Comparative research into animal communication has been and continues to be highly informative regarding the general principles underlying the evolution of communication (including human communication). However, our tendency to focus on specific modes of production of these signals (i.e. facial expressions, gestures or vocalisations) in isolation of each other, and in a limited number of species, may be obstructing our progress. Therefore, in this thesis, I adopt a novel and more comprehensive approach to a highly understudied primate, the crested macaques (Macaca nigra).
First, I consider the effects of the strength of social bonds and dominance relationships between individuals (and, when possible, their kin relationships) when investigating the function of communicative signals. The findings show that communication can be flexible depending on social factors, possibly reflecting functional relevance to the context. Social bonds in particular, influenced communication between individuals facing immediate socio-ecological challenges (finding food and deterring predators). Second, I address the significance of multimodal communication in this species. I test the influence of the composition of communicative signals on the outcome of social interactions.
The results show that subtle changes in the composition of communicative signals (number of components and combination of different sensory modalities) can have a profound effect on the outcome of social interactions. The findings resulting from this work constitute one of the first quantitative accounts of the communication system of crested macaques, thereby adding to the pool of data available to study communication from a comparative perspective. The comprehensive approach adopted in this thesis provides much needed insight into the importance of considering communication as multimodal and highly intertwined with species’ social style. Such an approach seems highly productive and can inform us regarding aspects of social and communicative complexity that have been overlooked so far.