Repertoire Sizes of the Whistle and Trill Parts of the Song of the Grey Thrush Turdus cardis in Relation to the Mating Success of the Males

Abstract

The relationship between the song repertoire and breeding success of birds has been studied for several species. In some species, the different components of the songs have different functions and are suggested to have evolved under different intra- and intersexual selection pressures. The song of the Grey Thrush Turdus cardis consists of the whistle and trill parts. In this study, it was clarified that the repertoire sizes of the syllables in both parts did not correlate with each other, suggesting the possibility that both parts have evolved under different sexual selection pressures. The repertoire sizes also did not correlate with the age of the birds. The relationship between the repertoire size and the mating status of males was also examined. The whistle repertoire size was not related to the mating status, while the trill repertoire size in polygynous males was larger than that in monogamous males. This result suggests that the functions of the two parts of the song are not similar, a finding consistent with the results of previous studies indicating that the complexity of trills has evolved under intersexual selection pressure.