Condition and brightness of structural blue-green: motmot tail-racket brightness is related to speed of feather growth in males, but not in females

Coloration plays an important role in sexual and social communication, and in many avian species both males and females maintain elaborate colours. Recent research has provided strong support for the hypothesis that elaborate female traits can be maintained by sexual or social selection; however, most research on female ornamentation has focused on pigment-based colours, and less is known about how structural colours are maintained. Both sexes of the turquoise-browed motmot (Eumomota superciliosa) have a blue-green racket-tipped tail, and it remains unknown if tail coloration serves as a sexual or social signal in one or both sexes. Here, we describe sexual dichromatism in the blue-green portion of the tail racket, and we test for a relationship between coloration and condition, as indicated by growth bars. Tail colour of both sexes has a similar spectral shape, and there is significant, although moderate, sexual dichromatism: males are brighter than females, and males have marginally greater blue-green saturation than females. The length of feather grown per day is positively related to overall feather brightness, but this relationship is only present in males. The relationship between male coloration and condition suggests that tail colour has the potential to convey information about individual quality during mate choice or contest competition. The lack of a similar relationship in females suggests that female tail colour does not convey the same condition-dependent information that we suggest may be reflected by male colour. Female tail colour may therefore reflect other aspects of condition, be involved in other (non-condition-dependent) forms of communication, or be expressed as a non-functional byproduct of genetic correlation between the sexes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 673–681.