High capacity of chimpanzees for complex vocalizations

Chimpanzees have an exceptional ability to produce complex vocalizations. A team of scientists has identified nearly 400 distinct sequences, which describe an elaborate communication system in this primate, the closest to humans.

“They don’t speak, of course, if we take human language as a reference,” warns evolutionary biologist Cédric Girard-Buttoz, lead author of the study published Monday in Nature communications biology. But chimpanzees have an exceptional ability to combine a reduced range of cries, ‘twelve simple vocalizations’ according to the researcher, into at least 390 distinct sequences.

This sort of syntax, the meaning of which remains to be clarified, associates from two to ten cries. “We have some ideas about the meaning of certain sequences, one of which, for example, is exclusively linked to nesting and which has no connection with the meaning of the calls taken in isolation”, explains to AFP the CNRS researcher from the Institut des cognitive sciences Marc Jeannerod.

The team, some of whose members are also affiliated with the German Max Planck Institute for Evolutionary Anthropology, worked on the basis of nearly 5,000 recordings made with 46 wild adult chimpanzees in the Ivorian reserve of the Taï National Park.

‘Hou’

The twelve types of vocalizations in chimpanzees include the very common ‘hoo’, associated or not with a gasp, or even growling or barking. They are well known to specialists and their significance may vary with intensity. ‘The ‘hou’ linked to an alarm cry is stronger in tone than that which is linked to rest, softer,” says Mr. Girard-Buttoz. The ‘hoo’ linked to a gasp is used, for example, to identify individuals.

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Some animals have a richer ‘vocabulary’, species of monkeys having up to 38 types of calls. ‘We can consider the vocal repertoire of chimpanzees, which is innate, as limited’, remarks Mr. Girard-Buttoz, but the species, which has a very complex social life, may have found with the sequences a way of ‘ generate new meanings that expand their communication capacity.

The study showed that a third of the vocalizations were sequences combining several of the twelve calls, the whole range of which was used at one time or another. It also established a notion of order, with some calls always or almost always in the same position in a ‘bigram’, a sequence that associates two calls. Some bigrams are reused, perhaps as keywords, in longer sequences, with five or six other calls.

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