Ecology and Conservation of Mountain Birds 1108837190, 9781108837194

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Ecology and Conservation of Mountain Birds High mountain habitats are globally important for biodiversity. At least 12 per cent of bird species worldwide breed at or above the treeline, many of which are endemic species or species of conservation concern. However, due to the challenges of studying mountain birds in difficult-to-access habitats, little is known about their status and trends. This book provides the first global review of the ecology, evolution, life history and conservation of high mountain birds, including comprehensive coverage of their key habitats across global mountain regions, assessments of diversity patterns along elevation gradients and adaptations for life in the alpine zone. The main threats to mountain bird populations are also identified, including climate change, human land use and recreational activities. Written for ecologists and naturalists, this book identifies key knowledge gaps and clearly establishes the research priorities needed to increase our understanding of the ecology of mountain birds and to aid in their conservation. Dan Chamberlain  is Professor of Ecology at the University of Turin. His research is centred on the impacts of environmental change on biodiversity, including climate change, urbanization and agricultural intensification, with a particular focus on alpine birds. Aleksi Lehikoinen is the Senior Curator and Coordinator of the Finnish bird monitoring schemes at the Finnish Museum of Natural History, University of Helsinki. His research focusses on birds as indicators of environmental change, birds in changing climates, protected areas and management, and bird migration. Kathy Martin  is Professor of Wildlife Ecology at the University of British Columbia. She investigates how alpine birds cope with their extreme and increasingly unreliable environmental conditions. Kathy studies the adaptations, ecology, life history and conservation of alpine songbirds and grouse in the Americas.

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ECOLOGY, BIODIVERSITY AND CONSERVATION

General Editor Michael Usher, University of Stirling Editorial Board Jane Carruthers, University of South Africa, Pretoria Joachim Claudet, Centre National de la Recherche Scientifique (CNRS), Paris Tasman Crowe, University College Dublin Andy Dobson, Princeton University, New Jersey Valerie Eviner, University of California, Davis Julia E. Fa, Manchester Metropolitan University Janet Franklin, University of California, Riverside Rob Fuller, British Trust for Ornithology Chris Margules, James Cook University, North Queensland Dave Richardson, University of Stellenbosch, South Africa Peter Thomas, Keele University Des Thompson, NatureScot Lawrence Walker, University of Nevada, Las Vegas The world’s biological diversity faces unprecedented threats. The urgent challenge facing the concerned biologist is to understand ecological processes well enough to maintain their functioning in the face of the pressures resulting from human population growth. Those concerned with the conservation of biodiversity and with restoration also need to be acquainted with the political, social, historical, economic and legal frameworks within which ecological and conservation practice must be developed. The new Ecology, Biodiversity and Conservation series will present balanced, comprehensive, up-to-date and critical reviews of selected topics within the sciences of ecology and conservation biology, both botanical and zoological, and both ‘pure’ and ‘applied’. It is aimed at advanced final-year undergraduates, graduate students, researchers and university teachers, as well as ecologists and conservationists in industry, government and the voluntary sectors. The series encompasses a wide range of approaches and scales (spatial, temporal and taxonomic), including quantitative, theoretical, population, community, ecosystem, landscape, historical, experimental, behavioural and evolutionary studies. The emphasis is on science related to the real world of plants and animals rather than on purely theoretical abstractions and mathematical models. Books in this series will, wherever possible, consider issues from a broad perspective. Some books will challenge existing paradigms and present new ecological concepts, empirical or theoretical models, and testable hypotheses. Other books will explore new approaches and present syntheses on topics of ecological importance. Ecology and Control of Introduced Plants Judith H. Myers and Dawn Bazely Invertebrate Conservation and Agricultural Ecosystems T. R. New

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Risks and Decisions for Conservation and Environmental Management Mark Burgman Ecology of Populations Esa Ranta, Per Lundberg, and Veijo Kaitala Nonequilibrium Ecology Klaus Rohde The Ecology of Phytoplankton C. S. Reynolds Systematic Conservation Planning Chris Margules and Sahotra Sarkar Large-Scale Landscape Experiments: Lessons from Tumut David B. Lindenmayer Assessing the Conservation Value of Freshwaters: An International Perspective Philip J. Boon and Catherine M. Pringle Insect Species Conservation T. R. New Bird Conservation and Agriculture Jeremy D. Wilson, Andrew D. Evans, and Philip V. Grice Cave Biology: Life in Darkness Aldemaro Romero Biodiversity in Environmental Assessment: Enhancing Ecosystem Services for Human Well-Being Roel Slootweg, Asha Rajvanshi, Vinod B. Mathur, and Arend Kolhoff Mapping Species Distributions: Spatial Inference and Prediction Janet Franklin Decline and Recovery of the Island Fox: A Case Study for Population Recovery Timothy J. Coonan, Catherin A. Schwemm, and David K. Garcelon Ecosystem Functioning Kurt Jax Spatio-Temporal Heterogeneity: Concepts and Analyses Pierre R. L. Dutilleul Parasites in Ecological Communities: From Interactions to Ecosystems Melanie J. Hatcher and Alison M. Dunn Zoo Conservation Biology John E. Fa, Stephan M. Funk, and Donnamarie O’Connell Marine Protected Areas: A Multidisciplinary Approach Joachim Claudet Biodiversity in Dead Wood Jogeir N. Stokland, Juha Siitonen, and Bengt Gunnar Jonsson Landslide Ecology Lawrence R. Walker and Aaron B. Shiels Nature’s Wealth: The Economics of Ecosystem Services and Poverty Pieter J. H. van Beukering, Elissaios Papyrakis, Jetske Bouma, and Roy Brouwer

