Conspicuousness of passerine females is associated with the nest-building behaviour of males

Abstract

Factors affecting the evolution of plumage conspicuousness in females are nowadays the focus of debate, and here we explore the possibility that the conspicuousness of female plumage and male participation in nest building are associated in birds. We hypothesize that males that participate in nest building will gain higher fecundity from high-quality ornamented females, whereas ornamented females will adjust fecundity to the costly nest-building behaviour of males. Large-sized species might experience higher costs of nest building and, thus, body size should affect the scenario described above. We used information on male contribution to nest construction (yes/no), male and female conspicuousness (conspicuous or cryptic plumage) and body size of Western Palaearctic passerines. In accordance with the hypothesis, we found that female conspicuousness, in interaction with body mass, was strongly associated with male participation in nest building. For large-sized species, female conspicuousness was positively associated with male participation in nest building. Discrete analyses of correlated evolution rendered evidence of female conspicuousness determining the evolution of male contributions to nest building, with the loss of female conspicuousness occurring more frequently before the loss of male participation in nest building. We discuss possible adaptive scenarios explaining the detected evidence because of mutual sexual selection in males and females