Sex differences in the acquisition of communicative competence by pigtail macaques (Macaca nemestrina).

Previous study of captive pigtail monkeys (Macaca nemestrina) revealed that victims of an attack by a group member employed one of four acoustically different recruitment calls (Gouzoules&Gouzoules: Animal Behaviour 37:383-401, 1989). The calls appear to provide allies with information pertinent to decisions about fight intervention. Each call was associated with an agonistic context distinguished by the relative rank of the opponent and the severity of the attack. Monkeys younger than 3 years of age were significantly less likely to use a contextually appropriate call than were older animals and their calls tended to be acoustically less like the prototype for a given context. Analyses reported on here revealed that, among juveniles, females were more proficient than males in both the proper contextual use and the production of these calls. These findings suggest parallels with human sex differences in the development of communicative competence. The evolutionary origins for these sex differences in macaque vocal development may be based in the different life history patterns males and females exhibit.