Elsevier

Animal Behaviour

Volume 77, Issue 6, June 2009, Pages 1525-1532
Animal Behaviour

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

https://doi.org/10.1016/j.anbehav.2009.02.027Get rights and content

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.

Section snippets

Field Methods

We studied two populations of colour-banded red-backed fairy-wrens near Herberton, Queensland, Australia (145°23′E, 17°23′S) over the course of four breeding seasons (2003–2006); breeding occurs from early October through March. Our study sites were located in open sclerophyl forest with tall eucalypt overstory and grass understory. Red-backed fairy-wrens moult twice per year, with males acquiring breeding plumage during a prenuptial moult that occurs between August and December (i.e.

Timing of Breeding and Moult

Red-backed fairy-wrens in our population start a prenuptial moult in August, with most birds moulting heavily in September, October and November. Breeding can start in September, with most birds nesting in December and January (Fig. 1). The mean capture date for males considered to be moulting (moult ≥ 2) was 19 November, during the peak of moult for the population (see Fig. 1). Nonmoulting males were trapped significantly later in the season (ANOVA: F1,145 = 19.96, P < 0.0001, R2 = 0.121), with mean

Androgens and Breeding Phenotype

Species that show discrete, yet flexible adult breeding phenotypes offer uniquely powerful models for studying the evolution of adaptive plasticity in behaviour and morphology (Moore et al., 1998, Knapp, 2004). Our results for the red-back fairy-wren support the hypothesis that phenotypic differences between breeding male types are mediated seasonally by activational actions of androgens (see Moore 1991). The association between elevated androgens and red/black plumage production during the

Acknowledgments

We are grateful to our many volunteer field assistants, to Tim Daniel, Jane Harte, Brad Congdon and James Cook University for logistical support, and to Jordan Karubian, Melissah Rowe, Elizabeth Yohannes, and the members of the Webster and Schwabl labs for comments and advice. This study was supported by National Science Foundation grant 0213075 to M.S.W. and Washington State University.

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