Tool-use for drinking water by immature chimpanzees of Mahale: prevalence of an unessential behavior |
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Authors: | Takahisa Matsusaka Hitonaru Nishie Masaki Shimada Nobuyuki Kutsukake Koichiro Zamma Michio Nakamura Toshisada Nishida |
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Institution: | (1) Laboratory of Human Evolution Studies, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan;(2) Department of Cognitive and Behavioral Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan;(3) Primate Research Institute, Kyoto University, Inuyama, Japan;(4) Japan Monkey Centre, Inuyama, Japan |
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Abstract: | Use of leaves or sticks for drinking water has only rarely been observed during long-term study of wild chimpanzees (Pan troglodytes schweinfurthii) at Mahale. Recently, however, we observed 42 episodes of tool-use for drinking water (73 tools and two cases of using tool-sets ) between 1999 and 2004. Interestingly, all of the performers were immature chimpanzees aged from 2 to 10 years. Immature chimpanzees sometimes observed the tool-using performance of others and subsequently reproduced the behavior, while adults usually paid no attention to the performance. This tool-use did not seem to occur out of necessity: (1) chimpanzees often used tools along streams where they could drink water without tools, (2) they used tools for drinking water from tree holes during the wet season when they could easily obtain water from many streams, and (3) the tool-using performance sometimes contained playful aspects. Between-site comparisons revealed that chimpanzees at drier habitats used tools for drinking water more frequently and in a more conventional manner. However, some variations could not be explained by ecological conditions. Such variations and the increase in this tool-use in recent years at Mahale strongly suggest that social learning plays an important role in the process of acquiring the behavior. We should note here that such behaviors that lack obvious benefits or necessity can be prevalent in a group. |
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Keywords: | Chimpanzees (Pan troglodytes schweinfurthii) Culture Mahale Tool-sets Tool-use to drink water |
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