Quantification of song learning is complicated by variety in both learning and failure to learn.

(A) Typical sample of song from an adult Bengalese finch. Song is composed of a set of categorically distinct syllable types (labeled ‘A’, ‘B’, ‘C’…) that are organized into larger, repeated, sequences (gray bars). Both the spectral structure of syllables and their sequencing are learned features of song. Hence, song is a complex, high dimensional behavior that differs across individuals. (B) Song of an adult male ‘tutor’ and (C) songs of four juvenile ‘tutees’ that were all exposed to the same tutor song, illustrating variation in the quality of song learning. (Ci) Song from a tutee that learned the spectral content of the tutor song well, producing a song with accurate copies of all syllables. (Cii) Song from a tutee that copied all syllables, but with noisier versions than those present in the tutor song. (Ciii) song from a tutee that failed to copy some of the syllables from the tutor song. (Civ) song from a tutee that included ‘new syllables’ that were not clearly present in the tutor song.