The quality of winter territory can have important consequences for migratory songbirds throughout the year. In the American Redstart (Setophaga ruticilla), a warbler in which plumage maturation is delayed, yearling males winter in a variety of habitat types that vary in quality. Little is known regarding which physical traits allow some yearlings to occupy higher-quality sites. Here, we measured eight variables characterizing the plumage and morphology of yearling males in two habitats that differ in suitability to determine which aspects of phenotype predict winter habitat occupancy. Yearlings wintering in high-quality mangrove habitat in Jamaica had more extensive adult-like black plumage on their breast than those in low-quality scrub. No other phenotypic differences associated with winter habitat were detected. Additionally, yearling males arriving earlier on the breeding grounds in Ontario had more extensively black breasts than those arriving later. Previous studies using stable carbon isotopes have linked adult male American Redstarts' date of arrival in the breeding range with quality of their winter habitat. Our findings indicate an association between the extent of adult-like plumage and habitat occupancy, suggesting that variation in yearling males' appearance may be correlated with their ability to compete for high-quality habitat.
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Vol. 112 • No. 4