Ecophysiological Aspects of the Annual Cycle of Barnacle Geese, Branta Leucopsis
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ECOPHYSIOLOGICAL ASPECTS OF THE ANNUAL CYCLE OF BARNACLE GEESE, BRANTA LEUCOPSIS by Steven J. Portugal A thesis submitted to The University of Birmingham For the degree of DOCTOR OF PHILOSOPHY Centre for Ornithology, School of Biosciences, Faculty of Science, The University of Birmingham, April 2008 36 The essence of life is statistical improbability on a colossal scale - Richard Dawkins 37 Dedication This thesis is dedicated to my family, who, from a very young age, supported my enthusiasm for the natural world, and my desire to find out what makes things tick. I will never forget how much time my family have dedicated to my interests, and how encouraging they have been over the years. 38 Acknowledgements First and foremost I am indebted to Pat Butler and Jon Green, for what I consider to truly have been a fantastic and enjoyable four years of research. Thank you for taking such interest and enthusiasm in my work, and for all the advice and guidance you have given me over the duration of my PhD. It has been a pleasure. I am eternally grateful to Craig White, whose skills and knowledge of respirometry and statistics, and more importantly, his patience, have been invaluable throughout my studies, thank you. I feel I have gained a colleague and a friend for life. I am appreciative to Lewis Halsey also, for the many stimulating discussions we have had over the years, and for his willingness to help. I have been fortunate throughout my PhD. to collaborate with some of the world leaders in their field. During visits to various institutions I have been lucky enough to learn many techniques and skills, and I would like to thank the following people who have helped and been involved in various aspects of my work: John Speakman, Paula Redman, Susannah Thorpe, Julia Myatt, Julian Wiseman, Marcus Mitchell, Magella Guillemette, Richard Bevan, Rona McGill, Robert Ker, McNeil Alexander and Richard Bonser. In particular I would like to express thanks to Peter Frappell for his technical assistance during fieldwork in Svalbard. Thanks also to Tony Woakes for assistance with the loggers. Many people have gone far and beyond their duties to help me with practical work (particularly an extra pair of hands when handling the birds), and my life would have 39 been much more difficult without them, in particular I would like to thank Norman Day, Laine Wallace, Pete Jones and everyone in BMSU. For many small reasons I would also like to thank; Graham Martin, Jim Reynolds, Zoe Davies, Rachel Payne, Claire Tyler, Ruth Hayes, Kerstin Fink, Phill Cassey, Richard Tudor, Tim Boswell, Alan Gardner, Richard Inger, Johnny Kahlert, Emma Watkins, Jen Smith, Tim Blackburn, Campbell Murn and Jackie Chappell. All of these people created a stimulating atmosphere to work in and provided useful discussions, suggestions and ideas. None of this would have been possible without funding from the BBSRC. I was also fortunate enough to receive funding from NERC to undertake isotope work at the SUERC, and to undertake an expedition to Svalbard to study barnacle geese in the wild. I have also been fortunate enough to attend conferences, funded by the SEB, BBSRC and the School of Biosciences. I also feel I should mention all the geese I worked with over the years. On a personal note, I am eternally grateful to my family, Mum, Dad, Dave, Tracey and my Grandparents, for all their support over the years. For creating a stable, fun environment for me to enjoy and relax in, for running me all over the place to attend meetings, collect geese, for making me breakfast when I had done 62 overnighters in a row, and for generally being incredibly supportive. I would also like to thank Gillian Christensen, Davina Harman, Sarah Pilling and Lucy Van Baars, for being such great friends and mentors 40 I: GENERAL INTRODUCTION IA: The annual cycle and the management of time and energy The timing of annual cycles in birds has evolved to minimise the overlap of energetically demanding events, such as migration, breeding and moult. Such events often place additional nutritional and energetic demands upon the individual over and above the normal demands of general maintenance. Each species has evolved a strategy that is best suited to its own annual requirements and the environmental conditions in which it lives. The importance of the timing of these potentially energetically demanding events in a bird’s annual cycle is particularly acute when events such as migration, breeding and moult take place in a relatively short time span, as is the case for many species of bird that breed in the high Arctic. Birds dedicate considerable effort and time to preparing themselves for these energy draining activities (i.e. events that require high energy expenditure), and favourable conditions for deposition of stores are relatively rare, and preparation can only take place during peaks in food availability. Therefore, birds must time the events in their annual cycle to take advantage of foraging opportunities. In the present study, body mass, body composition, heart rate, body temperature and behaviour were measured year-round in captive and wild barnacle geese, in an attempt to answer questions about aspects of their ecology, behaviour and physiology, and in particular, how these change in response to demanding events, throughout the annual cycle. 