The behavioural mechanisms underlying temporal coordination in black-bellied wren duets

Duetting is a form of animal communication in which two individuals produce temporally coordinated vocal signals. Describing the individual-level patterns of behaviour that structure duets is an integral step towards understanding the adaptive function(s) of duet participation. We investigated the fine scale timing of duet contributions in male and female black-bellied wrens, Pheugopedius fasciatoventris, by analysing recorded duets and by stimulating birds to ‘duet’ with recorded songs in the field. Previous research on this species revealed that most duets consist of alternating male and female phrases, and that females abide by individually distinctive ‘duet codes’, which link each male phrase type with a specific answer from the female's repertoire. In the present analysis, we found that the timing of male duet phrases was primarily influenced by the time that the prior female phrase began, and secondarily influenced by an internal tempo. Female phrase timing, however, was most strongly influenced by the time that the prior male song ended, and secondarily influenced by the female's internal tempo. The average answering time for both sexes was less than 0.08 s before the end of the mate's prior phrase. Coordination at the beginning of the duet appears to limit duet length; duets with large gaps or overlapping phrases were always short. We conclude that both sexes make ‘on-the-spot’ adjustments in timing that function to minimize gaps and overlap between duet phrases. Overall, our results are consistent with the hypothesis that well-coordinated duets benefit both partners by communicating that their shared territory will be defended by a high-quality defensive coalition.