Vervet monkeys get a callback: Acoustic and developmental perspectives on their vocalisations (Chlorocebus pygerythrus)

Four decades ago, breakthrough studies on vervet monkeys’ vocalisations provided prime comparative models of communication. Their apparent ability to associate specific contextual functions, such as different types of predators, with distinct calls that elicit appropriate response from their kin greatly impacted how we understand primate communication and even sparked suggestions of primitive semantics. However, more recent data may challenge these appealing, straightforward perspectives. This systematic review provides an updated assessment of the literature on vervets’ vocal signalling, highlighting historical, acoustic, and developmental evidence gathered across 40+ years of research. It suggests that early studies, albeit significantly relevant, may have been biased by function-driven approaches and labelling. More recently, research interest has surged again through new approaches encompassing a greater variety of vocal signals, used in multiple social contexts, and placing greater emphasis on the acoustic structure of calls. These approaches highlight greater functional flexibility of vervet calls, which exhibit greater acoustic and contextual overlap than functional views suggested; however, inconsistencies in labelling may hinder the comparability of research progress. We therefore suggest a shift towards data-driven, structural perspectives (i.e., fine-grained acoustic level) which could more accurately capture the full extent of vervets’ expressive abilities. Thorough investigations of vocalisation development and early acoustic trajectories could be key to rethinking the vervet vocal signalling and its impact on our understanding of animal and human communication.