Facial Displays in Cebus apella

Abstract

Tufted capuchins are diurnal New World primates whose social interactions involve vocal and visual communication. We aimed to describe their facial displays and assessed the use (in relation to rank and age/sex classes of the sender or the receiver or both) and the social function of the most frequent ones. More specifically, we analyzed the temporal relationship between each facial display and specific classes of behaviors, e.g., play, aggression, performed by the sender and by the receiver (Pre-Post-Event Histogram [PPEH]). We observed 20 captives, belonging to 2 groups, for a total of 320 h. The capuchins displayed relaxed open-mouth, silent bared-teeth, open-mouth threat, lip-smacking, open-mouth silent bared-teeth, scalp lifting, and, rarely, protruded lips. The repertoire and the meanings of the different facial expressions are similar to those described for Catarrhini. In some cases, such as for the silent bared-teeth display, the meaning depends on the age of the sender. Silent bared-teeth is associated with play in juveniles and with submissiveness of the sender to the receiver and affiliative interactions in adults. The finding, and the fact that silent bared-teeth display is used during courtship (Carosi and Visalberghi, 2002), support Preuschoft and van Hooff’s (1995, 1997) power asymmetry hypothesis of motivational emancipation, according to which there is convergence between affiliative and submissive behaviors in species with a high degree of social tolerance.