Yawning in an Old World Monkey, Macaca Nigra (Primates: Cercopithecidae)

Abstract

The yawn of the black ape appears to be structurally homologous to the behavior pattern widely described for other vertebrates, even in its finer details. The pattern is highly stereotypic, showing only minor structural variants and not exhibiting any tendency to grade continuously into other expressive or communicative behavior patterns. The yawn occurs in many different contexts, in association with a variety of social and nonsocial situations. Yawns tend to be occur in contexts which elicit some level of stress in the performer. Yawns commonly follw demonstrations in which a performer vigorously manipulates an environmental object, with the result of producing a loud noise which draws the attention of others. Adult males yawn significantly more frequently than any other age-sex class. The highest ranking or alpha male tends to yawn at a higher rate than other group members, and in at least one case this was found to be true even following a dominance reversal involving alphas. An ontogenetic trend appears in males: yawning rates increase with age. The most dramatic change occurs during adolescence preceding the eruption of permanent canine dentition. Typical adult male rates are probably reached prior to the completed eruption of the canine teeth.