The Natural History of The Bahamas: A Field Guide 2018035574, 2018035782, 9781501738029, 9781501738036, 150173802X

Citation preview

The Natural History of The Bahamas

01 Currie 3PP pi-143.indd 1

5/24/19 1:43 PM

01 Currie 3PP pi-143.indd 2

5/24/19 1:43 PM

The Natural History of The Bahamas A FIELD GUIDE

Dave Currie, Joseph M. Wunderle Jr., Ethan Freid, David N. Ewert, and D. Jean Lodge

Comstock Publishing Associates An imprint of Cornell University Press Ithaca and London

01 Currie 3PP pi-143.indd 3

5/24/19 1:43 PM

Copyright © 2019 by Cornell University, with the exception of the section on fungi, portions of the introduction, photographs by Joseph M. Wunderle Jr., and illustrations and photographs by D. J. Lodge, which were written, drawn, and photographed by federal employees and cannot be copyrighted. All rights reserved. Except for brief quotations in a review, this book, or parts thereof, must not be reproduced in any form without permission in writing from the publisher. For information, address Cornell University Press, Sage House, 512 East State Street, Ithaca, New York 14850. Visit our website at cornellpress.cornell.edu. First published 2019 by Cornell University Press Printed in China Library of Congress Cataloging-in-Publication Data Names: Currie, Dave 1967– author. | Wunderle, Joseph M., author. | Freid, Ethan, author. | Ewert, David N., author. | Lodge, Deborah Jean, 1953– author. Title: The natural history of the Bahamas : a field guide / Dave Currie, Joe M. Wunderle Jr., Ethan Freid, David N. Ewert, and D. Jean Lodge. Description: Ithaca [New York] : Comstock Publishing Associates, an imprint of Cornell University Press, 2019. | Includes bibliographical references and index.  Identifiers: LCCN 2018035574 (print) | LCCN 2018035782 (ebook) | ISBN 9781501738029 (pdf) | ISBN 9781501738036 (epub/mobi) | ISBN 9781501713675 | ISBN 9781501713675 (pbk. ; alk. paper) Subjects: LCSH: Natural history—Bahamas—Guidebooks. | Bahamas—Guidebooks. Classification: LCC QH109.B3 (ebook) | LCC QH109.B3 C87 2019 (print) | DDC 508.7296—dc23 LC record available at https://lccn.loc.gov/2018035574 Front cover photos: (top) Cyclura rileyi rileyi, by Dave Currie; (bottom left) Melocactus intortus, by Ethan Freid; (bottom middle) Coereba flaveola bahamensis, by Bruce Hallett; (bottom right) Papilio andraemon, by Dave Currie. Spine photo: Setophaga flavescens, by Bruce Hallett. Cover design and book design and composition by Julie Allred, BW&A Books

01 Currie 3PP pi-143.indd 4

5/24/19 1:43 PM

The Bahamas National Trust (BNT) was created by an act of Parliament in 1959 to build and manage the national parks system of The Bahamas. The BNT is a science-based organization dedicated to effectively managing national parks to conserve and protect Bahamian natural resources. This comprehensive network of effectively managed national parks and protected areas is important for biodiversity conservation, environmental education, and green spaces for public recreation. Today, 32 national parks are designated to protect more than 2 million acres of The Bahamas. The Trust is the only known nongovernmental organization in the world with the mandate to manage a country’s entire national park system. The Bahamas National Trust P.O. Box N-4105, Nassau, The Bahamas 242-393-1317 • [email protected] • www.bnt.bs

01 Currie 3PP pi-143.indd 5

5/24/19 1:43 PM

Contents Introduction: Geology 1; Climate 11; Habitat 17; Biogeography 25; Human History 29; Conservation 40; How to Use This Book 42

Fungi 49

Plants 63

Invertebrates 145

Fish 233

01 Currie 3PP pi-143.indd 6

5/24/19 1:43 PM

Amphibians 241

Reptiles 249

Birds 291

Mammals 387

Acknowledgments 403 Appendix: List of Cetaceans  405 Glossary 407 Selected References  417 Photo Credits  431 Index 438

