Capuchin monkeys' complex behavior reveals their intelligence.
There's a good reason why a capuchin monkey was picked to play "Dexter" in "Night at the Museum;" they are some of the most curious and intelligent of the monkey species. Capuchins are New World primates known for their complex social relationships and traditions, large-sized brains, tool use and extensive cooperation.
White-faced Capuchins
Since 1997, Costa Rican white-faced capuchin monkeys, Cebus capucinus, have been under near-continuous observation by a group of researchers associated with the UCLA Department of Anthropology, as part of a "Capuchin Traditions Project." The group found the monkeys commonly engage in some quirky social interactions like eyeball-poking and hand-sniffing. In eyeball-poking, one monkey inserts a finger deep in the space between the eyelid and eyeball of another monkey, often leaving it there for several minutes. A version of hand-sniffing involves two monkeys simultaneously inserting their fingers in one another's nostrils, sometimes holding the pose for several minutes.
Brown Capuchins
Sarah Brosnan, biology Ph.D. candidate at Emory University, published a study in the science journal "Nature" demonstrating a highly developed sense of fairness in brown capuchin monkeys, Cebus apella. Pairs of female monkeys were willing to exchange a rock with each other and a researcher when rewarded equally for their efforts, but the minute the food rewards were distributed unequally, the brown capuchins reacted strongly. Some refused to participate in any more rock exchanges, others refused to eat their rewards and some tossed the food at the researchers.
Tufted Capuchins
According to the University of Wisconsin's Primate Info Net, tufted capuchins, Cebus apella, are attentive mothers. An infant's average birth weight is 7.4 oz. and, for the first 3 weeks of life, it clings to the mother while she suckles and grooms it. The mother carries the baby monkey everywhere for the first month, and feeds it for the first two months. For the first 8 to 12 weeks, the young monkey stays in constant contact with its mother, after which it is also tended to by other females in the tribe -- called "allomothering."
Brazilian Capuchins
Wild Brazilian capuchins, Cebus libidinosus, are adept tool-users, according to a 2004 study published in the "American Journal of Primatology." Lead researcher and University of Georgia psychologist Dorothy Fragaszy was the first to document an entire group of wild capuchins using stones to crack open palm nuts. Remarkably, some of the stones weighed nearly 9 lbs. -- one-third to one-half of their body weight. Before her study, only chimpanzees and captive capuchins had demonstrated this skill to humans.
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