Sharing songs within a local dialect does not hinder neighbour-stranger discrimination in ortolan bunting (Emberiza hortulana) males

Neighbour-stranger (hereafter N-S) discrimination in birds is common and has most likely evolved to settle repeated disputes more efficiently and without physical fights. We tested whether an oscine bird, the ortolan bunting (Emberiza hortulana), with a small repertoire size from a population with a local dialect and a high level of song sharing is able to discriminate between the songs of neighbours and strangers. We performed playback experiments with eighteen males to measure the response to a repeated single rendition of a single song type derived randomly from a repertoire of a neighbour or stranger. Subjects responded more aggressively to the songs of strangers than neighbours (faster approach, more calls and songs uttered), suggesting that ortolan buntings can discriminate between the songs of neighbours and strangers. Our results also suggest that cues for N-S discrimination may be based on individual within-song type variation regardless of song-type repertoire composition. We contrast our results with an earlier study where ortolan buntings from a non-dialect population were tested. Finally, we predict a positive relationship between the level of song sharing and within-song type variation, which may be maintained by selection for N-S discrimination in songbirds with small and moderate repertoire sizes.