Apparent mismatch between stable isotopes and foraging habitat suggests high secondary ingestion of Antarctic krill in brown skuas

GRAÑA GRILLI. M.; DI VIRGILIO AGUSTINA; ALARCÓN, P.A.E. ; CHEREL, Y

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2023

0171-8630

Changes in seasonal resource availability as well as changes in energetic requirements as offspring grows up, may force parents to change their trophic ecology throughout the breeding season. Brown skuas breed in a highly seasonal environment where the availability of its main food resource, and its location, changes during the season. We studied the feeding plasticity of breeding brown skuas by assessing their diet in different stages of their breeding cycle and their movement patterns. The analysis of stable isotopes indicated that penguin chicks and Antarctic krill constitute most of the diet of brown skuas, and that there is an increase in the ingestion of lower trophic level prey throughout the breeding period. Movement analysis indicated that penguin rookeries are more used for foraging than the marine environment through the whole breeding season. The contradiction between the results from both techniques may be explained by secondary ingestion of marine resources from the penguins’ gut. Krill obtained in that way may provide a content of protein necessary to replenish reserves before the next migration, and of globulins through the intake of carotenoids. These results highlight the fact that the trophic ecology of a species can be more complex than that suggested by one single technique, and the importance of using more than one technique to draw conclusions from the integration of the range of results. Also, the study opens the hypotheses of a behavioral selection of parts of a prey to obtain certain resources to fulfill nutritional requirements.