Evol Ecol Res 1: 251-260 (1999)     Full PDF if your library subscribes.

A comparative study of breeding traits in colonial birds

Guy Beauchamp

Faculty of Veterinary Medicine, University of Montréal, CP 5000, St.-Hyacinthe, Québec J2S 7C6, Canada


e-mail: beauchgu@medvet.umontreal.ca

ABSTRACT

I examined the effect of an evolutionary transition to coloniality on several breeding traits in birds using 29 pairs of congeners that included one colonial and one solitary breeding species. Males in colonial and solitary species, as well as females, had similar body masses. The extent to which the sexes differed in body mass and plumage characteristics was also similar in colonial and solitary species. Although sexual selection is often assumed to be stronger in colonial species, coloniality appears to be a weak force in the sexual diversification of body mass and plumage characteristics in birds. Colonial species produced heavier eggs and invested more in their offspring per unit of female body mass than their solitary counterpart. The results support the hypothesis that coloniality is associated with greater foraging efficiency, which allows colonial birds to increase parental effort. Although offspring predation risk is often assumed to be smaller in colonial species, a fact that could lead to the production of larger clutches, colonial and solitary species produced clutches of similar size. The results thus provide little support for an effect of differential predation pressure on changes in clutch size in colonial species.

Keywords: birds, clutch size, colonial breeding, egg mass, pairwise comparative method.

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