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Using census data on three species of pygoscelid penguins, we tested the hypothesis that competition for food during the chick-provisioning stage of reproduction limits the number of conspecific seabirds in a region. This prey-depletion hypothesis predicts that a negative correlation should exist between colony population size and the total number of breeding pairs from other colonies within parental foraging range. We also tested whether or not a negative correlation exists between colony size and the population size of, or distance to, the nearest neighboring colony. Suitable data were available for Adélie, Chinstrap, and Gentoo penguins (Pygoscelis adeliae, P. antarctica, P. papua) along the coasts of Victoria Land and the Antarctic Peninsula, where major portions of these species' world populations nest. Results indicated that colonies were highly clustered, with small colonies grouped around one or two …