Song syllable discrimination by song sparrows (Melospiza melodia)

A habituation test paradigm was used to examine the responses of free-living territorial adult male song sparrows (Melospiza melodia) to a range of synthetic songs. The three-phrased test songs differed from one another in having either conspecific or heterospecific (swamp sparrow, M. georgiana) syllables, or silence, in the second phrase. Subjects were exposed to repeated presentations of one song type until their approach distance to a loudspeaker increased. In one experiment, birds were habituated with a song consisting of three phrases of song sparrow syllables and then tested for generalization to either novel song sparrow syllables in the second phrase, swamp sparrow syllables, or silence. Birds discriminated between song sparrow syllables on two response measures, and between song sparrow and swamp sparrow syllables on one measure. In a second experiment, after habituation to a song with swamp sparrow syllables in the second phrase, birds did not generalize to novel song sparrow syllables, but they did generalize to novel swamp sparrow syllables. Thus song sparrows make finer distinctions among conspecific syllable variants than with alien syllables. The results further suggest that subtle species-specific differences in note structure within syllables are discriminated by song sparrows and potentially provide an adequate basis for individual recognition by song.