Foraging ecology and reproductive energetics of Antarctic fulmarine petrels

It is commonly assumed that seabird reproduction is energy limited, and that nestling growth rate may be particularly sensitive to variations in food delivery rate and quality. To evaluate the putative link between diet, energy flow, and seabird reproductive performance, I studied the breeding biology, trophic structure, and nestling growth and energetics of four species of Antarctic fulmarine petrels: Antarctic fulmar (Fulmarus glacialoides), Antarctic petrel (Thalassoica antarctica), cape petrel ( Daption capense), and snow petrel (Pagodroma nivea). The breeding biology of these four species (Chapter one) is characterized by a breeding cycle, on average, 50% shorter than predicted allometrically. Timing of laying and duration of the breeding cycle did not vary interannually, suggesting that breeding patterns of these species may be shaped by a short season in which environmental conditions, including weather and relative food availability, are conducive to breeding. I used stable isotope (13 C/12C and 15N/14N) and conventional analyses to determine diet composition and trophic relationships among the four species (Chapter two). Although diet varied interspecifically, there was considerable overlap in trophic positions amongst the species, with diet dominated by two krill species (Euphausia superba and E. crystallorophias) and one fish species (Pleuragramma antarcticum ). Nestlings of all four species occupied higher trophic levels (i.e. higher proportions of fish in diet) than adults, suggesting selective provisioning of nestlings by adults. Chapter three focuses on the potential influence of dietary differences on nestling growth and energy allocation patterns. Absolute growth rates of all four species were at least 50% higher than predicted allometrically. Growth did not vary interannually, and growth patterns, after controlling for body size, were similar for all four species despite considerable interspecific size differences. Nestling energy expenditure, determined by doubly labeled water and oxygen consumption, was higher than predicted, although the proportions devoted to tissue growth and resting metabolism were consistent with general avian patterns. Based on diet and energetics information, I calculated instantaneous and cumulative energy and prey consumption by nestling populations of each species.