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Birds and Climate Change: Impacts and Conservation Responses James W. Pearce-Higgins and Rhys E. Green Marine Ecosystems: Human Impacts on Biodiversity, Functioning and Services Tasman P. Crowe and Christopher L. J. Frid Wood Ant Ecology and Conservation Jenni A. Stockan and Elva J. H. Robinson Detecting and Responding to Alien Plant Incursions John R. Wilson, F. Dane Panetta and Cory Lindgren Conserving Africa’s Mega-Diversity in the Anthropocene: The Hluhluwe-iMfolozi Park Story Joris P. G. M. Cromsigt, Sally Archibald and Norman Owen-Smith National Park Science: A Century of Research in South Africa Jane Carruthers Plant Conservation Science and Practice: The Role of Botanic Gardens Stephen Blackmore and Sara Oldfield Habitat Suitability and Distribution Models: With Applications in R Antoine Guisan, Wilfried Thuiller and Niklaus E. Zimmermann Ecology and Conservation of Forest Birds Grzegorz Mikusin´ski, Jean-Michel Roberge and Robert J. Fuller Species Conservation: Lessons from Islands Jamieson A. Copsey, Simon A. Black, Jim J. Groombridge and Carl G. Jones Soil Fauna Assemblages: Global to Local Scales Uffe N. Nielsen Curious About Nature Tim Burt and Des Thompson Comparative Plant Succession Among Terrestrial Biomes of the World Karel Prach and Lawrence R. Walker Ecological-Economic Modelling for Biodiversity Conservation Martin Drechsler Freshwater Biodiversity: Status, Threats and Conservation David Dudgeon Joint Species Distribution Modelling: With Applications in R Otso Ovaskainen and Nerea Abrego Natural Resource Management Reimagined: Using the Systems Ecology Paradigm Robert G. Woodmansee, John C. Moore, Dennis S. Ojima and Laurie Richards The Species–Area Relationship: Theory and Application Thomas J. Matthews, Kostas A. Triantis and Robert J. Whittaker Ecosystem Collapse and Recovery Adrian C. Newton Animal Population Ecology: An Analytical Approach T. Royama Why Conserve Nature? Perspectives on Meanings and Motivations Stephen Trudgill

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Invading Ecological Networks Cang Hui and David Richardson Hunting Wildlife in the Tropics and Subtropics Julia E. Fa, Stephan M. Funk and Robert Nasi The Life, Extinction, and Rebreeding of Quagga Zebras Peter Heywood Impacts of Human Population on Wildlife Trevor J. C. Beebee

Conservation Translocations Martin J. Gaywood, John G. Ewen, Peter M. Hollingsworth and Axel Moehrenschlager

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Ecology and Conservation of Mountain Birds Edited by

DAN CHAMBERLAIN University of Turin

ALEKSI LEHIKOINEN Finnish Museum of Natural History, University of Helsinki

KATHY MARTIN University of British Columbia, Vancouver, and Environment and Climate Change Canada

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Shaftesbury Road, Cambridge CB2 8EA, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia 314–321, 3rd Floor, Plot 3, Splendor Forum, Jasola District Centre, New Delhi – 110025, India 103 Penang Road, #05–06/07, Visioncrest Commercial, Singapore 238467 Cambridge University Press is part of Cambridge University Press & Assessment, a department of the University of Cambridge. We share the University’s mission to contribute to society through the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781108837194 DOI: 10.1017/9781108938570 © Cambridge University Press & Assessment 2023 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press & Assessment. First published 2023 Printed in the United Kingdom by TJ Books Limited, Padstow Cornwall A catalogue record for this publication is available from the British Library. Library of Congress Cataloging-in-Publication Data Names: Chamberlain, Dan, editor. | Lehikoinen, Aleksi, 1978– editor. | Martin, Kathy, 1949– editor. Title: Ecology and conservation of mountain birds / edited by Dan Chamberlain, University of Turin, Aleksi Lehikoinen, Finnish Museum of Natural History, University of Helsinki, Kathy Martin, University of British Columbia, Vancouver, and Environment and Climate Change Canada. Description: Cambridge, United Kingdom ; New York, NY : Cambridge University Press, 2023. | Series: Ecology, biodiversity and conservation | Includes bibliographical references and index. Identifiers: LCCN 2022062033 | ISBN 9781108837194 (hardback) | ISBN 9781108938570 (ebook) Subjects: LCSH: Mountain birds – Ecology. | Mountain birds – Conservation. Classification: LCC QL677.79.M68 E26 2023 | DDC 598–dc23/eng/20230503 LC record available at https://lccn.loc.gov/2022062033 ISBN 978-1-108-83719-4 Hardback ISBN 978-1-108-94042-9 Paperback Cambridge University Press & Assessment has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

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Contents

List of Contributors page xiii Preface xix Acknowledgements xxii

1 Mountain Birds and Their Habitats 1 Dan Chamberlain, Aleksi Lehikoinen, Davide Scridel and Kathy Martin

1.1 Defining a Mountain 1.2 Mountain Biodiversity 1.3 Mountain Birds 1.4 Environmental Challenges for Mountain Birds 1.5 Anthropogenic Impacts Acknowledgements References



2 4 10 15 25 27 27

2 Avian Adaptations to High Mountain Habitats: Solving the Challenges of Living in Alpine Ecosystems 35 Kathy Martin, Devin R. de Zwaan, Davide Scridel and Tomás A. Altamirano

2.1 Defining ‘High’ in High Mountain Birds 2.2 Abiotic Challenges for Alpine Birds 2.3 Biological Adaptations for High Mountain Birds 2.4 Seasonality, Migration and Connectivity 2.5 Ecological Consequences 2.6 Life Is Slow on the High Mountains 2.7 Advantages to Living and Breeding at High Elevation 2.8 Conclusions Acknowledgements References

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38 42 47 62 66 71 74 76 77 77

x · Contents

3 Global Bird Communities of Alpine and Nival Habitats 90 Devin R. de Zwaan, Arnaud G. Barras,Tomás A. Altamirano, Addisu Asefa, Pranav Gokhale, R. Suresh Kumar, Shaobin Li, ­Ruey-shing Lin, C. Steven Sevillano-Ríos, Kerry A.Weston and Davide Scridel



3.1 What Defines ‘Alpine’ Habitat? 91 3.2 A Global Overview of Alpine Habitats and Their Avian Communities 93 3.3 A Global Comparison of Alpine Breeding Bird Communities 108 3.4 Ecology of Alpine Habitats 118 3.5 Snow Dynamics and the Changing Alpine Environment 124 3.6 Conclusions 127 Acknowledgements 127 References 128



4 Birds of Treeline Ecotones 137 Dan Chamberlain, Evgeniya Melikhova, Susanne Jähnig and C. Steven Sevillano-Ríos



4.1 Introduction 4.2 Defining the Treeline Ecotone 4.3 Treeline Ecotone Bird Communities 4.4 Vegetation Structure 4.5 Drivers of Reproductive Success and Survival 4.6 Anthropogenic Influences on the Treeline Ecotone Bird Community 4.7 Conclusions Acknowledgements Appendix 4.1 References





137 138 145 158 159 162 165 166 167 169

5 Population Trends of Mountain Birds in Europe and North America 176 Aleksi Lehikoinen, Åke Lindström, John Calladine, Tommaso Campedelli, William V. DeLuca,Virginia Escandell, Jirˇí Flousek†, Sergi Herrando, Frédéric Jiguet, John Atle Kålås, Romain Lorrilliere, Timothy D. Meehan, Ingar Jostein Øien, Clara Pladevall, Brett K. Sandercock, Thomas Sattler, Benjamin Seaman, Laura Silva, Hans Schmid, Norbert Teufelbauer and Sven Trautmann 5.1 Introduction 5.2 Methods

