Multiple functions for pair duets in a Neotropical wren Henicorhina leucophrys

In some bird species, males and females coordinate their songs into duets. Variation in the level of coordination in these displays may reflect cooperation or conflict. In grey-breasted wood-wrens, Henicorhina leucophrys, both sexes initiate duets with equal frequency, so duets are the product of both male and female behaviour, but the level of coordination in duets varies. This makes them an ideal system to test the motivation of both males and females for answering their partner to form duets. We played back male and female solos and duets to territorial pairs to test for evidence of cooperation or conflict in the use of duets in this species. If duets serve a cooperative function, pairs should coordinate their response to simulated intrusions and respond most strongly to duet playback. If duets reflect conflict, individuals should respond most strongly to same-sex solos. In response to duet playback, pairs approached the speaker together and sang duets at a high rate, suggesting that males and females work cooperatively to defend their territory from an intruding pair. However, females initiated more songs and answered more of their partner's songs in response to female playbacks, supporting the conflict hypothesis. Males also initiated more songs in response to male solo playback, but answer rate was consistently high across all treatments. These results support a growing body of evidence that suggests that duets are multifunctional and may result from both cooperation and conflict within a pair.