Audience effects on food calls in captive brown capuchin monkeys, Cebus apella

Brown capuchins give distinct calls upon encountering food. Based on studies on other species that point at divisibility of food and audience as critical variables, we predicted that capuchins would adjust their food calling for both the amount of food and the nature of their audience. We predicted that the food-associated call serves to attract conspecifics in certain conditions. Twelve female capuchins were tested in two food-quantity conditions (large and small) and four audience conditions with a control (higher-ranking female, lower-ranking female, high-ranking male, entire group and alone). All subjects called more for larger than smaller amounts and the highest-ranking females called less than others. Subjects called more in the presence of a group than for any other audience, and this applied most strikingly to high-ranking subjects. This result may be related to the presence of kin rather than group size. We also analysed the acoustic parameters of the calls, predicting that, under conditions where call production rose, those acoustic variables associated with heightened arousal would rise in value. However, call production and those acoustic features were not always correlated. These results suggest that food calls in this species do not solely reflect arousal caused by food and are influenced by multiple audience effects.