The relationship between social and vocal complexity in primates

Primate vocal communication complexity is driven by phylogenetic and ecological factors, as well as social complexity. While group size is a well-studied predictor of social complexity in animal communication, the influence of other key social components, such as mating systems and social organization, remains less clear. We used a systematic review and mixed models to test the influence of group size, mating system, and social organization on four measures of vocal complexity: number of call types, number of syllables, number of calls with multiple syllables, and number of alarm calls. We identified 53 publications concerning 46 primate species. We found a complex relationship between social and vocal complexity. Monogamous species produced fewer syllables than polygynous, polygynandrous, and flexible-mating species. Likewise, dispersed-solitary species produced fewer syllables than species living in some forms of group-based social organization. In contrast, repertoire size, number of combined calls, and number of alarm calls were not significantly associated with the social predictors examined. These results suggest that syllable repertoire may be particularly associated with social complexity, especially mating system and social organization. The social traits are also closely related to ecological factors, such as food distribution, habitat type, and predator risk. Future studies incorporating ecological factors are important for a better understanding of these individual and combined effects on vocal evolution.