Rufous horneros perceive and alter temporal coordination of duets during territorial interactions

Abstract

Temporal coordination of duets consists of nonrandom overlap, alternation or association between rhythms of acoustic elements. Since duet coordination presumably requires high attentiveness between signallers, the coalition quality hypothesis suggests it may indicate the ability or motivation of partners to engage cooperatively in aggressive interactions against intruders. To test this hypothesis, we monitored behavioural as well as vocal responses in a playback experiment conducted with a polyphonal duetting bird, the rufous hornero, Furnarius rufus. We used three categories of treatments in the experiment, which totalled six treatments: duet playbacks that varied in phrase overlap and coordination of temporal rhythms; nonoverlapped (consecutive) solos; and a control heterospecific song. We predicted that birds would respond more strongly to playbacks of coordinated duets than to uncoordinated duets, and also to playbacks of uncoordinated duets than to nonoverlapping male and female solo songs. Coordinated duets (degree of phrase overlap) provoked the weakest response across conspecific stimuli, whereas the responses to uncoordinated duets and nonoverlapped solos were similar. However, partners produced more highly coordinated duets (degree of phrase overlap) in response to coordinated duets (association of phrase rhythms), when compared to all other stimuli. These results suggest that territorial pairs not only perceive but also alter their degree of temporal coordination of duets during territorial interactions. In addition, partners seem to behave cautiously and with more coordinated duets when responding to paired intruders that produce coordinated duets. Our results partially support the coalition quality hypothesis, suggesting that duet coordination may indicate the ability of partners to cooperatively engage in aggressive interactions.