Figure 6. Left syringeal devocalization prevents sound production of syllables with a higher peak frequency.

A) A representative example of the intact song from a Bengalese finch. B) Thirty days after devocalization the bird sang many of the song syllables from the intact song, with the important exception of syllables with a higher peak frequency. Box 1 indicates a silent area during the syllable that may correspond to the failure to produce higher frequency sounds without the left sound source. Box 2 shows that the lower frequency sounds are retained, and have pulse-tone like characteristics.