Chimpanzee vocal control: Don't get so emotional

An experiment was carried out to determine if and to what extent chimpanzees control the production of their vocalizations. Previous studies in our laboratory have indicated that chimpanzees are more likely to produce "attention-getting" (AG) calls when food is present in conjunction with a human experimenter than when the food or human are present alone. Here we examined the effect that the presence of an audience has on this signaling behavior. The number of AG and food bark (FB) vocalizations produced by chimpanzees (N=25) in response to the presentation of a preferred food item followed by a human experimenter were recorded in one of two conditions. In condition 1, subjects were briefly separated from their social group. An experimenter then placed a preferred food item just outside of the subject's outdoor enclosure (1 meter), and immediately left the area. Following a delay, the experimenter returned and the subject's behavior recorded. Condition 2 procedures were identical to the first with the exception that the subject animal remained with their group. The data indicate that production of attention getting calls in the presence of the experimenter did not differ between the two conditions (Z = -1.63, NS). Thus, the presence of other animals did not have a facilitative effect on the production of "attention-getting" vocalizations.