, 464 Hogstedt, G., 493-94 Hohman, William L., 128-89; on molting, 30; on protein intake, 120; on remiges, 149 Holekamp, K. E., 378 Home range: of species, 272-73, 278-81? Homing rate, 366-67 Hooded Merganser, 267, 294, 304, 408, 581 Hori, J., 90, 254, 457, 466 Horn, H. S., 271 Hornbill, 130 Horsetails: as calcium source, 14-15 Host, brood parasitism and: aggression and nest guarding, 305; antiparasitism responses, 306; benefits of being parasitized, 303-4; costs of being parasitized, 303; egg recognition and manipulation, 305-6; evolution of host response, 306-7; nest desertion, 306;

precocial young hypothesis, 303-4; reduced brood mortality hypothesis, 304 Hottentot Teal, 265 House finch, 72 Houston, A. L., 253 Howard, Eliot, 252 Howey, P. W., 66 Hudson, M. S., 601 Huggins, R. A., 72 Humphrey, P. S., 129, 268; on plumage, xv Hunter, M. L., Jr., 116,408 Hutchinson's 1.3 Rule, 554, 554? Hybridization, 383 Hydrosere, 591 Hypothalmus, 324, 325/", 326; control of hypothalamic functions, 326-28; folliclestimulating hormone (FSH), 324; gonadotropin-releasing hormones (GnRH), 324, 326; luteinizing hormone (LH), 324; luteinizing hormone-releasing hormone (LHRH), 324, 326; steroid hormones, inhibitory feedback by, 32627; steroid hormones, stimulatory feedback by, 327 Ibister, R. J., 428 Immelmann, K., 229 Imprinting, 82, 220; filial imprinting, 229; sexual imprinting, 229, 231 Inbreeding avoidance, 231, 376-77, 379 Inciting displays, 222, 230, 235, 237, 266 Inclusive fitness, 190 Increased fecundity hypothesis, 301 Incubation of waterfowl, 62-83; air-cell temperature, 63f, 63?, 67f, 68, 69f; body size and, 73-75, 76?; body weight and, 77-81, 78-79?, 80?; breaks, 62; brood patch and, 67, 67f, 68?; commencement of, 62-63; defined, 62; egg turning, 66, 72-73; energetic needs of parents, 77-81, 78-79?; evolution of, 62; feeding during, 78, 80?; female-only incubation, 64; gaseous environment, 70-72; hiding postures, 68; incubation constancy, 62, 76t, 81; incubation metabolic rate (INCMR), 79; incubation period, 62; incubation rhythms, 73-77, 74-75?, 76?; incubation rhythms, interspecific analyses, 73-77; incubation rhythms, intraspecific analyses, 74-75?, 77; males and, 64-66; mechanical environment, 72-73; methods of study, 66; nest environment and, 66-73; nest humidity, 66, 71-72, 71?; nocturnal incubation, delay of, 63-64; nutrient acquisition and, 4; ovarian responses to, 329-30; predation and, 62, 64, 75-76, 83; recess metabolic rate (RECMR), 79-80; recesses, 62, 73, 74-75?, 76?, 80?, 81; resettling rates, 68; sessions, 62; shared incubation, 64; sitting spells, 62; strategies, diversity of, 64-66; thermal environment of, 67-70, 67f, 68?, 69?, 70?; weather and, 73. See also Hatching and nest exodus; Nest(s); Nest success

INDEX Indiangrass, 603 Indirect selection (kin parasitism) hypothesis, 304-5 Inglis, I. R., 93, 256 Injury-feigning, 90 Insects: as food source, 7, 9t, 11, 22 Instability Hypotheses, 558-59 Intention movements, 221, 222 Interegg communication, 507 Interference competition, 551 Interior Canada Goose: calcium requirements, 15; timing of nutrient acquisition, 3, 4 Intermediate Disturbance Hypothesis, 558 Intermediate wheatgrass, 603 Interspecific competition: foraging and, 17-18 Intraspecific competition: agonistic interactions, 17; dense nesting and, 38; foraging and, 17 Invertebrates, 12f, 256, 575-77; breeding female ducks and, St, 13; contaminants and, 408, 409; drawdown and, 595; as food source, 1, 7, 8t, 14; prefledgling survival and, 116; recruitment rates and, 22; resource distribution, 256; size of, 546f; wetland ecology and, 592-93; wetland management and, 605-6 Isakov, Y. A., 426, 436 The Island Waterfowl (Weller), xv Islands: brood parasitism on, 299; constructed, upland management and, 604; natural, upland management and, 604; oceanic islands and clutch size, 496-97; predators and, 604 Isolation Fields: spacing patterns and, 274 Jackson, D. H., 455 Jackson, S. L., 571 Jacobson, J. D., 430 Jaegers, 407, 412, 433 Jallageas, M., 337 Japanese Quail, 231 Jarvinen, O., 550, 554 Jarvis, R. L., 464, 466; on survival, 422 Jeffries, R. L., 559, 601 Johnsgard, P. A., xv, 385, 517; on courtship, 228, 229; on hybridization, 383; on incubation, 62, 65; on males and nests, 202; on signal systems, 233, 235; taxonomy, xiv, 214, 218, 219, 220 Johnson, A. L., 32 Johnson, Douglas H., 446-85; on breeding, timing of, 453-54; on brood size, 465; on habitat and breeding, 574; on mortality, 404-5, 413; on nest success, 398, 419, 607; on philopatry, 373, 451, 452; on population, 424, 430, 431, 432, 437, 440; on predation, 460; on recruitment, 442; on weather and reproduction, 468 Johnson, D. J., 308 Johnson, D. W.: on nest success, 398 Johnson, F. A., 449, 473 Johnson, K. L., 451

Jolly, G. M., 435-36 Jolly-Seber, G. A., 430 Jones, P. J., 491 Jones, R. E., 309 Jones, W. T., 378, 380 Jorde, D. G., 455 Joyner, D. E., 309, 576 Juanes, E, 273 k-selection, 335 Kaczynski, C. E, 436 Kadlec, John A., 590-610; on burning, 596; on food provisioning, 493; on habitat, 576, 577, 588; on invertebrates, 592, 595 Kaiser, P. H., 601 Kalmbach, E. R., 398, 430 Kaminski, Richard M., 568-89; on age ratios, 468, 469; agriculture and habitat, 561; counts by helicopter, 428, 432; on determinants of diversity, 551; on habitat, 575, 576, 577, 587; on nesting, 570, 571 Kantrud, H. A., 424, 435-36, 574-75, 578; on burning, 596; on predation, 593 Kasul, R. L., 447 Kauppinen, J., 427 Kear, J., 62, 204, 459, 561; on daylength and nesting, 341; on evolutionary trends, 244; on radiotelemetry, 102; on signaling, 233, 234 Kehoe, F. P., 319, 465, 554; on brood amalgamation, 100 Kelp Goose, 261; genetic variation, 385 Kendeigh, S. C., 62, 65 Kennamer, R. A., 455, 480 Kentucky bluegrass, 600 Kerbes, R. H., 376, 429, 432 Kesterson National Wildlife Refuge: selenium concentrations, 15, 597 Khaki Campbell Duck, 328, 329, 336 Kielanowski, J., 46 Killing: interspecific, 268; of intruders, 306 Kimball, C. E, 434, 439 Kin parasitism (indirect selection) hypothesis, 304-5 Kinetic energy, 31 King Eider, 267, 580; mortality, 405; nest success, 461; predation, 406; timing of nutrient acquisition, 6 King, J. G., 427 King, J. R., 18, 35, 505, 514; Avian Biology, xv; on feather composition, 136; on molt, 139, 152; on plumage, 129; on reproductive energy costs, 31, 38, 39, 40 Kingsford, R., 237, 263 Kinship, 375; genetic structure and, 377-78 Kirby, R. E., 427 Kirikov, S. V, 478 Kirsch, L. M., 600, 601, 603 Kit fox, 411 Klaasen, M., 42 Klein, D. R., 410 Kleptoparasitism: as competition, 551

625 Klett, A. T., 456, 577, 603; on nest success, 398, 405, 413, 432; on recruitment, 442 Klint, T., 154, 229 Knapton, R. W., 271 Knighton, M. D., 595 Koenig, W. D., 517 Koskimies, J., 92, 267, 455, 512 Krapu, Gary L., 1-29; on clutch size, 458, 459, 526; on egg size, 33; on habitat, 283, 456, 585; on mortality, 405, 464; on nutrient storage, 54, 56, 57; on nutrition and reproduction, 576; on survival, 107, 126, 422, 466; on weather and reproduction, 343 Krasowski, T. P., 579 Krebs, J. R., 225, 272 Krebs cycle, 47 Krementz, D. G., 447, 449 Kroodsma, D. E., 215 Kruijt, J. P., 228-29 Kruse, A. D., 600 Kutz, H. L., 336 Labrador Duck, 410 Lack, David B., 253, 497, 500, 502-3, 51517; clutch-size hypothesis, 30; on competition, 552, 555, 558; on egg size, 32-33, 110; on food limitation, 489; on site familiarity, 375 Lacki, M. J., 574 Lahti, L., 92 Lamprecht, J., 499 Lamson, G. H., 71 LANDSAT, 434 Lank, D. B.: on philopatry, 378 Lapwing, 494 Larids: as prey and predator, 461 Late nesting index, 434 Laughlin, K. E, 295, 298 Laurie-Ahlberg, C. C., 229 Laurila, T., 455, 459, 517 Laying-delay hypothesis, 489 Laysan Duck: timing of breeding, 454 Laysan Teal, 194, 220, 385 Lazarus, J., 93, 257 Lead: as contaminant, 407-8, 409 LeBlanc, Y., 464, 465 Lebret, T., 226-27, 254 Lee, F. B., 451 Leech parasitism, 409 Lehner, P. N., 243 Lehrman, D. S., 227 Leitch, W. G., 468, 561, 569 Lendrem, D., 274 Leopold, A. S., 309, 542 Lessens, C. M., 148, 459, 497, 499, 503; on egg size/clutch size, 504; on molting, 133, 148, 153; on philopatry, 372, 376 Lessels, K., 56 Lesser Magellan Goose: molt, 130 Lesser Scaup, 93, 161, 163, 258, 336; activity metabolism, 141; age and reproduction, 453, 467; breeding, timing of, 454; brood care, 87, 93; brood parasitism, 293; brood-rearing areas, 82;

