Aggressive responses of male and female rufous-and-white wrens to stereo duet playback

Abstract

Hypotheses for the function of animal vocal duets fall into three broad categories. Male and female breeding partners may use duets to communicate with each other, to communicate with same-sex outsiders, or to communicate with opposite-sex outsiders. To evaluate these categories of duet function, I gave stereo duet playback to territorial pairs of duetting rufous-and-white wrens, Thryothorus rufalbus , in northwestern Costa Rica. I simulated duets of a rival pair of wrens by simultaneously broadcasting male and female duet components through separate loudspeakers. Territorial males and females responded aggressively to duet playback by rapidly approaching the speakers and singing both solo songs and duets. Males sang more songs in response to playback than females, but both sexes responded to approximately half of their partner's songs to create duets. The aggressive responses of territorial pairs were consistent with a territorial defence hypothesis for duet function. Males spent more time near the male speaker and approached the male speaker more closely, suggesting that male duet contributions play a role in intrasexually aggressive extrapair communication. Females approached the male and female speakers with similar intensity, although they tended to respond more strongly to the male speaker. In the few cases where females responded independently of their partner, they responded more strongly on the side of the female speaker. Taken together, responses of rufous-and-white wrens to stereo duet playback suggest that duets play a role in territory defence against conspecific rivals, and, for males, duets may play an additional role in mate guarding and paternity guarding.