Comparison of the diets of breeding royal (Eudyptes schlegeli) and rockhopper (Eudyptes chrysocome) penguins on Macquarie Island over three years

A 3 year study of the diets of breeding royal Eudyptes schlegeli and rockho pper E. chrysocome penguins was carried out at two nearby colonies on Macqu arie Island. Diets of both species were dominated by euphausiids and myctop hid fish, in particular Euphausia vallentini and Krefftichthys anderssoni. Prey items were those found in the region of the Polar Frontal Zone, confir ming the importance of this zone to these penguins. Diets of both species b efore hatching of the chicks were variable between years, and differences i n quantity of food brought ashore and degree of digestion of prey suggested inter-annual variation in distribution of prey resources. No dietary diffe rences were detected in either penguin species across the breeding season, which reflected variability in diet at all stages, indicating that individu al penguins foraged in separate areas. Significant differences between the two species were found, royal penguins consuming more myctophid fish and ro ckhopper penguins consuming more euphausiids. Differences were also found i n the size class of prey items taken and the degree of digestion of food by both penguin species, indicating that prey were taken from different secto rs of the ocean. It is concluded that the overlap in diet is small in indiv iduals from these two spatially close colonies and, contrary to previous st udies, indicates a separation in the resources used by both species. The co ntrast with previous studies is most likely a reflection of the different m ethods used to assess overlap and, to a lesser extent, the years and coloni es in which the comparisons were made.