Dietary change over winter migration in Spheniscus magellanicus yearlings inferred though stable isotopes analysis

SILVA, LAURA ALEJANDRA; CRESPO, ENRIQUE ALBERTO; SILES, L.; VALES, DAMIÁN GUSTAVO; GARCÍA, NÉSTOR ANÍBAL; SAPORITI, FABIANA; TAVARES, MAURICIO; OLIVEIRA, LARISSA ROSA DE; CARDONA, LUIS

Brest

Conferencia; 8th ISOECOL, International Conference on Applications of Stable Isotope Techniques to Ecological Studies; 2012

Stable isotope analysis is a powerful tool to infer and compare trophic relationships and diets between different habitat types during animal movements. Feathers have been the most widely used tissue to the track the migration of seabird species with a well known patter of sequential molt. This is not possible, however, with penguins, as they moult all their feathers simultaneously. In order to solve this problem we measured the stable isotope ratios of carbon and nitrogen along the claws of yearlings of Magellanic penguin (Spheniscus magellanicus) to infer the existence of ontogenic dietary changes and gain a further insight into the poorly know winter throphic ecology of young Magellanic penguins. A capture-tag-recapture experiment conducted in a nesting colony in Península Valdes revealed a mean growth rate of 0,11 ± 0,02 mm day -1. These results show that an entire penguin claw represents an average time span of 6 months and hence the claws of yearling penguins collected in Brazil during the winter months would inform about the diet offered by parents while in the nesting colonies (claw tip), the diet consumed during fall off Argentina (claw center) and the diet consumed during winter off southern Brazil (claw base). The results indicate that there is a significant change in the isotope signatures between the portions of the claw corresponding to the breeding season and the wintering period (MANOVA, p<0.001). However, these differences are not explained by an ontogenic change in diet as a result of a shift in prey selection when yearlings begin to forage independently as has been suggested by stomach contents analysis studies, but are the consequences of shifting baselines. The general pattern of diet of yearling penguins found in the three study areas was basically the same: the most important prey item was the anchovy, Engraulis anchoita, followed by a group of four cephalopods species.