Persistence and Vulnerability of Island Endemic Birds
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PERSISTENCE AND VULNERABILITY OF ISLAND ENDEMIC BIRDS Jonathan E M Baillie July 2001 Thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College. Imperial College at Silwood Park Ascot Berkshire SL5 7PY UK And The Institute of Zoology Zoological Society of London Regent's Park, London, NW1 4RY UK 1 LIBRARY HSIJLIBB IMAGING SERVICES NORTH Boston Spa, Wetherby West Yorkshire, LS23 7BQ www.bl.uk THESIS CONTAINS CDs/DVDs Persistence and vulnerability of island endemic birds ABSTRACT This thesis investigates the dynamic relationship between the processes of extinction on islands and the traits of oceanic island endemic birds associated with persistence and vulnerability. This is explored using the comparative method and a data set of all birds endemic to oceanic islands. Two case studies are then presented to examine the resilience of the island endemic birds of Principe and Boné de Joquei in the Gulf of Guinea. When comparing closely related oceanic island and mainland birds, clutch size is lower on islands and, within islands it continues to decline as the distribution area of a species decreases. Small birds (<27 cm in body length) tend to get larger, and there is a trend for sexual size dimorphism to increase on oceanic islands. Recent extinction rates are lower on islands that have been exposed to humans for a long period of time. The birds on such islands are also less threatened by the introduction of exotics. A long period of exposure to humans also reduces the probability that the remaining species are flightless, ground-nesting, or non-forest- restricted endemics. When comparing island and mainland species that have similar areas of distribution, there is no significant difference in extinction risk. However, island birds are more threatened by introduced species. On oceanic islands, flightless birds, ground-nesting birds, birds with larger body size, and habitat specialists are associated with a greater risk of extinction than other birds. Sexually selected traits such as sexual body size dimorphism and dichromatism are not associated with elevated extinction risk. The resilience of the island endemic birds on Principe appears to be associated with a unique land use history and evolutionary exposure to predators, competitors and disease. Finally, a state of super abundance may be essential for the long-term persistence of endemic birds on small remote oceanic islands. 2 Persistence and vulnerability of island endemic birds ACKNOWLEDGEMENTS First I would like to thank my parents and family for their support and encouragement over the past 30 years. I am extremely grateful to my principal advisors Georgina Mace and Andy Purvis for their guidance, encouragement, and inspiration. It has been a great honour to work with them and they have played a critical role in the development of my thoughts on conservation and evolutionary biology. I am also grateful to my advisors Guy Cowlishaw and John Lawton. As people that have been particularly inspirational during my academic career I would like to thank Cricket Ule, Katherine Wynne-Edward, Dan Gady, Charles Remington, Tim Clark, Ozwald Schmitz, Simon Stuart, John Lawton, and of course Andy Purvis and Georgina Mace. I am grateful to the Overseas Research Studentship, the Harshman Fellowship, and the Canadian Centennial Scholarship, for providing the funding that has made my research possible. For reviewing and commenting on drafts or sections of this thesis, I would like to thank Georgina Mace, Andy Purvis, Guy Cowlishaw, Janice Long, Alexandra Baillie, Peter Bennett, Tim Blackburn, Chris Carbone, Charles Baillie, Marilyn Baillie, Brett House, James Fotheringham, Amy French, Phil Atkinson, Peter Jones and Angus Gascoigne. The analyses in the thesis would not have been possible without the generous offer of data from Rob McCall, Peter Bennett, Tim Blackburn, WCMC, and BirdLife International (with special thanks to Ali Stattersfield and Martin Sneary). I have had a wonderful experience at the Institute of Zoology and everyone has been extremely helpful. In particular I would like to thank the finishing club (Jakob Bro- Jorgensen and Susanna Paisley), Peter Bennett, Chris Carbobe, Janice Long, Theresa Jones, Roselle Chapman, Dave Cope, Daniela De Luca, Andrew Bourke, Marcus Rowcliffe, Christine Mueller, Sarah Durant, Stephan Funk, Richard Pettifor and Peter Cotgreave. I also would like to thank my lab mates at Silwood Park, Nick (Pendek) Isaac, Kate Jones, Richard Grenyer, Paul-Michael Agapow, Andrea Webster as well as other members of Silwood that have been particularly helpful, Michael Crawley, Tim Barraclough, Ian Owens, and Cheryl Case. At Cambridge I would like to thank Tim Coulson, Andrew Balmford, Rhys Green, and Sue O’Brien. For collaborative research during my thesis it has been a pleasure to work with Georgina Mace, Tim Blackburn, Peter Bennett, Ian Owens, Steve Beissinger, Kent Redford, Paul Clark, Neil Cumberlidge, Barry Clarke, Bob Drews, Angus Gascoigne, Gilles Joffroy, Tariq Stevart, and Elodie Hudson. For getting me out of the office and way from work, I would like to thank Brett House, Gill Mann, Andrew Hurst, Tash Perrin, James Porteous, Elizabeth Passey, Camille Loxley, Gord Ray, James Fotheringham and Genevieve Burgess. Finally, I would like to thank Amy French for her support and for listening to me natter on about birds. 