Capuchin monkeys are renowned tool users 鈥� they famously wield hammers and anvils to crack nuts 鈥� but the newest addition to their arsenal combines ingenuity with a certain bravado.
Quite by chance the monkeys have been spotted using an improvised shovel to steal eggs from caiman nests in the Amazon rainforests of the Mamirau谩 Sustainable Development Reserve in Brazil.
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The monkeys grab a long stout stick and then dig away at the caiman鈥檚 nest mound, flicking the rotting vegetation aside until they reach the eggs.
The monkeys then pick up one egg at a time, carry it away to the relative safety of a nearby tree, eat it and then come back for more.
It鈥檚 a risky strategy. The metre-high nest mounds are often guarded by the mother caimans, who only leave occasionally to feed. 鈥淛aguars also visit those nests,鈥� says at the University of Sao Paulo, Brazil. 鈥淢amirau谩鈥檚 capuchins must really love eggs.鈥�
At around 140 grams each, the energy-rich eggs come in clutches of 30 to 60, so seem to be worth the risk. The monkeys may even be stacking the odds in their favour.
鈥淭he capuchins probably dig the nests when the mother is away because we haven鈥檛 registered any attack by caiman mothers on them. And they defend their nests really vigorously,鈥� says Kelly Torralvo, a herpelogist at the Mamirau谩 Institute in central Amazonia.
Along with Rafael Rabelo, a primatologist at the institute, Torralvo presented the chance discovery at the that ran from 9 to 13 November in Manaus.
鈥淥ur study was designed to look at nests not monkeys,鈥� says Rabelo. 鈥淲e have three years of data from camera traps monitoring 61 caiman nests in forests along the Rio Solim玫es. But this is the first time we鈥檝e seen this digging behaviour.鈥�
Sometimes the capuchins dug the nests out with their hands. Even without the tool use its pretty impressive, says Rabelo. 鈥淭he nests are large, the eggs are buried deep and those mothers are really aggressive.鈥�
It鈥檚 not clear how new the behaviour is. 鈥淚t probably been there for a while,鈥� says Rabello.
The biologists now plan a new study to look specifically for this behaviour around nests across the 11,000 square kilometre reserve. 鈥淚f we find it at several sites, then it鈥檚 clearly well established,鈥� he adds.
While individual caiman nests may be raided, the population overall is unlikely to suffer.
鈥淢amiraua has one of the highest caiman densities in South America,鈥� says Torralvo. 鈥淭he monkeys might get some, but that鈥檚 not even going to dent the population.鈥�
鈥淭hese exciting observations confirm that capuchin monkeys, wherever they live, are opportunists of the first order,鈥� says at the University of Georgia, who studies nut-cracking capuchins in eastern Brazil鈥檚 dry caatinga forests. 鈥淐learly, they still have much to teach us about what an opportunistic omnivorous primate, with active hands and curious mindset, can find to eat.鈥�
鈥淓lsewhere capuchins use sticks to fish for termites and smash and ,鈥� says Izar. 鈥淎nd on the Amazon forest floor clearly there are plenty of wood pieces.鈥�
Read more: Tools maketh the monkey
(Images: Instituto Mamirau谩)
