Plumage coloration predicts paternity and polygyny in the American redstart

Many animals display multiple signals that can be used by conspecifics to gather information about the condition or quality of potential mates or competitors. Different signals can indicate different aspects of individual quality or function in spatially or temporally separated periods. However, for long-distance migratory birds, it is unclear if signals, such as plumage traits, function in different phases of the annual cycle. We investigated the potential role of carotenoid-based tail and flank plumage, and bib size, in relation to extrapair paternity and polygyny in the American redstart, Setophaga ruticilla. This work complements our previous research suggesting tail feather brightness acts as a status signal, mediating territory acquisition during the nonbreeding season in Jamaica. Here, we show that tail feather brightness also serves as an important signal during the breeding season. Specifically, our results indicate that polygyny, a behaviour highly dependent on obtaining and defending multiple territories, is significantly predicted by tail brightness. Interestingly, flank redness best predicted whether individuals secured paternity at their nest and the proportion of within-pair offspring sired. We suggest that by expanding the study of plumage function in long-distance migrants to events occurring throughout the annual cycle, we gain a critical perspective on the function and evolution of ornamental traits.