Color patterns, such as bars or dots that cover the body surface of animals are generally thought to play roles in signaling and camouflage. In birds, however, the macroscopic aspects of plumage coloration are less well understood, as past studies typically described plumage colorations by using spectrophotometric analyses. To provide insight into the evolution of plumage patterns as sexual signals, we characterized interspecific and intersexual variations in the plumage patterns of estrildid finches and tested their associations with other courtship signals and life-history traits using a comparative phylogenetic approach. Our results support the idea that plumage patterns in estrildids are favored by sexual selection because large-sized conspicuous plumage patterns are possessed by species with an elaborate courtship dance. These plumage patterns may also play roles in social signaling because patterns are more conspicuous in species with intraspecific brood parasitism. We predict that pattern traits can be favored by mate choice or intrasexual competition when they can serve as honest indicators of individual condition. As our results are consistent between the sexes, we suggest that the same selective force is acting on the evolution of plumage patterns in males and females in parallel. Finally, we also found a trade-off between large size and vivid color patterns, suggesting that too conspicuous patterns are costly, presumably because of the risk of catching the eyes of potential predators. Therefore, plumage patterns are also shaped by natural selection.

This study was supported by the JSPS Grant-in-Aid for Young Scientists (23680027 and 16H06177) and Hokkaido University WinGS Global Networking Award 2015 to Masayo Soma, and by the Ministry of Economy and Competitiveness (Spain) (CGL2015-70639-P) and the National Research, Development and Innovation Office (Hungary) (K-115970) to L.Z.G.