Effects of dyadic vocal interactions on other conspecific receivers in nightingales.

During vocal interactions birds can time their song output so that their songs overlap those of a conspecific. Such overlapping is usually interpreted as a directed signal of arousal or as a signal of readiness to escalate contests. Inevitably, these interactions can often be heard by other conspecifics. To investigate if these conspecifics would perceive and use information derived from listening to others' interactions we conducted playback experiments in the field on male territorial nightingales, Luscinia megarhynchos. We tested whether asymmetric interactions, in which one bird overlaps the song of another individual, influences the behaviour of additional, passive conspecific receivers. To test the influence of song overlapping on a third individual, each subject received one playback treatment in which two intruders were simulated by a dual speaker playback design. Songs broadcast from one loudspeaker overlapped those from the other loudspeaker. Subjects responded more intensely at the side of the overlapper than at the side of the loudspeaker from which the song that was overlapped was broadcast. These differences in response persisted in a second test in which songs of only one of the formerly interacting rivals were played. The results suggest that, even if song overlapping is a signal directed towards the singer whose song is overlapped, this information is perceived and used by additional receivers. Such information on rivals' behaviour during an interaction might help an individual decide which strategies to adopt in possible future interactions with these conspecifics.Copyright 1997 The Association for the Study of Animal Behaviour