Plumage colour acquisition and behaviour are associated with androgens in a phenotypically plastic tropical bird

Androgens regulate male reproductive behaviour and may be a mechanistic link between sexual signals and physiological condition. However, the role of these hormones in regulating prenuptial moult and male plumage signals of passerine birds is unclear. In the red-backed fairy-wren, Malurus melanocephalus, plumage colour is a sexually selected trait and males express three reproductive phenotypes: males can breed in bright red and black plumage or in dull brown plumage, or assume dull plumage and act as nonbreeding auxiliaries; each phenotype differs in parental and reproductive behaviour. We found that plasma androgen concentrations differed significantly between male phenotypes, with red/black breeding males having the highest levels and auxiliaries having the lowest levels across all nesting stages. These hormonal differences were also present during the prebreeding moult when nuptial plumage is acquired. Males also differed significantly in body condition during moult based on the phenotype acquired in the subsequent breeding season, with red/black breeding males being in the best condition and auxiliaries being in the poorest condition. Moreover, androgen concentrations were positively correlated with body condition during prenuptial moult. Thus, in this species, androgens may determine plumage coloration and provide a link between the expression of sexual signals and body condition. The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.