Subspecies discrimination on the basis of acoustic signals: a playback experiment in a Neotropical songbird

When animal mating signals diverge between populations, reproductive isolation and speciation may occur. Variation in animals' responses to these signals may reveal whether differences in perception contribute to behavioural differences between populations. We tested whether signal divergence influences receiver responses to playback in the rufous-capped warbler, Basileuterus rufifrons, a Neotropical resident songbird with a contact zone between two divergent subspecies, B. r. delattrii and B. r. rufifrons, in southern Mexico. Studying nearby populations of birds living in allopatry and sympatry, we presented warblers with playback-simulated territorial male rivals of each subspecies. In sympatry, both delattrii and rufifrons responded more strongly to songs of their own subspecies than to songs of the other subspecies, whereas in allopatry, delattrii responded strongly to songs of both subspecies, suggesting possible reproductive character displacement. Our research demonstrates that sympatric delattrii and rufifrons discriminate between each other's songs, suggesting that song is a premating isolating barrier between these divergent subspecies. This study adds to the growing literature on receiver response to vocal signal divergence in closely related sympatric and allopatric animal populations.