The capuchins appear to use noise to ward off potential predators

A scientist has observed capuchin monkeys banging stones together, apparently as a signalling device to ward off potential predators.

The researcher says the animals appear to be learning this skill from each other - and even teaching incomers to the group how it should be done.

The research is reported in the scientific journal Folia Primatologica.

Dr Antonio Moura from the University of Cambridge, UK carried out his work in the Serra da Capivara National Park, in the Piaui state of north-east Brazil.

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The use of stone technology in foraging for food is well known in non-human primates; monkeys will use rocks to crack open nuts.

Stone-banging could be a social tradition in the population studied

Antonio Moura

Dr Moura describes how the monkeys, as he approached several groups of them, would first search for a suitable loose stone, then hit it on a rock surface several times in an aggressive manner.

Only as they became more used to his visits over time did the stone-banging decrease.

Noisy lessons

The scientist said he saw adults and juveniles hitting the stones together without paying him any attention at all - suggesting that the younger monkeys were learning the skill from their elders.

What is more, captive monkeys released into the area to join the study animals appeared to learn to bang stones as well.

"Although banging objects is an innate behaviour in capuchin monkeys (Cebus apella libidinosus), in all wild groups observed so far it has been observed only in a foraging context," Dr Moura said.

"Stone-banging is a novel behavioural variant that is most likely learned socially. The absence of this display in other populations of capuchins, which have access to stones, suggests that stone-banging could be a social tradition in the population studied."