Facial displays in red-capped mangabeys (Cercocebus torquatus): Repertoire, social context, and potential intentionality

Primate communication relies strongly on the visual modality, notably through the production of a wide range of expressive facial signals. We investigated here the facial display repertoire of a relatively little-studied cercopithecid species, red-capped mangabeys (Cercocebus torquatus), and questioned whether their facial displays were dependent on social contexts and accompanied by indices of intentionality. Although the dual intentional and emotional use of apes’ facial expressions has recently been suggested, the question of whether monkeys produce facial expressions intentionally to communicate remains open. We described 6 facial displays produced by captive red-capped mangabeys in social contexts. They are based on movements of the mouth, eyebrows, and ears, possibly graded in intensity and produced independently or in combination. We showed that most of the facial displays were produced preferentially in specific social contexts and that repertoires varied with subjects’ characteristics, highlighting the communicative function of these displays. Moreover, behavioral markers of intentionality commonly used in gestural studies were found to accompany the production of some of the facial signals observed. Particularly, playful “open mouth” appeared strongly associated with intentionality indices, as previously noticed in ape species. All other facial displays, except yawns, did not exhibit all defined intentional indices but were, at least, directed toward a recipient. Interestingly, yawns presented different variants of intensity associated presumably with different social functions. Altogether, these results emphasize the communicative function of red-capped mangabeys’ facial displays and provide a basis for further research on their intentional communication.