The Relationship Between Carotenoid-Based Coloration and Pairing, Within- and Extra-Pair Mating Success in the American Redstart

Abstract

This study examines the relationship of carotenoid-based plumage coloration to mating and reproductive success in a migratory songbird, the American Redstart (Setophaga ruticilla). Adult male redstarts have several highly variable orange carotenoid-based patches of plumage on their wings, flanks, and tail. We tested the prediction that males with larger and more intensely orange plumage patches have higher pairing success, as well as higher within-pair, extra-pair, and total reproductive success. We also quantified nestling-provisioning rates, to determine if carotenoid-based coloration was related to males' provisioning behavior. Males that paired successfully had significantly brighter orange flanks than unmated males. Paternity testing with microsatellites showed that 64% of broods (18 of 28) had extra-pair young and 44% of nestlings (36 of 81) were extra-pair. We found no relationship between carotenoid-based coloration and within- or extra-pair paternity. Contrary to our predictions, males with less saturated orange flanks sired more total young than more saturated males. Males with brighter orange flanks also provisioned nestlings at rates lower than did less bright males. These unexpected results highlight the need for further research on the mechanisms governing the production and maintenance of carotenoid-based signals in redstarts, as well as incorporating the ecology of migratory species into the study of carotenoid-based signals, which heretofore has been based primarily on nonmigratory species.