UCLA Dept. of Anthropology


Capuchin Traditions Project

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handsniffingSince 1997, a group of 10 researchers has been collaborating on a study of traditions in white-faced capuchin monkeys. We have concentrated our efforts on three behavioral domains: social conventions, foraging techniques, and interactions with members of other species. We have worked at 4 different research sites in Costa Rica, which are ecologically similar and close enough geographically that there is unlikely to be much genetic variation between sites. The map indicates the locations of the study groups and sites within Costa Rica. We have collectively observed these monkeys for over 19,000 hours over a 13-year period: this table gives some details on the database.

image: Sharon Kessler









Much of our work thus far has focused on social conventions: dyadic social behaviors or communicative behaviors that are unique to particular groups or cliques. We began this phase of the project by nominating various quirky social interactions or communicative signals that we had witnessed, soliciting data on these behaviors from the researchers at all sites, and subjecting them to a set of operational criteria that allowed us to classify a subset of the nominations as traditions.

What is a tradition?: We defined a tradition as "a behavioral practice that is relatively long-lasting and shared among members of a group, each new practitioner of the behavior relying to some extent upon social influence to learn to perform the behavior." We subjected candidate behaviors to the following criteria to determine whether they qualified as traditions:

  1. There must be intergroup variation in the behavior, such that it is common (i.e. seen at a rate of at least once/100 hours) in one or more group and absent in other groups that have been observed for at least 250 hours.
  2. The behavior must be observed to spread through a social network.
  3. The behavior must endure in the repertoire for at least a 6-month period.

Five behavior patterns were nominated as likely traditions: hand-sniffing, sucking of body parts (though this one did not meet criterion #2, perhaps due to the timing of our field seasons in relation to the onset of the tradition), and 3 kinds of games. This chart shows the distribution of each behavior pattern across the study groups.










Two basic variants of this behavior are observed: one in which the hand was cupped over the nose and mouth, and another in which the fingers were inserted in the nostrils. At Lomas Barbudal, it was quite common for the behavior to be mutual, with the two participants inserting their fingers in one another’s nostrils simultaneously. The hand-sniffers remain in this pose for several minutes at a time, sometimes swaying gently as they sniff. Observers often describe the facial expressions as "trance-like." In two groups (Cuajiniquil and Station Troop), handsniffing was often combined with finger-sucking behavior. This photo depicts the beta female (Squint) sniffing the alpha female's hand.

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eyeball pokingEyeball-Poking:

Since the publication of the original set of articles on capuchin social traditions, we have been documenting the spread of a new tradition in Pelon group – eyeball-poking. In this ritual, one participant inserts its finger in the other’s eyeball, slipping the finger deep between the eyelid and the bottom of the eyeball up to the first knuckle. As in handsniffing, the pair remains in this posture for up to several minutes, and often the one being poked in the eye inserts fingers in the partner’s nostrils or mouth during the eyeball-poking.

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suckingSucking of body parts:

In this behavior pattern, one individual inserts some body part of the partner (usually an ear, finger, or tail-tip) into its mouth and sucks on it for several minutes. Sometimes the behavior is mutual, especially with tail-sucking. As in hand-sniffing, the participants are relaxed, often grooming before the onset of the behavior, and a bit isolated from the rest of the group.

image: Sharon Kessler










Three behavior patterns were referred to as games, because they involved 2 roles and occurred in a relaxed social context, often stemming from slow-motion play wrestling, play biting or grooming of the mouth. In all of these games, one individual takes an object (finger, hair, or inanimate object) into his mouth and bites down hard enough that it is hard to extract. The partner tries to retrieve the object, sometimes using the other hand, feet and mouth to pry open the other’s mouth. When the object or body part has been retrieved, it is reinserted into a mouth, and the game is usually played for several more rounds. Sometimes the monkeys switch roles. Three basic variants were observed:

Finger-in-mouth game: This variant involves insertion of a finger into the partner’s mouth (either partner can be responsible for insertion of the finger). Sometimes this game starts in the context of grooming of the mouth or a “dental exam.” The biter usually bites down firmly enough that it is quite difficult to remove the finger, but not hard enough to draw blood. Sometimes this game is combined with elements of the finger-sucking behavior described elsewhere. This variant is observed only at Lomas Barbudal. The photo sequence alongside this page show Guapo biting the finger of a juvenile companion, who is trying to retrieve his finger.

Hair-in-mouth game: In this variant, one individual bites a large tuft of hair from the face or shoulders of the partner. The partner may flinch, but does not exhibit much pain. The partner then typically tries to pry open the mouth and retrieve the hair. The hair is passed with gentle force from mouth to mouth until most of it has fallen to the ground. Then one of the monkeys bites another tuft of hair from the partner so they can continue. The hair game is observed only at Lomas Barbudal.

Toy game: In this variant, an inanimate object (a stick, green fruit, leaf, or piece of bark) is passed from mouth to mouth in the same manner in which the hair or finger is transferred in the other games. No one consumes the toy at the end. This is the one game that is seen in multiple sites (Lomas Barbudal and Curú). This video clip (courtesy of Mary Baker) shows two males from Bette’s group in Curú, Bud and Angelo, playing the toy game (though the “toy” -- a piece of bark -- is very small and difficult to see in this clip). Angelo is soliciting the game, and Bud is trying to remove the bark from his mouth.

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UCLA Dept. of Anthropology - Susan Perry