Plain wrens Cantorchilus modestus zeledoni adjust their singing tempo based on self and partner's cues to perform precisely coordinated duets

Precise coordination appears to be an important signal in several duetting species. However, little attention has been directed to the proximate mechanisms that might drive this behavior. To perform highly coordinated duets, individuals can either have an intrinsic fixed singing tempo or modify their singing tempo based on cues in their own and their partner's songs. In this study I determined whether autogenous and/or heterogenous factors are associated with duet coordination in plain wrens Cantorchilus modestus zeledoni by analyzing recorded duets from 8 territorial pairs in the field. Previous research has determined that plain wrens perform highly coordinated antiphonal duets with almost no overlap. I found that to achieve such precise coordination individuals perform phrase-by-phrase modifications to the duration between two consecutive phrases (inter-phrase interval) based on a) whether their song is answered, b) the phrase type used in the duet and c) the position of the inter-phrase interval within the duet. Moreover, there are several sex differences in how individuals use these cues to modify their inter-phrase intervals. Females produce longer inter-phrase intervals when their mates do not answer a phrase, whereas males produce shorter inter-phrase intervals when their mates do not answer. Females modify their inter-phrase intervals based only on the phrase type their mates sing, whereas males modify their inter-phrase intervals based on both the phrase that they sing and the phrase the females use to answer. Both males and females produce longer inter-phrase intervals for longer phrase types sung by their partners, but males do so with more precision than do females. Finally both sexes increase their inter-phrase intervals as the duet progresses. That precise coordination is achieved by a complex and dynamic process supports the idea that this behavior could signal pair bond strength.