Dietary Segregation of Macaroni and Rockhopper Penguins at Heard Island

Abstract

This paper reports on the first quantitative study of the diet of macaroni and rockhopper penguins (Eudytes chrysolophus and E. chrysocome) undertaken on sub-Antarctic Heard Island. Stomach contents were sampled during the late incubation and early chick-rearing phase. Both penguin species generally fed on euphausiids and fish, albeit in different proportions and frequently on different species and sizes. In particular, macaroni penguins consumed considerably more fish on a per cent mass basis (23.2 v. 8.0%), selecting larger sized prey than rockhopper penguins did. It is hypothesised that these dietary differences provide macaroni penguins with a broader feeding niche leading to a greater availability of food and are thus an important factor contributing to the numerical dominance of macaroni penguins on the island.