Sexual dichromatism and assortative mating by multiple plumage color traits in wild Chestnut Thrush

Abstract

Sex differences in plumage color are common in bird species. Some bird species are regarded as sexually monochromatic in human visual systems, and in recent years, some species are found to be of cryptic (to human) sexual dichromatism by spectrophotometric techniques. However, the functions of plumage color are still less understood in these species. Here, we focused on plumage color traits in the Chestnut Thrush (Turdus rubrocanus), which is considered as a sexually monochromatic bird by human observers. We used spectrometer analyses and avian visual modeling to investigate the color traits of males and females, and whether these color traits are involved in assortative mating. We found that Chestnut Thrush showed sexual dichromatism in bill, throat and wing, and pairs mated assortatively with colorations of throat, chest, crown and wing. We also found that color of tarsus was different between two consecutive years. These results revealed that Chestnut Thrush is sexually dichromatic in the avian visual system, and plumage color traits play important roles in mate choice.