Fig. 1. Call coordination in zebra finches.

a, b Call responses to call playbacks presented once per second for a 10-minute session while Bird 1 (a) and Bird 2 (b) were each interacting with the playbacks alone. (top) Spectrogram of call playback and bird’s call response. (bottom) Call playback indicated in gray. Bird 1 or 2 call responses indicated by blue and green bars, respectively. Scale bar, 100 ms. c Call response probability distributions for Bird 1 (blue) and Bird 2 (green) with matched peak response latencies (202 ms, 198 ms). d Call responses of Bird 1 (blue) and 2 (green) when housed together and presented with call playbacks (in triad). e Response distributions for birds in (d) when calling in triad. Light green distribution represents catch cycles in which a call from Bird 1 did not precede a call from Bird 2. f Mean response latencies for 8 birds alone with call playbacks (coefficient of variation CV (response latencies across birds) = 0.16) vs. in triad with a latency-matched bird and playbacks (CV (response latencies across birds) = 0.45). Same shapes indicate matched pairs. Blue and green markers represent example pair from (a–e). g Difference (Δ) in response latencies between matched birds for 4 pairs when alone with playbacks vs. in triad (mean alone w/ playbacks ± standard deviation = 18 ± 12 ms, mean in triad = 165 ± 112 ms). The pair that did not change its latency developed an alternating strategy (see Supplementary Fig. 1). h Call response latencies (alone with playbacks vs. triad catch cycles) for those birds in each pair that had a greater shift in call timing. i Expected vs. Observed percent of overlapping calls for all 4 latency-matched pairs (expected overlap = 30.9% ± 4.3%, Observed overlap = 9.2% ± 7.6%, Wilcoxon rank-sum test, p = 0.029, n = 4 pairs). j Duration of calls when alone with playbacks or when in triad (mean duration alone w/ playbacks = 81 ± 13 ms, mean duration in triad = 81 ± 13 ms, Wilcoxon sign rank test, p = 0.779, n = 8 birds).