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HOME » Behaviors of chimpanzees in Bossou» Nut-cracking


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). Among all the tool use behaviors observed in the wild, nut cracking is probably the most sophisticated performed by chimpanzees. Indeed, this behavior is characterized by the requirement for both bimanual and asymmetric manipulation, which has thus far never been reported for any other tool use behavior observed in the wild.

1. This is an adult female chimpanzee, Jire, who is about to crack nuts using stones. She has carefully selected appropriate stones for the task ahead.

2. She reaches out on the ground below the palm tree for a nut to crack.

3. She then proceeds to place the nut on the anvil stone and with her other hand.

4. She takes her hammer stone and pounds the nut several times.

5.The nut is finally cracked and Jire can gain her reward. The nut contains a kernel, which is very tasty and full of energy. Chimpanzees at Bossou love eating oil palm nuts!

Matsuzawa and colleagues have also been conducting field experiments in an outdoor laboratory, in order to gain more insight into nut cracking behavior, mainly focusing on its acquisition by youngsters (Sakura & Matsuzawa, 1991; Matsuzawa, 1991,1994, 1999; Fushimi et al, 1991; Sugiyama et al, 1993, Inoue-Nakamura & Matsuzawa, 1997). They placed stones and nuts at the top of a hill in the core range of the chimpanzees (outdoor laboratory) and video-recorded the chimpanzees' behavior. They have also experimented with the introduction of a new species of nut (Coula edulis), which is cracked by chimpanzees at Tai and Yeale, Mt. Nimba, in Cote d'Ivoire. This experiment has enabled them to look at the social transmission of a new behavior within the community. The results of these experiments have yielded interesting insights into the transmission of cultural behavior among chimpanzees (Matsuzawa et al, 2001).