Bearded capuchin monkeys not only use stones as tools to crack open nuts, they also exploit tangible information like humans to increase their chances, scientists claim.
The monkeys deliberately place palm nuts in a stable position on a surface before trying to crack them open, revealing their capacity to use tactile information to improve tool use, researchers found.
The black-striped capuchin, Sapajus libidinosus, also known as the bearded capuchin, is a capuchin monkey from South America. It is the first non-ape primate where tool usage was documented in the wild.
Dorothy Fragaszy and colleagues from the University of Georgia analysed the monkeys' tool-use skills by videotaping adult monkeys cracking palm nuts on a surface they used frequently for the purpose.
They found that monkeys positioned the nuts flat side down more frequently than expected by random chance. When placing the nuts, the monkeys knocked the nuts on the surface a few times before releasing them, after which the nuts very rarely moved.
The researchers suggested that the monkeys may have learned to optimise this tool-use strategy by repeatedly knocking the nut to achieve the stable position prior to cracking it.
Scientists concluded in a statement that the monkeys' strategic placement of the nut reveals that the monkeys pay attention to the fit between the nut and the surface each time they place the nut, and adjust their actions accordingly.
In a parallel experiment, the scientists asked blindfolded people to perform the same action, positioning palm nuts on an anvil as if to crack them with a stone or hammer.
Like the monkeys, the human participants also followed tactile cues to place the nut flat-side down on the anvil.
The study was published in the journal PLOS ONE.
