Food-associated calls of tufted capuchin monkeys (Cebus apella nigritus) are functionally referential signals

In this paper I explore the possibility that tufted capuchin monkeys (Cebus apella nigritus) have food-associated calls, vocalizations that are functionally referential and may provide information about the presence of food to other individuals in the group. Functionally referential signals are those that meet two criteria: (1) they are context specific and (2) they elicit a response that is context independent. The study was conducted on a wild group, of capuchins in a subtropical rain-forest in NE Argentina. To evaluate the degree of context specificity of the vocalizations I obtained focal animal sound recordings of the vocalizations emitted by individually recognized animals and indicated the socio-ecological context of call emission. I performed playback experiments to see if animals can respond to the food-associated calls in the absence of contextual information. Two vocalizations, grgrs and whistle series, were considered putative food-associated calls, because previous observations suggested an association of these vocalizations with the presence of food. Grgrs and whistle series were given at a higher rate when the focal animal was feeding on fruit at a highly productive source than in other socioccological contexts. Whistle series were also produced, although at a lower rate, in contexts other than feeding but whistle series given when feeding belong to an acoustically distinct type. Animals responded to the playback of food-associated calls with a rapid and direct movement to the speaker in almost 50% of the trials. Capuchins did not show this response to the playback of control stimuli. Food-associated calls in tufted capuchins can thus be considered functionally referential signals.