There are three main species of monkeys in the areas of Costa Rica we visited and two of them don’t appear to be particularly wary of humans. The one we saw most frequently was the white-headed capuchin (cebus capucinus). These guys hang around the beaches in Manuel Antonio National Park and entertain tourists with their antics (which often involve trying to steal food and which, no doubt, explains the park’s strict policy of allowing no food other than pre-made sandwiches and peeled fruit through the gates).
For the technically inclined...