Supplementary Figure 5: Non-vocal response to song

(a) An example of non-vocal response in co-singing birds 3 and 4. The song oscillogram (blue) in bird 4 was recorded with the wearable microphone. The non-vocal response (body acceleration, red) in bird 3 is reflected in the root-mean-square (RMS) accelerometer signal (sliding window) in the non-vocal low-frequency band < 300 Hz. Bird 3 did not vocalize during this episode (not shown). (b) Normalized median RMS traces of body acceleration in all four birds aligned to the beginning of the song motif in bird 4 (onset of syllable A). Shown are the median filtered RMS traces of 72 motifs. We selected only episodes in which no vocalizations in birds 1 - 3 were detected within ± 2 s from motif onset in bird 4. The 3 SDs level (red dashed line) in bird 3 was estimated using bootstrapping. Note that significant (> 3 SDs) movements in bird 3 took place in a narrow interval -217 to 40 ms around the onset of the motif. Possibly, bird 3 reacted to the preceding introductory notes or to syllable C in the previous motif. By contrast, bird 4 did not show any detectable non-vocal response to the songs of bird 3, indicating asymmetry in movement responses in these two animals.