Single and multichannel signal composition:: Facial expressions and vocalizations of rhesus macaques (Macaca mulatta)

A method for simultaneously examining visual and vocal components of expressive behavior is described, compiled from video recordings of social behavior of a free-ranging group of rhesus macaques on Cayo Santiago, Puerto Rico. I developed a catalog of expressive movements, and chronicled detailed information on visual and vocal components of 1215 individual behaviors. Two thirds of the events recorded were silent, supporting the idea that visual behaviors are primary for short distance communication in these macaques. Clusters of expressive components detected by Principal Component Analysis and Multiple Correspondence Analyses corresponded to threatening, submissive, and affiliative behaviors described previously, providing quantitative support both for these previous descriptions and for the suggestion that these three poles of behavior are important in daily social interaction. Silent expressions involved a greater variety of mouth positions than did vocalizations, which were produced with stereotyped mouth shapes. Other components of the face, not involved with articulation, were nonetheless associated with particular vocalizations: specific associations were found among barks, ears retracted, and head lowered on the one hand, and pant-threats, ears forward, and head raised on the other. Screams and squeaks were highly stereotyped, combined with prototypical grimace mouth positions, crouching and retreating. Girney vocalizations were accompanied by lipsmacking. Grunts were unaccompanied by other expressive components, evoking the suggestion that they may be predominantly neutral in valence.