ONTOGENY OF VOCAL-TRACT MOVEMENTS DURING SONG PRODUCTION IN SONG SPARROWS

When adult songbirds sing, movements of the beak and other elements of the vocal tract are closely coordinated with the activity of the syrinx. The physical configuration of the vocal tract affects the tonal quality of sounds originating at the syrinx, and coordination between vocal tract movements and syringeal activity is thought to be necessary for the production of pure-tonal song. The ontogeny of this coordination in laboratory-reared song sparrows, Melospiza melodia, was examined. Developmental changes were quantified in (1) the acoustic structure of song notes, as measured by spectrogram cross-correlation, (2) the magnitude of beak movements during song, (3) the correlation between beak movements and acoustic frequency, and (4) the tonal quality of song. Each variable changed significantly over the course of song development, but at different rates. Note acoustic structure achieved adult-like form midway through song development, but increased use and coordination of beak movements were not observed until later stages of development. The late development of coordinated beak movements appears to correspond with the development of tonal quality. This finding suggests that the coordination of vocal tract movements with syringeal activity is delayed in ontogeny. (C) 1995 The Association for the Study of Animal Behaviour