626 clutch size, 458, 5l8f; drought and breeding, 468; fat reserves, 53, 53t; flightlessness, 130; food choices, 9, 43; forced copulation, 200; growth rates, 111; initial breeding and renesting, 455, 456; laying times, 491; molt, 133, 139, 143, 147, 148, 154; mortality, 407; nest success, 461; nesting, 343, 344, 345, 579; nocturnal incubation, 63; nutrient acquisition, timing of, 6; nutrient storage, 49; philopatry, 373, 374, 451, 452; spacing, 266; survival of young, 465; thermoregulation, 41; wetlands of, 578, 579 Lesser Snow Goose, 90, 232, 347, 491; activity metabolism, 140, 141; agonistic interactions of, 17; agriculture and, 21; banding and, 430; brood care, 93; brood parasitism, 292; clutch size, 19, 513; egg composition, 20, 34; egg laying frequency, 38; egg laying sequence, 34; egg laying, timing of, 38; egg size, 33, 459; endocrinology, 328, 329; energy/ nutrients, 143; fat requirements, 14; flightlessness, 152; follicle formation, 18; food habits of, 7; forced copulation, 200, 201; genetic variation, 384, 387; hatching reserves, 110; incubation, 69, 75, 80; maturing age, 335; mixed broods, 92; molt, 139; molt migration, 156; mortality, 402; nesting, 344, 571; nocturnal incubation, 64; nonbreeding of, 19; nutrient acquisition, 3-5; nutrient reserves, 49, 54, 55; nutrients and habitat, 30; pair formation, 328; philopatry, 372, 376; predation and, 494; protein and reproduction, 13; soil fertilization by, 559; spacing, 253, 256, 260, 261; weight and migration, 340 Lesser Whistling Duck, 65 Lesser White-fronted Goose, 156, 260 Leucocytozoon parasitism, 409 Leydig cells, 327 LH. See Luteinizing hormone LHRH. See Luteinizing hormone-releasing hormone Liaison, 226 Lieff, B. C, 116, 119, 120, 455 Lifespan: body size and, 334-35 Lightbody,J. P., Ill Lima, S. L., 272 Limpert, P. J., 374 Lincoln, F. C., 365, 424 Linde, A. E, 595, 600, 601 Linoleic acid: as essential fat, 14 Lipids. See Fat Little bluestem, 603 Livezey, B. C., 268, 433, 577, 593, 603; on classification, xvi Lockman, D. C., 569 Loggerhead Shrike: daily energy expenditures, 42 Lokemoen, J. T., 451, 461; on cover, 603; on electric fencing, 603; on nesting, 577,

INDEX 578, 584; on philopatry, 375, 388; on range management, 601 Long-tailed Duck, 22, 134, 147, 162, 240 Long-tailed Skuas, 461 Longcore, J. R., 408, 465, 579 Lorenz, K., 214-18, 228-29, 237 Lost opportunity, principle of, 16 Lostwood National Wildlife Refuge, 413 Lovvorn, J. R., 45-46 Low, J. B., 75, 309 Lumsden, H. G., 304, 406; on nest boxes, 581; on nest parasitism, 465; on pond use, 570 Lundberg, A., 493 Lure areas and crops, 602, 606 Luteinizing hormone (LH): action and levels, 326, 329, 330f, 33lf, 333f, 338; production, 322 Luteinizing hormone-releasing hormone (LHRH), 324-26 Lynch, G. M., 464 McAuley, D. G., 408, 465, 579 Maccoa Duck, 195, 199, 209, 241, 242; incubation, 75; molt, 130; polygyny, 203; spacing, 268 McCullough, G. B., 467 Mace, G. M., 273 McEnroe, M. R., 576 Maclnnes, C. D., 38, 455, 501, 504, 512; on brood rearing, 376; on clutch size, 56; on food selection, 125; on mortality, 414; on nesting studies, 433 McKinney, Frank, 214-50; on aggression, 305; on displays, 264; on forced copulation, 210; on mating, 380; on pairing, 229; on spacing, 254, 255, 256, 269, 270, 273, 281 McKnight, D. E., 130, 452 McLandress, I., 384 McLandress, M. R., 339, 384, 429, 570 McNab, B. K., 273 McNaughton, S. J., 258 Macoma, 45 Macroinvertebrates. See Invertebrates Macrophytes, 592 Madsen, J., 3, 162, 557 Magellan Goose: genetic variation, 385 Magellanic Flightless Steamer Duck, 262 Magnesium deficiency, 15 Magpie Goose, 159, 233-34, 345, 486; brood care, 86-87, 88; defense of young, 89; distribution, 155; family bonds, 84; incubation strategies, 64-65; male and incubation, 64, 147; molt, 130; parental feeding of young, 85, 88, 233; polygamy, 84, 195; polygyny, 196, 202, 204-5, 209; postbreeding movements, 155; sibling rivalry, 233; spacing, 259 Maj, M. E., 569 Majewski, P., 373 Makepeace, M., 465, 469 Male-male interactions, 228 Malecki, R. A., 427

Mallard, 161, 196, 198, 208, 215, 216; activity metabolism, 141; aerial chases (pursuit flights), 254; banding of, 430, 434; body fat and, 55f; body mass variations, 44, 49; breeding, timing of, 19, 451, 452; brood care, 87, 93; brood-pair ratios, 469; calcium requirements, 14; calls of, 220, 221; clutch size, 458, 459, 518/; contaminants and, 408, 409; counting, difficulty in, 431-32; counting methods, 439; courtship, 226, 227, 228, 346; defense of territory, 95; diet and breeding, 346; diet and eggs, 20, 34; diet and weight, 340; diseases, 409; drought and breeding, 468; egg loss, 462; egg size, 19, 459; endocrinology, 328-32, 335-39; fat reserves, 21, 53, 53t, 54; feather-growth cost, 140; feathers, composition of, 136; fire and, 600; flightlessness, 130; flooded habitats and food, 11; food choices, 16, 43; food and site selection, 257; food sources of, 1, 7, 9; forced copulation, 200-201; genetic variation, 385, 386; grazing and, 601; habitat productivity and, 545; harvest management, 387; hatching, 81; hatching reserves, 110; homosexual attachments, 228; imprinting, 229; incubation, 68, 71, 72, 75; initial breeding and renesting, 455, 456; laying times, 488; molt, 134, 139, 147, 148, 152, 154; molt migration, 158; mortality/survival, 398, 405, 407, 413, 447, 449, 450; mortality/survival of young, 466; nest baskets, 597; nest success, 460, 461; nest temperature, 72; nesting, 56, 342, 343, 344, 348, 577-78; nocturnal incubation, 63; nutrient acquisition, timing of, 5; nutrient storage, 49, 55f, 57, 491; nutrients and habitat, 30; pairing, 231, 232; pairing and dominance, 340; pairing and molt, 341; philopatry, 367, 372-76, 451, 452; photorefractoriness, 349; plumage, 134; population, 412-13, 424; a population model, 470-71; power requirements, 42; predation of, 406; protein utilization, 46, 47; renesting, 19; reproductive rate, 468; ritualized inciting, 222; signal systems, 238; spacing, 265, 268, 272-73, 274; territoriality, 253, 254, 259; thermoregulation, 40, 41; wetlands of, 575-76 Mallee Fowl, 71 Mandarin, 237, 263 Maned Duck, 237, 263, 345; food choices, 10 Manx Shearwater: postfledgling survival, 488 Marbled Teal, 265 Marcy, L. E., 597 Mark-recapture: population estimates by, 430 Marks, J. S., 380

