Seasonal male plumage as a multi-component sexual signal: insights and opportunities

Abstract

Seasonal breeding plumage of male fairy-wrens (Malurus spp.) shows significant inter-and intra-specific variation in several potential signalling components that we systematically review here. There is extensive colour variation in the genus, possibly related to variation in visual sensitivity. In many species, males can delay development of their first complete breeding plumage for one or more years, although males in more complete breeding plumage appear to be reproductively more successful. An additional sexual signal, and an evolutionary innovation, is the timing of the pre-breeding moult. A mechanism regulating this moult is testosterone, which can stimulate initiation of moult and development of male breeding colouration and is presumably required for maintenance of the breeding plumage. Males undertake pre-breeding moult earlier as they age, and early pre-breeding moult appears selected by female choice for extra-pair mates. Few studies have addressed variation in colour quality or the role of plumage in aggressive interactions. Condition-dependence of moult or breeding plumage has not been experimentally investigated. We argue that the genus is particularly suited to comparative analyses, as it provides informative contrasts in colour, plumage development, patterns of moult, colour vision and mating system, offering many exciting opportunities for testing evolutionary theories on function and maintenance of sexual signals.

Additional keywords:

• delayed plumage maturation
• endurance display
• extra-pair paternity
• moult
• multiple signals
• nuptial plumage
• pre-nuptial moult
• plumage colour
• sexual selection
• testosterone