In this case Dr Moura could find no environmentally-inspired cause for the Capuchins acquiring this skill, suggesting that they had indeed learned it by observing and replicating one another.
"One of the most interesting things is that they make a noise to scare off predators," he said. "They would seem to be communicating the danger to one another at the same time.
"We already know that these monkey populations use stones as tools to dig holes or to forage and questions remain about why this happens in this area. Because it is quite dry and barren, it is possible they learn these skills from one another because they have to develop them quickly. To be sure we would need to research more."
As well as using the noise to deter predators, Dr Moura also reports that in many cases the act of stone-banging, which often took place on higher ground, dislodged other stones that could hit the predator below.
The main function of the act would appear to be that of a "loudspeaker", however. Partly, this is to advise the predator that it has been spotted. But Dr Moura also speculates that because the Capuchins spread out widely in the dry forested areas of north-east Brazil when they forage, the noise could be an alarm-call.
In addition, the use of stones provides biological anthropologists with a rare and highly-prized example of primates using stone technology, adding to the archaeological record of primate behaviour. Most items used by primates in cases where they may be exhibiting socially-learned skills are perishable.
The simple example of percussive stone technology uncovered by Dr Moura adds to other types of stone technology already known. For example, new world capuchin monkeys u
Contact: Tom Kirk
University of Cambridge