Learning processes in a tool using task by captive chimpanzees (Pan troglodytes)

Muara Lucia Celli, M. Tomonaga, T. Udono, M. Teramoto, and K. Nagano

Kyoto University, Japan

     In the wild, chimpanzees (Pan troglodytes) are commonly found to use sticks to fish for termites, ants, or honey, as well as use other kinds of tools for foraging and communication purposes. These abilities seem to be socially transmitted across generations, and types of tool use can be considered as a part of a group's culture, as many long-term studies have shown. The occurrence in the wild, limited visibility, and the lack of control of variables in a natural environment, however, require the well-controlled studies in captivity, where the behavior with regard to choice of tools, understanding of the task, and learning processes underlying their activity can be better studied. This study explores the learning of tool use for fishing honey by six captive chimpanzees at the Kumamoto Primates Park, Sanwa Kagaku Kenkyusho, kept in pairs cages. The experiment was conducted under different conditions where changes in the subjects' behavior could be analyzed before and after the setting of the task, to measure reduction of abnormal behaviors and increase rates of manipulation and time engaged in tool use activity. The pairs were presented with 20 kinds of materials, of which only some were suitable for the task. In addition to tool selection, the conditions were such that only one subject at a time could perform the task, facilitating observation of transmission of the behavior (tool choice and technique) among conspecifics. The dominant chimpanzees tended to spend more time performing the task, and were subsequently prevented from participating in the experiment in an effort to provide the same opportunity to the subordinate individuals. We investigated the learning processes involved in the acquisition of this tool using technique. Trial and error was the main process allowing the development of the honey-fishing, however, observation of conspecifics occurred and appeared to influence orientation of the subjects' tool selection.

Celli, Maura Lucia

Section of Language and Intelligence, Primate Research Institute, Kyoto University

Inuyama, Aichi 484-8506, Japan

malu@pri.kyoto-u.ac.jp