Supplementary Figure 11: Cross-correlation (CC) and autocorrelations of songs

Correlations were computed after summing the number of song vocalization onsets in 50-ms sliding windows and subsequent convolution with a Gaussian kernel of width σ = 20 ms. (a) The CC function of song vocalizations of co-singing birds 3-4 has a wide peak in excess of 3 STDs. Shown is the same curve as in Figure 3e but without smoothing. (b, c) Autocorrelations of calls in birds 1 and 2 (b) and 3 and 4 (c). The autocorrelations exceeded 3 standard deviations (SDs, dotted lines of corresponding colors) in the relatively wide interval [-3 3] s. In some birds, high autocorrelation peaks were produced by complete motif matching and lower peaks by matching of non-identical syllables (b). The lower CC values in a compared to autocorrelations in c reveal that co-singing happened less frequently than production of two consecutive motifs by a single bird.