To assess how brown capuchin monkeys (Cebus apella) delay gratification and maximize payoff, we carried out four experiments in which six subjects could exchange food pieces with a human experimenter. The pieces differed either in quality or quantity. In qualitative exchanges, all subjects gave a piece of food to receive another of higher value. When the difference of value between the rewards to be returned and those expected was higher, subjects performed better. Only two subjects refrained from nibbling the piece of food before returning it. All subjects performed two or three qualitative exchanges in succession to obtain a given reward. In quantitative exchanges, three subjects returned a food item to obtain a bigger one, but two of them nibbled the item before returning it. Individual differences were marked. Subjects had some difficulties when the food to be returned was similar or equal in quality to that expected.

It is possible that non-specialised cues transmitted by conspecifics guide animals' food search provided they have the cognitive abilities needed to read these cues. Macaques often check the mouth of their group-mates by olfactory and/or visual inspection. We investigated whether Tonkean macaques ( Macaca tonkeana) can find the location of distant food on the basis of cues conveyed by group-mates. The subjects of the study were two 6-year-old males, who belonged to a social group of Tonkean macaques raised in semi-free-ranging conditions. In a first experiment, we tested whether the subject can choose between two sites after having sniffed a partner who has just eaten food corresponding to one of the sites. We found that both subjects were able to choose the matching site significantly above the chance level. This demonstrated that Tonkean macaques are capable of delayed olfactory matching. They could associate a food location with an odour conveyed by a partner. In a second experiment, the same subjects were allowed to see their partner through a Plexiglas window. Both subjects were still able to choose the matching site, demonstrating they could rely on visual cues alone. Passive recruitment of partners appears possible in macaques. They can improve their foraging performances by finding the location of environmental resources from olfactory or visual cues conveyed by group-mates.

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The exchange of information regarding the environment is continuous within social groups of non-human primates. As an outcome, knowledge and decisions are socially distributed. However, we lack evidence regarding the processes through which collective achievements are produced. The study aimed to analyze group performance in Tonkean macaques (Macaca tonkeana) in an experimental foraging task. Eight young individuals were used as subjects. They were released in a 1-acre wooded area during 5-min tests either singly or in subgroups of two, three or four individuals. They had to discover a fruit, whole or in scattered portions. The fruit was to be found either alone or in company of a snake. Results showed that subgroups located baited spots generally sooner than single individuals. The number of spots visited until finding the incentives was weaker as the number of subjects increased. Snake presence could increase finding latency and induce more cohesion among individuals. The balance between competition and snake effects appeared to differ between sexes. Performances improved through conspecifics' visual monitoring, stating the role of information transmission in the foraging task. While subjects behaved selfishly and did not actively communicate, subgroups proved to be effective information units and everyone of their members obtained benefits from them. Cognitive performances occurred in situation, they should be assessed simultaneously at the individual and group levels.

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