INDEX Marler, P., 215 Marshall, I. K., 461 Marshall, W. H., 398 Martin, F. W., 437, 439 Martin, Robert, 216 Masked Duck, 268; wetlands and nest sites of, 582 Masman, D., 42 Master, T. L., 94 Mate defense: social courtship and, 227-28; versus resource defense, 379-80 Mate-switching, 231 Mathiasson, S., 137 Mating systems of waterfowl, 190-213; alternative mating strategies, 191, 199202, 200*; breeding habitats, 174-81*; breeding patterns, 166-69*; brood parasitism and, 201-2; double brooding, 201, 455; ecology and evolution of, 195-99; environmental factors and, 208-9; extrapair copulations (EPC), 191, 193, 194, 226; history of, 190-91; inclusive fitness and, 190; intersexual competition, 190; intrasexual competition, 190; late or nonpairing waterfowl, 199; mating system theory, 191-92; operational sex ratio, 191; overview of, 193-94, 194*, 195/"; parental investment, 190; polyandry, 192; promiscuity, 191, 195; resourcedefense polygyny, 191, 198; secondary mating strategies, 195; secondary reproductive strategies, 199; sex ratios and, 207; social systems and, 190, 19293, 192f; territoriality and, 205-8. See also Courtship and pair formation in waterfowl; Forced copulation; Monogamy; Polygyny Maximum daily egg energy (MDEEG), 39-40, 40/" Maximum sustainable yield theory, 542 May, R. M., 561 Mayfield, H. E, 431, 437, 460; nest success method, 398,413,431 Maynard Smith, J., 190 Mayr, E., 214, 219, 383, 385; classification system, xv-xvi MDEEG. See Maximum daily egg energy Mednis, A. A., 375, 379, 451 Medullary bone: mineral storage and, 48 Megapodes, 67, 72 Mendall, H. L., 429, 457 Mendenhall, V. M., 464, 465 Mercury: as contaminant, 408 Mergansers: cooperative foraging, 257; food choices, 9-10; wetlands and nest sites of, 581. See also named species Mergini. See Sea ducks Metabolism: activity metabolism, 140-42; basal metabolic rate (BMR), 36-37*, 38, 41*, 80, 110; body size and, 334; egg size and, 110; incubation and, 77-81; incubation metabolic rate (INCMR), 79; maintenance metabolism, 139-40; metabolic rate, 32; productive

metabolism, 142-43; recess metabolic rate (RECMR), 79-80 Meyers,!. U, 451 Midge, 11 Miers, K. H., 65 Migration: ecological definition, 366; genetic definition, 366; nutrient storage during, 49; site fidelity, 374 Migratory Bird Treaty (1916), 410 Mihelsons, H. A., 375, 379, 451, 465 Milfoil, 598 Miller, E. H., 215, 243 Miller, H. W., 398 Miller, M. R., 554 Miller, R. S., 551 Miller, W. R., 451, 457 Milne, H., 374, 453, 458; on laying dates, 455; on mortality, 464, 465 Mineau, P., 256, 305 Minerals: mineral reserves, 48; requirements for reproduction, 14-15 Mink, 406, 407 Misra, R. L., 414, 433 Mitochondrial DNA (mtDNA) analysis, 384, 386 Mock, D. W., 233 Mollusks: as calcium source, 14; as food choice, 7, 9 Molt of waterfowl: adaptations for, 153-54; alternate plumage, 129; basic plumage, 129; body feather replacement, 131-33; defined, 129; definitive plumage, 129; delay of, 495-96; duration of, 131-32, 166-69*; endogenous reserves and, 14346; exogenous contributions to, 146-47; feather coat, 129; feather growth, efficiency of, 139; flightlessness, duration of, 130, 131*; molt intensity, 138-39; mortality/survival and, 154-55; occurrence, by taxa, 166-69*; patterns of, 129-34; plumage, defined, 129; plumage in postbreeding period, 134; sexual differences in, 133-34; supplemental plumage, 129; survival risks, 154-55; tribal differences in, 13233; wing feather replacement, 129-30; wing molt, simultaneous, 129-30. See also Bioenergetic (nutrition) of postbreeding waterfowl; Feather(s); Nutritional stress Molting sites: fidelity to, 374 Monk Parakeets, 263 Monogamy, 191, 226; annual, 193-94; annual with re-pairing, 194-95; demographic effects and, 197-98; female philopatry and, 196-97; female-biased parental care and, 195-96; pair-bond duration and, 197, 197*; perennial, 193; reproductive options and, 199-202, 200*; serial monogamy, 201; sex ratios and, 196; timing of pairing and, 198-99, 198* Moore, J. H., 48, 378, 380 Moorhen, 205 Moreau, R. E., 515

627 Morphology: evolved patterns of, 10-11, 10f; as mate choice criterion, 232; morphological adaptation, 42 Morse, T. E., 499, 581 Mortality/survival of breeding waterfowl, 50, 396-414, 447-50; age and, 447-49; annual survival rate, 447, 448*; of arctic tundra region, 396, 397map, 411-12; body size and, 447; capture/recapture as study method, 448, 450; collisions as mortality agent, 403-5; condition of birds and, 449; diseases and, 409; geographic variations, 449-50; methods of assessing, 396-98; molt and, 154-55; mortality agents, 399*, 400*, 403-10; mortality rates, 399*, 400*, 401; population density and, 450; postbreeding waterfowl, risks of, 15455; of prairie pothole region, 396, 397, 41lmap; predation and, 406-7; sex and, 449; social status of birds and, 449; species variations and, 447; subsistence hunting and, 409-10; survival rate estimates, 448*; weather and, 405-6, 450; wetland habitat and, 450. See also Brood mortality/survival; Eggs, mortality/survival of Mortensen, C. E., 162, 557 Morton, E. S., 222 Moss, D., 522 Moss, R., 276 Motivational conflicts, 216-17 Mottled Duck, 157; activity metabolism, 141; brood care, 87, 92, 93; broodrearing areas, 82; feeding pattern, 142; genetic variation, 385, 386; habitat selection, 94; hatching, 81; survival, 449 Mountain Duck, 112, 373, 382 Mowing: upland management and, 603; wetland management and, 597 Moyle, J. B., 547 mtDNA. See Mitochondrial DNA analysis Mulhern, J. H., 575 Mundinger, J. G., 602 Munro, J., 90, 465 Munro, R. E., 434, 439, 468 Munro, W. T., 432 Murdy, H. W., 253, 453 Murkin, H. R., 575-77, 592 Murphy, M. E., 18, 129, 136, 139, 152 Murphy, S. M., 577, 579 Murray, B. G., Jr., 376 Murton, R. K., 341 Muscovy, 195, 204, 209, 229; spacing, 262; wetlands and nest sites of, 574 Musk Duck, 158, 162, 195, 199, 209; breeding, timing of, 19; care (and carrying) of young, 88, 90, 294; clutch size, 496; display, 241, 242; philopatry, 282; polygyny, 203-4; source of odor, 242; spacing, 268; timing of breeding, 19 Muskrat, 569, 593, 596, 604; trapping, as mortality agent, 410 Mussels, 16, 580

628 Mute Swan, 23, 156, 160, 234, 403; breeding, timing of, 454, 455; carrying of young, 90; clutch size, 458, 459; dispersal, 384; duration of RFC, 35; egg composition, 20, 34; endocrinology, 337; feather growth, 137, 138; genetic variation, 384, 387; inbreeding, 377; initial breeding and renesting, 455, 456; interspecific killing, 268; mortality, 403; nesting, 19; nutrient reserves, 54, 493; philopatry, 375; spacing, 259-60, 268, 274; wetlands of, 569 Myers, J. P., 272 Natal dispersal, 366, 372?, 380 Natal philopatry, 366, 367 A Natural History of Ducks (Phillips), xv Nearctic Aythyini, 158 Nearctic Brant, 156 Nelson, J. W., 592, 604 Nelson, M. C, 569 Nenes, 111 Nereis spp., 94 Nest(s): counting methods, 432-33; in crop stubble, 602; desertion, 30, 461; gaseous environment of, 70-72, 71?; location and brood parasitism, 308; mechanical environment of, 72-73; nest baskets, 597; nest box program, 596-97; nest platforms, 597; nest site availability and, 494-95; nesting structures, 292, 570, 581, 596-97; predators and, 35, 347-48; thermal environment of, 67-70, 67f, 68?, 69t. See also Eggs, mortality/survival; and other Nest and Nesting entries Nest boxes, 292, 570, 581 Nest success, 398-402, 401*, 430-31, 46062; age of bird and, 460, 522?; artificial nests as study method, 398; bias in estimating, 398; breeding experience and, 460; condition of bird and, 460; human beings and, 461; Mayfield method, 398; nest abandonment and, 461; nest destruction, 398; nesting habitat and, 460-61; population density and, 461; predation and, 461; weather and, 461. See also Egg(s), mortality/ survival of; Hen success Nesting phase of reproduction, 324, 34148, 354-56?; daylength and, 341; nesting dates, 521?; non-mate conspecifics and, 347; nutrient storage during, 49; nutrition and, 346; predation and nest disturbance, 347-48; social factors, 34647; temperature and, 341-42; weather and, 343-46 Nesting phenology: nutrient storage and, 49 Nesting structures, 292, 570, 581, 596-97 New Zealand Brown Teal, 382 New Zealand Shelduck, 146, 157, 159, 161, 194; spacing, 262; territoriality and mating, 206-7 Newman, K.: Birds of Africa, xv Newton, I., 265, 276, 453, 456 Nice, M. M., 258, 375, 486

INDEX Niche Complementarity Hypothesis, 554-55 Niche Compression Hypothesis, 552 Niche Overlap Hypothesis, 552, 556 Niche shifts, 557-58; convergence from adaptation, 558, 558? Nichols, James D., 446-85, 447, 450, 576; on mortality/survival, 447, 450, 477, 576; on philopatry, 390, 391; on survival, 480 Night-lighting: population estimates and, 430 Nigus, T. A., 570 Nilsson, L., 434-35, 549, 577 Nitrogen: plumage content of, 136 Nocturnal calorigenesis, 41 Nol, E., 523 Nolan, V, Jr., 276 Nomadism, 373, 374 Noordwijk, A. J. van, 376-77 North American Black Duck, 157, 159, 161, 198, 231, 254, 268, 336; activity metabolism, 141; beaver ponds and, 596; breeding, timing of, 454; brood care, 87, 93; contaminants and, 408; daily energy demands, 490, 490f; diet and courting, 340; food choices, 43; genetic variation, 385, 386, 387; habitats, 425; incubation, 75; initial breeding and renesting, 455, 456; molt, 144, 155; mortality, 410; pairing and dominance, 340; philopatry, 371, 374; population estimate methods, 426; population estimate problems, 429; spacing, 264, 265, 272; survival, 447, 449; survival of young, 466; thermoregulation, 41; weight cycles, 506 North American Ruddy Duck. See Ruddy Duck North American Waterfowl Management Plan, 423 North American Wood Duck, 222, 229, 232 Northern Flicker, 310, 500 Northern Pintails, 193, 198, 222, 339; body mass variations, 44; brood care, 92, 93; current population, 412; egg destruction, 405; emigration, 373; fat reserves, 21; food sources of, 7, 9, 10; foraging habits, 11; genetic variation, 382; hatching reserves, 110; molt, 139, 147, 148, 149, 155; molt migration, 158, 159; mortality, 413; nest baskets, 597; nesting, 56, 342, 343, 348, 577-78; nomadism, 385; nutrient storage, 49; pairing and dominance, 340; philopatry, 367, 373, 374, 451; renesting and diet, 20; spacing, 253, 255, 258, 259, 265, 266; wetlands of, 575 Northern Shelducks, 147, 157, 161; brood parasitism, 292; nest success, 460; spacing, 262, 272; survival of young, 465, 466; territoriality and mating, 207 Northern Shoveler, 158, 193, 198, 208; activity metabolism, 141; air-cell temperatures, 63f; breeding, timing of, 454; clutch size, 23; convergent

