In a forest reserve in the savannah-like "Cerrado" biome of Central Brazil, an amazing display of planning, learning, and sophisticated tool use has been documented in a species of New World monkeys. Wild capuchin monkeys (Cebus libidinosus)— a species familiar to many as organ grinders—move along the ground, methodically tapping palm nuts that are produced at ground level to see if they are ripe. Those that pass the test are carried up into trees, where their outer cases are removed and the exposed nuts are dropped on the ground for two or three days to dry.
Then, the aged palm nuts are collected and carried to a separate nut-cracking area. There, the monkeys climb up on top of flat rocks or boulders and, using large stones they have previously selected, they start pounding the hard-shelled nuts, with the stones being used as a hammer and the boulder as an anvil. After a few whacks, the shells are broken and the monkeys extract the kernels.
The entire process involves several days of testing, harvesting, transporting, and hammering and appears to be a planned activity—a part of the monkeys' culture—that takes place year-round.
This discovery, first reported in The American Journal of Primatology (December 2004) by a multinational research team led by Dorothy Fragaszy, a psychologist with the University of Georgia, is remarkable in that, up to that time, routine tool use in wild primates had been routinely ascribed only to chimpanzees and orangutans and, although there had been anecdotal reports of tool-using capuchins dating back to the sixteenth century, this was the first time such behavior had been scientifically documented.
Furthermore, although the stone hammers had not been fashioned in any way, their use to open encapsulated nuts is recognized as being a complex form of tool use. A number of factors (i.e., material, resistance, friability, shape, and weight) affect an object's suitability to open a hard-shelled nut, with weight being one of the most important. The heavier the object, the fewer strikes are required to crack open a nut.
Fragaszy and her colleagues originally estimated that the stone hammers weighed 16 ounces, but in a subsequent trip, they were found to weigh over two pounds. Given that adult capuchins weigh between 6-8 pounds, they were selecting—and lifting—stones a third and sometime half their own body weight.
The effective use of hammer and anvil is seen only in adults. Although juvenile capuchins are interested in the activity and often play with the procedure, they are not effective at it. It takes years of practice—and maturation—to become effective at cracking open palm nuts with the properly chosen stone.
If you would like to see a video of this extraordinary behavior, go to: http://www.youtube.com/watch?v=-G60UCeXFp0&feature=player_embedded. It's an excerpt from a BBC documentary entitled "Clever Monkey", narrated by Sir David Attenborough. In his closing remark, note his reference to these monkeys as being another intelligent species on Earth.
And if you would like to meet other animals that are known to use tools in the wild, go to: http://www.mnn.com/earth-matters/wilderness-resources/photos/15-remarkable-animals-that-use-tools/handymen