3 Persistence and vulnerability of island endemic birds DECLARATION All the work presented in this thesis is my own except the following: Chapter 3: Collaborator: Georgina Mace Institute of Zoology, Zoological Society of London, Regent’s Park, London, NW1 4RY, UK. The analyses and first draft are my own work. Georgina was involved in the development of ideas for the study and made editorial and structural changes to the first draft. Chapter 4: Collaborator: Tim Blackburn School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK The analyses and first draft are my own work. Tim was involved in the development of ideas for the study and made editorial and structural changes to the first draft. Chapter 6: Collaborator: Angus Gascoigne CP 289, Sào Tomé, Sào Tomé e Príncipe. [email protected] Angus provided information on present land use history and current conservation measures being taken in the region. He also provided the map of Principe. The rest of the work is my own. Appendix The appendix contains two papers that were written in collaboration while conducting research for my thesis. Jofiathan E M Baillie Persistence and vulnerability of island endemic birds TABLE OF CONTENTS Abstract 2 Acknowledgements 3 Declaration 4 Table of contents 5 Table of figures 7 Table of tables 8 Table of illustrations 11 Introduction 12 Chapter 1: Introduction to the database and general methods 25 Introduction to the database 26 Comparative approach 29 General patterns in the database 32 Appendix 1.1 42 Chapter 2: Life history and morphological trends on islands 45 Introduction 47 Methods 51 Results 53 Discussion 57 Chapter 3: Humans as an extinction filter on islands and the 68 changing process of threat Introduction 70 Methods 71 Results 76 Discussion 79 Appendix 3.1 86 5 Persistence and vulnerability of island endemic birds Chapter 4: Humans as a selective force: filtration of life history and 88 ecological traits Introduction 90 Methods 93 Results 95 Discussion 96 Chapter 5: Avian extinction risk on oceanic islands 105 Introduction 107 Methods 110 Results 115 Discussion 120 Chapter 6: Conservation status of the endemic birds of Príncipe: 131 Insight into past resilience and future persistence Introduction 133 Methods 137 Results 139 Discussion 152 Chapter 7: Super abundance and persistence: 164 Lessons from a small oceanic island Introduction 166 Methods 170 Results 171 Discussion 176 Conclusion 186 Appendix 197 Assessment and management of species at risk 198 A new species of freshwater crab (Brachyura: Potamoidea: 218 Potamonautidae) from Príncipe, Gulf of Guinea, Central Africa CD This contains the phytogeny used for the analyses in this thesis (Back cover) 6 Persistence and vulnerability of island endemic birds TABLE OF FIGURES Figure 1.1. 33 The proportion of species in different avian orders found on oceanic islands. Figure 1.2. 34 The proportion of species threatened for different orders, considering only species that are restricted to oceanic islands. Figure 1.3. 37 The causes of recent extinction are compared to the processes in present threat. Figure 2.1. 56 The total distribution area contrasts in relation to the clutch size contrasts. Species that have smaller distributions are associated with smaller clutch size. Figure 2.2.. 56 Oceanic island passerine birds. The average latitude contrasts in relation to the clutch size contrasts. Passerines closer to the equator tend to have a smaller clutch size. Figure 2.3. 57 Oceanic island birds >=27cm. The total distribution contrasts in relation to body size contrasts. Large bodied species are not associated with smaller total distributions. Figure 3.1. 78 The relationship between the proportion of endemic birds that have become extinct on islands or island groups in historic times and the date of first human colonisation. Figure 3.2. 78 The relationship between the proportion of endemic birds threatened by introduced species on islands or island groups and the date of first human colonisation. Figure 5.1. 119 The habitat specialist contrasts in relation to the threatened status contrasts. Habitat specialists tend to be at greater risk of extinction than non-habitat specialists. Figure 5.2. 119 Birds exposed to humans for less than 1000 years. The body size contrasts in relation to the threatened status contrasts. Large bodied birds tend to be at greater risk of extinction. Figure 6.1. 135 Map of Principe in the Gulf of Guinea. Figure 6.2. 148 Gulf of Guinea thrush Turdus olivaceofus xanthorhynchus. Figure 7.1. 169 The island of Boné de Joquei. Figure 7.2.