In most seabirds, breeding success can be related to the ability to obtain a suitable nest-site within the colony, and this may result in competition for the limited number of available sites. Thus, if nest-site vary in quality, individuals of the same sex are expected to compete for access to the highest quality nest-sites to enhance their own fitness. It is therefore expected that intrasexual competition would result in a correlation between size in the competing sex, or the size of a trait used as a weapon, and nest quality. Chinstrap Penguins (Pygoscelis antarctica) fight with other conspecifics using the bill as a weapon. If bill size provides an advantage for intra-specific combat, we would expect stronger bills in males occupying the best nest sites. We studied patterns of some adult morphological traits in relation with nest position in a colony of Chinstrap Penguins. Bill morphology was related to nest position in the colony, with individuals occupying the central positions having the deeper bills. This relationship was found in both sexes. Our data suggest that competition for position within the colony is not an important factor involved in the sexual dimorphism shown by the Chinstrap Penguin. Received 31 August 2000, accepted 1 October 2000.

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