Effects of food preferences on token exchange and behavioural responses to inequality in tufted capuchin monkeys, Cebus apella

Abstract

We examined the extent to which female capuchin monkeys show an ‘aversion to inequitable work effort’ by providing the monkeys with the opportunity to engage in token exchange tasks to earn either a preferred (grape) or nonpreferred (oat cereal) food item. In experiment 1, monkeys were paired with partners such that both were required to exchange a token (work effort) for either a preferred or nonpreferred food reward. The subject's exchange behaviour was then compared to conditions in which the partner received the food reward for no work effort. We found no evidence that differential work effort influenced the percentage of incomplete exchanges. Furthermore, capuchins completed exchanges more rapidly for the preferred food item, regardless of the work effort of the partner. In experiment 2, we evaluated, in the absence of differential work effort, behavioural responses of monkeys to receipt of a preferred or nonpreferred food in conditions where their partner received either the same or different food. These conditions were compared to control conditions where either the same or different food was placed in an adjacent empty cage. Capuchins were less likely to accept nonpreferred food and consumed it more slowly than preferred food. We found no evidence that the presence of a partner influenced acceptance or consumption of the nonpreferred food under inequitable conditions. Overall, we found no indication that capuchins are able to evaluate either the relative work effort of a partner or the inequity of a food reward and are thus unlikely to possess an ‘aversion to inequity’.