Inoue-Nakamura, N, & Matsuzawa, T (1997) Development of stone tool use by wild chimpanzees (Pan troglodytes). Journal of Comparative Psychology, Vol.111, No.2, Pp.159-173.

Since 1987 in Guinea in West Africa, observations have been being made in the centre of free- range area, where experimenters provide stones and nuts.

Nut cracking consists of the following actions:

    1. picking up a nut

    2. putting it on an anvil stone

    3. holding a hammer stone

    4. hitting the nut with the hammer stone

    5. picking up and eating the nut kernel.

  1. Previous studies have shown that infants younger than 3.5 do not crack nuts themselves, but after that age they begin to.

  2. The present study focused on 3 infant animals observed for 4 years for 2-4 weeks in 4 dry seasons, when they were aged 0.5, 1.5, 2.5 and 3.5

  3. Observers stayed 20 m away behind a screen and videotaped from 7am to 6pm: there were about 80 hours of videotape. Using behavioural definitions, there were 159 episodes of infants observing adults crack nuts, and 692 episodes when infants performed actions themselves.

  4. At 1.5 yrs, almost 90% of behaviour was with either stones or nuts alone, but by 3.5 80% was with nuts and stones together (still quite a lot 20% of just stones).

  5. If they were in contact with another chimpanzee it was their own mother 100% in first year and 90% at 3.5. But observing another chimp went down from 100% own mother to 14% at 3.5

Discussion

The individual actions of ‘Take’, ‘put’ ‘hold’, ‘hit’ and eat, had all been performed by 1.5 yrs

At 2.5 they often put a nut on a stone, hit it with the back of their hand, then picked up a kernel from somewhere else or scrounged a kernel from their mothers

Holding the hammer was the a difficult part – chimps never hit nut with the hammer stone until the last stage.

“True imitation cannot explain the results of the present study. The infants showed a variety of fundamental actions. They gradually increased the relative frequency of adequate sequences of the basic actions through each stage of development. They did not copy the motor patterns or the way to relate nuts with stones………. As the present results suggest, they learned the general functional relations of stones and nuts and also learned the goals obtained by the demonstrator. This learning process might be called emulation.” (p.172).

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Extract —

"CHIMPANZEE BEHAVIOR

FEEDING

Chimpanzees are predominantly fruit-eating, but they also eat a variety of other foods. So far, we have observed that fruits, leaves, flowers, seeds, pith, bark, gum, sap, mashrooms, insects, honey, bird eggs, owls, and tree pangolins are included in food repartoire of Bossou chimpanzees. You can observe below chimpanzees feeding on figs, one of the most important foods for them.

TOOL USE

Chimpanzees make and use a diverse and rich kit of tools and, with the exception of humans, they are the only living primates to consistently and habitually use and make tools.

Nut cracking at Bossou:
Chimpanzees of Bossou are well known for using a stone hammer and anvil to crack open the nuts of the oil palm tree (Elaeis guineensis)."

photo of chimpanzees cracking nuts

photo in Netscape 6.1

[image located at
http://www.pri.kyoto-u.ac.jp/koudou-shinkei/shikou/chimphome/essay/bos_tool.jpg,
December 2001
Copyright (C) 1998 Primate Research Institute, Kyoto University
All rights reserved
As part of this essay]