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176 179

Contents · xi

5.3 Results 5.4 Discussion 5.5 Future Directions Acknowledgements Appendix 5.1 Appendix 5.2 References

189 200 203 205 206 207 209



6 Climate Change Impacts on Mountain Birds 215 James W. Pearce-Higgins and Kathy Martin



216

6.1 A Changing Mountain Climate 6.2 Climate Change Impacts Observed on Birds in High Mountain Habitats 6.3 Impacts at Larger Spatial Scales 6.4 Future Vulnerability 6.5 Conservation Strategies to Adapt to Climate Change 6.6 Conclusions Acknowledgements References



7 Anthropogenic Activities and Mountain Birds 260 Enrico Caprio, Antonio Rolando, Raphaël Arlettaz and Dan Chamberlain

7.1 Introduction 7.2 The Impact of Skiing on Birds 7.3 The Impact of Other Recreational Activities 7.4 Hunting and Persecution 7.5 Renewable Energy Development 7.6 Research and Conservation Perspectives Acknowledgements References



219 229 235 243 245 247 247

260 264 272 276 279 283 285 285

8 Modelling Large-Scale Patterns in Mountain Bird Diversity and Distributions 296 Mattia Brambilla, Matthew G. Betts, Ute Bradter, Hankyu Kim, Paola Laiolo and Thomas Sattler



8.1 Introduction 8.2 Modelling Distributions of Mountain Birds 8.3 Modelling Bird Diversity in Mountains 8.4 Assessing and Predicting Impacts of Environmental Changes and Implications for Conservation Acknowledgements References

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296 298 306 310 322 322

xii · Contents

9 The Alpine Avifauna of Tropical Mountains 336 Jon Fjeldså, Jesper Sonne and Carsten Rahbek



9.1 Introduction 336 9.2 Outlining Tropical Alpine Regions 339 9.3 The Physical Environment of Tropical Mountains 341 9.4 The Birds of High Tropical Mountains 345 9.5 Adaptations and Life History Strategies 356 9.6 Origin and Diversification of Tropical Alpine Avifaunas 359 9.7 Climate Change and the Future of Tropical Alpine Birds 362 9.8 Concluding Remarks 363 Acknowledgements 364 References 364



10 Priorities for Information, Research and Conservation of Birds in High Mountains 372 Kathy Martin, Dan Chamberlain and Aleksi Lehikoinen

10.1 High Mountain Birds, Avian Adaptations and Key Habitats 372 10.2 Monitoring and Modelling 377 10.3 Climate Change Impacts and Other Anthropogenic Influences 378 10.4 Impacts, Adaptations and Vulnerabilities to Climate Change and Interactions with Other Stressors: Modelling, Predicting and Mitigating 380 10.5 Key Knowledge Gaps and Research Priorities for High Mountain Bird Ecology and Conservation Problems 384 10.6 Conservation and Management Research Priorities for Birds Living in High Mountains 391 10.7 Concluding Summary 399 Acknowledgements 399 References 399

Bird Species Index 407 Subject Index 414 Colour plates can be found between pages 202 and 203.

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Contributors

TOMÁS A. ALTAMIRANO Audubon Americas, National Audubon Society, Chile and Cape Horn International Center, Universidad de Magallanes, Punta Arenas, Chile DOUGLAS L. ALTSHULER Department of Zoology, University of British Columbia, Vancouver, Canada RAPHAËL ARLETTAZ Conservation Biology Division, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland ADDISU ASEFA Department of Conservation Ecology, Faculty of Biology, PhilippsUniversity of Marburg, Marburg, Germany and Ethiopian Wildlife Conservation Authority, Addis Ababa, Ethiopia ARNAUD G. BARRAS Conservation Biology Division, Institute of Ecology and Evolution, University of Bern, Bern and Swiss Ornithological Institute, Sempach, Switzerland MATTHEW G. BETTS Forest Biodiversity Research Network, Department of Forest Ecosystems and Society, Oregon State University, Oregon, USA UTE BRADTER Norwegian Institute for Nature Research, Division for Terrestrial Ecology, Trondheim, Norway MATTIA BRAMBILLA Department of Environmental Science and Policy, University of Milan, Milan, Italy

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xiv · List of Contributors JOHN CALLADINE British Trust for Ornithology, Stirling, Scotland TOMMASO CAMPEDELLI DREAM Italia, Pratovecchio Stia (AR), Italy ENRICO CAPRIO Department of Life Sciences and Systems Biology, University of Turin, Turin, Italy DAN CHAMBERLAIN Department of Life Sciences and Systems Biology, University of Turin, Turin, Italy DEVIN R. DE ZWAAN Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, British Columbia, Canada and Mount Allison University, Department of Biology, Sackville, New Brunswick, Canada WILLIAM V. DELUCA National Audubon Society, New York, NY, USA VIRGINIA ESCANDELL SEO/BirdLife, Madrid, Spain JON FJELDSÅ Natural History Museum of Denmark, Copenhagen, Denmark JIrˇI´ FLOUSEK † Krkonose National Park, Vrchlabi, Czechia BENJAMIN G. FREEMAN Department of Zoology, University of British Columbia, Vancouver, Canada PRANAV GOKHALE Department of Endangered Species Management, Wildlife Institute of India, Chandrabani, Dehradun, Uttarakhand, India DOUGLAS R. HARDY Department of Geosciences, University of Massachusetts, Amherst, MA, USA SPENCER P. HARDY Vermont Center for Ecostudies, Norwich, VT, USA

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List of Contributors · xv

SERGI HERRANDO Catalan Ornithological Institute, Natural History Museum of Barcelona, Barcelona, Spain, and CREAF, Cerdanyola del Valles, Spain, and European Bird Census Council, Nijmegen, The Netherlands SUSANNE JÄHNIG tier3 solutions GmbH, Leverkusen, Germany FRÉDÉRIC JIGUET Centre d’Ecologie et des Sciences de la Conservation (CESCO, UMR 7204), Muséum national d’histoire naturelle (MNHN), and Centre national de la recherche scientifique (CNRS), Sorbonne Université, Paris, France JOHN ATLE KÅLÅS Norwegian Institute for Nature Research, Division for Terrestrial Ecology, Torgarden, Trondheim, Norway HANKYU KIM Department of Forest and Wildlife Ecology, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA R. SURESH KUMAR Department of Endangered Species Management, Wildlife Institute of India, Chandrabani, Dehradun, Uttarakhand, India PAOLA LAIOLO Biodiversity Research Institute (CSIC, Oviedo University), Mieres, Spain ALEKSI LEHIKOINEN The Helsinki Lab of Ornithology, LUOMUS – Finnish Museum of Natural History, University of Helsinki, Finland SHAOBIN LI Department of Zoology, College of Life Sciences, Yangtze University, Jingzhou, China RUEY-SHING LIN Habitats and Ecosystems Division, Endemic Species Research Institute, Jiji, Nantou, Taiwan ÅKE LINDSTRÖM Department of Biology, Biodiversity Unit, Lund University, Lund, Sweden

