The findings, outlined in the journal Current Biology, document the earliest evidence for tool use by monkeys outside of Africa. Humans might have even first learned about cashew nuts from the industrious little primates.
"One of the ways that modern hunter gatherers gain information about the landscape is to observe the behavior of other animals -- alarm calls by monkeys can signal a predator threat that also affects humans, for example," lead author Michael Haslam, a senior research fellow in primate archaeology at the University of Oxford, told Discovery News.
"It's speculative," he added, "but noisy and prominent cashew processing by capuchin monkeys was unlikely to have been missed by ancient Brazilians."
The following three videos show the capuchins at work:
To establish the antiquity of capuchin cashew processing at the site -- Serra da Capivara National Park in northeast Brazil -- the researchers conducted an excavation that recovered many capuchin stone tools. Small pieces of charcoal found with the large tool cache were radiocarbon dated to at least 700 years ago. This means that the tools predate the arrival of Europeans in the New World.
|A capuchin cashew-processing stone covered with residue from the nuts.|
Senior author Tiago Falótico, a postdoctoral research fellow at the University of São Paulo Institute of Psychology, said, "Cashews nuts are not a primary food source, but capuchins have a great preference for it when it is present. Some of the individuals even discarded apparently good cashew apples just to eat the nut."
He continued, "We know that cashew nuts are very energetic and balanced across carbohydrates, fat, and protein, characteristics that makes cashew nuts a good food choice."
|Researchers Lydia Luncz and Tiago Falótico, who is standing under a cashew tree. Both are at the study site, Serra da Capivara National Park in northeast Brazil.|
Co-author Eduardo Ottoni, a professor in the Institute of Psychology at the University of São Paulo, explained that "robust" capuchins split off from slenderer built ones as they left the Amazon forest and reached the Atlantic forest.
"That involved crossing much drier areas where hard-shelled fruit was probably a key resource, hence their robust jaws," Ottoni said. "In such a context, stone-aided nut cracking was arguably very useful."
Capuchins do not just use tools to process cashews. Ottoni said that some select even heavier stones to bust open hard palm nuts in certain regions. The Serra da Capivara monkeys use different stones to dig plant roots and tubers.
They also use sticks as probes to dislodge prey -- mostly lizards -- from rock cracks. They use sticks to pull spiders out of their burrows and to collect honey. Each tool is carefully selected for size, weight and usefulness to the particular task.
Other monkeys, such as macaques, are also adept at using tools. Last year, for example, Amanda Tan from Nanyang Technological University and her team documented how macaques use one-handed hammering with the points of small tools to crack open oysters with precision at Piak Nam Yai and Thao Islands in Laem Son National Park, Thailand.
Read more at Discovery News