The intensity of color expression in animals plays a key role in social environments as a mechanism to signal individual capacities in competitive contests. Selective pressures for resource competition differ at different stages of life and between sexes; therefore, coloration is expected to vary between juveniles and adults and between males and females. Exploring the covariance between coloration and other traits may help to understand the functional significance of color and the action of natural selection on multivariate phenotypes. Melanin-based plumage coloration was investigated in the masked booby Sula dactylatra in relation to melanin concentration, sex, hormone levels, and shy-bold behavior of chicks close to fledging. Darker brown boobies showed higher levels of both eumelanin and pheomelanin concentration and lower body mass. Males behaved bolder than females and showed on average 8% larger brown patches. Bolder females had smaller brown patches. Bolder individuals also had lower levels of circulating testosterone, but no differences in corticosterone levels were found. Stronger phenotypic integration was observed in females than males. Our study suggests that juvenile melanic coloration may reflect behavioral strategies by sex, endocrine profiles, and body mass indicating the convergence of different adaptive functions in a given phenotype, this being more evident in females. Direction of correlations differed from those predicted under the pleiotropic idea for color-related traits. These results suggest the possibility that juvenile plumage acts as a signaling system in a social context within the age class and suggest that plumage coloration may indicate different behavioral strategies.

Sub-lethal impacts of environmental pollution are difficult to detect and usually require invasive methods. We review the evidence that changes in ornamental colour in fish and birds can be associated with a variety of pollutants. Although these ornaments evolved for mate choice, they could also provide a non-invasive indicator of pollution exposure.

Ornamental coloration in birds has been identified as a powerful, noninvasive tool for identifying exposure to metal pollution. Despite this potential, few studies have examined the effects of metals on iridescent coloration or assessed related impacts on bird fitness. Iridescent coloration is likely to be sensitive to metal pollution because it is already known to affect melanin production and this form of coloration is produced when light is refracted through layers of keratin and melanin inside feather barbules. In this study, we measured variation in plumage coloration, health (via oxidative stress), and reproductive success (via number of young fledged) of Tree Swallows (Tachycineta bicolor) nesting adjacent to water bodies containing different levels of metal pollution. Plumage hue shifted from bluer to greener and feather brightness was greater, where concentrations of copper and zinc were higher. Both patterns would be expected from changes in the microstructure of the feathers. Unexpectedly, increasing exposure to these metals correlated with increased apparent health (lower oxidative stress) in female swallows, but not males. Number of young fledged decreased slightly with exposure to metals but did not vary with the color of parents. Our results suggest the relationships between ornamental color, including iridescence, and fitness metrics are complex and much more work will be needed before color of iridescent feathers can provide a proactive, noninvasive, and effective diagnostic tool for detecting subtle effects of pollution on birds. La coloration iridescente des hirondelles bicolores est liée à la pollution de l'environnement par les métauxRÉSUMÉ. La coloration ornementale des oiseaux a été identifiée comme un outil puissant et non-invasif permettant de connaître leur exposition à la pollution par des métaux. Malgré ce potentiel, peu d'études ont examiné les effets des métaux sur la coloration iridescente ou évalué les impacts connexes sur la santé des oiseaux. La coloration iridescente est probablement sensible à la pollution par les métaux car on sait déjà qu'elle affecte la production de mélanine et que cette forme de coloration est produite par les reflets de la lumière dans les couches de kératine et de mélanine qui se trouvent dans les barbules des plumes. Dans cette étude, nous avons mesuré les variations de la coloration du plumage, la santé (via le stress lié à l'oxydation) et le succès de la reproduction (via le nombre de jeunes oiseaux) chez l'hirondelle bicolore (Tachycineta bicolor) nichant à proximité de plans d'eau affectés par différents niveaux de pollution par les métaux. La nuance du plumage variait du bleu au vert et l'éclat des plumes était plus important dans les endroits où les concentrations de cuivre et de zinc étaient les plus élevées. Ces deux tendances sont des conséquences normales de l'évolution de la microstructure des plumes. Étonnamment, l'exposition croissante à ces métaux était liée à une amélioration apparente de la santé (baisse du stress oxydant) chez les hiron...

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