evolution, 558; diet, 117; fat reserves, 53, 53?; feather-growth cost, 140; food choices, 9, 10; foraging behavior, 548; incubation, 68, 69, 75; molt, 145, 147, 148; mortality, 413; nesting, 348; nocturnal incubation, 63, 64; pairing and dominance, 340; philopatry, 373, 541, 542; plumage, 134; spacing, 254, 255, 257, 259, 264; wetlands of, 575, 576 Nudds, Thomas D., 540-67; on bill morphology, 18; on brood amalgamation, 100, 319; on Climatic Stability Hypothesis, 559; on communities, 542, 545-49; on habitat selection, 587; on Hutchinson's Rule, 554; on population size correlations, 557; on prey size, 552, 556; on spacing, 273 Nuechterlein, G. L., 236, 268 Nutrient reserves. See Egg laying and nutrient reserves Nutrition: animal diets and, 43; diet specialization, 43; early winter phase and, 337; growth, nutritional effects on, 120; nesting phase and, 346; nutrient reserves, 143-44; prebreeding phase and, 339-40; of prefledglings, 114-20; reproduction and, 339-40. See also Bioenergetics (nutrition) of postbreeding waterfowl; Foraging ecology and nutrition; Nutritional stress Nutritional stress, molt and, 149-53; adaptations to molt, 153-54; biosynthetic inefficiency, 152; flightlessness and, 152; protein limitation, 151-52; reduced body mass, 149-51, 150-51?; time-activity budgets, 152-53 Nystrom, K. G., 580 Obrecht, H. H., 447 Odonata, 7 Oedipus hypothesis. See Parent/offspring competition hypothesis Getting, R. B., 603 Ogilvie, M. A., 132, 133, 162, 570 Oil spills: as contaminants, 163, 408-9 Oksanen, L., 554 Oldsquaw, 194, 195, 267; monogamy, 95, 194; philopatry, 374; re-pairing, 371; wetlands and nest sites of, 581 Olive Baboons, 376 Olson, D. P., 309, 427 Operational sex ratio, 191 Oplinger, C. S., 94 Optimal discrepancy hypotheses, 377, 379, 380 Optimal-rearing hypothesis, 489-91, 490f; tests of, 491-92, 492? Organophosphates: as contaminants, 409 Orians, G. H., 190, 252, 253, 295 Oring, Lewis W., 190-213; on mating systems, 190-91; on philopatry, 378 Orinoco Goose, 261

INDEX Ovary and ovulatory cycle, 327-31; follicle stimulating hormone (FSH) action on, 328; follicular atresia, 511; gonadal recrudescence, 329; incubation, changes during, 329, 331/; nesting behavior and RFC, 328-29; oocyte development, stages of, 328; ovarian atresia, 496; ovulation and oviposition, 329-30, 330f, 33 If; renesting, responses to, 330; steroidogenesis, 328. See also Rapid follicular growth (RFC) Owen, M., 162, 229-30, 256, 305, 517; on molting, 132, 133 Owen, R. B., Jr., 41, 339 Oxygen consumption. See Metabolism Oxyurini. See Stiff-tailed ducks Pacific Black Duck, 345 Pacific Eider, 580 Pacific Salmon, 581 Pacific White-fronted Goose, 414 Packer, C. R., 376, 380 Pair bonds, 278-8If; duration and monogamy, 197, 197*; spacing systems and, 269 Pair displays, 227 Pair formation in waterfowl. See Courtship and pair formation in waterfowl Pair-reinforcing signals, 240 Palmer, R. S., 233, 401, 403, 457, 572; on plumage, 129 Panmixia, 382, 386, 451 Paradise Shelduck, 235, 372; philopatry, 372* Parasitic diseases, 409 Parent-quality hypothesis, 509 Parent/offspring competition (Oedipus) hypothesis, 380-81, 380* Parental age and reproduction, 521-27, 521*, 522*; age at first breeding, 527; constraint hypothesis, 522, 523-24; constraint versus restraint, 526-27; deferred maturity, 527; feeding efficiency and, 524; hypotheses for, 522-23; quality-correlation hypothesis, 522-23; restraint hypothesis, 522, 524-26; senescence, 524-26, 525* Parental feeding of young, 233 Parker, G. A., 302 Parkes, K. C., 129; Avian Biology, xv; on plumage, xv Parr, D. E., 430 Passerines: circannual periodicities of, 332; dispersal, 378; incubation delay, 507; protein differentiation, 386 Passive counts, 427 Paternity: defense of, 270 Pattenden, R. K., 458 Patterson, I. J., 449, 469; on brood care, 90; on mortality, 464, 465; on spacing, 272, 276 Patterson, J. H., 56, 547, 576-77 Paulus, Stuart L., 62-108; on incubation, 30; on pairing, 198, 229 Payne, R. B., 303

Paynter, R. A., Jr., 516 PCBs: as contaminants, 408 Peat, 596 Peatlands, 592 Pehrsson, O., 116, 135, 152, 546, 580; on fish/waterfowl competition, 605 Pekin ducks, 331, 336, 337, 338, 339 Pelecaniformes, 303 Pellis, S. M., 499 Pellis, V. C., 499 Pendant grass, 580, 581 Penguin: incubation, 66, 77 Perch, 605 Perching ducks, 218, 237-38; brood parasitism, 292; diet, 117; postbreeding habitats, 161; postbreeding movement, 157; signal systems, 237-38; spacing, 262-63; wetlands and nest sites of, 57274, 573*. See also named species Percival, H. E, 481 Periodic breeding, 487 Periphyton, 592 Periwinkles, 92 Permethrin: as contaminant, 409 Perrett, N. G., 552 Perrins, C. M., 455, 489, 515, 522; on philopatry, 376, 391 Perry, M. C., 45 Persistent quacking, 224 Pesticides, 594, 597; impact on breeding, 22 Petersen index, 430, 432 Peterson, B., 580 Petral, 77 Phainopepla, 72 Phalaropes, 193, 379 Pheasant, 593 Phillips, C. L., 500 Phillips, John C., 385; A Natural History of Ducks, xv Philopatry of waterfowl, 365-95; age and, 367, 451; breeding birds, numbers of and, 450-52; breeding philopatry, 366, 367-73, 377; breeding-site fidelity, 366; brood-rearing success, 376; comparative studies of, 366; definitions, 366-67; demographic models, 376; emigration, 373; feeding efficiency, 375-76; female philopatry and mating systems, 196-97; genotype/phenotype and, 382-87; homing rate, 366-67; migration, ecological definition, 366; migration, genetic definition, 366; migration sites, 374; molting site fidelity, 374; natal philopatry, 366, 367; nesting success and female survival, 375; population density and, 452; population management and, 387; population settling, 373, 377; return rate, 366; seasonally monogamous ducks and, 36772, 368-69*, 370*, 371*, 372*; site familiarity, 374-75; unpaired males and, 369; wintering sites fidelity, 374, 377. See also Dispersal of waterfowl; Genetic structure of waterfowl; Migration; Territoriality; Territory

629 Phosphorus: reproduction and, 15, 15* Photoelectric sensor: incubation study by, 66 Photography: aerial photographs and counts, 429; incubation study by, 66; time-lapse, as study method, 304, 308 Photoperiod: as nesting stimulus, 18 Photoperiodic variations: testicular size and, 332, 332f Photorefractoriness, 348-49 Pianka, E. R., 312, 556 Pied Flycatcher, 523-24 Pied Wagtails, 253 Pienkowski, M. W, 295, 298, 299, 307, 465 Pin oak, 572 Pink-eared Duck, 158, 265, 270; nomadism, 373; timing of breeding, 18, 345, 346 Pink-footed Goose, 156, 160, 163, 410; activity metabolism, 140, 141; agriculture and, 21; brood care, 93, 94; calcium requirements, 15; digestion of plant foods, 3; food habits of, 7; foraging habits, 11; genetic variation, 385; mixed broods, 92; molt, 133; spacing, 256, 257, 260 Pintails: body size, 49, 336; breeding, timing of, 19, 454, 455; clutch size, 458; diet and egg composition, 48f; drought and breeding, 468; initial breeding and renesting, 455; nutrients and habitat, 30; philopatry, 451, 452; survival, 447, 449; thermoregulation, 41 Pituitary gland, 32, 326-28; control of pituitary functions, 326-28; folliclestimulating hormone (FSH), 326; hormones produced, 326; inhibitory feedback by, 326-27; luteinizing hormone-releasing hormone (LHRH), 326; luteinizing hormone (LH), 326; prolactin (Prl)-releasing cells, 326; steroid hormones, inhibitory feedback by, 326-27; steroid hormones, stimulatory feedback by, 326-27 Plant foods: for breeding ducks, 10 Ploeger, P. L., 382 Plumage: bioenergetics and, 135-36 Plumed Whistling Duck, 65, 155, 259 Pochards, 199, 582; brood care, 87; brood parasitism, 228, 292, 293; displays, 23940; duration of RFG, 35; food choices, 7; foraging, 11, 17; genetic variation, 385; inciting, 222; laying frequency, 38; molt, 154; monogamy, 193; philopatry, 367; recess frequency, 76; signal systems, 239-40; spacing, 259, 266-67 Pollock, K. H., 450 Polygyny, 190, 191, 196, 226; by species, 202-4; ecological analysis of, 204-5; environmental potential for, 190; polygyny threshold model, 190; resource-defense polygyny, 190, 198, 205; territoriality and, 207-8 Pondweed: as food source, 7; nutritional requirements and, 114