01 Currie 3PP pi-143.indd 7

5/30/19 1:28 PM

01 Currie 3PP pi-143.indd 8

5/24/19 1:43 PM

The Natural History of The Bahamas

01 Currie 3PP pi-143.indd 9

5/31/19 12:58 PM

01 Currie 3PP pi-143.indd 10

5/24/19 1:43 PM

Introduction

T

wo political entities—​­The Commonwealth of The Bahamas (henceforth The Bahamas), an independent country, and the British Overseas Territory of The Turks and Caicos Islands (henceforth TCI)—​­comprise The Bahamas Archipelago, a chain of islands that share a common subtropical or tropical climate, geography, geology, ecology, and human culture as well as many plant and animal species. The archipelago is in the western Atlantic Ocean, east of Florida where it runs southeasterly to just north of the Greater Antilles, namely the islands of Cuba and Hispaniola. The islands extend over an enormous expanse of ocean (c. 215,000 km2 [83,000 mi2]) from Walker’s Cay, east of Ft. Pierce, Florida, for more than 1000 km (621 mi) to Salt Cay, just south of Grand Turk Island north of the Dominican Republic. The archipelago comprises low-­lying limestone islands. The Bahamas consists of 29 large islands, 661 cays, and 2387 islets (total land area: 13,878 km2 [5358 mi2]). The highest point in the archipelago is 63 m (206 ft) on Cat Island. The Bahamas’ closest islands to the United States (the Biminis) are just 85 km (53 mi) from Miami, and the southernmost island in the chain (Great Inagua) is located 80  km (50  mi) from Cuba and Hispaniola. Spread over The Bahamas on 32 inhabited islands is a human population of about 393,000 (2016) of which 70% reside on New Providence Island (site of the capital, Nassau) and 18% on Grand Bahama. The other 30 inhabited islands are collectively referred to as the “Family Islands.” The TCI are located southeast of The Bahamas and east of Cuba. The TCI include 8 inhabited main islands (total land area: 616 km2 [238 mi2]), with a population of approximately 35,500 people, most of whom live on the island of Providenciales. Geology Limestone: The Bedrock of the Archipelago

Compared with other islands in the region and most of continental North and South America, the archipelago is geologically young with a relatively simple geology derived from calcium carbonate (limestone) sediments. The archipelago’s geology differs from the Greater Antilles, which is derived from continental, volcanic, and igneous rock and limestone sediments, and the Lesser Antilles islands that are mostly 1

01 Currie 3PP pi-143.indd 1

5/24/19 1:43 PM

of volcanic origin. The Bahamas Archipelago lies off the North American continent on a 6000 m (19,685 ft) shelf or bank consisting of multiple layers of shallow water limestone sediments. The weight of these limestone sediments has depressed the crust underlying the archipelago. The archipelago’s limestone sediments are derived primarily from the abundant marine life of the banks. Owing to its primarily biogenic origins, limestones are typically excellent sources of fossils. Some limestones are composed entirely of fossil reefs. Corals, particularly those along the edge of the banks where substantial walls have developed, together with other marine animals and algae have contributed sediments to the banks. Rapidly growing marine algae, especially the green calcareous algae, extract great quantities of calcium carbonate from the seawater and deposit it as sand or mud. The sediments of the banks are derived mostly from these algae. Another major sedimentary source is the oolitic sands, especially on the edge of the banks. Oolitic sands are derived from dissolved calcium carbonate, which precipitates out as ooliths (small and near spherical grains of calcium carbonate) when the waters warm while flowing over the shallow banks. The oolitic sands of the archipelago have played an important role in island formation. This process started about two million years ago during the most recent ice age when much water was bound up in ice, and global sea levels were 100 m (330 ft) lower than present day. As a result of the lower sea levels, the round oolitic grains were exposed to the powerful easterly trade winds and blown into lines of tall sand dunes. Over time, these oolitic sand dunes hardened into rock ridges. Sea levels rose following the end of the ice age, and ridges became islands. Islands formed in this manner are always located along the edge of banks, as expected for wind-­derived sand dunes (Figure 1). Oolitic sand dunes are not the only source of islands in the archipelago, as some islands or parts of islands consist of limestone rocklands, exposed seabed from an earlier time of higher sea level (6 m [20 ft]; mainly from 125,000 BP [before present] when sea level was highest). The rocklands, originally formed from the seabed, undergo erosion by karst processes (see below) once exposed by sea level decline. These rocklands are evident in the broader islands such as Andros and Grand Bahama, whereas the long, thin islands, such as Acklins and Long Island, are composed mostly of ridges derived from oolitic sand dunes. Some islands, such as New Providence, are a mixture of both ridges and rocklands. The carbonate banks of the archipelago are believed to have played an important role in facilitating dispersal of terrestrial organisms among islands on the same bank, at least during the ice ages when the sea levels were lower and banks were exposed. Movement of terrestrial organisms between the banks has been constrained, even at the lowest sea levels of the past, because of deep water trenches separating the individual banks. Eight significant carbonate banks are found within The Bahamas, most of which are now partially submerged. These include the Little Bahama Bank (encompasses Grand Bahama and Great Abaco); the Great Bahama Bank (Andros, the Biminis, the Berrys, New Providence, Eleuthera, Exuma, Cat Island, Long Island, 2  INTRO DUC TI O N

