What makes a ‘local song’ in a population of ortolan buntings without a common dialect?

Ortolan buntings, Emberiza hortulana, have local dialects in central and southern Europe. Neighbouring males typically share the same final phrase of a song, which seems to be important for dialect recognition. We studied ortolan buntings in Norway, where a small and isolated population occurs with no local dialect in the above-mentioned sense. Norwegian males often have song types with different final phrases in their repertoire, and have larger repertoires and less song type sharing than other populations. We experimentally tested (1) whether male ortolan buntings from Norway discriminate between local and foreign or hybrid songs, and (2) what part of the song is used to discriminate between local and foreign songs. We studied the response to typical local songs (L), conspecific foreign songs from a remote population (F), and computer-created hybrid songs with a local final phrase and foreign initial phrase (F–L) and vice versa (L–F). Only local songs evoked a strong response, measured as latency to flight and approach, number of flights and closest distance from the loudspeaker. For F, F–L and L–F song playbacks, the majority of males did not respond at all, or responded significantly less than to L songs. Our results suggest that at least in this population, the final phrase of the song is not a sufficient cue for local song dialect recognition. We discuss the adaptive value of discriminating between own and foreign songs based on specific cues versus full songs in relation to dispersal and song-learning pattern in the ortolan bunting.