Smart chimps get their reward

Chimps' use of tools has been recognised for some time

The way chimpanzees in West Africa use stone tools to crack open nuts for food and pass on the trick to their offspring has been revealed in an intriguing study published in the journal Science.

[The nut-cracking] is a very difficult task to do and it takes the chimpanzees about seven years to learn

Dr Melissa Panger

Researchers from Germany and the United States dug up piles of nutshells and stone flakes at a decades-old nut processing site in the Tai rainforest in Ivory Coast.

The chimps are using precise techniques to obtain their food that take years to learn, say the scientists.

The research team believes its work could tell us something about the way early human-like creatures used stone tools.

Big meal

The Ivory Coast chimps have special processing stations where they crack their nuts. These are stumps of hardwood trees.

The animals collect the panda nuts from up to 300 metres away and bring them to the wooden "anvils" to bash them with stone "hammers" to get at the nutritious flesh inside.

During the nut-smashing season, some chimps spend two or three hours a day opening as many as 100 panda nuts. A chimp can gain up to three thousand calories a day this way.

One of the lead researchers on the study was Melissa Panger, who told the BBC that nut-cracking was far from easy.

Old tools

"The chimps have to use fairly large stones, up to about 15 kilogrammes," the George Washington University scientist said. "It's a very difficult task to do and it takes the chimpanzees about seven years to learn.

"It's not like cracking into a snack nut or an almond; they have to hit the nut hard enough to crack it. But if they hit it too hard, it obliterates the nut and they can't get at the kernel.

"The chimps have to learn to control the force of the stone and hit the nut just right."

Dr Panger said the hammer stones had to be of a certain size and shape. "Some of these hammers have been used so many times that they have deep pits, suggesting that they have been used for many generations, over and over again."

Local behaviour

Mothers teach their children to bang on nuts and some young chimps have been seen hitting nuts with smaller stones, going through the motions learned from their parent.

Around some of the tree-stumps, Dr Panger and colleagues found huge piles of nutshells and stone flakes, indicating that the same site has been used to crack nuts for over a century.

Although it has been known for many years that chimps and other animals do use tools, this is the first time that researchers have observed such complex learned behaviour.

Moreover, it is behaviour not found in chimps in other parts of Africa.

Improved tools

During their expedition to the Tai Forest last year, the scientists recovered 479 stone pieces, chips of granite, laterite, feldspar and quartz broken from the hammers.

Another lead researcher, Dr Julio Mercader, also from George Washington University, said the study could help us better understand the behaviour of human-like species from several million years ago.

"We do not say that [old hominid] sites look like our chimp sites. What we do say is some of the flakes we found in some of the pieces of shatter resemble those found at some of the technologically simplest [hominid] sites in East Africa," he said.

"The implication is that older hominids practised nut-cracking link the chimps."

It is likely our ancestors learned how to improve on what nature provides by making tools of different shapes and sizes - a trick which chimps have yet to master.