Emergence of individual recognition in young macaques

Few studies have addressed the development of nonhuman primate infants' responses to conspecific vocalizations. Previous studies showed that the appropriate response to alarm, intergroup and long-distance contact calls emerged at about 6 months of age. It remained unclear whether this age constitutes a watershed in terms of infants' sociocognitive development or whether it was due to the types of stimuli used in the experiments. I therefore examined the development of infant Barbary macaque, Macaca sylvanus, responses to maternal calls, under the assumption that recognition of the mother is one of the tasks that infants should master as early as possible. I presented infants of different age categories with short bouts of screams recorded from their mothers or another female of the same social group. Experiments on yearlings confirmed the suitability of the experimental approach: yearlings responded significantly more strongly to maternal calls than to calls from unrelated females. Infants were tested at 4, 10 and 16 weeks of age. In the youngest age group, they failed to respond to the playbacks, whereas from 10 weeks of age on they responded significantly more strongly to maternal calls, suggesting that by this age they recognized their mothers by voice. These results suggest that the developmental trajectories in the domain of comprehension learning may be flexible, in the sense that infant responses may depend on the salience of, and the exposure to, the call type under study. The experiments also show that screams may transmit individual-specific characteristics that are perceptually salient to the listeners