Vocal recognition of individuals and kin in free-ranging rhesus monkeys

The social behaviour of many species of non-human primates suggests a capacity for both individual and kin recognition. In these species, the ability to signal and perceive identity at a distance may be an important adaptation facilitating intra-group social communication. Variation in vocalizations is hypothesized to provide a basis for this ability. Playback experiments were conducted to test for vocal recognition of contact calls between adult female rhesus macaques,Macaca mulatta. Single-trial playbacks of the contact call of either a matrilineal relative or a familiar, non-relative group member were used to test for discrimination of kin from non-kin. Females responded significantly faster and longer to the contact calls of matrilineal relatives. A habituation–discrimination paradigm was then used to test for individual recognition. Females habituated to successive presentations of different exemplars of the contact calls of one matrilineal relative, then showed a significant rebound in response to the subsequent presentation of a contact call from a second matrilineal relative. These results indicate an ability for vocal recognition of both individuals and kin. Females' responses to playbacks suggested the additional possibility for categorical recognition of matrilineal kinship, or its correlates.