Transport of functionally appropriate tools by capuchin monkeys (Cebus apella)

Capuchin monkeys (Cebus sp.) are notable among New World monkeys for their widespread use of tools. Like chimpanzees, they use both hammer tools and insertion tools in the wild to acquire food that would be unobtainable otherwise. Recent evidence indicates that capuchins transport stones to anvil sites and use the most functionally efficient stones to crack nuts. We further investigated capuchins' assessment of functionality by testing their ability to select a tool that was appropriate for two different tool-use tasks: A stone for a hammer task and a stick for an insertion task. To select the appropriate tools, the monkeys investigated a baited tool-use apparatus (insertion or hammer), traveled to a location in their enclosure where they could no longer see the apparatus, made a selection between two tools (stick or stone), and then could transport the tool back to the apparatus to obtain a walnut. We incorporated tool transport and the lack of a visual cue into the design to assess willingness to transport the tools and the monkeys' memory for the proper tool. Six brown capuchins (Cebus apella) were first trained to select and use the appropriate tool for each apparatus. Four animals completed training and were then tested by allowing them to view a baited apparatus and then travel to a location 8 m distant where they could select a tool while out of view of the apparatus. All four monkeys chose the correct tool significantly more than expected and transported the tools back to the apparatus. Results confirm capuchins' propensity for transporting tools, demonstrate their capacity to select the functionally appropriate tool for two different tool-use tasks, and indicate that they can retain the memory of the correct choice during a travel time of several seconds.