A female songbird out-sings male conspecifics during simulated territorial intrusions.

While birdsong is a model system for animal communication studies, our knowledge is derived primarily from the study of only one sex and is therefore incomplete. The study of song in a role-reversed species would provide a unique opportunity to study selective pressures and mechanisms specific to females, and to test the robustness of current theories in an empirically novel manner. We investigated function of female song in stripe-headed sparrows (Aimophila r. ruficauda), a Neotropical, duetting passerine, and found that during simulated territorial intrusions by a female, male or duetting pair, females: (i) sang more than males to same-sex and duet playback, (ii) played a leading singing role in all contexts, and (iii) showed a longer term song response than males. These results suggest that females sing competitively against other females, and that intrasexual selection may be greater among females than among males. This is the first songbird study to show a stronger vocal role in territory defence for females than males. Stripe-headed sparrows are group-living cooperative breeders, and preliminary data suggest that polyandry and/or resource defence may explain strong female singing behaviour. Stripe-headed sparrows may be a useful study species for expanding our knowledge of vocal communication in female animals.