Repertoire matching between neighbouring song sparrows

A male song sparrow, Melospiza melodia, has a song repertoire of about eight or nine distinct song types, and he typically shares several of these song types with each of his several neighbours. In the prevailing theoretical view, the song types in a bird's repertoire are interchangeable and multiple song types exist primarily to provide diversity. The present study was designed to test a contrary hypothesis concerning one particular context, counter-singing between neighbours. Specifically, the hypothesis was tested that song sparrows reply to the songs of particular neighbours with particular songs from their repertoire: they select a song type they share with that neighbour ('repertoire matching'). In a field experiment, neighbour song was played to the subject from just inside the neighbour's territory. Subjects responded with a song shared with that neighbour in 87.5% of trials (chance expectation for this sample is 42%). In control trials, where stranger song was presented from the same location, subjects responded with songs shared with the neighbour at that location in only 17% of the trials. It is suggested that 'repertoire matching' may be one advantage of a song learning strategy that produces song sharing between neighbours. (C) 1996 The Association for the Study of Animal Behaviour