630 Poor body condition/nest loss hypothesis, 295 Population density, 272-73, 273?; mathematical model of, 469-74 Population density hypothesis, 379 Population dynamics of breeding waterfowl, 446-85; age of reproductive maturity, 453; breeding, timing of, 453-55; breeding birds, potential numbers of, 446-53; breeding incidence, factors affecting, 453-57; brood-pair ratios, 467, 467?; Canadian study areas, 437; clutch size and, 457-58; cooperative breeding ground surveys, 437-38, 438/"; double brooding, 455; egg size and, 459-60; egg survival, 460-64, 462-63?; genotype/phenotype and philopatry, 38287; hatchlings, sex ratio of, 464; hatchlings, survival of, 464-66; homing and pioneering, impact of, 450-52; indices to reproductive rates, 467; initial breeding, 455-57; nest success, 460-62; population density and breeding, 457, 469; renesting, 455-57; reproductive statistics, composite, 466-69. See also Mortality/survival of breeding waterfowl; Population estimates Population estimates, 426-30, 435-40; aerial photographs and, 429; air-ground correction ratio, 428; apparent success rate, 431; average brood size, 430; band recovery and, 430; beat outs, 427, 432; belt transects, 435; biological basis of, 426-27; brood counts, 431-32; brood survival, 431; cooperative breeding ground surveys, 427-28, 430, 436-39, 438/; counting methods, 427-30; counts from aircraft, 427-29; CowardinJohnson model, 430-31; fall age ratio, 433, 434-35; float counts, 432; ground counts, 427; habitat availability and, 430; hen success rate, 430-31; indicated breeding pairs, 426; indices to breeding populations, 429-30; mark-recapture and, 430; mathematical models and, 430; Mayfield's method, 431; nest success, 430-31; night-lighting and, 430; pair counts, 431-32; passive counts, 427; Petersen index, 430, 432; radiotelemetry and, 431, 433; recruitment rate, 430; relative recovery rate, 434; renesting rates, 433; roadside transects, 435; roll up, 427, 435; roost counts, 429-30; sample design, 436; sample plots, 435-36; sampling methods, 435-36; stratification, for sampling, 436 Population settling, 373 Pospahala, R. S., 465, 467, 469; on philopatry, 452; on survival, 450 Postbreeding movement, 158 Postbreeding waterfowl, ecology of, 128-89; activities, initiation of, 495; habitats, 155-63, 174-81?; management of, 16365; management recommendations, 16465; movements of, by taxa, 169-73?;

INDEX movements of, by tribe, 155-58; postbreeding areas, fidelity to, 158-59, 159?; survival risks, 154-55. See also Bioenergetics (nutrition) of postbreeding waterfowl; Molt of waterfowl Postcopulatory displays, 224, 234 Potamogeton, 46, 595 Potassium deficiency, 15 Potential energy, 31 Poysa, H., 18, 542, 548-49, 552-54, 557 Prairie pothole region, 396, 397map; cereal grains and, 7; description, 411; drought/ dry cycles, 592; duck mortality in, 41214; egg fertility studies, 20; fairy shrimp and, 9; food availability, 11; grasses and, 10; loss of wetlands, 22; mortality agents in, 411; population model for Mallards of, 470-71; renesting at, 21 Prebreeding phase of reproduction, 324, 338-41, 353-55?; daylength and, 33839; nutrition and, 49, 57, 339-40; social factors and, 340-41; temperature and, 339; weather and, 339 Precocial young hypothesis, 303-4 Precocial/atrical dichotomy, 311-12 Precociality of hatchlings: egg composition and, 32 Precopulatory displays, 218, 220, 240 Predation Hypothesis: of waterfowl ecology, 543/", 544f, 545-46 Predators, 406; in arctic tundra region, 412; body size of waterfowl and, 114; breeding-season mortality and, 406-7; brood care and, 83, 86, 88-89, 121; female predation and, 494; incubation and, 62, 64, 75-76; injury-feigning and, 89; islands and, 604; nest sites and, 347-48, 461, 577-78; nesting structures and, 597; in prairie pothole region, 411; predation hypothesis, 520; predator fences, 603; spacing patterns and, 270, 357; timing of laying and, 494; wetland ecology and, 593 Prefledging waterfowl, ecology of, 5, 10927; brood movement, 120-21; diet of, 117-19, 118?; digestion and metabolism, 114-15, 115?; food intake, limitation of, 115-16; food preferences, 119-20; foraging behavior, 116-17, 116?; green vegetation, processing rates of, 115; habitat use, 121-22; nutrition/growth relationship, 120; nutritional effects, 116; nutritional requirements, 114; predators and, 121; thermoregulation and, 110. See also Brood mortality/ survival; Growth and development of waterfowl Preflight signaling, 221, 225 Prevett, J. P., 434, 471 Prince, H. H., 428, 510, 551; on egg size, 459; on feather-growth cost, 140; on habitats, 575, 576, 577; on laying, 455; on mortality, 464; on nesting, 570, 571, 573, 581 Principle of lost opportunity, 16

Prins, H. H. Th., 257, 258 Procellariiformes, 303 Producer/scrounger model, 301 Production ratio, 438 Productivity Hypothesis, 545f, 547-49, 547f, 548f Profitability, role of: food selection and, 16 Progesterone, 327-28, 330/", 33If Progestins, 328 Prolactin (Prl), 326, 329-30, 330f, 3 3 I f , 348-49 Prop, J., 460-61, 465 Protein: albumen synthesis, 32, 33; analysis in diet, 3, 4?; during wing molt, 145?; egg protein and yolk protein, 33?; feather protein, 136, 142-43, 142f, 143?; nutritional stress and, 151-52; production efficiency of, 46-47; reproduction and, 12-14, 45-48, 51f; requirements, 142-43, 142f; reserves, 45-48, 47?, 53, 53?; utilization by prefledglings, 112, 115?; in vegetation, 601 Protocooperation, 304-5 Provan, T. H., 429 Proximate environmental factors and reproduction, 323-24, 331-41; phasing factors as Zeitgebers, 324, 332; proximate inductive factors, 324, 332, 350?; proximate phasing factors, 324, 331-32, 332f, 333f; scaling factors, 324, 332 Psychosomatic effects: of courtship, 227 Puccinellia phryganodes, 119, 122 Pugesek, B. H., 524 Pusey, A. E., 379-80 Pyrethroids, synthetic: as contaminants, 409 Quality-correlation hypothesis, 522-23 r-selection, 335 r/K hypothesis, 519 Rabbit, 299 Raccoons, 411, 573, 597 Radioactive isotopes: incubation study by, 66; waterfowl studies and, 42 Radiotelemetry: incubation study by, 66; mortality rates and, 398; plus aircraft, 435-36; population estimates by, 431; recruitment estimates and, 433; wing molt study by, 155 Radjah Shelducks, 157, 261, 345 Rahn, H., 32, 71-72 Raitasuo, K., 226 Rails, K., 377 Rangel, E., 574 Rank correlation analysis (Spearman), 269 Rapid follicular growth (REG), 6, 32, 32829, 496; duration and pattern of, 34-38, 34f, 35f; nesting behavior and, 328-29; nutrient reserve threshold and, 54-55, 54f Raptors, 66, 408 Rarefaction Hypothesis, 558 Ratcliffe, L., 467

INDEX Raveling, Dennis G., 396-422; on brood loss, 465; on clutch size, 458; on incubation, 76; on laying, 38; on management, 387; on nesting, 148, 398, 405, 496, 570; on nutrient reserves, 339; on population, 430, 434; on predation, 406; on signaling, 221; on spacing, 270 Re-pairing, 371 Recruitment: enhancement of, 387-88; food resources and, 1. See also Recruitment, measures of Recruitment, measures of, 430-35; definitions, 430-31; estimates and indices, 431-36; fall age ratio, 434-35; fall flight estimate and, 438-39; habitat evaluation and, 425; harvest management and, 425; late nesting index, 434; nesting studies, 432-33; pair and brood counts, 431-32; population models and, 425; production ratio, 438; radiotelemetry and, 433; recruitment, defined, 423-24; recruitment rate, defined, 424; social index, 433-34; species differences and, 425-26; summer survival and, 435; uses of, 425. See also Breeding population inventories; Population estimates Red Deer, 274 Red fox, 6, 406, 407, 411, 546 Red Shoveler, 264 Red-billed Pintail, 158, 265 Red-billed Quelea, 328; nutrient reserves, 491 Red-breasted Goose, 260 Red-breasted Merganser, 267, 294, 408; clutch size, 458; creche formation, 91; diseases of young, 465; food choices, 10; wetlands and nest sites of, 581 Red-crested Pochard, 158, 240, 266, 293; activity metabolism, 141 Red-fronted Coot, 294 Red-necked Duck, 266; survival of young, 466 Redheads, 163, 220, 229, 239, 257; activity metabolism, 141; breeding, timing of, 454; brood parasitism, 293, 307, 308, 309; bulrush and, 601; clutch size, 458; courtship, 346; endocrinology, 336; food sources of, 1; incubation, 75; initial breeding and renesting, 455; laying frequency, 38; molt, 135, 144, 147, 148, 152, 154; nest baskets, 597; nesting, 343, 344, 348, 579; parasitic egg-laying, 410; philopatry, 372, 373, 451, 452; population estimate methods, 426; spacing, 266, 269; temperature and nesting, 342; wetlands of, 578, 579 Redmond, R. L., 380 Reduced brood mortality hypothesis, 304 Reed, A., 436 Reed Bunting, 155 Reese, K. P., 493, 571 Reeves, H. M., 434, 468 Reid, B., 502

