Agonistic screams differ among four species of macaques: the significance of motivation-structural rules

Abstract

We compared screams of four species of macaques (rhesus monkey, Macaca mulatta; pigtailed monkey, M.nemestrina; Sulawesi crested black macaque, M.nigra; stumptailed macaque,M.arctoides ) with respect to predictions of Morton's motivation-structural rules (Morton 1977, American Naturalist, 111, 855–869). We examined screams produced by victims of attack that involved contact aggression (pulling, pushing, slapping, grappling and biting) from a higher-ranking opponent. For each macaque species, we digitized 100 screams from females 3 years of age or older and measured acoustic features of each call. We used discriminant function analysis to determine whether the 400 vocalizations could be assigned to the correct caller species on the basis of their acoustic structure. Calls were assigned to the correct species at a significantly higher rate (93.5%) than expected by chance (25%). Each of the four macaque species used acoustically distinct screams in a shared context. While the differences in the macaque species' vocalizations suggest no simple correlation between immediate context and the acoustic forms of screams, there was general correspondence between the acoustic structure predicted by motivation-structural rules and inferences about the internal state of the vocalizer derived from the typical intensity of aggressive patterns that characterize each of the four species.