Diet and foraging areas of Southern Ocean seabirds and their prey inferred from stable isotopes: review and case study of Wilson's storm-petrel

Analysis of stable isotope ratios in animal tissues has emerged as a powerful tool for determining the trophic level and composition of prey and foraging location. We summarize here data on the stepwise trophic enrichment in d15N and latitudinal gradient in d13C in the Southern Ocean, and derive a regression equation to estimate latitudes from d13C values. We analysed isotope ratios of feathers of the small, pelagic seabird Wilson's storm-petrel <i>Oceanites oceanicus</i>, in different breeding stages, in comparison to isotope ratios of 4 other seabird species breeding in close vicinity on King George Island, South Shetland Islands. d15N analysis of feathers and albumen from Wilson's storm-petrels indicated a shift in diet from mainly crustaceans during egg formation to an increased proportion of fish during chick-feeding and moulting. d15N values of Wilson's storm-petrels during the chick-rearing season were closer to the mainly piscivorous-carnivorous skuas than to krill-feeding penguins, confirming that fish is an important part of their diet. d13C analysis of feathers identified 4 distinct foraging areas: d13C values in egg-white suggest that egg-forming females moved south to the sea ice edge. This coincides with the distribution of their main prey, Antarctic krill <i>Euphausia superba</i>, during this period