1B: Introducing the study species: the barnacle goose - a model bird? 41 General biology There are four populations of barnacle geese, Branta leucopsis, which are distributed in Western Europe. These are the Greenlandic, Svalbard, Russian and Swedish breeding populations, all of which spend the winter in distinct, separate wintering grounds. The Greenlandic population winters in Ireland and western Scotland, the Svalbard population in northern Britain, and the Russian and Swedish populations winter in Germany and the Netherlands (Owen, 1981; Owen, 1990; Black et al., 1998). Recent censuses estimated there to be around 309,000 individuals for the four barnacle goose populations combined (Owen, 1990). The Svalbard population occupies discrete breeding and wintering areas, in winter occupying one of the smallest wintering ranges of any goose population in the world, the Solway Firth (Phillips et al., 2003). Numbers on the Solway declined to only 300 in 1948 (Black et al., 1998), however, the population responded well to conservation measures, and estimates now for the wintering population on the Solway Firth is in the region of 23,000 individuals. Barnacle geese tend to mate for life (i.e. once paired, they stay with the same partner until death) and such a strong bond must have a powerful selective advantage. Studies have shown that long-established pairs breed better than newly established pairs (Owen, 1990). If an individual loses its mate during the winter, its chances of breeding successfully in the following summer are only a third of those of mates that 42 stay together (Owen, 1990). This is because the division of labour between partners is essential to successful breeding, particularly with regards to defending the nest and goslings from predators. Barnacle geese breed in a potentially unpredictable environment and perfect co-operation between mates is required to hatch eggs and rear young successfully, as the goslings need protection from the parents to feed once hatched to prepare for the autumn migration. Because of their size, barnacle geese are unable to defend their nests against predators such as Arctic foxes (Alopex lagopus), so, therefore, they must try and find a suitable nest site that is inaccessible to such predators (Owen and Ogilvie, 1979). In some parts of Svalbard, the geese breed on cliff ledges, sometimes at heights of over 200 feet. The female takes sole responsibility for the nest, whilst the male offers protection. When the eggs hatch, the parents and their young leave the nest and head for the rearing areas on nearby tundra. At this stage, the female can be exhausted from fasting through incubation, so the male takes full responsibility for guarding the young, while the female feeds for anything up to 20 hours a day (Owen, 1984). The goslings become fully fledged at 7 weeks of age. Reproduction – capital breeders Nesting late in the short Arctic summer can have deleterious effects on reproduction, as there is a strong pattern of seasonal decline in reproductive success (Lepage et al., 2000). Birds arriving too early in spring, however, may have restricted feeding opportunities owing to snow cover. Therefore, pre-migratory body stores can allow 43 egg-laying to begin before local foods become available, thereby avoiding any delays in breeding and maximising opportunities for reproductive success (Raveling, 1979; Sandberg and Moore, 1996; Klaassen et al., 2006). A true capital breeder relies on body stores brought from the wintering sites or migration areas, to the breeding grounds to produce eggs (Drent and Daan, 1980). Whether geese are exclusive capital breeders (as opposed to income breeders) has been a subject of debate (e.g. Ankney et al., 1991; Klaassen et al., 2006), as many species of geese will feed on the breeding grounds prior to egg laying, suggesting not all species are strictly capital breeders (e.g. lesser snow geese, Chen caerulescens caerulescens, Wypkema and Ankney, 1979). In general, the further north breeding sites are located, the later birds arrive at the sites (Owen and Gullestad, 1984). At these more northerly locations, the summer season is relatively short, and the birds are under severe time constraints. Therefore, to breed successfully, the birds must commence egg-laying soon after arrival. When egg-laying commences within 10 days after arrival on the breeding grounds, the production of eggs must occur mostly from residual body stores. This is because follicle maturation takes about 10-12 days in geese, with an additional 1-2 days for albumen synthesis (Alisauskas and Ankey, 1992).