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xvi · List of Contributors ROMAIN LORRILLIERE Centre d’Ecologie et des Sciences de la Conservation (CESCO, UMR 7204), Muséum national d’histoire naturelle (MNHN), and Centre national de la recherche scientifique (CNRS), Sorbonne Université, Paris, France KATHY MARTIN Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, and Wildlife and Landscape Science, Environment and Climate Change Canada, British Columbia, Canada TIMOTHY D. MEEHAN National Audubon Society, New York, NY, USA EVGENIYA MELIKHOVA Department of Biodiversity, All-Russian Research Institute for Environment Protection, Moscow, MKAD, Russia INGAR JOSTEIN ØIEN BirdLife Norway, Trondheim, Norway JAMES W. PEARCE-HIGGINS British Trust for Ornithology, Thetford, UK CLARA PLADEVALL Andorra Research + Innovation, Sant Julià de Lòria, Principality of Andorra CARSTEN RAHBEK Center for Macroecology, Evolution and Climate, Copenhagen, Denmark ANTONIO ROLANDO Department of Life Sciences and Systems Biology, University of Turin, Turin, Italy BRETT K. SANDERCOCK Norwegian Institute for Nature Research, Department of Terrestrial Ecology, Trondheim, Norway THOMAS SATTLER Swiss Ornithological Institute, Sempach, Switzerland HANS SCHMID Swiss Ornithological Institute, Sempach, Switzerland

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List of Contributors · xvii

DAVIDE SCRIDEL CNR-IRSA National Research Council-Water Research Institute, Brugherio (MB), Italy and Museo delle Scienze di Trento (MUSE), Sezione Zoologia dei Vertebrati, Trento, Italy BENJAMIN SEAMAN BirdLife Österreich, Vienna, Austria C. STEVEN SEVILLANO-RI´OS The School for Field Studies, Center for Amazonian Studies, Loreto, Perú and Centro de Ornitología y Biodiversidad, Corbidi, División de Ecología Animal y Ciencias de la Conservación, Perú LAURA SILVA Lipu BirdLife Italia, Parma, Italy JESPER SONNE Center for Macroecology, Evolution and Climate, Copenhagen, Denmark NORBERT TEUFELBAUER BirdLife Österreich, Vienna, Austria SVEN TRAUTMANN Dachverband Deutscher Avifaunisten (DDA) e.V., Geschäftsstelle, Münster, Germany KERRY A. WESTON Biodiversity Group, Department of Conservation, New Zealand Government, Christchurch, New Zealand

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Preface

Humans have long held a fascination for mountains; these typically striking and beautiful landscapes are perceived as wild, challenging, and both inviting and hostile environments. For the naturalist, mountains are important as they host many iconic species that are rare or have restricted distributions. For the ecologist, mountains provide useful models to study the ecological and evolutionary mechanisms driving species diversity as environmental conditions and habitat types change dramatically across small increases in elevation, diversifying niche availability. Mountains are globally important for biodiversity as mountain regions cover one quarter of the earth’s terrestrial surface, but support disproportionately high avian diversity and contain nearly one half of its biodiversity hot-spots. Mountains host many charismatic and highly sought-after species such as giant hummingbird and glacier finch in the Andes, white-tailed ptarmigan in North America, white-winged snowfinch in the European Alps, grandala in Asia, scarlet-tufted sunbird in Africa or rosy finches in the Holarctic. Whether you are a birder or a professional ornithologist, the challenges of locating alpine birds adds to their allure given that they often have cryptic plumage and behaviour and occur in low densities in difficult to access habitats. We should stress that mountains are important for both specialist species and birds that live across elevation gradients. There is often extensive avian use all-year-round. Increasingly, mountains provide refugia for many open-country species that were formerly widespread, but are now declining in the lowlands due to increasingly intensive anthropogenic activities at low elevations. Given their sensitivity to climate change and habitat degradation, birds in high mountains can be very useful sentinels of environmental change. Although often perceived as pristine and natural, many mountain areas have been shaped by a long history of human influence, given centuries-old management practices for hunting and agriculture, and the more recent use of mountains for recreation. Mountain biodiversity is

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xx · Preface increasingly threatened by growing pressure caused by human activities, especially climate change, that put at risk the many key ecosystem services provided by mountain habitats. Despite escalating threats, mountain biodiversity is poorly studied compared to many lowland habitats. Thus, there is a high priority to conduct further ecological and biodiversity conservation research for mountain ecosystems. Cumulatively, we editors have spent over 75 years studying high mountain birds on four continents. We feel a strong urgency to assess the current state of mountain ornithology given the rapidly increasing pressures on high elevation ecosystems. Although there are some publications that focus on individual mountain bird species, this is the first book dedicated to research on mountain birds that addresses alpine habitats globally. In this volume, we aim to fill a large gap in the ornithology of mountain bird species and their associated ecological processes, threats and conservation. The 10 chapters in our book focus on research at and above the treeline ecotone with an emphasis on the alpine zone, although we use examples that consider wider trends across elevation gradients from montane forest to the nival zone (the highest elevation habitats). The first chapter includes our working definition of ‘mountains’, global estimates of mountain habitats and an introduction to mountain bird communities and their habitats. The second chapter addresses the many adaptations that birds employ to live in high mountains. The following two chapters summarize knowledge on avian ecology in the open alpine and nival zones and the treeline ecotone. Chapter 5 assesses mountain bird population trends, mainly drawing on national-level monitoring schemes or long-term surveys in Europe and North America. Chapters 6 and 7 deal with potential threats to mountain bird populations, respectively climate change and human disturbance, assessing the evidence of likely impacts and conservation actions required to minimize those impacts and improve prospects for the future. Chapter 8 includes the current and potential future contributions of large-scale modelling approaches to mountain bird ecology and conservation. Chapter 9, as the first global treatment of alpine birds in tropical systems, reviews the impressive levels of avian species diversity and endemism, and contrasts ecological and systematic patterns with high latitude mountain avifauna. The final chapter synthesizes the main points from each chapter and highlights the key knowledge gaps and research priorities needed to increase our knowledge of mountain birds to aid in their conservation. Our ‘roadmap’ to guide mountain bird research over the next decades

