Ecology and evolution of extravagant feather ornaments

The ancestral conditions that permit the evolution of extravagant secondary sexual characters are of considerable theoretical and empirical interest because they allow identification of necessary ecological conditions, but also allow empirical tests of models of female mate preferences. We investigated the ancestral and derived state of a range of ecological and evolutionary variables that might have been implicated in the evolution of secondary sexual characters. Extravagant feather ornaments have evolved independently at least 70 times in birds, and the context of these evolutionary events was investigated statistically. The acquisition of feather ornaments was significantly associated with a change in social mating system from monogamy to polygyny or lekking. This association is consistent with the Fisherian mechanism of sexual selection. However, very often also the acquisition of feather ornaments occurred without change in mating system. Therefore, ornamentation can develop for reasons other than polygyny. We did not find any indication of male parental care, kind of food, foraging mode, coloniality, nest site, migration or body mass being significantly associated with a change in the state of ornamentation.