Sexual differences in the diet of little Penguins Eudyptula minor

Abstract

Sexual differences in the diet of Little Penguins Eudyptula minor at four geographically isolated colonies in Victoria, Australia were investigated over 12 breeding seasons, between 1985 and 2005. The weighted relative occurrence of each prey species consumed was calculated and compared at a seasonal, annual as well as locational scale, and differences in prey size were examined. Penguin body masses differed significantly between sexes and locations, with males consistently being the significantly heavier sex, whereas stomach content masses varied significantly between locations, with samples from males usually being heavier. Fish was the principal prey group in the diet of penguins at all sites, and was more dominant in the diet of males overall. Females tended to take slightly more cephalopods and crustaceans than did males. The contribution of fish to the diet varied between locations, with Rabbit Island and St Kilda penguins feeding almost exclusively on fish, while Phillip Island and Port Campbell birds consumed more cephalopods and crustaceans. Prey composition differed both annually and between breeding stages at Phillip Island, with males and females utilizing different food resources between certain years and breeding stages. Dietary resources were segregated by prey size, with males generally preying on significantly larger Anchovy Engraulis australis and Gould’s Squid Nototodarus gouldi at all sites than did females. Such local and sexual differences in diet composition and prey size suggest a considerable separation in feeding niche between the sexes. Partitioning of foraging depths and temporal prey availability may be implied as the proximate cause, and sexual dimorphism in bill and body size, as the ultimate cause behind the observed dietary variation. Copyright