Turn-taking is a common feature in human speech, and is also seen in the communication of other primate species. However, evidence of turn-taking in vocal exchanges within a short time frame is still scarce in nonhuman primates. This study investigated whether dynamic adjustment during turn-taking in short calls exists in Japanese macaques Macaca fuscata. We observed exchanges of short calls such as grunts, girneys, and short, low coos during social interactions in a free-ranging group of Japanese macaques. We found that the median gap between the turns of two callers was 250 ms. Call intervals varied among individuals, suggesting that call intervals were not fixed among individuals. Solo call intervals were shorter than call intervals interrupted by responses from partners (i.e., exchanges) and longer than those between the partner’s reply and the reply to that call, indicating that the monkeys did not just repeat calls at certain intervals irrespective of the social situation. The differences in call intervals during exchanged and solo call sequences were explained by the response interval of the partner, suggesting an adjustment of call timing according to the tempo of the partner’s call utterance. These findings suggest that monkeys display dynamic temporal adjustment in a short time window, which is comparable with turn-taking in human speech.

We investigated how the context of the production of vocalizations used in social interactions among Japanese macaques (Macaca fuscata) affects their outcome. We focused on a variety of soft vocalizations, including three acoustically distinct call types: grunts, girneys, and coo calls. We predicted that call outcomes would be influenced by call combinations and exchanges, and by the relationship between the caller and the recipient. We observed social interactions among female Japanese macaques, and found that individuals were less likely to initiate agonistic behaviour when they emitted calls. Call exchanges and call combinations increased the occurrence of affiliative interactions. The probability of affiliative interaction following a given type of call differed according to the relationship between the caller and the recipient. These findings suggest that recipients interpret these calls within a social context; they also demonstrate the existence of complex communicative abilities that integrate vocalizations and context in these monkeys.