Extended Data Fig. 8: Behavioural variability and stratification in an example syllable.

a, Songs of an example bird for three days during development. Only those spectrogram segments that belong to a particular syllable and location in the motif (68-ms window of interest; red dotted lines) are analysed in the subsequent panels. b, Developmental changes over the course of weeks. Renditions are binned by production day, and averaged. The most apparent changes are an increase in pitch and the later successive appearance of additional spectral lines at low frequencies. c, Within-day and across-day changes for days 60–69. Renditions are binned into five production-time periods spanning a day and averaged within bins. On many days, the changes within a day do not appear to recapitulate the changes occurring across days (for example, days 60 and 65; within-day progression does not smoothly transition between the vocalizations on preceding and subsequent days; see b). The averages also reveal occasional overnight ‘jumps’ in the properties of the vocalizations (see, for example, the vertical black arrows). d, Comparison of within-day change and change on longer timescales. Renditions within each period and day were split into strata according to their repertoire times (for example, the quintiles in Fig. 2d), resulting in 25 averages, one for each combination of stratum and period within the day. Only the upper part of the spectrogram is shown (red rectangle in c). The progression along strata (x axis) emphasizes the large extent of motor variability along the DiSC existing within a single day (day 62). e, Same averages as in d, but with x and y axes swapped. In particular for regressive renditions (quintile 1), change within day 62 (x axis) does not recapitulate developmental changes occurring over months (x axis in d). f, Repertoire dating based on repertoire time (as in Extended Data Fig. 3c). Each point corresponds to a production-time period and the average of all repertoire times of renditions in that period. Error bars show bootstrapped 95% confidence intervals. The change in repertoire time, which is computed without using a low-dimensional parametrization of vocalizations captures the movement along the DiSC.