Song sharing correlates with social but not extrapair mating success in the white-crowned sparrow

Bird song is a prominent example of a trait under inter- and intrasexual selection. Performance-related aspects of bird song have been shown to vary among males and to influence territorial interactions as well as female mate choice. In oscine songbirds, song is different from many other sexually selected traits in that it is learned. As a result of learning, territorial neighbors share songs in some species. Thus, social interactions may be influenced not only by how well a male performs song but also by whom he shares song with. Here, we test the hypothesis that song sharing indicates local song learning and experience from which females may benefit. We examine the prediction that song sharing correlates with reproductive success. During our 4-year field study on white-crowned sparrows Zonotrichia leucophrys pugetensis, we found that yearling males that shared song with at least one territorial neighbor had higher social mating success than nonsharers. At the same time, song performance did not significantly correlate with social mating success but did correlate with paternity loss. Males with high performance were more likely to lose paternity than males with low performance. No song feature correlated with gaining paternity. We conclude that song sharing may be an indicator of male quality and stable social neighborhoods which may be a direct benefit to females. Furthermore, our results may provide a functional explanation for a developmental process where songbirds adjust their song to the local social neighborhood.