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Preface · xxi

involves improving programmes for monitoring populations, increasing our basic ecological knowledge of mountain species, identifying the key drivers of their distributions and population trends, and providing an assessment of their resilience to environmental change, in particular climate change. All of this must be accompanied by an expansion of research and funding opportunities, especially in currently under-­ represented mountain systems which are often hot spots of avian diversity in the Global South. Achieving the goals set by our roadmap will greatly improve the future prospects for mountain birds, and mountain biodiversity more generally, especially in the face of global environmental change. To conclude, high mountain systems support astounding levels of avian biodiversity and provide an impressive breadth of important services. Despite the warmer future faced by mountain birds, mountain areas are becoming increasingly important climate and habitat refugia for wildlife. As the cold upper limits on distributions for birds are relaxed, formerly unsuitable habitats may potentially support species that have been lost from more productive lower elevations. Thus, despite the threats posed by climate change, mountain ecosystems may, with appropriate management, become more important centres for bird conservation in a changing climate than they are at present. Dan Chamberlain, Aleksi Lehikoinen, Kathy Martin

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Acknowledgements

We are first and foremost grateful to Rob Fuller for giving us the impetus to write this book which would not have happened without his ideas and encouragement. We wish to extend our gratitude to all authors who have contributed to this book. In particular, we acknowledge the great job done by chapter leads in assembling a diverse group of coauthors representing a broad level of expertise and experience, covering 24 countries across 6 continents. Each chapter was evaluated by at least two referees and we acknowledge the great improvements that their feedback made to the book. Cambridge University Press were ever ready to give advice and support, and we thank in particular Michael Usher, Aleksandra Serocka and Dominic Lewis. DC wishes to thank all co-editors and authors for their input and enthusiasm. He is also grateful for the many useful discussions and insights from the field from his colleagues in Italy, especially Riccardo Alba, Camille Mermillon, Domenico Rosselli and Maria Sander. Finally, he extends his heartfelt thanks to his family, Emanuela, Giorgia and Tom, for their extreme patience during the writing of this book! AL wishes to express his gratitude to all authors of the inspiring international network of mountain bird enthusiasts. KM wishes to thank the many undergraduate and graduate students, postdoctoral fellows and colleagues who have inspired her with their hard work and keen insights along her journey to learn how alpine birds live successfully in their high mountain habitats. As well, many keen naturalists and hikers have contributed ‘Citizen Science’ observations to provide broader insights for alpine bird ecology and conservation. Kathy also thanks managers from Environment and Climate Change Canada, who have supported her alpine bird research programme over the past three decades, in particular Dr Robert Elner and Dr Elizabeth Krebs.

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1 · Mountain Birds and Their Habitats DAN CHAMBERLAIN, ALEKSI LEHIKOINEN, DAVIDE SCRIDEL AND KATHY MARTIN

Mountains are high relief habitats that occur across all continents. Their impressive features define landscapes and human societies. These high elevation,1 topographically complex habitats provide key ecosystem services (Körner & Ohsawa 2006), host high levels of diversity and endemism (Antonelli et al. 2018), and are characterized by many specialized and charismatic species, in addition to many generalist species that are distributed across broad elevation gradients (Boyle & Martin 2015). Mountain regions are highly valued by people in terms of their natural beauty and wildlife, and they are common tourist destinations yearround. However, these regions are under threat from a range of factors (Alba et al. 2022), including climate change (e.g., Gottfried et al. 2012; Freeman et al. 2018), changes in livestock management (MacDonald et al. 2000; Laiolo et al. 2004), increasing pressure from tourism and recreational activities (Rixen & Rolando 2013), and exploitation of natural resources, including renewable energy (Svadlenak-Gomez et al. 2013), all of which may have implications for mountain bird populations. In this chapter, we first define our key terms of reference, including what we consider to be ‘mountains’ and ‘mountain birds’. We then summarize the importance of mountains to biodiversity in general and to birds in particular, focussing on key drivers of avian community assembly and variation along elevation gradients encompassing a wide range of habitats (i.e., from relatively low elevations to the highest mountain peaks). Subsequently, we provide an overview of the particular conditions faced by mountain birds at higher elevations, especially 1

The term ‘elevation’ is used to represent the height of the ground above sea-level (e.g., a mountain summit); ‘altitude’ is the height above ground (e.g., a bird in flight). Both are expressed as metres above sea-level.

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2 · Dan Chamberlain, et al. at and above the treeline. Finally, we identify some of the key anthropogenic pressures that have shaped high elevation habitats historically. In so doing, we set the scene for the diversity of topics covered in the following chapters.

1.1  Defining a Mountain What is a mountain? This is a simple question for which there is no simple answer. Several researchers have attempted to define methods and delineate estimates of regional or global mountain areas, typically involving the key characteristics of elevation and steepness of terrain (e.g., Kapos et al. 2000; Körner et al. 2011; Karagulle et al. 2017; Körner et al. 2017; Sayre et al. 2018), although the importance put on specific characteristics varies (Körner et al. 2021). The definition of Kapos et al. (2000) and Blyth et al. (2002) developed for the United Nations Environmental Programme (UNEP), is based on defining different mountain classes, largely in relation to elevation, the minimum being 300 m to be included as part of a mountain system. This classification (which we term K1 following Sayre et al. 2018), results in 24.3 per cent of global terrestrial surface being classed as mountainous (Plate 1). This does, however, exclude areas that have many ecological characteristics of mountains. Körner et  al. (2011) developed a different classification (termed K2) for the Global Mountain Biodiversity Assessment, mostly based on terrain ruggedness, that resulted in the inclusion of a greater area at lower elevations (particularly coastal mountains), but an overall lower area of global mountain systems (12.3 per cent of global terrestrial surface) compared to Kapos et al. (2000). This was due to the exclusion of high elevation plateaus, intermontane valleys and hilly forelands (Plate 2). Using a higher resolution (250 m versus 1,000 m), Karagulle et al. (2017) based their classification (termed K3) for the US Geological Survey on gentle slopes (a virtual mean inclination), ruggedness and profile type (the amount of gently sloping land in upland areas), resulting in an estimate of 30.4 per cent mountain cover of global terrestrial surface (Plate 3). Testolin et al. (2020) used an even higher resolution (30 m) to identify a global alpine zone (areas above the treeline) based on unforested areas and modelled estimates of the limits of regional treelines, using the classification of Körner et al. (2011) as an initial template. Excluding Arctic and Antarctic mountains, this resulted in an estimated 2.6 per cent of the global terrestrial surface being covered by alpine zones which matches well the alpine areas defined in K2. Plate 4 shows

