This study analyses the acoustic structure of the song and individual song repertoires of the Grey Thrush
Turdus cardis. A method to identify individuals by song is also investigated. Songs of 14 color banded males were recorded during April to August in 1994 and 1996, in seacoast woodlands in Kanazawa, Ishikawa Prefecture, central Japan. A full song lasted 2.85±0.38 s (mean±SD), and was divided to a ‘whistle part’ (1.8-3.4 kHz) and a ‘trill part’ (3.4-8.0 kHz). The trill part was often omitted. When a male encountered intruders or a female, long continuous trills were produced. The repertoire size of whistle syllables was 20.1±7.0 (mean±SD), with that of the primary whistle syllable being 11.1±4.9 (mean±SD). Among seven males in which 300 syllables were recorded, the repertoire size of trill syllables was 70.3±24.7 (mean±SD). The rates of common use of whistle syllables tended to be high between near territory owners, but that of trill syllables did not. The repertoire of the primary syllable of the whistle part was almost stable throughout the breeding season. Primary syllables of ‘higher rank of frequency’ differed between individuals. Only one male, of which whistle syllables were all original in the early season, changed his repertoire during the four-month study period, reducing his syllable types to those two which were most frequent in this population. The use of song to individually identify the Grey Thrush is a promising method for several reasons: 1) males have a large repertoire sizes of syllables, and repertoires differ between individuals, 2) an individual produces all variations of it's primary whistle syllable in only a few minutes, 3) there are numerous changing patterns in the frequency of whistles, and those patterns are recognizable audibly, and 4) preliminary testing of this method using field recordings to differentiate individuals was entirely successful.
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