01 Currie 3PP pi-143.indd 2

5/24/19 1:43 PM

Figure 1. Creation of ridges and dunes in the archipelago occurs as a consequence of alternating glacial expansion and retreat as sea level (MSL) changes in the archipelago as illustrated here by Sealey (2006). Before the ice ages is portrayed in (a). As sea level falls, oolite sands from the beach are blown into dunes (b), which are subsequently colonized and stabilized by vegetation (c) during glaciation. When sea level rises and returns to normal at the start of the interglacial period, new limestone particles are washed up on new beaches (d) from which winds blow the particles into new dunes (e). During subsequent glaciation events (lowering of sea levels) and interglacial periods (accompanied by a rise in sea level), the cycle will be repeated.

3

01 Currie 3PP pi-143.indd 3

5/24/19 1:43 PM

Figure 2. An example of a rock from rockland surface that has been pitted by solution weathering of the solid rock. Rainfall becomes slightly acidic when it passes through the atmosphere and soil, and as a result it dissolves limestone. As weathering proceeds, small holes connect and enlarge and eventually the larger rock breaks into smaller pieces.

and Ragged Island); the Cay Sal Bank; the Crooked-­Acklins Bank; Mayaguana; and the Inaguan Bank (see inside cover for islands and the major banks). Within the TCI are found three carbonate banks, two of which are currently emergent (Turks Bank and Caicos Bank) and another, which is now submerged (Mouchoir Bank). An additional two submerged carbonate banks lie farther southeast: the Silver Bank and Navidad, which are politically part of the Dominican Republic, although geologically they are a continuation of The Bahamas Archipelago. Other smaller or minor banks are found in the archipelago and are indicated for certain species in the species accounts. A different karst type. Limestone is easily eroded by water, especially fresh­ water in the form of rainfall and surface runoff. Carbon dioxide in the atmosphere and in the soil dissolves in water and creates carbonic acid, a mild acid that dissolves limestone (Figure  2). This freshwater erosion or “solution weathering” results in surface and subterranean features, such as caves, characteristic of limestone areas. These formations are collectively referred to as “karst,” after the limestone area first studied in Europe. The archipelago, however, lacks many of the features of typical karst landscapes from which it differs in terms of the purity of its limestone (i.e., 98% calcium carbonate), its formation from shallow warm water sediments, its young age, and a relatively high water table. Continual erosion. The highly porous nature of young Bahamian limestone allows rainwater to permeate rapidly through the rock. Consequently, no permanent freshwater streams or rivers occur in the archipelago. Over time, rainwater and its runoff erode the limestone surface and produce a latticework of pits or sinkholes 4  INTRO DUC TI O N

01 Currie 3PP pi-143.indd 4

5/24/19 1:43 PM

Figure 3. Sinkholes are common surface features in the archipelago. They are formed when subterranean chambers collapse or when surface chemical weathering results in the creation of shallow depressions or holes, such as the example here from San Salvador. These holes accumulate soil, vegetation debris, and rainwater, providing an excellent site for growth of trees as well as a location for growing crops, such as bananas and pineapples from which they derive their local names. Sinkholes also provide microclimates for some mesic plant species, such as the Maidenhair Ferns seen here growing on the walls of this sinkhole.

ranging from a few centimeters to several meters across (Figure  3). These sinkholes are variously termed “solution holes” and “potholes” and are known locally as “banana holes” (or “pineapple holes” for the smaller ones). Banana holes are circular to oval chambers, 5 to 10 m (16–33 ft) in diameter, and 1 to 3 m (3.3–9.8 ft) deep. They are a common surface feature found throughout the archipelago and are formed when subterranean caves and chambers collapse, resulting in the creation of shallow pits. Following collapse, accumulation of soil, vegetative debris, and water in the hole provides an excellent location for growing crops, including bananas or pineapples from which they derive their local names. Rainwater ultimately permeates through the limestone and collects on top of the subterranean saltwater. Here, because of its lower density, the subterranean freshwater floats on the saltwater and forms a convex layer or a freshwater lens. Saltwater or saline wetlands or marshes occur when low elevation land meets the underlying water table. As the limestone surface dissolves in rainwater, the runoff flows off or down various pores, cracks, and sinkholes and increases erosion of the rock. Left behind is a honeycombed surface of sharp, jagged ridges with occasional upright projections or “castles” of hard limestone. The honeycombed limestone surface continues to dissolve in rainwater, causing the remaining pieces of limestone to fall in on one another. Thus, the surface may become littered with loose rocks, boulders, and flat rocks or plates that may rest loosely on more solid rock below. Rainwater runoff not only dissolves limestone, it also carries the dissolved calcium carbonate to other locations where it may be redeposited and form a hard crust due to (water) evaporation. This limestone crust, locally referred to as “flint rock” INTRO DUC TI O N   5

