Niche separation in burrowing seabirds of Bass Strait by Nicole Schumann B.Env.Sc.(Hons) Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy Deakin University October, 2012 Abstract Bass Strait, south-eastern Australia, is an important region for seabirds, with > 20.5 million individuals estimated to breed in the region. Competition for breeding habitat and prey may influence this assemblage of seabirds. However, patterns of abundance and distribution, and the mechanisms that drive these are not well-known. Similarly the trophic dynamics of the abundant seabirds of the region are poorly understood. Since seabird islands are difficult to access and resources often limited, optimal survey regimes for little penguins (Eudyptula minor) and short-tailed shearwaters (Ardenna tenuirostris) were determined using bootstrapping and simulation techniques. Survey effort could be reduced using line transect methods, though this varied between species, probably due to differences in burrow distribution, island- specific attributes and seasonal variations in abundance. It was found that effort could be considerably reduced under a pseudo-random sampling regime for both species on relatively simple islands with habitat areas ≤ 25 ha. Islands in northern Bass Strait were surveyed in winter 2008 – summer 2011 to investigate distribution patterns. These islands were found to support significant populations of little penguins, short-tailed shearwaters, fairy prions (Pachyptila turtur) and common diving-petrels (Pelecanoides urinatrix). Distribution patterns appeared to be influenced by species-specific breeding habitat quality, predators and the location of foraging areas. Breeding habitat features used by the four most abundant burrowing species in the region were assessed using regression modelling techniques. A range of physical and floristic attributes were used, potentially reflecting adaptations for particular physical features and biological pressures. Despite overlap in habitat use, the total iv suite of attributes diverged between species and different microhabitats within colonies were occupied. This would moderate competition for breeding sites. The trophic niches of the four seabird species were determined using stable isotope and stomach contents analyses. While little penguins consumed mainly fish, coastal krill (Nyctiphanes australis) was a key prey item of all three procellariiformes. Competition for this resource may be alleviated by differential consumption of coastal krill, and divergent foraging behaviour and breeding phenologies. Dependence on a few prey taxa suggests that these seabirds are vulnerable to declines in prey availability. Climate change is predicted to produce significant changes in the terrestrial and marine ecosystems of Bass Strait, potentially resulting in a decline in suitable breeding habitat and prey availability, particularly for the krill-eating species. The four seabirds consume an estimated 1 270 200 tonnes of prey throughout Bass Strait during their respective breeding seasons. Any decrease in breeding habitat and prey availability is likely to result in increased inter-specific competition which may have negative consequences for the reproductive success and population sizes of seabirds. v Preface All research for this work was conducted under permit from the Department of Sustainability and Environment (Permit numbers 10004530 and 10004531). The procedures undertaken for this research were approved by the Deakin University Animal Welfare Committee (AWC A9-2008). The core chapters of this thesis (Chapters 2 – 5) have been submitted for publication in peer-reviewed journals. Chapter 1 introduces the work while Chapter 6 provides a discussion of the main findings of the study. I am the primary investigator and contributor to all aspects of the work presented in this study. The exceptions were analyses of stable isotope ratios in blood of seabirds, and the collection of blood samples from seabirds on Lady Julia Percy Island in two seasons and Gabo Island in one season (Chapter 5). These were obtained by Dr Roger Kirkwood and Dr Michael Lynch on Lady Julia Percy Island and Lauren Angel on Gabo Island. I have acknowledged the laboratory that conducted stable isotope analyses in the text of the relevant chapter. In addition, Andrew J. Hoskins developed the R code for the simulations section in Chapter 2. Dr John P.Y. Arnould and Dr Peter Dann are co-authors of the submitted chapters since they provided field assistance, field gear, mentoring and editorial advice throughout the research. Chapter 2 is co-authored with Andrew J. Hoskins for his contribution to the simulations section in this chapter. vi Acknowledgements First and foremost, I would like to thank my supervisors, Dr