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Abstract

Four series of song playbacks to paired and unpaired resident birds were used to test hypotheses proposed for the function of male song, female song and vocal duets in the bay wren, Thryothorus nigricapillus, in the Republic of Panama. One series of experiments served as a control and established that bay wrens distinguished the duets of conspecifics from those of heterospecifics; a second series indicated that these results were not dependent on which type of male vocalization was used as a stimulus. Two series of experiments compared the responses of paired and unpaired males and females to playbacks of male versus female song. Both paired and unpaired females responded strongly to playback of female song and weakly to playback of male song. These data are consistent with previous results that showed no effect of mating status on female song rates and support the hypothesis that female song functions in intra-sexual aggression, probably in the context of territorial defence. Furthermore, because females initiate all duets in this species, females may be singing independently of males, and thus it is only male behaviour that produces a duet. In contrast to what was observed in females, males responded strongly to playback of both male and female song, but paired males responded more strongly to playback of male song, and unpaired males responded more strongly to playback of female song. These results provide a preliminary indication that female songs are attractive to males and that males may participate in duets as a means of acoustically guarding their mates from other males.