Isotopic (δ15N and δ13C) evidence for intersexual foraging differences and temporal variation in habitat use in waved albatrosses

Waved albatrosses (Phoebastria irrorata Salvin, 1883) forage close to their breeding grounds on Isla Espanola, Galapagos, during the short chick-brooding stage and make long trips to the Peruvian upwelling during incubation and chick rearing. Previous studies have suggested foraging segregation by sex: females spend more time searching than males do while foraging in the Galapagos Marine Reserve (GMR), and band recoveries suggest higher bycatch vulnerability of males in the Peruvian upwelling. We used stable isotope analysis (delta N-15 and delta C-13) of whole blood of adult mate and female albatrosses to test for intraspecific foraging segregation in this sexually dimorphic species. Analysis of serial blood samples revealed higher delta N-15 values in males, suggesting consumption of prey items of higher trophic level. We also detected seasonal variation in foraging ecology, with higher delta N-15 values at the beginning of the breeding season. Sex and regional differences in delta C-13 values were not significant, reflecting primarily pelagic foraging sites of both sexes, both in the GMR and the Peruvian upwelling. Our results provide evidence of trophic segregation, suggestive of competitive exclusion, and novel information on marine isoscape values in the Eastern Equatorial Pacific.