Response to neighbors and strangers by capuchin monkeys (Cebus apella)

Capuchin monkeys in the laboratory were observed when another monkey was introduced to their group. The introduced monkey was either from a hostile neighboring group; from a completely strange group, or from the host group. Attacks were directed primarily toward strange males but were rare. The results were discussed in terms of the neighbor effect, mere exposure theory, and species differences in responses to strangers.