Reinecke, Kenneth]., 1-29; on survival, 449, 450; on thermoregulation, 41 Remsen, J. V., 382 Renesting, 455-57, 501, 506, 510; clutch size and, 513-15; egg mortality and, 398-99; food availability and, 20-21; as manipulative technique, 505; multiple renesting attempts, 457; ovarian responses to, 330; rates, estimation of, 433; renesting energetics, 505, 505f Repeated calls, 224 Reproduction, food resources and, 18-21; agriculture and, 21-22; clutch size and, 19-20; egg fertility and hatchability, 20; egg mass and composition, 30; failure to breed and, 19; renesting and, 20-21; timing of reproduction, 18-19. See also Egg laying and nutrient reserves Reproductive effort (RE), 299, 524-26; mortality and, 519-20; reproductive stages and, 86?; residual reproductive value and, 497f; seasonal shifts in, 515 Reproductive error hypothesis, 295 Reproductive patterns, evolution of, 486539; delay of molt and, 495; nesting period, length of, 495-96; postbreeding activities, initiation of, 495; rapid follicular growth (RFC) and, 496. See also Breeding, timing of; Clutch size; Parental age and reproduction; Reproductive effort (RE) Resource defense: versus mate defense hypothesis, 379-80 Resource holding potential (RHP), 274 Resource predictability: spacing systems and, 269 Restraint hypothesis, 522, 524-26 Restriction-fragment length polymorphisms (RFLP), 386 Return rate, 366 Reuniting, 231, 235 Reynolds, C. M., 54, 455-56, 493, 512 RFG. See Rapid follicular growth RFLP. See Restriction-fragment length polymorphisms Rhymer, Judith M., 365-95; on growth rates, 111; on philopatry, 365-66 Richardson, M. G., 435 Ricklefs, R. E., 38, 110, 517, 519 Riggert, T. L., 206, 270, 373, 382 Ring Dove, 227, 347 Ring-billed Gull, 407 Ring-necked Duck, 158, 159, 161, 163, 293; contaminants and, 408; diet, 117; fat reserves, 53, 53t; food choices, 43; incubation, 80; molt, 133, 134, 139, 144, 149; mortality, 410, 447, 449, 450; nesting, 342, 344, 406; nutrient acquisition, timing of, 5-6; nutrient storage, 49; philopatry, 451; protein reserves, 5If, 52, 55; wetlands of, 578, 579 Ringed Teal, 237 Ringelman, J. K., 453, 459 Rising, J. D., 383

631 Risk spreading (variance reduction) hypothesis, 300-301 Ritualization of signals, 241 Roadside transects, 435 Robb, J. R., 573 Robinson, J., 587 Robinson, R. H., 572 Rockwell, R. E, 455, 459, 467, 471-72; on clutch size, 503, 534; on genetic variation, 366, 384, 387; on nesting, 586; on recruitment, 442; on survival, 399, 402 Roderick, C., 502 Roemers, E., 229 Rogers,]. P., 299, 399, 515 Rohwer, Frank C., 365-95, 486-539; on clutch size, 458, 459, 529; on egg loss, 463; on molt sites, 162; on parasitism, 311; on philopatry, 366, 381, 452; on renesting, 34; on spacing, 270 Roll up, 435 Rollins, G. L., 595 Romanoff, A. J., 32 Romanoff, A. L., 32 Roost counts, 429-30 Ross' Goose, 156, 256, 260, 410; clutch size, 31, 458; egg laying, timing of, 38; follicle formation timing, 18; foraging habits, 11; forced copulation, 201; genetic variation, 384; nesting, 342, 495, 570-71; nesting and weight loss, 500; nutrient acquisition, timing of, 4; population estimate methods, 429; weight and migration, 340 Rostovskaya depression, 164 Rosybills, 240, 294 Rotenone: as contaminant, 598 Routamo, E., 267 Routledge, R. D., 428 Rubenstein, D. I., 276, 300, 378-79 Ruddy Duck, 158, 162, 199, 236, 241, 242; area-restricted search, 17; breeding, timing of, 6; brood care, 93; brood parasitism, 294; courtship, 346; endocrinology, 329; fat requirements, 14; food choices, 7; foraging habits, 11, 16; incubation, 75; molt, 130, 134, 143; mortality, 404; nesting, 344, 348, 579, 581-82; nutrient acquisition, timing of, 6; nutrient storage, 49, 56; philopatry, 382; polygyny, 203; power requirements, 42; spacing, 254, 266, 268; wetlands of, 578, 579 Ruddy Shelduck, 262, 385 Ruddy-headed Sheldgoose: genetic variation, 385; molt, 130 Rumble, M. A., 427, 431, 601, 602 Russell, D., 434 Ruwaldt, J. J., 575 Ryder, J. P., 461, 499-501, 570-71; clutch size hypothesis, 30-31; on territoriality, 256 Sadura, A., 458 Safriel, U. N., 498

632 Sago pondweed, 595 Salmonids, 10 Salomonsen, E, 155 Salt marshes, 17 Saltgrass, 596, 603 Saltmarsh grass, 7 Salvadori's Duck, 157, 205, 239, 263; carrying of young, 90 Salyer, J. W., 458 Sample plots, 435-36 Sanderlings, 253, 272 Sargeant, Alan B., 396-422; on mortality, 404-5; on nest success, 607; on predation, 413, 460 Sauder, D. W., 426 Savard, J.-P. L., 310, 374, 465, 581; on brood amalgamation, 91; on interspecific aggression, 268; on polygamy, 195 Sayler, Rodney D., 190-213, 290-322; on brood parasitism, 297, 300, 304, 305; on displays, 240; drought and body weights, 344; on pairing, 229 Scaling factors: of environmental information, 324, 332 Scanes, C. G., 45 Scharloo, W., 376 Schindler, M., 499 Schlatter, R. P., 524 Schmidtke, K., 542, 557 Schoener, T. W., 272, 273 Schommer, M., 229 Schutz, R, 229 Schwartz, Michael D., 446-85 Scirpus americanus, 7, 14 Scoters: signal systems, 240-41; wetlands and nest sites of, 580 Scott, D. K., 493 Scott, M. D., 430 Scott, M. L., 46 Scuds, 9 Sea ducks, 47, 154, 411; age of reproductive maturity, 453; brood care, 87; brood parasitism, 292, 294; courtship displays, 228; diet, 117; foraging habits, 11; genetic variation, 385; laying frequency, 38-39; mixed broods, 91-92; nutrition of, 6; philopatry, 368, 374, 381; rate of RFC, 35; re-pairing, 371; signal systems, 24041; signals, 240-41; size and recesses, 76; spacing, 267-68; spacing and sex roles, 269; wetlands and nest sites of, 579-81. See also named species Sea lettuce, 7 Seasonal-productivity hypothesis, 517-19 Sebeok, T. A., 215 Seber, G. A., 447 Sedinger, James S., 109-127; on habitat, 148; on nutrient values, 3 Seed banks, 598 Selenium: as contaminant, 15, 408, 597 Selfish signalers, 224-25, 242 Semel, B., 297 Semipalmated Sandpiper, 498

INDEX Seney National Wildlife Refuge, 409 Serie, J. R., 433 Sertoli cells, 327 Settling pattern, 377 Sewage: as contaminant, 407 Sex roles: spacing systems and, 269-70 Sex-biased dispersal: genetics and, 379; hypotheses, 378-82 Sexual imprinting, 229, 231 Seymour, R. S., 71-72 Shaiffer, C. W., 449-50, 456, 458, 460 Shannon-Weaver formula, 549 Sharp, D. E., 375, 451, 461 Sheehan, P. J., 409 Sheldgeese, 193, 235; convergent evolution, 558; genetic variation, 385; signal systems, 235; spacing, 261-62 Shelducks, 218, 222, 235-36, 292-93; brood amalgamation, 90, 91; brood care, 93, 94; brood parasitism, 292-93; defense of territory, 95; genetic variation, 385; habitats, 94, 160-61; monogamy, 193; postbreeding movements, 156-57; signal systems, 235; spacing, 261-62. See also named species and subspecies Shell glands, 32 Sherman, P. W, 297 Sherrod, L., 229 Sherwood, G. A., 406 Shields, G. E, 377, 384, 386 Sibbald, I. R., 18 Sibley, C. G., 219-20 Sibling rivalry, 233 Siegfried, W. R., 18, 237, 241-42, 582; on forced copulation, 200; on pair bonds, 202, 203, 204, 207; on signaling, 237, 242; on territoriality, 241, 281, 286 Signal systems of waterfowl, 233-45; contact calls, 224, 225; cooperative signals, 225; ducting calls, 238, 243; evolution of, 243-44; pair-reinforcing signals, 240; preflight signaling, 221, 225; repeated calls, 224; species recognition signals, 219; territorydefense signals, 238; vocalizations as, 221. See also Courtship and pair formation in waterfowl; Displays of waterfowl Silver maple, 14 Silver Teal, 208; brood care, 86 Simkiss, K., 32 Simmons, K. E. L., 62, 222, 240, 265; Birds of Europe, the Middle East, and North Africa, xv; on breeding latitudes, 517; on pair courtship, 226; on signal systems, 233 Single-species management, 542-43 Site familiarity, 374-76 Sjoberg, K., 138, 426, 491, 577; on foraging behavior, 548; lake size, 576; on population, 606; on resource partitioning, 553 Skead, D. M., 269 Skutch, A. E, 65, 73

