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Tool use by wild monkeys

A male capuchin. Image courtesy of A. Moura.
Click here for a high resolution photograph.

Researchers have spotted wild capuchin monkeys using stones to dig up edible roots -- a type of tool use that hasn't been seen before in any other wild animals.

Capuchins are intelligent little monkeys that are sometimes kept as pets. In old stories and pictures, organ grinders often had capuchins that would pass a hat around for money while the organ grinder played. These days, the most popular capuchin may be Ross' pet monkey on the television show, Friends.

Researchers used to think that only humans used tools, but now they know that some other animals, like chimpanzees, do too. But typically chimps use sticks, for example, to poke into termite mounds. No one has reported seeing wild animals use stones for digging before, according to Science authors Antonio C. de A. Moura and Phyllis C. Lee of the University of Cambridge in Cambridge, U.K

Scientists know that capuchins use tools in captivity but have only occasionally observed them doing this in the wild. Moura and Lee watched capuchins in a region of northeastern Brazil known as the Caatinga dry forest. They saw the monkeys using tools almost daily to collect food.

The monkeys used rocks and sticks as tools for digging, for cracking seeds, hollow branches and tubers, and for probing tree holes or rock crevices. Digging was the most frequent type of tool use. The monkeys typically held a stone with one hand and hit the ground quickly several times while scooping away the soil with the other hand.

The researchers report their discovery in the 10 December issue of the journal, Science. They propose that the monkeys may only use tools under certain conditions, such as the long dry seasons of the Brazilian Caatinga, when food is relatively hard to find.


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