Do social interactions predict similarities in audio-visual courtship signals in spotted bowerbirds?

Abstract

Spotted bowerbirds perform a multi-modal courtship display on dedicated structures -bowers -that are built by one resident male. Bower owners tolerate the presence of specific subordinate males at their bowers, yet the role of these male-male associations remains unclear. One explanation is that these immature males are learning the skills required for successful sexual signalling. Courtship in this species consists of a sequence of harsh calls, body postures and movements. If social learning occurs, male-male associations may result in similarities in acoustic and visual signals within owner-subordinate pairs. In this study, we tested whether the magnitude of social interactions can predict similarities in audio-visual display patterns in a single population of spotted bowerbirds. We video-recorded their courtship behaviour to examine whether bowerbirds (i) exhibit micro-geographical similarities in their audiovisual displays and (ii) are more similar in their courtship to conspecifics with whom they interact more frequently at bowers. For both acoustic and visual courtship components, we found evidence for micro-geographical variation that was not explained by genetic distance. However, social proximity covaried with similarities in acoustic -but not visual -displays. Our findings raise relevant questions about the mechanisms of social learning in audio-visual sexual signalling.