Individual Variation in the Use of Acoustic Signals to Coordinate Group Movements among Tibetan Macaques (Macaca thibetana)

Simple Summary Vocal communication is widely used in most primate groups as one of the most effective ways to transmit information. However, the role of sound signals in group movements and their influencing factors are not well understood. In this study, we not only confirmed the recruitment function of vocalizations in group movements, but also found the effect of sex and social centrality on vocalizations. Social centrality indicates the degree of proximity relations between two individuals in a social network. Female Tibetan macaques and individuals with high social centrality were more likely to use vocalizations during collective movements. This study helps us understand the cooperative mechanisms of animal populations. To maintain group cohesion, social animals need to coordinate their actions during group movements. Several species use vocalizations to communicate with each other during coordination. However, the process of vocal communication and its influence in collective decision making is not clear. We studied a group of free-range Tibetan macaques (Macaca thibetana) at Huangshan, China, and recorded acoustic signals during their group movements. It was found that three kinds of sounds were used in their movements. Group movements with vocalizations recruited more participants than the movements without sound. Moreover, during group departures, individuals in the front emitted a higher frequency of vocalization than individuals in the rear. Sex and social centrality both had a significant influence on vocalizations. Social centrality indicates the degree of proximity relations between two individuals in a social network. Females and individuals with high social centrality emitted more sound in group movements. However, social rank and the number of relatives did not affect the emission of sound. These results suggest that the function of calls in collective movements relates to coordinating group movements. This study provides an insight into the association of acoustic communication with collective decision making.