EFFECTS OF DYADIC VOCAL INTERACTIONS ON OTHER CONSPECIFIC RECEIVERS IN NIGHTINGALES

During vocal interactions birds can time their song output so that the ir songs overlap those of a conspecific. Such overlapping is usually i nterpreted as a directed signal of arousal or as a signal of readiness to escalate contests. Inevitably, these interactions can often be hea rd by other conspecifics. To investigate if these conspecifics would p erceive and use information derived from listening to others' interact ions we conducted playback experiments in the field on male territoria l nightingales, Luscinia megarhynchos. We tested whether asymmetric in teractions, 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, eac h 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 resp onded 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 so ngs of only one of the formerly interacting rivals were played. The re sults suggest that, even if song overlapping is a signal directed towa rds the singer whose song is overlapped, this information is perceived and used by additional receivers. Such information on rivals' behavio ur during an interaction might help an individual decide which strateg ies to adopt in possible future interactions with these conspecifics. (C) 1997 The Association for the Study of Animal Behaviour.