Choose your partner: Social evaluation of skilfulness at cooperative co-action tasks in Tonkean macaques ( Macaca tonkeana )

Social evaluation – inferring individual characteristics of others from their past behaviours – is an adaptive strategy that helps to inform social decisions. However, how nonhuman primates form and use impressions about others to select their social partners strategically is still unclear. In this study, we investigated whether Tonkean macaques, Macaca tonkeana , can spontaneously use information, acquired by observation, to choose the optimal partners for cooperation in two co-action tasks from the same domain. The subjects (N=5) did not prefer to cooperate with the skilful partner compared to the unskilled partner, irrespective of the task or how much attention they paid to the partners’ actions solving a solo version of one task prior to the test. The probability of optimal choices did not increase through trials either, indicating no learning by experience with the partners across the 16 test trials. Our results contradict findings of previous studies that tested monkeys in different domains of competence and contexts, and thus encourage further investigation on monkeys’ social evaluation abilities. Our experimental design presents a promising way to investigate different contexts, the inter-individual differences, the different types of social information involved, and the cognitive mechanisms underlying social evaluation and partner selectivity in nonhuman primates.