Samplings: May 2009

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Bearded capuchin hammers open a nut.

Elizabetta Visalberghi

Come lunchtime, bearded capuchin monkeys place hard nuts on one stone and crack them open with another. That skill places them in the elite tool-using set among animals. The monkeys, it now seems, are quite deliberate in their work. New research shows that they carefully select the right “hammer” for the job, and carry it to an “anvil” some distance away, a habit until now known only in chimpanzees.

A team of primatologists led by Elisabetta Visalberghi, of the Institute of Cognitive Sciences and Technologies in Rome, tested wild bearded capuchins in the Brazilian forest. Along with nuts, they offered the monkeys two or three kinds of hammer stones—hard siltstone versus brittle sandstone, or heavy versus light quartzite, for example. The capuchins almost always picked one that was heavy and hard enough for nutcracking, then carried it and the nuts to an anvil a few feet away. When the researchers slyly presented different stones made to look alike, the monkeys handled them first to judge their usefulness.

What’s more, field observations suggest that to open softer food items, such as seeds or fruits, the monkeys choose lighter, easier-to-carry stones that are still hard enough to do the job. The behavior shows that capuchins can plan ahead for a task, Visalberghi and her team say.

Those feats of intelligence aren’t limited to one species. Another team of biologists recently reported hammer and anvil use in yellow-breasted capuchins. (Current Biology, Primates, American Journal of Primatology)