What challenges wild bearded capuchin monkeys (sapajus libidinosus) in learning to crack nuts?
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Young capuchins handle stones and hard-to-access foods for several years until they reach full efficiency at cracking foods with stone hammers. Eight juveniles and seven adult bearded capuchins were followed in three periods from 2011-2013 focusing on their manipulative behavior. I categorized individuals in each collection period into three expertise classes: novice, intermediate and expert. Our results described how manipulative behaviors changed relating to three hypotheses: a) monkeys crack nuts when they are large enough (size driven), b) monkeys initially explore objects and what they can do with them using species-typical actions, and nut-cracking follows a period of learning through practice and exploration (action-perception) and c) monkeys begin to crack nuts using a tool when they reach the necessary cognitive status to understand means-ends relations involved in using a tool (Piagetian). I suggest that consistently positioning the nut is a key feature predicting efficient nut-cracking in young capuchins.