Diet of the Brown Skua (Stercorarius antarcticus lonnbergi) at Hope Bay, Antarctic Peninsula: differences between breeders and non-breeders

Top predators exhibit a critical role in ecosystem functioning and in the stability of the food web, so research on diet is relevant to understand their foraging behavior. Seasonal variation in diet and prey selection may be the result of fluctuations in the physiological demands during the different annual life cycles, and ecological factors such as resource availability, which may influence the foraging behavior. Moreover, the competition for the feeding territories between conspecifics in a population or with other predators may also lead to diversification of the diet. In this work, we determined the diet of breeding and non-breeding Brown Skuas (Stercorarius antarcticus lonnbergi) at Hope Bay, Antarctic Peninsula, to understand prey selection and the feeding habits of groups with different physiological and energy demands. To assess the breeders' diet, 204 pellets were collected near the nests, while for non-breeders, 330 pellets were obtained from different areas where they usually group, and prey items were determined. Pellet dimensions were larger in non-breeding skuas. Breeding skuas' pellets showed a higher content of energy-rich items such as penguin eggs, fishes and molluscs, while in non-breeding skuas, pellets consisted mainly of penguin feathers and bones. The differences in diet between the groups may be a consequence of the supplementation of the food obtained on land by traveling to the ocean by breeding skuas, in order to compensate the energetic demands during reproduction. Our results highlight differences in the feeding habits and prey selection, as well as a variation in the flexibility of the foraging strategy of both groups.