Evolution of female song and duetting in the Chaffinch (Fringilla) species complex

Female song is ancestral to songbirds and shows considerable phylogenetic signal, but its presence also appears to be labile and correlated with life-history and ecology. While previous studies have examined the evolution of female song across species-rich families, here we studied female song in island populations of a recently diverged species-complex, the chaffinches (genus Fringilla). We show this behaviour has recently evolved in these populations, and probably on two independent occasions. In F. teydea, female song is performed in loose duets with males, while in F. coelebs, female song is produced solo. Populations with singing females showed year-round territoriality and were found in regions with low seasonality – both factors previously connected with high rates of female singing. To determine the relative saliency of female songs to conspecifics, and the degree to which they instigate territorial defence behaviours, we performed a series of speaker playback experiments. In F. c. canariensis, female song could induce comparable responses to male song, whilst duetting F. teydea playback produced similar responses to solo songs, and therefore may relate to within-pair communication instead. Our results suggest female song can be a highly labile trait that can evolve over short evolutionary timescales.