Figure 3.

Gradual emergence of memorized tutor syllable structures. Unstable and noisy syllables became more stable and acquired distinct forms with time after release from noise. a, Bengalese tutor song. b, Noisy song of a zebra finch pupil sung 2 d after release (A2), the mean similarity score (%) seldom becomes 0 because of resemblances by chance. c, Song of the same bird 7 d after release (A7). d, Thirty-eight days after release. Note how the mean similarity increases with time. e, Song of a zebra finch pupil that heard the same Bengalese tutor, but not exposed to noise. f, Song of a zebra finch for comparison.