01 Currie 3PP pi-143.indd 5

5/24/19 1:43 PM

Figure 4. Blue holes, such as this one on San Salvador, are formed from rainwater erosion of sinkholes that reach the water table. In the foreground and surrounding this blue hole is a dense growth of the Golden Leather Fern, which is found in wet areas including saltwater associated with mangroves.

because of its hardness, is deposited in layers coating the surfaces of rocks and edges of sinkholes. Crusts are most frequently formed beneath the soil where they can prevent erosion of the underlying softer limestone and crusts may also block plant roots from reaching water contained in softer limestone below. Sinkholes, blue holes, and caves. Sinkholes grow in width as rainwater erodes the limestone surface between neighboring holes, eventually causing them to connect, enlarging the overall width of the sinkhole. This process of sinkhole enlargement can continue for decades or centuries. Although some channels may be formed below the water table, their rate of formation is slow because of slow carbonate dissolution rates under water, and large sinkholes can occur only in sites with very deep water tables. By contrast, the rocklands, which have shallow water tables, do not have large sinkholes. The deepest sinkholes in the archipelago are known as blue holes. In the present day they are filled with water, but they were created during the four Pleistocene Ice Ages (2.5 million to 11,700 years BP) during each of which the sea level fell. In the last of these ice ages, the sea level was approximately 122 m (400 ft) lower than present day. As glaciers advanced and sea level fell, the islands’ water tables were also correspondingly lower. Blue holes can be very deep; the deepest in the archipelago is Dean’s Blue Hole on Long Island (depth 201 m [663 ft]). All the major islands of The Bahamas have blue holes (Figure 4). They are most prevalent on Andros, which has 6  INTRO DUC TI O N

01 Currie 3PP pi-143.indd 6

5/24/19 1:43 PM

Figure 5. The Conch Bar Caves of Middle Caicos Island are the largest caves in the Turks and Caicos Islands and are protected by the Turks and Caicos National Trust. These caves were mined for bat “guana” or guano for ten years in the 1880s, when bat guano was used as fertilizer and exported overseas. During the mining period, evidence of Lucayan habitation of the caves was uncovered, suggesting that aboriginal people used the caves as places of worship and as shelter from hurricanes.

178 on land and about 50 in the nearby ocean (on the currently submerged carbonate banks). Those found in the ocean are believed to have been formed by the same rainwater erosion process when the banks were exposed during the ice ages. Terrestrial blue holes are connected to the ocean and are tidal; when the tidal response is marked, they are locally known as ocean holes. Although most of the water moving through blue or ocean holes is saltwater, some blue or ocean holes penetrate through a freshwater lens and therefore have a freshwater layer on top. Caves are characteristic of karst regions and are widely distributed throughout the archipelago. Flooded caves are found below the water table as exemplified by the caves associated with blue holes. Above the water table are the dry caves, which are accessible on some islands (Figure 5). Usually the dry caves consist of a vertical section formed by rainwater dissolution of the limestone as it flows downward and a horizontal section as the rainwater continues to dissolve the limestone as it flows laterally or along fissures, often toward the sea. Some caves may have multiple levels resulting from changes in the water table associated with sea level changes during glacial and interglacial periods. The freshwater lens, both at its surface where acidic rainwater accumulates and at its bottom layer where it meets the underlying salt­ water, provides the chemical conditions for increased limestone dissolution resultINTRO DUC TI O N   7