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Mountain Birds and their Habitats · 3

the classification of Testolin et al. (2020) superimposed on a composite map of the other three main classifications (K1–K3; Kapos et al. 2000; Körner et al. 2011; Karagulle et al. 2017) and thus gives an estimate of the maximum extent of mountainous area combining different ‘mountain’ definitions. It should be noted that only K1 includes all of Greenland or Antarctica. These areas were excluded from K2 (except for coastal mountains of Greenland) and K3 because their overall aims were not to identify ruggedness per se (a purely topographic view), but to apply the classifications to fields such as forestry (Kapos et al. 2000), biodiversity and climatic life zones on earth (Körner et al. 2011, 2017), and human populations living in or near mountains (Körner et al. 2021). We argue that Greenland and Antarctica should be included in future mountain mapping exercises as they hold relevant mountain features (high elevation sites at high latitudes), they host mountain birds (e.g., golden eagle Aquila chysaetos and rock ptarmigan Lagopus muta in Greenland, snow petrel Pagodroma nivea in Antarctica), and many ice-covered sites currently without birds are subject to fast ice-melting processes and are likely to become suitable in the near future. Which of these methods is preferred depends on the objectives of a given study (Sayre et al. 2018), but there are situations where clear and objective definitions of mountain areas are needed (Körner et al. 2017). In this book, we focus on the ecology of the bird species that use these zones for at least a part of their life cycle. Our goals are most in line with the definition of Körner et al. (2011), that is, the K2 classification in Plate 2, in that we are primarily concerned with mountain biodiversity quantity and condition, species–habitat relationships and species–­climate relationships. However, we do not formally adopt a strict and static definition of a ‘mountain’ which could risk the exclusion of important examples from low mountains (e.g., coastal, or where boreal mountains grade into arctic tundra) or from high elevation plateaus where species are still subject to many of the same constraints (in particular climatic) as mountain birds in steeper terrain. For example, the K2 classification does not include the whole Tibetan Plateau as it does not meet the requirements for terrain ruggedness, but ecologically we would consider this area as mountainous. Our philosophy mirrors that of Nagy & Grabherr (2009) in that we are mainly concerned with areas that can be considered part of mountain systems from an ecological, rather than a topographic, point of view. In other words, mountain systems should have significant influences

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4 · Dan Chamberlain, et al. on the ecology of habitats and species due to factors associated with a combination of elevation and topography with respect to the surrounding landscape. For much of this book, we maintain a focus (albeit not exclusively) on areas above the natural elevational limit of continuous forest, where the treeline ecotone forms the lower limit of our main area of interest. Thus, the Testolin et al. (2020) classification probably matches that focus most closely. However, it does not include treeline ecotone areas, and in particular those that have been formed at elevations lower than the climatic limit of the treeline, which are also of interest (Chapter 4). It also underestimates the area of alpine zones that have less rock and bare ground, particularly in the tropics (Chapter 3).

1.2  Mountain Biodiversity Mountainous areas tend to have disproportionately high biodiversity, covering around a quarter of the world’s terrestrial surface (Kapos et al. 2000), supporting an estimated one-third of terrestrial biodiversity (Körner 2004), and harbouring almost 50 per cent of terrestrial biodiversity hot-spots globally (Myers et al. 2000). Mountain specialists (i.e., those dependent on and restricted to high elevation habitats for key parts of their annual cycle) often show very narrow geographic (and vertical) distributions. The range of individual species may sometimes be restricted to a single mountain or valley (Antonelli et al. 2018), or more typically a narrow elevational range, hence mountains are important centres of endemism (Körner et al. 2017) and speciation (Fjeldså et al. 2012; Rahbek et al. 2019). Mountains thus often harbour a greater proportion of threatened species than other habitats (Franzén & Molander 2012). Biodiversity is also increased by the upshifting of generalist species (those normally occurring over a wide range of elevations) that have lost their low elevation habitat due to anthropogenic impacts, such as farmland birds in France (Archaux 2007). What drives the high biodiversity in mountains? From an evolutionary perspective, geological heterogeneity and its interaction with historical long-term fluctuations in climate has led to enhanced speciation rates and hence high diversity in mountainous regions (Rahbek et al. 2019). At a fairly large scale (1° latitude), tetrapod species richness is closely and positively correlated with temperature, precipitation and topographic relief (Antonelli et al. 2018), showing the importance of the complexity of mountain environments (evolutionary processes are considered further in Chapter 9). At finer scales, high biodiversity arises over relatively small

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Mountain Birds and their Habitats · 5

spatial scales (e.g., one or a few kilometres) as a consequence of the steep terrain and subsequent zonation along elevation gradients (Section 1.2.1). Species diversity, in particular species richness, varies strongly with elevation. There are competing hypotheses to explain such patterns, and typically these are linked closely to hypotheses explaining trends in relation to latitude. Moist, tropical regions have a more stable yearround climate which, over evolutionary time, may result in greater divergence and niche packing with fine-scale specialization. More fluctuating, higher latitude environments facilitate generalists with broad niches. Analogously, the more fluctuating climatic conditions at higher elevations may contribute to broader niches (Mermillon et al. 2022) and decreasing species richness along elevation gradients. However, the latitude gradient shows a fairly constant decrease in species richness towards the poles, whereas there is much more evidence of an intermediate peak in terms of elevation patterns, suggesting that latitudinal and elevational trends are driven, at least in part, by different factors (Rahbek 1995). Temperature is in general the most important factor driving biodiversity trends along elevation gradients (Peters et al. 2016; Laiolo et al. 2018). Ambient temperature varies with elevation, or more strictly air pressure, in a fairly predictable way termed the adiabatic lapse rate. Typically, there is an approximately 0.6°C decrease for every 100 m increase in elevation, with local variation caused by humidity, wind exposure, cloud cover and other factors (e.g., Dillon et al. 2006; Colwell et al. 2008). Since temperature may constrain the number of organisms that a given area can support, the decrease in temperature at higher elevations may limit the richness of a given community and affect its community structure (White et al. 2019). Water availability (precipitation, soil water retention and evaporation) is an additional critical climatic factor (McCain 2009; Antonelli et al. 2018), influencing, for example, tree formation at high elevation. Primary productivity, which decreases with temperature (and hence elevation) and is also affected by precipitation, is integrated with these two abiotic drivers. High elevations have lower productivity, hence there is insufficient energy to support species rich communities (Newton 2020; Schumm et al. 2020). Indeed, there is evidence that bird species richness is closely correlated with measures of productivity (e.g., Acharya et al. 2011; Abebe et al. 2019). However, these relationships show considerable geographic variation – stability, in situ speciation and accumulation of species over a long time are considered to be more important drivers of species richness within regions with high landscape complexity (Rahbek et al. 2019).

