The effects of duet coordination on territory defence in an Australian arid zone passerine

Duetting, a cooperative vocal behaviour performed by mated pairs, is a distinctive behaviour among many species in specifically primates and birds. Duetting behaviour is most seen in tropical birds and is often studied in a territorial context. However, we still know little about what elements of duets make them a stronger territorial signal. One hypothesis is that the level of duet coordination can indicate the degree of threat posed to a rival pair. Only a few studies have investigated this, and mixed results have been found. To further address the implications of duetting precision in a territorial context, we determined to what extend the duetting behaviour in the chirruping wedgebill (Psophodes cristatus), a bird that is found in the arid regions of the Australian outback, predicts - and is affected by - the level of duet coordination. We tested this with playback experiments where we broadcast coordinated and uncoordinated duets at mated pairs, predicting that pairs would exhibit stronger responses to coordinated duets than to uncoordinated ones and sing more coordinately after the simulated intrusion than before. Our results provide further insights into the role of fine vocal coordination and contributes to the broader understanding of cooperative vocal behaviours in the context of territory defence.