Sexual segregation in rockhopper penguins during incubation

Many animals show sex differences in foraging behaviour, which can be related to sex-specific size dimorphism, avoidance of intersexual competition for depletable resources or different energetic requirements of males and females. In southern rockhopper penguins, Eudyptes chrysocome, both sexes differ in their roles during breeding, which leads to differences in their energetic requirements. We therefore examined sex differences in the foraging behaviour of southern rockhopper penguins during the incubation period, using GPS and time–depth data, stable isotope analysis and an automated weighbridge system. While males carried out mostly long trips lasting several days, females often used coastal foraging areas on day trips. Stable isotope data suggested differences in prey composition between the sexes, with consistently higher trophic levels in males as expected for their larger size and ability to catch larger prey items. We applied ecological niche models to compare the environmental conditions in the utilized incubation season habitat between the sexes, using MaxEnt modelling. MaxEnt models suggested that the niche spaces of males and females are largely overlapping, but males have slightly larger niche width. The most important environmental parameter was sea surface temperature. The different energetic requirements related to the birdsʹ incubation and chick-provisioning pattern seem to be the driving force behind the observed spatial segregation. Males make use of highly productive areas to prepare for subsequent fasting periods whereas females forage in coastal waters for themselves as well as for the chicks during the subsequent guard stage.