John Arnould and Dr Peter Dann, for inspiring me and introducing me to the world of seabirds. John has been instrumental throughout my candidature, from the conception of the research to the final writing stages. Peter has also cheerfully provided valuable advice, support and encouragement throughout this research. I am immensely grateful to both of you and hope I have managed to meet both of your expectations. Parks Victoria provided boat support for this project. In particular, I am enormously indebted to Steve Voros and Jeff “Swampy” Thomas from the Foster Office who went well out of their way to move my crews and I between islands, even when conditions were far from ideal, and occasionally stocked up our food supplies. Jeremy “Jezza” Cicero, Scott Griggs, Matt Hoskins, Scott Douglas and Danny Hudson from the Tidal River office braved some challenging ocean conditions to move us between (or more aptly, rescue us from) the islands, making use of the most marginal windows of opportunity. It meant a great deal that you were all so willing to help us wherever possible. Thank you also to Geoff Boyd for providing boat transport to some of the islands. Funding for this research was provided by Parks Victoria, the ANZ Holsworth Research Endowment, the Winifred Violet Scott Charitable Trust fund and the Stuart Leslie Bird Research Award. I would like to thank the many volunteers whose assistance was vital to achieving my field work goals – you know who you are. In particular, thank you, Sherrie Caarels, for always keeping things entertaining in the most hilariously inappropriate ways possible; Emma Carlos, for your interesting pirate stories and for providing the fodder for our penguin sock song; Andrew Hoskins, for your endless vii terrifying stories on Cliffy Island and your method of keeping the fleas at bay (I’m not sure it worked but it was a most entertaining way of trying); Sarah Ludlow, for indulging my odd culinary cravings and sharing many “fried rat bait balls in chocolate sludge” with me; Linda Moon, for racing out into the cold winter dawn in your rat-nibbled boots, jacket and underpants to rescue my clothes from the ocean after the bush rats and wind joined forces to wreak havoc on the tent; Tanya Pyk, for remaining cheerful despite the wind doing its utmost to cause injury while being marooned for 13 extra days; and, finally, Spencer Unthank, for sharing and enthusing us with your knowledge of seabird anatomy and never complaining, even when you were being battered by weather and had to eat the occasional cold meal. In addition, Danny Hudson, Tamara Leitch, Amelia Featherstone, Bryce Masuda, Meaghan Conway and Tony Dornom accompanied me to several islands, and never once complained despite the hard work, long hours and somewhat exciting weather conditions. Likewise, Roger Kirkwood and Michael Lynch were instrumental in ensuring the success of the field work on Lady Julia Percy Island. Thank you so much for all of your efforts – I couldn’t have done this without you. I am grateful to Tiana Preston and Megan Underwood for teaching me the water offloading technique and for lending me their equipment. Leanne Renwick and Tiana Preston also taught me how to collect blood samples. Bruce Robertson acted as a good sounding board in the early stages of my candidature. I thank Victorian Wader Study Group, particularly Clive Minton and Dr Ross Jessop, who gave me valuable banding and mist-netting experience. Dr Tom Montague provided information on the identification of fish prey remains using mouth parts and scales. Thank you to my colleagues, Emma Carlos, Andrew Hoskins, Sarah Brown, Tanya Pyk and Megan Underwood, for providing many opportunities to brainstorm. viii Andrew, your help with R was invaluable. Thank you also to Dale Nimo and Luke Kelly for their advice on statistical modelling. Thank you to my close friends, particularly Helene Talia and Linda Moon, who not only subjected themselves to island life but provided me with much support and encouragement. Thank you, Helene, for cheerfully listening to my endless monologues about my research, and Linda, for always providing an ear and an endless supply of snacks and ‘support’ packages. Most importantly, Linda, thank you for taking care of my “children” for me while I was in the field – I will be forever grateful. Finally, I’d like to thank my family for their support throughout my candidature. Thank you, Mum, Dad, Mark and Fiona for tasty dinners, the occasional ear when things didn’t go as planned and for looking after my animals while I was on the islands. Mark, thank you also for your technical support when my computer temporarily died (and then died again before finally giving up entirely), and to Micky, Daisy, Furby, Tigerlily and the