Slatkin, M., 366, 383, 386-87 Smart, G., 135 Smew, 267, 294 Smith, A. G., 405, 437, 468, 591 Smith, C., 271 Smith, J. N. M., 310, 461, 523, 527, 580; on aggression, 268 Smith, Loren M., 590-610; on burning and flooding, 596; on island habitats, 588 Smith, R. H., 377, 426 Smith, R. I., 467 Smith, R. L., 429 Smith, W. J., 215 Smooth bromegrass, 600, 603 Snails, 11, 15 Snow Goose, 256, 259, 387; age and reproduction, 468; agonistic interactions of, 17; breeding, timing of, 454; body mass variations, 44; clutch size, 56, 458, 459, 511, 519; diseases, 409; egg size, 459; endocrinology, 328, 329; feather length, 137; foraging habits, 11; grazing and, 601; initial breeding and renesting, 456; interspecific competition and, 17; molt, 132, 133, 150, 151; mortality, 405, 414; nesting, 342, 571; nutrient reserves, 56, 491, 510; pair bonds, 452; philopatry, 37 31; population estimate methods, 429; population model, 47172; postfledgling survival, 488; predation, 406; sex ratio of hatchlings, 464; specific plant-dependence, 571; survival of young, 465, 466. See also named subspecies Snowstorms: as mortality agent, 405 Snowy Owl, 406 Social courtship, 225-27; bond reaffirmation, 228; contexts of, 227-28; extrapair courtship, 228; history of ideas on, 226-27; male-male interactions, 228; mate-defense situations, 227-28; psychosomatic effects of, 227; unpaired birds and, 227 Social index, 433-34 Sodium deficiency, 15 Song Sparrows, 272, 523 Sooter, C. A., 569 Soper, M. E: on incubation, 66 Sorensen, M. E, 428 South African Spur-winged Goose, 157 Soutiere, E. C., 229 Sowls, L. K., 253, 254, 451, 453; on counts from aircraft, 427; on nest movement, 348; on philopatry, 365 Spaans, A. L., 159 Spaans, B., 468 Spacing patterns, 192/", 251-89, 278-8U; Activity Fields and, 274; Aggression Fields, 274; aggression, interspecific, 268-69; agonistic behavior and, 258-71; animal contests, 274; body size and, 270-71, 273, 273^; coloniality and, 27071; costs and benefits of, 254, 255?; defense, timing of, 270; dispersion, models of, 271-72; economic

INDEX defendability and, 252-53; evolution of, 251, 252, 254-56, 274-75; function versus motivation, 253-54; game theory and, 274-75; group living, benefits of, 256-58; group living, conflict and, 285; group living, costs of, 258; home range and, 272-73; hypotheses about, 253-56; Isolation Fields, 274; management of, 277; mate defense, 270; pair bonds and, 269; paternity, defense of, 270; population density, 272-73, 273?; predators and, 257, 270; resource holding potential (RHP), 274; resource predictability and, 269; sex roles and, 269-70; spacing behavior, approaches to study of, 252; theories of, 252-56; types of, suggested, 258-59. See also Dispersal of waterfowl; Territoriality; Territory Spartina, 7, 14 Spatcher, C. S., 575 Spatial Heterogeneity Hypothesis, 549-51, 550f, 550t, 55 If Spearman rank correlation analysis, 269 Species recognition signals, 219 Speckled Teal, 208, 222, 228, 229, 263 Spectacled Eider, 267, 580; initial breeding and renesting, 456; laying frequency, 38; timing of nutrient acquisition, 6 Spencer, D. L., 410 Spinner, G. P., 429 Spotted Sandpiper, 193, 379 Spotted Whistling Duck, 385 Springer, P. R, 576 Spur-winged Goose, 204 Spurr, E. B., 374, 453, 455 Standen, P. J., 229 Starlings, 349, 597 Steamer ducks, 193, 236-37, 243, 270; convergent evolution, 558; grit size differences, 553; interspecific killing, 268; nomadism, 373; philopatry, 373; spacing, 262 Stearns, S. C., 312 Steen, J. B., 72 Steller's Eider, 162, 241, 267; ritualization of signals, 241; timing of nutrient acquisition, 6 Stereotypy, of displays, 215-16 Sterling, R. T, 374 Steroid hormones: inhibitory feedback by, 326-27; stimulatory feedback by, 327. See also named hormones Stewart, R. E., 424, 435-36, 574-75, 578 Stickleback, 10, 217 Stiff-tailed ducks, 195, 218, 241-42; brood care, 87; brood parasitism, 292, 294; clutch size, 516f; displays, 228, 241-42; egg production energy, 39; egg size and body mass, 33; mating systems, 304; philopatry, 382; postbreeding habitats, 162; postbreeding movement, 158; signal systems, 241-42; spacing, 268; wetlands and nest sites of, 581-82. See also named species Storer, R. W., 236, 268

Stott, R. S., 427 Stoudt, J. H., 430, 468, 578, 602 Stout, I. J., 403, 410 Strange, T. H., 574 Stratification: for sampling, 436 Street, M., 466 Strong, D. R., Jr., 551 Subsistence hunting: as mortality agent, 409-10, 412 Succession theory, of wetland ecology, 591-92 Sugden, L. G., 409, 426, 435, 602 Sulzbach, D. S., 430 Summers, R. L, 559 Suomi, S. J., 229 Superbroody females, 91 Surf Scoter, 267, 580 Surface area: egg size and, 32 Surrendi, C. R., 428 Surrendi, D. C., 372 Survival. See Brood mortality/survival; Eggs, mortality/survival of; Mortality/survival of breeding waterfowl Swan Goose, 259; laying frequency, 38 Swanon, G. A., 1, 43, 458 Swans: adaptations to molt, 153; age of reproductive maturity, 113, 453; brood parasitism, 292; defense of young, 89; family bonds, 84; feeding ecology, 2; food habits, 6-7; foraging habits, 11; as full-time vegetarians, 43; genetic variation, 383-84; growth, duration of, 112-13; habitats, 160, 425; laying frequency, 38; molt, sexual differences in, 133; mortality, 400?, 401, 402, 403?; nutrient acquisition, timing of, 3; philopatry, 372-73, 372?; population estimate methods, 427, 428; postbreeding movements, 155-56; predators and, 406; preflight signals, 225; signal systems, 234; spacing, 25960; wetlands of, 569. See also named species and subspecies Swennen, C., 461 Switchgrass, 603 Syroechkovskiy, Ye. V., 461 Szaro, R. C., 408 Tadorini: brood care, 87; genetic variation, 385; inciting, 222; pair bonding, 84; postbreeding habitats, 161; postbreeding movement, 156-57; signals, 235-36; spacing, 261-62 Takekawa, J. Y., 41 Talent, L. G., 83, 121, 407, 466; on drought and breeding, 456; on weather and mortality, 464 Tamisier, A., 229 Taxonomy: displays and, 218-19; of family Anatidae, xviii-xx Taylor, E. J., 2 Taylor, T. G., 32, 48 Telemetric eggs: incubation study by, 66 Television: incubation study by, 66

633 Temperature: early winter phase and, 337; nesting phase and, 341-42; prebreeding phase and, 339 ten Gate, C., 229 Terns, 577, 581 Territoriality, 375; as competition, 551; foraging and, 17; interspecific, 17-18, 268-69; mating systems and, 205-8. See also Territory Territory: defined, 252; home range, 27273, 272?, 278-81?; size of, 272-73, 272?, 278-81?; territorial behavior, 277; theories of, 252-56. See also Territoriality Territory in Bird Life (Howard), 252 Territory-defense signals, 238 Testis: functions of, 327; luteinizing hormone (LH) as stimulator, 327; photoperiodic variations in size, 332, 332f Testosterone, 326-27 Teunissen, W., 18,468 Thermoneutral zone, 40 Thermoregulation: as energy cost, 40-41, 41?; prefledglings and, 110 Thermostasis. See Thermoregulation Thomas, D. L., 2 Thomas, V. G., 43, 554 Thompson, D. Q., 466 Thompson, J. D., 154 Thompson, S. C., 76 Threat signals, 222 Three-bird flights, 254, 264, 265, 266, 273, 274 Three-square, 7, 14 Tienderen, P. H., 377 Timing of nutrient acquisition, 3-6 Tinbergen, N., 217, 252 TIROS, 434 Titman, Roger D., 251-89; on habitat, 587; on parasitism, 272; on pursuit flights, 254; on territoriality, 265, 272; on three-bird flights, 274 Todd's Canada Goose, 340 Toepfer, J. E., 464 Toft, C. A., 453, 515, 552, 555, 576 Tome, M. W., 16, 49, 453 Torrent Duck, 157, 205, 218, 220; nomadism, 373; philopatry, 373; signal systems, 238; spacing, 256, 263 Toxicants. See Contaminants Trace elements: overdose hazards, 15 Trauger, D. L., 453, 602 Travis, J., 42 Tree ducks: egg size and body mass, 33; laying frequency, 38 Tree Swallow, 509 Trichoptera, 7, 119 Triglycerides: synthesis of, 14 Triumph ceremonies, 217, 223-24, 230, 260, 261, 347; as formalized interactions, 224; of named species, 234, 235, 236, 240, 243 Trivers, R. L., 93, 190, 224-25

