The Acoustic Structure and Ontogeny of Vervet Monkey Vocalizations

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Vervet monkey (Chlorocebus pygerythrus) vocalizations have been the subject of considerable research, most notably for their putative language-like qualities. While this focus has inspired a productive research effort investigating vocal communication in non-human primates, it has diverted attention away from other, non-linguistically inspired mechanisms by which vocal signals exert their effects on receivers. My research focuses on two vocal classes, grunts and alarm calls, and how their acoustic structures vary according to sender-specific attributes, including age, sex, body size, and identity - all of which have the potential to influence receiver response. I recorded calls from three wild groups of vervet monkeys over a 7-month period on the Samara Game Reserve, South Africa. I used random forest models to determine whether grunts varied in structure in relation to caller age, sex, identity and context, and whether alarms varied with sex and caller identity. I performed a cluster analysis to determine whether alarms segregated into different call types based on variation in acoustic structure. Finally, I used a series of mixed effects models to determine whether call structure in males and females correlated with overall body size (using body weight as a proxy). I found grunts varied in structure with age and sex, but not among individuals or contexts. Alarm calls varied with both sex and identity. My cluster analysis identified two qualitatively distinct alarm call types corresponding to the calls of males and females respectively. My analysis demonstrated that the relationship between body weight and the distribution of acoustic energy throughout alarm calls differed between the sexes. Relative to females, acoustic energy in the calls of males was concentrated at disproportionately lower frequencies. These results suggest that alarm calls may be under selection to exaggerate caller body size and/or extend the effective range of these signals in males. My results highlight that vocalizations can vary in structure along a number of dimensions simultaneously. While it is possible that in some instances, vocalizations convey specific information surrounding their context of production, it is likely that the mechanisms by which vocal signals exert their effects on receivers are more numerous and diverse.
Animal vocal communication, referential signaling, bioacoustics, vervet monkeys, Sexual selection, primates, Allometry
Dubreuil, C. (2019). The Acoustic Structure and Ontogeny of Vervet Monkey Vocalizations (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from