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Abstract

We investigated the ability of monkeys to use referential information about environmental resources from cues passively transmitted by conspecifics. The subjects and their companions were four young males belonging to a group of semifree-ranging Tonkean macaques (Macaca tonkeana) raised in a 2-acre wooded park. In a first experiment, a subject had to orient its search strategy from the information obtained from a conspecific. It first had to smell the mouth of a companion having just eaten a food item, and then search for same quality food in the field. The results showed that subjects adjusted their foraging speed according to the value of the reward to be found. They were able to recognize the food resource on the basis of the item previously eaten by their companion. In a second experiment, we asked whether the subjects could anticipate a given food quantity from smelling a companion associated with that given food quantity. When testing whether subjects oriented their search strategy on the basis of companion's identity, they did not appear to use it as a referential cue to food quantity. They nonetheless adapted their foraging speed according to food value. Both experiments indicated that macaques are liable to assess and select food from information extracted from conspecifics, and hence avoid some costs associated with individual food searching.