634 Trumpeter Swan, 153, 260, 333, 403; daylength and laying, 341; genetic variation, 383; hatching, 82; male and incubation, 64; maturing age, 335; molt pattern, 133; mortality, 403; nest sites of, 569; nocturnal incubation, 64; nutrient acquisition, timing of, 3; thermoregulation, 40; wetlands of, 569 Tufted Duck, 158, 266, 293, 298; breeding, timing of, 454; clutch size, 19, 458; food choices, 16; initial breeding and renesting, 455, 456; nest sites of, 579; philopatry, 375, 379, 451; survival of young, 465, 466 Tule Goose, 387 Tundra Swan, 153, 333, 341, 410; food habits of, 7; genetic variation, 383; interspecific killing, 268; maturing age, 335; molt pattern of, 133; nutrient acquisition, timing of, 3; power requirements, 42; spacing, 260, 268, 269 Turcek, F. J., 135, 141, 153 U.S. Department of Agriculture: Section of Economic Ornithology, 1 U.S. Fish and Wildlife Service, 1, 413, 423, 425, 429, 434, 439 Upland Goose, 235 Upland management, 600-604; cover, establishment of, 603; crops and, 602; fencing and, 601-2; fire and, 600-601; grazing and grazing management, 601-2, 603; herbicides, 602-3; islands and, 604; lure crops, 602; mowing, 603; no-till agriculture and, 602; predator fences, 603; predators and islands, 604 Urban, E. K.: Birds of Africa, xv Uropygial gland, 242 Vaisanen, R. A., 453, 550 Vallisneria tubers, 45 van der Kloot, W. G., 215, 217 van der Merwe, J. F., 241-42 van der Valk, A. G., 591, 592, 596 van Eerden, M. R., 460-61, 465 Van Tyne, J., 64 Van Wagner, C. E., 384, 386 Vancouver Canada Goose: nest sites of, 570 Vangilder, L. D., 339 Variable reproductive effort hypothesis, 300 Variance reduction (risk spreading) hypothesis, 300-301 Vehicles, moving: as mortality agent, 404 Velvet Scoter, 342 Vermeer, K., 407 Vermeer, L., 464 Vickery, W. L., 545 Vince, M. A., 507 Vocalizations: persistent quacking, 224 Der Vogel und Sein Leben (Altrum), 252 von de Wall, W, 226, 228, 229 Voorhees, L. D., 603 Wagner, F. H., 561

INDEX Wald, P., 491 Walsberg, G. E., 38, 49, 72, 77, 81 Walter, P., 459 Walters, J. R., 499 Wandering Whistling Duck, 155, 259, 345, 385; incubation strategy, 65; timing of breeding, 455 Wang, Y. T., 465 Ward, Edward, 336 Waser, P. M., 271, 273, 274, 376, 378-79 Water flea, 9, 11 Water sedge, 580, 581 Water shield, 14 Watson, A., 276 Wayland, M., 603 Weasel, 406 Weather: body size and, 334; breeding and, 19, 454-55, 468; feeding and, 11-12; incubation and, 73; mortality and, 405-6, 411; nest success and, 461; nesting phase and, 343-46; prebreeding phase and, 339; survival and, 450 Weatherhead, P. J., 449 Weaver bird, 190, 215 Webster, H. R., 405, 591 Weidmann, U, 222, 226, 228, 254 Weller, Milton W, 568-89; on brood parasitism, 299, 301, 302, 303, 305, 307, 308; on clutch size, 516; on competition, 551; on displays, 239; on feather growth, 137; on geese feces, 559; on hemi-marsh, 575, 592; The Island Waterfowl, xv; on incubation, 62; on mortality, 401; on muskrats, 596; on nest success, 461; on pairing, 229; on philopatry, 372; on plumage, 129; on signals, 236; on spacing, 265, 266 Wells, R. L, 256, 305 Weremiuk, S., 110 Western Canada Goose: renesting, 20 Western Grebe, 224 Wetland ecology, 591-93; algae, 592; drawdown and, 593, 595, 595f; emergents and, 594, 595, 596, 598, 600; environmental sieve, 591; hemi-marsh, 592; hydrosere, 591; invertebrates, 59293; macrophytes, 592; peatlands, 592; periphyton, 592; predators, 593; succession theory, 591-92; vertebrates and plant structure, 593; water regime and, 592; zonation, 591. See also Wetland management Wetland management, 594-600; burning, 596; carp control, 598, 599f; contour furrowing, 598, 605; drawdown, 593, 595, 595/; earth moving and, 598, 599f; fertilizing, 605; heavy metals, 597; herbicides, 597-98; indirect management, 594; intensive management, 594; invertebrates and, 605-6; level ditches, 598; mowing, 597; nesting structures, 596-97; pesticides, 597; potholes, 598; predators and, 597; seed bank studies, 598; seeding and planting, 598, 600; silt and, 597;

toxicants, 594; vertebrates and plant structure, 593; water level control, 59496; water quality, 597-98; water quality control, 594. See also Wetland ecology Wetmore, A., 154 Wheatgrass, Western, 603 Whistling ducks, 22, 218, 234, 292; brood parasitism, 292; convergent evolution, 558; family bonds, 84; feeding of young, 88; genetic variation, 385; incubation strategies, 65; male and incubation, 64; mating systems, 193, 202; signal systems, 234; spacing, 259; wetlands and nest selection, 569. See also named species and subspecies Whistling Swan: genetic variation, 383; incubation energetics, 81; male and incubation, 64 White, D. H., 408 White yolk, 328 White-backed Duck, 65, 218, 385 White-cheeked Pintail, 208, 220, 228, 266, 269 White-crowned Sparrow, 23, 136, 147, 349 White-faced Whistling Duck, 65, 259; initial breeding and renesting, 456 White-fronted Goose, 90; activity metabolism, 140; age and reproduction, 467; corn consumption, 7; egg laying, timing of, 38; fat requirements, 14; genetic variation, 385; mortality, 405, 410; nest destruction, 405; nest success, 398; pairing and dominance, 340; postbreeding period, 156, 158, 160, 162, 163; protein and reproduction, 13; spacing, 257, 260 White-headed Duck, 158, 204, 268 White-headed Flightless Steamer Duck, 262 White-winged Scoter, 22, 47, 267; breeding, timing of, 455; brood amalgamation, 90; brood care, 92, 94; clutch size, 458; fat reserves, 53, 53t; food choices, 9, 45; incubation constancy, 81; molt, 134; nutrient acquisition, timing of, 6; nutrient reserves, 49, 54; RFG and laying interval, 35; survival of young, 465; wetlands and nest sites of, 580 Whitetop, 597, 601, 603 Whitetop grass, 46, 47 Whitman, W. R., 576 Whooper Swan: genetic variation, 383, 410; incubation, 68, 72, 75; incubation energetics, 81 Wickler, W, 226 Wielicki, D. J., 136 Wiens, J. A., 253, 271 Wigeons: drought and, 343; nesting, 343; nutrient reserves, 54 Wight, H. M., 499 Wild celery, 7 Wildfowl (journal), xv Wildfowl Trust (Great Britain), xv Wiley, R. H., 271, 273, 274 Williams, C. S., 398, 569 Williams, D. M., 229

INDEX Williams, G., 561 Williams, G. C., 253, 522 Williams, M., 206, 235, 465, 469, 498; on incubation strategies, 66 Willow, 161, 571, 596, 600 Willow Ptarmigan, 72 Wilson, A. C., 384 Wilson's Phalarope, 196 Wing noise: as signaling, 237 Winkler, D. W, 499 Winter: copulation, 233; nutrient storage, 48-49, 57; philopatry, 377; site fidelity, 374 Winterstein, S. R., 449 Wire-strikes: as mortality agent, 403-4 Wishart, R. A., 229, 232, 264, 269, 574 Wittenberger, J. R, 527 Wobeser, G. A., 409 Wolfe, M. L., 461 Wood, C. C., 16 Wood Duck, 155, 157, 263; age of reproductive maturity, 453; band recovery and, 430; beaver ponds and,

596; breeding, timing of, 454, 455; brood parasitism, 293, 303; brood size and survival, 498; clutch production, 35; clutch size, 458; diet and weight, 339; double brooding, 201, 457; dump nesting, 473; egg composition, 20; egg destruction, 405; egg production energy, 39; egg size, 459; fat requirements, 14; foraging habits, 11; incubation, 64, 75; initial breeding and renesting, 455, 456; nest box program, 596-97; nest success, 460; nesting, 56, 572-74, 573t; nutrient acquisition, timing of, 5, 6; nutrient storage, 491; philopatry, 367, 375; population estimate methods, 429; population model, 472-73; predation and, 406; protein and reproduction, 13; survey techniques for, 429-30; survival, 447, 449, 450; survival of young, 465, 466; wetlands of, 572 Wood-Gush, D. G. M., 32 Woodpecker, 581

635 Woolfenden, G. E., 276 Wrangham, R. W, 276, 378-79 Wright, H. A., 601 Wright, R., 466 Wright, S., 387; F statistic, 386 Wright, V, 447 Wiirdinger, I., 120 Wust, W, 254 Wynne-Edwards, V. C., 253, 277 Ydenberg, R. C., 257, 258 Yellow-billed Duck, 158, 265, 410 Yom-Tov, Y., 299, 311 Young, A. D., 294 Youngs, W. D., 447 Zeitgebers, 324, 332, 333, 338 Zero-tillage, 602 Zicus, M. C., 94, 162 Zinc phosphate: as contaminant, 407 Zink, R. M., 382 Zonation, of ponds, 591 Zugunruhe, 338