A Winter's Tail: Stable isotope analysis of feather amino acids identify contrasting seasonal trophic niches in Antarctic penguins with differing migration strategies

Abstract

**Abstract:** Penguins are common model organisms in basic and applied research on climate change, marine pollution, and fisheries management in Antarctica. For example, Adélie (Pygoscelis adeliae) and Chinstrap (P. antarctica) penguins are focal species in krill fisheries management efforts in the Southern Ocean because their diets contain high proportions of Antarctic krill (Euphausia superba) and their performance is assumed to be an indicator of ecosystem status. However, most studies of penguin foraging ecology have focused on the breeding season and little is known about these species' diets during the winter. Stable isotopes analysis can be used to infer seabird diets when they are away from their colonies, but often cannot distinguish the influence of a consumer's diet (i.e. what it eats) from geographic or temporal differences in baseline isotopic values (i.e. where and when it is eating). To address these challenges, we used compound-specific stable isotope analysis of amino acids in feathers to compare the breeding (i.e. chick rearing) and non-breeding (i.e. winter) trophic niches of Adélie and Chinstrap penguins from the South Shetland Islands, Antarctica while explicitly accounting for varying isotopic values at the base of the food web. We found that these species had similar trophic positions (~3.3) reflective of krill consumption during the chick rearing period similar to past studies using more traditional methods. However, trophic position was higher in Chinstrap penguins wintering in ice free areas (3.9), relative to Adélie penguins wintering in ice covered areas (3.1). Moreover, trophic position differed between Chinstrap penguins migrating eastward into the Scotia Sea (3.6) or westward to the Pacific sector of the Southern Ocean (4.0). These results suggest that estimates of Adélie and Chinstrap penguin diets and krill consumption from the breeding season may not be necessarily reflective of the trophic niches of these species year-round. **Authors:** Michael Polito¹, Katelyn Lamb¹, Jefferson Hinke² ¹Louisiana State University, ²National Oceanic and Atmospheric Administration