FOOD-ASSOCIATED CALLS IN RHESUS MACAQUES (MACACA-MULATTA) .2. COSTS AND BENEFITS OF CALL PRODUCTION AND SUPPRESSION

In field experiments, free-ranging rhesus macaques (Macaca mulatta) ga ve food-associated calls in 45% of the trials in which they were prese nted with food, either monkey chow or coconut; they did not call in co ntrol trials when sticks were presented. Consistent with prior natural istic observations, adult females called in a higher proportion of tri als than adult males. Coconut, one of the most highly preferred food i tems in the diet, elicited different call types and a higher rate of c alling from ''discoverers'' than did chow. The call types produced to coconut (warbles, harmonic arches, and chirps) were primarily those th at, under nonexperimental conditions, were associated with relatively rare and preferred foods. In contrast, coos and grunts were primarily produced in response to chow. The relative hunger level of the discove rer had no significant effect on the call type produced but did affect the rate of call production; discoverers called at higher rates when they were hungry. Upon hearing food-associated calls, individuals with in the vicinity of the discovery responded by rapidly approaching the caller. A larger number of individuals approached when discoverers cal led than when they did not. Discoverers who failed to call received si gnificantly more aggression from group members and, in the case of fem ales, actually consumed less food than discoverers who called. The pro bability of receiving aggression did not appear to be associated with the discoverer's dominance rank. Results suggest that food-associated calls are ''honest'' signals reflecting food possession. Those who fai l to signal and are caught with food are apparently punished.