CONICET | Buscador de Institutos y Recursos Humanos

RATIONALE: The use of stable isotopes for ecological studies has increased exponentially in recent years. Isotopic trophicstudies are based on the assumption that animals are what they eat plus a discrimination factor. The discrimination factor isaffected by many variables and can be determined empirically. The Magellanic penguin is a highly abundant marine birdthat plays a key role in the southern oceans. This study provides the first estimation of the Magellanic penguin blooddiscrimination factor for 13C and 15N.METHODS: A two and a half month feeding experiment was performed, in which ten captive penguins were fed theirmain natural prey (anchovy Engraulis anchoita). The discrimination factors were estimated by comparing anchovy δ13Cand δ15N values (obtained with isotope ratio mass spectrometry using lipid-extracted and bulk anchovy muscle) withpenguin blood δ13C and δ15N values.RESULTS: Penguin blood was shown to be enriched, compared with anchovies, for 13C and 15N. No changes wereobserved in the stable isotope ratios of anchovies and discrimination factors during the experiment. The overalldiscrimination factors were 0.93 ± 0.12 (bulk) and 0.41 ± 0.12 (lipid-free) for 13C; and 2.81 ± 0.17 (bulk) and 2.31 ± 0.17(lipid-free) for 15N.CONCLUSIONS: Having an accurate discrimination factor for the studied species is key in any trophic or food webisotopic study. Comparisons of estimated diet-to-blood discrimination factors with published values of aquatic piscivorebirds showed that the 13C discrimination factor is particularly variable, and therefore ecologists should be cautious whenusing a surrogate value from other species. In this study, the Magellanic penguin discrimination factor of a tissue that doesnot require euthanasia was obtained, a fundamental input for trophic isotopic modeling of the species.