Neighbour–stranger discrimination by Yellow-bellied Tit Parus venustulus : evidence for the “dear-enemy” effect

Neighbour–stranger discrimination has been demonstrated in many taxa, but the mechanism employed in discrimination varies across species. We tested whether an oscine bird with a small repertoire size, the Yellow-bellied Tit Parus venustulus , discriminated between songs of neighbours and strangers. We carried out playback experiments on 18 males to detect the response of each male to the song of a neighbour as well as its response to the song of a stranger. In both cases the songs were broadcast from the territory boundary shared by the subject male and the neighbour. Subjects responded more aggressively to songs of strangers than neighbours. They approached the loudspeaker faster and closer, and performed more flights during playbacks of stranger songs than neighbour songs. There were no significant differences in vocal response between treatments. We conclude that the Yellow-bellied Tit can discriminate between songs of neighbours and strangers. As there is no song-type match across subjects, neighbours and strangers, and no differences of shared song type numbers between familiar pairs and stranger pairs, we think that song characteristics may play a role in neighbour–stranger discrimination.