Male calling between courtship sequences in whitethroats: a way to counter intrusions from neighbouring rivals.

In whitethroats (Sylvia communis) unmated and recently mated males often emit a specific call, the woid-call, after a sequence of courtship diving songs when the female is still present. In the experiments we tested the deterring function of the woid-calls.A simple playback experiment showed that unmated males react to woid-calls played at their territory border by initially increasing their distance to the speaker in an escape-like manner before they approached in the same way as to territorial song. In another experiment we simulated a courtship event at a neighbour by playing back sequences of courtship songs from the territory border until the territory owner started to approach the speaker. We then either continued with one sequence of courtship song or switched to woid-calls. The results showed that the woid-calls delayed approaches from the territory owner. Together, the two experiments suggest a deterring effect of woid-calls. The implications of this for their use in courtship contexts where courting males often suffer intrusions from neighbouring males are discussed. We believe that woid-calls are used both preventively and defensively to avoid intrusions when other males have obtained information about female presence and courtship.