Elsevier

Animal Behaviour

Volume 74, Issue 3, September 2007, Pages 487-496
Animal Behaviour

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

https://doi.org/10.1016/j.anbehav.2007.01.015Get rights and content

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’.

Section snippets

Subjects

The subjects were five laboratory-bred female capuchins, Cebus apella, aged 3.5 to 21 years at the start of experiment 1. The animals were fed monkey chow twice per day and received water ad libitum. They received fresh fruit five times per week. Animals were fed their normal evening rations and received their morning rations after testing was completed. All animals were pair-housed either with a male or their offspring in the same colony room. This study was conducted in compliance with

Social Dominance

The results of our dominance tests (Table 3, Table 4) indicate that females do establish dominance when placed together in a competitive situation where a preferred food reward is available. Dominance was established between the two capuchin females almost immediately and with minimal overt aggression from the dominant female to the more subordinate female.

Based on the results of the dominance trials prior to experiment 1, we determined that the order of hierarchy from dominant to subordinate

Discussion

Brosnan & de Waal (2003) reported that capuchins decrease the exchange rate when a partner receives a preferred food item relative to their own, particularly if the work effort is inequitable (i.e. no effort is required from the partner). Based on these findings, Brosnan & de Waal (2003) suggested that capuchin monkeys ‘measure reward in relative terms, comparing their own rewards with those available, and their own efforts with those of others’ (page 299). Moreover, they suggested that the

Acknowledgments

We wish to thank Amy Dupuy, Michelle Grisham, Mandi Wilkes, Destiny M. Galentine and Jessica L. McGettigan for technical assistance. We are grateful for the support of Jeff Rowell, DVM, Director of the University of Louisiana at Lafayette-New Iberia Research Center.

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    Citation Excerpt :

    In a seminal study, female (but not male) capuchin monkeys refused food rewards and stopped participating in a token exchange task when they observed how a conspecific received higher value food rewards for engaging in the same activity (Brosnan and de Waal, 2003). This effect was particularly pronounced when the subject had to work harder (i.e. exchange more tokens) for a lower-value reward compared to the partner (van Wolkenten et al., 2007, but see Fontenot et al., 2007). Extending these findings, in the prosocial choice task, capuchins prefer a prosocial choice to a selfish one, but only if the subject and its partner receive equal rewards (de Waal et al., 2008).

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S. L. Watson is at the University of Southern Mississippi, 118 College Dr., Box 5025, Hattiesburg, MS 39406, U.S.A.

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