The Ecological Design of the Affiliative Vocal Communication Style in Wild Japanese Macaques: Behavioral Adjustments to Social Contexts and Environments

Coo calls, contact calls used by Japanese macaques for intragroup vocal communications, have been proposed as functioning to maintain interindividual spatial cohesion in wild populations and have served as the primary focus of previous investigations. Although behavioral variations in communication have been reported on the basis of group membership, social status, and individual differences, accumulating evidence generally shows that macaques adjust their communication style to avoid spatial separation from group members. We propose that two fundamental causes underpin these phenomena: the risk of separation and the internal motivation to coordinate the group. Separation risks and internal motivation induce variations in vocal communications relying on contact calls and likely determine the type of vocal communication used in wild primate social groups.