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6 · Dan Chamberlain, et al. A range of other hypotheses have been proposed to explain variations in species richness with elevation. Rapoport’s rule states that the latitudinal range size of animals and plants is greater at higher latitudes (Stevens 1989). This has been extended to range sizes in relation to elevation, that is, species of higher elevations show a greater elevational range as they are adapted to a wider range of conditions (Stevens 1992). This results in greater species richness at lower elevations as higher elevation species are more likely to ‘spill down’ to lower elevations (Acharya et al. 2011). There are also hypotheses that are more related to spatial effects, rather than biological effects per se. For example, some have argued that lower species richness at higher elevations in mountains is due to the speciesarea relationship and the fact that a ‘typical’ conical-shaped mountain has a greater area at the base than close to the summit (Šekerciog˘ lu et al. 2012). An alternative hypothesis is the Mid-Domain Effect (Colwell & Lees 2000), which proposes that the ranges of species are randomly distributed within a given area, thus more ranges will overlap near the middle of the area than at the edges, resulting in a mid-elevation species richness peak. There has been only limited support for Rapoport’s rule (Gaston et al. 1998; Achayra et al. 2011), the species-area relationship (Elsen & Tingley 2015) and the Mid-Domain Effect (McCain 2009; Reynolds et al. 2021) for explaining patterns in species richness along elevation gradients. Environmental drivers (e.g., productivity and climate, in particular water and temperature) are thus likely to be more important (McCain 2009), although a range of complex factors interact to produce location-specific patterns (Reynolds et al. 2022). Whilst much research on biodiversity trends along the elevation gradient has focussed on species richness, other studies have instead considered variations in functional diversity, that is, the role of organisms in communities and ecosystems (Petchey & Gaston 2006), usually expressed through the analysis of species traits (e.g., diet type, clutch size, foraging niche, migratory strategy). Trends in functional diversity along elevation gradients vary according to latitude. In the tropics, bird communities show a disproportionately high functional diversity in relation to their species richness (i.e., functional overdispersion) in stable lowland habitats, but the opposite pattern (functional clustering) in higher elevation habitats (Jarzyna et al. 2021). However, increasing functional overdispersion is shown in temperate and boreal bird communities at higher elevations (above c. 2,000 m, Martin et al. 2021). Temperate mountains are therefore functionally rich and distinctive ecosystems, despite their overall low species richness. These findings further suggest that higher

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Mountain Birds and their Habitats · 7

latitude mountains are disproportionately susceptible to the loss of critical ecological functions because they harbour species assemblages with high functional distinctiveness and low species richness (Jarzyna et al. 2021). 1.2.1  Zonation Along the Elevation Gradient

Mountains are defined by their greater elevation with respect to the surrounding landscape, thus a key characteristic, in particular in relation to biodiversity, is the rapid change in environmental conditions along the elevation gradient  – and obviously the steeper the gradient, the more rapidly conditions will change over a given spatial scale. The decrease in temperature with elevation is one of the key environmental factors that affects variation in biotic communities along elevation gradients (see earlier in section 1.2). Additionally, wind speed, air pressure, partial pressure of oxygen and UV radiation vary more-or-less predictably with elevation (Nagy & Grabherr 2009; Chapter 2). The changing conditions over small spatial scales result in fairly distinct vegetation zones along the elevation gradient that are normally bounded by the upper limit of particular growth forms dictated by the environmental conditions. In a natural state (i.e., with little or minimal human influence), these correspond to the bioclimatic zones listed in Table 1.1. There are two features separating different zones that are of particular relevance to the scope of this book. First, the timberline, which is the upper limit of closed forest. Much of this book is concerned with the area above the timberline (i.e., it forms the lower limit of the bioclimatic zones considered). Second, the treeline, the approximate line that links the highest groups of mature trees, which is often limited by temperature (Körner & Paulsen 2004). The treeline typically represents an area of marked change in bird communities (e.g., Altamirano et al. 2020; Martin et al. 2021). Given the inconsistencies in the use of these terms to describe vegetation zones and boundaries around the treeline, we discuss them in more detail in Chapter 4. The zones set out in Table 1.1 are, of course, generalizations – there are many situations where some of them are absent, often due to human activity (see Section 1.5), but also due to ecological or climatic conditions (e.g., the extent of treeline habitat for temperate mountains is often v­ ery limited; Nagy & Grabherr 2009). There are also regional or local climatic constraints that may influence zonation such as aspect. In dry climates, the forest may be largely absent (e.g., some central Asian ranges, Potapov 2004; the dry central Andes, Chapter 9). Furthermore, the limit of the

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8 · Dan Chamberlain, et al. Table 1.1  Habitat zonation and key divisions between zones along the elevation gradient (based largely on Nagy & Grabherr 2009), as used in this book. Zone

Description

Lowland Montane forest

Areas not classified as mountain. Closed canopy forest, mature trees – note that transitions may occur between different types of forest within this zone (e.g., subtropical and temperate broad-leaved forest; Acharya et al. 2011). The line where the closed forest ends, marking the transition between montane forest and treeline ecotone. The zone between the timberline and the tree species line. Also sometimes termed the upper subalpine, this is typically characterized by a mosaic of trees, shrubs and meadows. The approximate line that links the highest growing groups of mature trees. The maximum possible elevation of tree growth (including seedlings and saplings). The treeless area above the tree species line that is dominated by dwarf-shrub communities (sometimes termed lower alpine) and grassland, steppe-like and meadow communities (sometimes termed upper alpine). The elevation at which there is permanent snow cover (often considered equal to the upper limit of the alpine zone; Körner 2012). Patchy vegetation, often cushion or rosette plants, within a largely unvegetated landscape (some authors separate nival and subnival zones according to the snowline). Beyond the elevation limit at which vascular plants grow. Wind is important in providing nutrient input and maintaining food chains.

