Dietary differentiation and trophic relationships in the sub-Antarctic penguin community at Marion Island

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Abstract
We compared the diets of 4 co-occurring species of penguin at Sub-Antarctic Marion Island in light of mechanisms thought to result in dietary differentiation. Calculation of overlap indices and correspondence analyses indicated a clear separation in the diets of the 3 penguin genera but considerable similarity between the congeneric species pair. The pelagic foraging king penguin Aptenodytes patagonicus consumed mainly myctophid fish, whereas the near- to offshore foraging macaroni penguin Eudyptes chrysolophus and rockhopper penguin E. chrysocome both consumed predominantly small pelagic crustaceans, although in different proportions. The inshore foraging gentoo penguin Pygoscelis papua fed largely on benthic nototheniid fish. Although king penguins rarely take small prey, differences in diet cannot be accounted for solely on the basis of prey size selection. Different diving capabilities may hae some role in dietary differentiation, however, we consider prey availability in the apparently distinct feeding zones to explain most of the differences in the diets of the 4 species of penguins at Marion Island. The daily population food requirements of the respective penguin species at the Prince Edward Islands (comprising Marion and Prince Edward islands) increased with increasing species foraging range. The mainly benthic nature of the prey in the inshore area, compared with the more easily replenished pelagic food stocks, probably explains the differences in food availability that sustain the greater food demans of the large populations of pelagic and offshore foragers.