Grunting chimpanzees are talking language of lunch

Chimpanzees may not talk like humans, but they understand the language of lunch.

Researchers have found that chimps make different calls when given different kinds of food.

High grunts denote a highly prized treat, such as bread, and low grunts food of low value, such as apples.

Other chimps seem to know exactly what the calls mean.

When scientists played recordings of the noises to a chimpanzee at Edinburgh Zoo, he searched in the appropriate places for the food in question.

Researcher Katie Slocombe, from the University of St Andrews, said: "This is the first demonstration that chimpanzee calls function to refer to the nature of discovered food and these calls are meaningful to fellow animals. It shows that, by simply listening to each other's calls, chimpanzees can infer what kind of food the caller has found.

"Our focal animal adjusted his foraging behaviour on the basis of the calls he heard."

The scientists are planning further studies to test how specific the calls are - whether they refer to "bread" and "apples", or merely high and low value foods.

The calls are a demonstration of "functionally referential" signals given in response to specific events or objects, such as a particular predator or type of food.

Although a similar kind of communication has been found in monkey species, until now there has been no evidence of it in any of the great apes.

This is surprising given that apes are more advanced mentally than monkeys and more closely related to humans.

The scientists believe that the calls must have a social function since chimps rarely produce the same kind of rough grunts when eating alone.

Observations in the wild have shown that chimps only produce grunts when another individual approaches.

Dr Klaus Zuberbühler, who led the research, published in the journal Current Biology, said: "Chimps may find it genuinely unpleasant to eat without others doing the same.

"The same seems to be the case for humans. We don't like to eat in the presence of others who are not eating.

"In many cultures humans co-ordinate the timing of starting a meal, for example with vocal cues such as 'bon appetit'.

"These 'rough grunt' calls are specifically produced when chimpanzees find food.

"Subtle but consistent acoustic variation is present within this call type and this study indicates chimpanzees use this variation to indicate the presence of different foods. This study is special because it provides the first evidence that listening chimpanzees are sensitive to this variation. They seem to understand that the calls refer to the food encountered by the caller."