How do capuchin monkeys (Sapajus spp.) innovate in a tool-manufacturing task?

Innovation has been defined as the ability either to find a solution to a novel problem by using motor and cognitive strategies already acquired, or to find a novel solution to an old problem through new motor and cognitive strategies. Innovation can improve fitness by allowing animals to adapt flexibly to social and ecological changes, but it could also be detrimental by exposing animals to potential risks and costs. Little is known about how this capacity emerges and whether/how innovators differ from non-innovators. The major aim of the study was to investigate the innovation capabilities of capuchin monkeys and 4-year-old children in a task requiring tool-manufacturing. Here we report on the results of 16 capuchins presented with an innovative tool-manufacturing task in which they had to modify a tool to obtain a reward from a transparent apparatus. Each individual was given 3 trials: in each trial a different material set was presented to the subject. Each set consisted of 4 potential tools; if appropriately modified and put into a different opening in the apparatus, each tool provided the opportunity to reach the reward. Thirteen out of 16 capuchin monkeys successfully modified objects and used them as tools to obtain the reward. Detaching the tool from a substrate was the most common type of modification. Successful innovators differed from unsuccessful innovators in the amount of interaction with the apparatus and the tools, but not in the latencies to approach the task stimuli. Moreover, previous experience in tool-use tasks affected success and time needed to solve the task. These results are discussed in light of the cognitive and motor skills potentially affecting innovative tool behaviour in primates.