Timberline Treeline ecotone Treeline Tree species line Alpine

Snowline Nival Aeolian

alpine zone is influenced by slope exposure. For mountain ranges that are generally orientated from east to west (e.g., Himalayas, European Alps, Pyrenees), the alpine zone is typically lower on northern facing slopes in the northern hemisphere and on southern facing slopes in the southern hemisphere (Nagy & Grabherr 2009). There are oceanic influences on the treeline as well, mediated by precipitation patterns that influence the elevation of the different zones in major mountain chains that are orientated from north to south (e.g., the Andes, Chapter 9) and also mountains on islands. Zonation may also vary according to the geographic position of a particular location within a mountain range, whereby central areas have warmer temperatures and thus higher elevations for any given zone

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Mountain Birds and their Habitats · 9 A

B

C

D

Figure 1.1  Examples of the elevation zones that are the main focus of this book. A.  Suntar-Khayata Range, Eastern Siberia, showing gentle elevation gradients resulting in a wide treeline ecotone (Photo: E. Melikhova); B.  Peruvian Andes, with patches of Polylepis woodland (Photo: S. Sevillano-Ríos). C.  Gradient from montane forest to the alpine zone in the Italian Alps, where grazing has a major impact on vegetation structure and in particular on the elevation of the treeline ecotone (Photo: D. Chamberlain). D.  A high elevation lake in the Tantalus Range, British Columbia, Canada, within a diffuse treeline ecotone transitioning into alpine shrubs and a rocky nival zone towards the peak (Photo: D.R. de Zwaan).

relative to external slopes (the mass elevation effect; Körner 2012). Some examples of elevation gradients in mountains from different geographic regions are shown in Figure 1.1. Despite these variations, the definitions in Table 1.1 serve as a useful reference for the typical zonation found along elevation gradients in many mountains. At very high latitudes, Arctic mountains do not have a treeline as they are beyond the latitudinal limit of tree growth. Indeed, latitude is the main determinant of the elevation of these various zones (Table 1.1); the treeline in tropical mountains can occur at very high elevations (Nagy & Grabherr 2009), whereas in sub-arctic areas at high latitudes, the treeline is at sea-level. Furthermore, this classification does not apply in many areas due to human influence (see Section 1.5).

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10 · Dan Chamberlain, et al.

1.3  Mountain Birds 1.3.1  What Is a Mountain Bird?

Defining a mountain is difficult, so it follows that defining a mountain bird is equally challenging. Objective definitions of mountain birds have been developed based on definitions of mountain areas as outlined above and their overlap with the range maps of the geographical distribution of species. In this way, mountain birds are identified as those with a large proportion of their range in mountain areas (e.g., Scridel et al. 2018; Lehikoinen et al. 2019; Alba et al. 2022). However, such range maps are usually restricted to breeding season distributions and thus do not represent the use of mountains by birds throughout the year. The number of species that use mountains may be particularly high. One field study of temperate mountains in the Americas during the breeding season detected 44 to 63 per cent of the regional species pool in western Canada and southern Chile, respectively (Martin et al. 2021). At a continental level and including migrants, Boyle & Martin (2015) found that c. 35 per cent of the birds that breed in North America use mountains at some point in their annual life cycle. In this book, we are interested in how mountain habitats are used by birds. We define a mountain bird in this book as a bird species where at least some populations somewhere in their distribution spend at least one critical stage of their life cycle at or above the elevational limit of continuous forest (i.e., above the timberline). In doing so, we recognize that our knowledge of avian use of mountains is incomplete from a seasonal point of view (as research is biased towards breeding seasons) and from a geographic point of view (as many of the world’s mountain ranges are under-researched – see Section 1.3.2). 1.3.2  Extent of Knowledge of Birds using Alpine Habitats Compared to Other Systems

Given the particular logistical challenges to mountain research, it has been suggested that knowledge of mountain birds is relatively poor compared to other major habitat types (European Environment Agency 2010; Chamberlain et al. 2012; Scridel et al. 2018). For example, nearly one quarter of all alpine breeding species have no nest records or have less than five nests described, in addition to deep data deficiency for most other basic life-history traits (Chapters 2 and 3). A systematic search of published articles in the Web of Science online database between

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Mountain Birds and their Habitats · 11 Mountain/alpine Arctic/antarctic Desert Farmland/agriculture Forest/wood Grassland/steppe Lake/river Marine/sea Urban/city Wetland/marsh 0

500

1000

1500

Number of publications

Figure 1.2  The number of research articles on Web of Science (articles referenced in the Science Citation Index, all languages) between 2011 and 2021 according to different search terms based on habitats. The general topic search (TS) term was ‘TS=((bird* OR avian*) AND (HAB1* OR HAB2*) AND (ecology OR conservation))’, where HAB1 and HAB2 represent the search terms on the x-axis (with the exception of desert for which there was only a single habitat term in the search). Only a maximum of two habitat-based terms were used in order to try to produce a more comparable search. A study was only included if the research therein was restricted to a given habitat (e.g., a landscape-level study including both forest and farmland would not have been included).

2011 and 2021 was undertaken to determine the level of relatively recent research on birds in mountains compared to other major habitat types. Of the ten different habitats considered, the number of publications on birds restricted to mountain/alpine habitat (n = 403) was comparable to the total from grasslands and lake/river, and was higher than Arctic/ Antarctic and desert habitats (Figure 1.2). Birds associated with forests had the most publications, followed by farmland and urban habitats. At first sight, the contention that mountain birds are under-studied compared to birds in other habitats does not seem to be supported. However, considering the number of publications in mountain/alpine habitat according to elevation zone (Table 1.1), it is clear that much

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12 · Dan Chamberlain, et al.

Figure 1.3  The number of research articles on mountain birds grouped according to elevation zone (Table 1.1). ‘Open general’ refers to largely treeless habitats that are usually anthropogenic in nature and that occur below the climatic treeline in a given location. Gradient studies encompass more than one elevation zone. N = 403.

research has been carried out exclusively in montane forests (50% of 403 studies), and on elevation gradients across zones (20%), but comparatively little has been conducted specifically in the alpine zone (13%) and even less in the treeline ecotone (8%; Figure 1.3). Hence, our knowledge of the ecology of mountain birds at high elevation does indeed seem to be lower than those in most other major habitat types based on research carried out in the last ten years. Only desert habitats (n = 83; Figure 1.2) had fewer publications than those specifically undertaken either at the treeline or in the alpine zone (n = 84). A further examination of the ‘mountain’ and ‘alpine’ references was carried out in order to assess geographical biases in research. Most studies had been conducted in Asia and Europe, with somewhat fewer in North and South America (Figure 1.4). At the national level, there were more studies in China (n = 45) than any other country. There were very few studies (