Primates using tools isn't exactly a new trick. Researchers have long observed apes using sticks to dip for ants, monkeys using mirrors to investigate their own bodies, and even chimpanzees using 'spears' when hunting. Now, however, researcher have found the first evidence that not only do monkeys crack nuts with rocks, but they use various and changing techniques to do it.
Animal behaviorists and investigating researchers have long known that bearded capuchin monkeys love their nuts. Showing off the ingenuity of old world primates, these little guys take hammer (rock) to anvil (a predestinated flat/hard surface) to crack their nuts. However, this process that researchers have long through was trial and error may actually be a developed practice, with strategy and technique exhibited by expert nut crackers in the Fazenda Boa Vista forest of northeast Brazil.
"Wild bearded capuchin monkeys dynamically modulate their strikes based on the outcome of the preceding strike while using stone hammers to crack nuts," Madhur Mangalam of the University of Georgia at Athens explained in a statement.
Mangalam and his colleagues recently videotaped 14 capuchin moneys cracking nuts. They carefully analyzed the tapes to determine the height and velocity of each and every stone strike, determining exactly what each monkey did to get to the soft tasty kernels within each nut. (Scroll to read on...)
The results were published in the journal PLOS One.
According to the researchers, they had expected the monkeys would likely apply the same amount of force each and every strike, or with increasing force, until there were nutty bits on the 'anvil.' Instead, they observed something quite different.
"It was a 'eureka' moment when we realized that the monkeys modulated the strikes systematically according to the condition of the nut following the preceding strike," Mangalam said.
This "finding opens our eyes to the fact that non-human primates modulate their actions with a tool to accommodate the rapidly changing requirements of the task, which is a cognitive accomplishment," he added. "Until now, this level of dexterity was not suspected of any monkey."
[Video citation: Fragaszy DM, Liu Q, Wright BW, Allen A, Brown CW, et al. (2013) Wild Bearded Capuchin Monkeys (Sapajus libidinosus) Strategically Place Nuts in a Stable Position during Nut-Cracking. PLoS ONE 8(2): e56182. doi:10.1371/journal.pone.0056182]
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