The study of song development has focused on temperate zone birds in which typically only males sing. In the bay wren, Cantorchilus nigricapillus, both sexes sing, performing precisely timed, female-initiated duets in which birds alternate sex-specific song phrases. We investigated the origin of these sex differences by collecting bay wren eggs and nestlings and hand-raising them in individual acoustic isolation chambers. Each bird was tutored with either monophonic or stereophonic recordings of bay wren duets, or heard no song. As adults, each tutored bird individually sang complete duets, singing both male and female song phrases. On occasion, birds learned only the male or female part of a duet to which they were exposed. However, mono-tutored birds showed no sex-specificity in these solo songs, whereas stereo-tutored birds only sang solos consistent with their sex. In addition, stereo-tutored birds acquired songs over a longer period than did mono-tutored birds. In both groups, females showed more sex-specificity during the song learning process. Finally, we observed that tutored and acoustically isolated birds invented male-like songs, whereas only males invent songs in the wild. These results reveal the relative roles played by social versus innate influences in the development of sex-specific song in this species.

Data were collected from recordings of lab-raised male and female bay wrens individiually raised in acoustic isolation and tutored with duets from wild-caught birds. Duets were presented to one tretament group from a single monoaural speaker, and stereophincally to another group, with male and female contributions to the duet coming from separate speakers. Spectrograms of songs produced during and after song development were sorted into types and scored by independent observers to sdtermine repertoire size and,for sero-tutored birds, quality of song performance during song development.