Fig. 2.

An example of song ontogeny in chipping sparrows. (A) Recordings from a same individual show subsong (63 days old), early plastic song at 265 days old (as recognizable song and syntax have just started to emerge), late plastic song at 288 days old (when precursor song types are well developed), and stable adult song (325 days old). Each color dot in the sonogram identifies one song type in the cluster analysis. (B) In the syllable clusters from cluster analysis, six song features are measured (see Materials and Methods for details). During the early and late plastic song stage, each song type was denoted by a cluster of color dots, but the color dots shown in subsong are arbitrarily assigned. The sounds were obtained from a single day (i.e., 0500–2000 hours) of continuous song recording.