The signal function of overlapping singing in male robins

Songbirds can vary the timing of song production with respect to other singing individuals on a song-by-song timescale, for example birds may overlap songs or alternate singing and thereby avoid overlap. Playback was used to study the information contained in such timing of song exchanges in territorial male robins, Erithacus rubecula. The results are consistent with the idea that interacting with a singer either by overlapping or alternating is a way of indicating the intended receiver whereas non-interactive (loop) playback does not give this information. Furthermore, an overlapping pattern of singing generally elicited responses characteristic of highly aroused males. In robins this is shown by a rapid approach and change to an almost continuous, low amplitude pattern of singing referred to as twittering. Thus overlapping could be taken as indicating a high degree of arousal or a willingness to escalate. The response changed during the experimental period, with twittering responses becoming more common regardless of playback treatment. This result is consistent with experimental males having gathered information from interactions between playback and their neighbours in previous trials, that is, they collected information by eavesdropping. (C) 1997 The Association for the Study of Animal Behaviour.