Size and Plumage Dimorphism in Lek-Breeding Birds: A Comparative Analysis

It has often been taken for granted that, among lekking avian species more than among species with other mating systems, males are larger and more brightly colored than females as a result of strong sexual selection. This assumption, however, is not supported by a phylogenetic analysis. In families with at least one lekking species, where phylogenies could be reconstructed, both plumage dimorphism (males being more brightly colored) and size dimorphism were not correlated with lekking. It was also found that lekking did not precede dimorphism more often than the reverse in the phylogenies for which the temporal order of these two events could be determined. Larger males are found particularly in species with ground displays. It is suggested that size monomorphism may be explained by selection for small agile males in species with aerial and/or arboreal displays. Although lekking seems to have favored the evolution of plumage dimorphism in some groups, it is suggested that in other groups sexual selection may have acted on acoustic displays.