A temporal rule in vocal exchange among Large-billed Crows Corvus macrorhynchos in Japan

We investigated whether vocal communication in wild Large-billed Crows (Corvus macrorhynchos) is governed by a temporal rule as an evidence for vocal exchange. In order to examine this potential temporal rule, we analyzed the intervals between two single-note ka calls produced sequentially by two crows in gregarious situations. Two different individuals sequentially uttered ka calls at approximately 0.2-0.8-sec intervals. Such a specific time window was not observed in a simulation of 'imaginary' flocks, in which multiple crows independently emitted ka calls at their own pace, similar to the calls of solitary crows in the wild. These results suggest that the specific time window of inter-call intervals between different crows is not an incidental phenomenon in a crowded situation, but rather a specific event that follows a temporal rule organizing vocal communication of two crows. Our findings provide the first evidence of vocal exchange using ka calls that are organized following a precise temporal pattern in Large-billed Crows.