Food-associated calls in rhesus macaques (Macaca mulatta): I. Socioecological factors

Abstract

Upon discovering food, free-living rhesus macaques (Macaca mulatta) on the island of Cayo Santiago, Puerto Rico, produce a complex of vocal signals consisting of five acoustically distinguishable calls. This report examines the socioecological factors eliciting call production and the information protentially conveyed to others. The primary contexts for three vocalizations (“warbles, ” “harmonicarches, ” and “chirps”) are encounters with rare and highly preferred foods (e.g., coconut). Two other vocalizations (“coos” and “grunts”) are produced both in food (primarily provisioned chow) and in nonfood contexts, such as during mother-infant separation and grooming interactions. Grunts given upon encountering food are acoustically distinct from those given in nonfood contexts. In contrast, coos associated with food are statistically indistinguishable from coos given in other contexts. When conspecitics hear these food-associated calls, they typically approach the caller. Coos are less likely to lead to approach than other food-associated calls, Results from all-day follows on adult males and adult females reveal that changes in hunger level influence call rate but not call type; the different call types are produced throughout the day. We infer that the structure of food-associated calls provides information about the quality of the food discovered, whereas call rate conveys information about the relative hunger level of the caller. In this population, adult males give fewer food-associated calls than adult females. In addition, females within large matrilines call more than females within smaller matrilines, and males who are resident in a group are more vocal than peripheral males.