Monkeys crying wolf? Tufted capuchin monkeys use anti-predator calls to usurp resources from conspecifics

The use of 'tactical deception' is argued to have been important in the cognitive evolution of the order Primates, but systematic studies of active deception in wild non-human primates are scant. This study tests whether wild tufted capuchin monkeys (Cebus apella nigritus) use alarm calls in a functionally deceptive manner to usurp food resources. If capuchins use alarm calls 'deceptively', it was predicted that false alarms should be: (i) given by subordinates more than by dominants, (ii) more frequent when food is most contestable, (iii) more frequent when less food is available, and (iv) given when the caller is in a spatial position in which it could increase its feeding success if conspecifics react to the call. These predictions were tested by observing subjects in experimental contexts, in which the amount and distribution of a high-value resource (banana pieces) were manipulated using wooden platforms suspended from tree branches. While false alarms were non-significantly more common when more food was available, the three remaining predictions were supported. These results generally support the hypothesis that alarm calls are used by capuchins to reduce the effects of feeding competition. Whether this is intentional on the part of the caller requires further investigation.