Chimpanzees using stones to crack open oil palm nuts in Liberia

@article{Hannah2006ChimpanzeesUS,
  title={Chimpanzees using stones to crack open oil palm nuts in Liberia},
  author={Alison C. Hannah and William C. McGrew},
  journal={Primates},
  year={2006},
  volume={28},
  pages={31-46}
}
The use of stone-tools to open palm nuts (Elaeis guineensis) was studied in a group of 16 chimpanzees (Pan troglodytes) released from captivity to a natural island setting in Liberia. The behaviour was started by one female of the group; it then spread to 12 others over periods varying from a few seconds to a few weeks. Nut-cracking soon spread to three other sites, both spontaneously and with human encouragement. Both nuts and tools were carried distances of several hundred meters. Social… 
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