The effects of experience on tool use by Capuchin monkeys
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This thesis investigated effects of manipulative experience on tool-using ability of tufted capuchins. Two groups of capuchins were tested on variations of a tool-using task, involving use of an object as a tool to dislodge a reward from a tube. The tasks were modelled after those developed by Visalberghi and Limongelli (1994) and Visalberghi and Trinca (1989). One group of monkeys was provided the opportunity to manipulate task materials without reward; the other group was not. Experiment 1 required subjects to push a rod through the tube. Experience with task materials improved capuchins' efficiency, evidenced by faster completion of trials. In Experiment 2, short pipes could be combined to create a tool of sufficient length. Due to procedural problems, results were inconclusive. Experiment 3 required subjects to manufacture the appropriate tool. Experience with task materials improved capuchins' performance, evidenced by faster completion of trials, less frequent performance of inefficient behaviours, and decrease in errors across trials. When capuchins' performance was compared with enculturated chimpanzees tested previously on the task (Visalberghi, Fragaszy, and Savage-Rumbaugh, 1995), experienced capuchins performed as efficiently after 15 trials as had chimpanzees originally. In Experiment 4, subjects had to dislodge the reward from a tube containing a trap. Because successful levels of performance were not reached, results were inconclusive. In Experiments 5 and 6, appreciation of object affordances was examined. The capuchins demonstrated an ability to distinguish between functional characteristics of objects. These results suggest previous claims regarding limitations of capuchin tool-use may have underestimated their abilities. Further, because object experience enhances tool-using ability, previous comparisons of capuchins with enculturated chimpanzees seem to have misrepresented the magnitude of difference in their abilities. However, future research comparing species with the same experiential backgrounds is necessary to elaborate on differences in cognitive processes underlying capuchin and chimpanzee tool-using behaviour.
Thesis, PhD Doctor of Philosophy
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