Introducing tool-based feeders to zoo-housed chimpanzees as a cognitive challenge: spontaneous acquisition of new types of tool use and effects on behaviours and use of space

Cognitively challenging environments are vital to the welfare of captive animals. However, practical enrichment devices that can facilitate animals’ natural behaviours and accommodate individual variation are still limited. We created two types of feeders to facilitate tool-using behaviour in captive chimpanzees: pounding and dipping feeders. The pounding feeder was inspired by pestle-pounding behaviour observed in wild chimpanzees, and we expected that chimpanzees would pound soft foods. The dipping feeder was designed to stimulate actions similar to ant-dipping behaviours observed in wild chimpanzees. We investigated (1) how chimpanzees acquire tool-using behaviours and (2) the effects of the feeders on chimpanzee behaviour and use of space. The subjects were five chimpanzees housed in the Kyoto City Zoo, Japan. In study 1, conducted between March and May 2014, we introduced the feeders and examined the chimpanzees’ behaviours and the characteristics (length, width, etc.) of any tools they used. In study 2, conducted between September and October 2014, random days were designated when feeders were available (enriched condition) and not available (control condition). In study 1, all adult chimpanzees could use the dipping feeder, and two females could obtain foods from the pounding feeder by hitting the foods several times. The ability to acquire new tool-using behaviours was consistent with ability in existing tool-use behaviours. One infant started to use tools by trial and error. Study 2 showed that under the enriched condition, tool-using behaviours increased, stress-related behaviours decreased, and the use of space changed. These results suggest that these tool-based feeders provided an appropriate challenge for the chimpanzees.