Responses of southern house wrens to rhythmicity of alarm calling sequences

Identifying the signal features that receivers use to respond to the vocalisations of conspecifics is one of the main goals of animal communication studies. In this study, we analysed the temporal structure of alarm vocalisations given by southern house wrens (Troglodytes musculus) when they detect a risk near the nest and evaluated the response of conspecifics to sequences of calls that vary in the organisation of signals in time (rhythmicity). House wrens typically respond to perceived risks by repetitively calling a simple vocalisation. We performed an experiment using a plastic owl model placed at different distances from the nest, and we found that, as risk increased, house wrens called at a higher rate, with less regular and shorter inter-call intervals. We also performed a playback experiment using isochronous, rhythmic, and arrhythmic (random) sequences of a similar number of calls. Receivers did not respond to changes in the rhythmicity of the calling, although they tended to move closer to the speaker when we played back arrhythmic calls. We propose that house wrens may use mainly a simpler temporal calling feature, such as the interval between calls, to assess the perceived risk.