01 Currie 3PP pi-143.indd 7

5/24/19 1:43 PM

ing in cave formation. These dissolution conditions are especially potent where the top and bottom layers come together at the edge of a freshwater lens. Because the freshwater lenses often diminish at the coast, this is where many caves are formed, but not all (e.g., Salt Pond, Cartwright’s, Hatchet Bay, and Conch Bar caves). Caves initiated where the top and bottom layers of the freshwater lens meet have been termed by some as “flank margin caves”. Most archipelago caves were initiated in this manner, and flank margin caves are found along the coast and provide an indication of previous sea levels. The Ephemeral Islands (Campbell 1978). Since the archipelago’s islands are low lying, as a consequence of the slow processes involved in their creation (slow growth of corals, slow rate of sedimentation, and the fact that corals can never be higher than sea level at a given time), they are highly susceptible to variation in sea level. Changes in sea level have played an influential role in the creation of these islands and their landforms and subterranean traits. The principal cause of these sea level changes, as mentioned previously, was large-­scale glaciation events. During past ice ages, sea levels fell as freshwater was taken up in ice sheets, which subsequently thawed in the interglacial periods releasing the water and causing sea levels to rise. During the Pliocene (5 million to 2.5 million years BP), sea levels were, on average, 25 m (82 ft) higher than present-­day levels. More recently in the Pleistocene (2.5 million to 11,700 years BP), sea levels varied by up to 140 m (459 ft). As recently as 125,000 years BP, sea levels were approximately 6 m (20 ft) higher than present day, and the vast majority of the archipelago was submerged. By contrast, during the height of the last significant ice age (the Wisconsin Ice Age; c. 16,000 years BP), sea levels were as much as 122 m (400 ft) lower than now. This fall in sea level exposed the carbonate banks thereby consolidating the present-­day Bahamas into five major islands and several smaller islands with a resulting tenfold increase in land area from the present day by c. 13,900 km2 (5366 mi2 to approximately 124,716 km2 [48,149 mi2]). Similarly, in the TCI the Caicos group was consolidated into a single island c. 1500 km2 (579 mi2) while the Turks island group was consolidated into an island of c. 300 km2 (116 mi2). The three currently submerged carbonate banks southeast of the Turks Bank were formed as separate islands including the Mouchoir Bank, Silver Bank, and Navidad Bank. With the lower sea level of the Wisconsin Ice Age, the highest points on the archipelago were more than 200 m (656 ft) higher above sea level than present-­day levels. At the end of the Wisconsin Ice Age, 12,000 to 13,000 years BP, sea levels rose and much of the low-­lying land was submerged, re-­f ragmenting the large islands into smaller ones. The archipelago achieved its present size around 6000 years ago, and the shallow seas (3–30 m [10–98 ft]) around the modern archipelago are the submerged remains of these larger islands. Lithified Sand Dunes. During the Ice Ages, the sea level fell and exposed the carbonate banks at least four times. During each interglacial period, as the sea rose and covered the banks, fresh oolitic sands were produced, which on subsequent exposure to the wind created new sand dunes as the sea level fell during each Ice Age. Thus, 8  INTRO DUC TI O N

01 Currie 3PP pi-143.indd 8

5/24/19 1:43 PM

Figure 6. Cross-­bedding in the exposed ridge, as shown here in southern Eleuthera, is typical of oolitic sands deposited by wind and subsequently cemented into solid rock (lithification).

the supply of oolitic sands was replenished during each interglacial period and was then exposed to the winds, producing a new row of sand dunes on the islands. With time, the oolitic sand dunes became solidified (lithified) and formed the ridges of the modern archipelago’s islands. Layers of lithified soils, some running in different directions (termed “cross bedding”) and with fossil origins, make up the oolitic ridges, some of which may be partially eroded (Figure 6). Although the ridges on most islands tend to run north–south as a result of the northeastern trade winds, some islands, such as New Providence, have ridges running east–west as a result of the north and northwesterly winds associated with cold fronts from North America. On islands on small banks, such as San Salvador, all of the surface and ridges have been built up from drifting sands. Southerly winds played an important role in ridge formation in some of the southeastern islands of the archipelago. Soils. Soils include a layered mix of organic and inorganic materials resulting from the combined interaction of parent material or rock with climate and vegetation. Given that the archipelago’s soils are primarily derived from the weathering of limestone, the soils are alkaline. These soils are young, reflecting the geologically young age of the limestone parent material. This time frame is evident in soil texture, INTRO DUC TI O N   9

01 Currie 3PP pi-143.indd 9

5/24/19 1:43 PM

which is dominated by stones and sand, whereas smaller-­sized particles such as clay are usually rare. The lack of clay in most soil types limits soil water-­holding capacity, which is further exacerbated by the rarity of humus in some of the archipelago’s soils. Because of their immaturity, the soils are thin with one or two discontinuous layers or horizons above the bedrock in contrast to mature soils, which are deeper and have several distinct layers present, as found in the Greater Antilles and on the continents. Soil is absent or patchy in distribution on some islands, especially on the southeastern islands and on small cays, where plant cover is sparse due to inadequate rainfall or wind exposure. Three major soil types are generally recognized and include: Organic soils. Often called “black soils” because of their color, these soils are characteristic of rocklands (sometimes termed “blacklands”) in the forested northern and central islands of The Bahamas. The soil contains a mix of decomposing vegetable matter, humus, and scattered pieces of varying-­sized limestones. In texture, black soils contain particles that range in size from sand to gravel. Although black soils are generally shallow (