DETERMINANTS OF VARIATION IN PRODUCTIVITY, ADULT SURVIVAL AND RECRUITMENT IN A DECLINING MIGRANT BIRD: THE WHINCHAT (SAXICOLA RUBETRA) Jennifer A. Taylor BSc (Hons.) Lancaster Environment Centre Lancaster University Submitted for the Degree of Doctor of Philosophy June 2015 Declaration I declare that the work presented in this thesis is my own, except where acknowledged, and has not been submitted elsewhere for the award of a degree of Doctor of Philosophy. Jennifer A. Taylor June 2015 i Acknowledgements Firstly I would like to thank the Ministry of Defence (MOD). Jeff Elson especially went out of his way to try to help by finding ways I could still access my field sites when large scale military operations were on. Without his help I would not have been able to collect nearly as much data. Dominic Ash and Lisa Wade provided information on the Plain management and helped in liaison with farmers. I also want to thank the range security services for looking out for me on my field site and assisting with 2 punctures and 3 flat batteries during my field seasons, as well as the BTO for providing me with a suitable vehicle for fieldwork. The Imber Conservation Group were a great help with some of the Whinchat surveys - especially Andrew Bray, who offered assistance with fieldwork too when needed and Tilly Gregory and Iain Perkins, who made a point of looking out for whinchats during their other survey work on the plain. I would especially like to thank my main supervisors, the two Ian’s. Ian Hartley, for allowing me the freedom to manage the project independently, explore my own ideas, but still always being on hand with suggestions, support and encouragement when things went wrong and somehow always managing to make me feel more optimistic about problems; Ian Henderson, for initiating the project in the first place, and for his help and support early on in my fieldwork which gave me the knowledge base and confidence to take charge of the project. My minor supervisor, Andy Wilby also offered a valuable second opinion when needed and included me in his lab group ICE, a wonderful venue for exchanging and developing ideas. I would also like to thank NERC for funding (NE/J500161/1) and for giving me the opportunity to attend statistical training courses for free that were invaluable. I’d like to thank several people for their advice and suggestions towards my data analysis. John Redhead, from the Centre of Ecology and Hydrology, kindly helped with habitat suitability modelling using Maxent and ARCGIS; Innes Sim, Martin Grüebler and his team at the Swiss Ornithological Institute, and Rob Robinson all gave advice on survival and population models; David Lucy and Andrew Titman from the postgraduate statistics centre for statistical advice, and Terry Shaffer from the Northern Prairie Wildlife Research Center, helped advise how to ii implement logistic exposure models; while Vitor Tomezella was very helpful with insect identification. I owe a huge debt of gratitude to Lydia Aktinson and Mark Mainwaring. Lydia helped me with fieldwork in my final year. She put in an enormous amount of work without ever complaining, and her bubbly, cheerful disposition made my last season by far the happiest and most fun, though the advent of ‘Tache Tuesdsays’ may have convinced most of the soldiers that we were both insane. Mark Mainwaring has been a true friend throughout my PhD, always available as a sounding board for work, and ready with helpful comments and advice. Additionally Mark came to help for a week every field season at the busiest time, providing a much needed pair of hands and good company - despite the quality of his jokes. I would also like to thank the other students at Lancaster University, especially Emily, Ali, Rachel, Marina, Phil, Yamini, Anni, George, Beth, Jo, Joe, Catherine, Bobby, Clare, Al, Tom and the 4 Chris’s, for making my time at Lancaster so enjoyable and Ellie Owen for inspiring me to do a PhD in the first place. Finally I want to thank my parents, who have always supported me in all my endeavours, particularly my dad for making the 5 hour journey between Salisbury and Manchester 10 times during the cause of my PhD without complaint and my partner Ed, without whom I doubt I would have managed to get this far. He provided continued support and a much needed voice of reason throughout my 3.5 years, helped me through all the ups and downs and kept me sane and happy. ©Alice Tams iii Abstract Populations of many species of Afro-Palearctic migrant birds, including the Whinchat (Saxicola rubetra), have shown severe declines over the last few decades. Habitat change on the breeding grounds, especially agricultural intensification, is thought to be the main driver of the decline in Whinchats. However, recent evidence also suggests that the decline may have a common source, such as low over-winter survival, which affects the whole UK population. To better understand the declines, this study investigated the key demographic parameters driving the breeding Whinchat population change on Salisbury Plain, UK, which is an area of agriculturally unimproved grassland where Whinchats are still relatively common. Territory settlement and nesting attempts of colour-ringed individual Whinchats were monitored intensively during 2012-2014. Pairs were significantly more likely to breed in sheltered valleys with long, grassy, structurally diverse vegetation and a high density of tussocks. Territories with an abundance of perches, for use in foraging, were also preferred. The first occupied territories, by returning birds in spring, tended to have higher invertebrate availability, and the order of territory occupancy was positively correlated between years, which suggests that territory quality was consistently perceived. Nestling starvation was rare because food availability did not limit reproductive output. Neither did the availability of suitable breeding habitat apparently limit the population, but nest productivity was lower than expected, mainly because of a high rate of nest failure due to nocturnal predators. Adult apparent survival was high relative to other open-nesting passerine migrants; however, the survival and recruitment of Whinchats in their first breeding year was low. This low apparent survival could partly be explained by natal dispersal, which was greater than breeding dispersal. From the reproductive output, survival and recruitment quantified in this study, it is apparent that the Salisbury Plain population is not currently self-sustaining. iv Contents Declaration ..................................................................................................................................... i Acknowledgements ....................................................................................................................... ii Abstract ........................................................................................................................................ iv List of figures ................................................................................................................................ 7 List of tables ................................................................................................................................ 11 Chapter 1: General Introduction .................................................................................................. 16 1.1 Understanding population change ..................................................................................... 17 1.2 Population change in migrants .......................................................................................... 18 1.3 Limiting factors operating in the breeding season ............................................................ 19 1.3.1 Loss of suitable breeding habitat ................................................................................ 19 1.3.2 Limited food supply ................................................................................................... 21 1.3.3 Predation and disturbance .......................................................................................... 22 1.4 Limiting factors during the non-breeding season .............................................................. 23 1.4.1 Limiting factors during migration .............................................................................. 24 1.4.2 Limiting factors on the wintering grounds ................................................................. 24 1.5 Carry-over effects ............................................................................................................. 25 1.6 Difficulties in determining population limitations ............................................................ 26 1.7 Conclusions ....................................................................................................................... 26 1.8 The Whinchat ................................................................................................................ 27 1.8.1 Current threats ............................................................................................................ 27 1.8.2 Conservation action .................................................................................................... 29 1.8.3 Why Whinchats? ........................................................................................................ 29 1.8 Thesis outline ...................................................................................................................