Figure 1.

Bengalese finch song and variable sequencing. a, Spectrogram showing part of a song produced by BF01. Syllables are labeled with unique letters. Note that some syllables are found embedded in multiple sequences. b, Syllable transition diagram for the song of BF01. The directions of the arrows represent possible transitions from one syllable to another, with all possible syllable transitions shown, including those not displayed in the segment of song shown in a. Syllables X and Y are not produced in the fragment of song displayed in a. We refer to a syllable that can be followed by more than one syllable as a divergent syllable (e.g., syllable C, highlighted in red, is a divergent syllable that can be followed by syllable D or H). c, Spectrogram of part of a song produced by BF02. d, Transition diagram for the song of BF02 with plotting conventions as in b. We refer to a syllable that can be preceded by more than one syllable as a convergent syllable (e.g., syllable L, highlighted in blue, is a convergent syllable that can be preceded by syllable K or P). In both b and d, some introductory notes (see Materials and Methods) have been excluded from the transition diagrams for visual clarity.