Observer choices during experimental foraging tasks in brown capuchin monkeys (Cebus apella)

We investigated whether capuchin monkeys (Cebus apella) would choose to observe a high- or low-status adult female from their group during experimental foraging tests. The subject was located in the center of a test chamber, with a low- and high-ranking demonstrator on either side of two partitions. A peephole allowed the subject to observe the models by looking through either respective partition. Each model was trained on one of the two different methods, lift or pull, for retrieving food from a foraging apparatus. There were 22 subjects and four models. During the 40-trial test sessions, subjects could choose which model they would watch in each trial. It was predicted that subjects would prefer observing the model with whom it was closer in rank, and therefore share greater affiliation with. Results showed that only half the subjects showed a preference and that preference was not linked to status. Relatedness played a larger role in determining if a subject showed a preference for a model, and a correlation was found for relatedness and observer preference. After the observer preference tests, subjects were presented with the foraging apparatus to determine if they displayed a preference for one of the two tasks. The majority of subjects (17/22) showed a preference for the pull method, suggesting that this method may have been more salient to the monkeys in this study.