Chimpanzees in a remote West African rainforest use crude stone tools to crack open nuts, a skill which they teach to their young, researchers have found.

The chimpanzees used hammer stones to break open hard, golfball-sized nuts from panda trees.

Melissa Panger of George Washington University studies primate tool use and is a co-author of the nut cracking report, which appears in Friday's issue of the journal Science.

Panger said the chimps showed precise control over the force needed to break open the nuts. It takes a lot of pressure, but if too much is applied then the nuts shatter into inedible pieces, she said.

Panger's colleagues on the study were Christophe Boesch, an expert on chimpanzee behaviour at the Max Planck Institute for Evolutionary Anthropology in Germany and Julio Mercader, a specialist in rainforest archaeology at the George Washington University Department of Anthropology.

The team found the nut shells and remains were concentrated in a nut cracking area called Panda 100 in Ivory Coast's Tai National Park.

The area is what archeologists call a site, and the researchers say their study is the first time archeology has been successfully applied to past chimpanzee behaviour.

At the nut cracking sites, the chimps gather their nuts, put them on trees which are used as anvils, and pound the nuts with heavy stones.

Mothers showed their young how to crack the nuts, the same way humans teach their children.

Clever chimps

The nut cracking behaviour is limited to chimps living in Ivory Coast, Liberia and Guinea-Conakry, even though the nuts and stones are available to chimps in central Africa. Experts say the difference may mean it is a cultural, learned behaviour.

The chimps must also select hammer stones suited to smashing nuts and carry them to where the nut trees grow – sophisticated behaviour for an animal.

The unearthed materials included more than 470 stone pieces that may have flaked off when smashed against the anvils. The flakes resemble those used by early humans as knives and other tools.

"Some of the stone by-products of chimpanzee nut-cracking are similar to what we see left behind by some of our ancestors in East Africa during a period called the 'Oldowan,'" said Mercader, the lead author of the study.