An adult female capuchin monkey holds a palm nut that she has collected from the ground (see palm photo below).

Credit: E. Darvin and R. Silva, Univ. of São Paulo, Brazil

An adult capuchin monkey stands erect while pounding a palm nut on an anvil with a stone. Notice the very large stone he is holding.

Credit: Marino G. de Oliveira, Fundação BioBrasil

A capuchin monkey cracks a nut on an anvil using a very large stone.

Credit: Marino G. de Oliveira, Fundação BioBrasil

A young female capuchin monkey searches a small cavern in a cliff face, presumably looking for birds' eggs, nestlings or other edible prey.

Credit: Marino G. de Oliveira, Fundação BioBrasil

Dorothy Fragaszy counts the numerous depressions in a stone produced by the monkeys' hammering activities. The small white dots scattered on the surface of the stone are dried beans, each placed in a depression to aid an accurate count.

Credit: Marino G. de Oliveira, Fundação BioBrasil

Several species of palms in the study site produce nuts at ground level.

Credit: Elisabetta Visalberghi, CNR, Italy

Mara Fonseca de Oliveira, 13 years old, is a young Brazilian biologist in training. Here she is recording her observations of the monkeys' behavior as part of a study of the monkeys' development.

Credit: Elisabetta Visalberghi, CNR, Italy