A Comprehensive Metric Unveils Unstable Points in a Motor Program for Song Generation in Birdsong

The acquisition of an acoustic template is a fundamental component of vocal learning. In the absence of a model, birds fail to develop species typical songs. In zebra finches (Taeniopygia guttata), tutored birds produce songs with a stereotyped sequence of distinct acoustic elements, or notes, which form the song motif. Songs of untutored individuals feature atypical acoustic and temporal structure, including repetitions of sound elements. Here we studied songs and associated respiratory patterns of tutored and untutored male zebra finches to investigate whether similar acoustic notes influence the sequence of song elements. A subgroup of untutored animals developed songs with multiple acoustically similar notes that are produced with alike respiratory motor gestures. These birds also showed increased syntactic variability in their crystallized motif. Sequence variability was associated with the presence of song elements which showed high similarity in acoustic structure and underlying respiratory motor gestures. The results of this study indicate that the note is a fundamental acoustic unit in the organization of the motif and the neural code for song syntax.