Data from: Strategic use of affiliative vocalizations by wild female baboons

Although vocal production in non-human primates is highly constrained,
individuals appear to have some control over whether to call or remain
silent. We investigated how contextual factors affect the production of
grunts given by wild female chacma baboons, Papio ursinus, during social
interactions. Females grunted as they approached other adult females 28%
of the time. Supporting previous research, females were much more likely
to grunt to mothers with young infants than to females without infants.
Grunts also significantly increased the likelihood of affiliative
interactions among all partners. Notably, however, grunts did not simply
mirror existing social bonds. Instead, they appeared to perform a very
different function: namely, to serve as signals of benign intent between
partners whose relationship is not necessarily close or predictable.
Females were less likely to grunt to their mothers or adult daughters—the
individuals with whom they shared the closest and least aggressive
bonds—than to other females. In contrast, patterns of grunting between
sisters were similar to those between nonkin, perhaps reflecting sisters’
more ambivalent relationships. Females grunted at higher rates to
lower-ranking, than to higher-ranking, females, supporting the hypothesis
that grunts do not simply signal the signaler’s level of arousal or
anxiety about receiving aggression, but instead function as signals of
benign intent. Taken together, results suggest that the grunts given by
female baboons serve to reduce uncertainty about the likely outcome of an
interaction between partners whose relationship is not predictably
affiliative. Despite their limited vocal repertoire, baboons appear to be
skilled at modifying call production in different social contexts and for
different audiences.