Relationships between carotenoid-based female plumage and age, reproduction, and mate colour in the American Redstart (Setophaga ruticilla)

Most studies investigating the function and evolution of ornaments have focused on males. Variation in ornaments may also reflect individual quality and convey information in females. We examined correlations between female plumage colour and reproductive variables in the sexually dichromatic songbird, the American Redstart (Setophaga ruticilla (L., 1758)). Female American Redstarts display yellow, carotenoid-based plumage patches on their tails, wings, and flanks. Using reflectance spectrometry, we quantified brightness (feather structure) and “yellowness” (hue and chroma) of tail and flank feathers to examine whether female plumage colour varies with age, reproductive success, parental care, and the plumage colour of mates. Female plumage varied with age, with adult (after-second-year) females having brighter tail feathers than first-year females. We failed to find a relationship between female plumage colour and pairing or first-egg dates. However, adult females with brighter tails visited their nests less frequently and first-year females with brighter tails fledged fewer offspring. Adult females with brighter tails also mated with males who provided less care. In addition, adult females with yellower flanks paired with males with brighter flanks and with males who provided less parental care. We suggest that plumage colouration in female American Redstarts can act as a signal of individual age and quality.