Our interest in social traditions began when a group of 10 capuchin researchers collaborated on a study of traditions in white-faced capuchin monkeys. We 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. This map indicates the locations of the research sites within Costa Rica. We have collectively observed these monkeys for nearly 70,000 hours over a 13-year period. Researchers involved in this cross-site collaborative project included Susan Perry, Linda Fedigan, Katharine Jack, Lisa Rose, Katharine Mackinnon, Mary Baker, Melissa Panger, Joe Manson, Julie Gros-Louis, and Kendra Pyle.
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:
- 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.
- The behavior must be observed to spread through a social network.
- The behavior must endure in the repertoire for at least a 6-month period.
Observed Traditions at Lomas Barbudal
Five behavior patterns were nominated as likely traditions: hand-sniffing, sucking of body parts, finger-in-mouth game, hair-in-mouth game, and toy game. The last three behavior patterns are referred to as games because they involved two roles and occurred in a relaxed social context, often stemming from slow-motion play wrestling, play biting, or grooming of the mouth. Another variant, eyeball poking, comes close to meeting the criteria. This chart shows the distribution of each behavior pattern across the study groups.
Sucking of body parts
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. This video clip shows two males from Flakes group at Lomas Barbudal playing the hair game. Adult male Napoleon has juvenile male Jade’s hair in his mouth, and Jade is trying to remove the hair from his mouth. When Jade starts to lose interest, Napoleon once again shows him the remaining hair.
Capuchin Monkey Rituals
One of the current research topics is the rituals that capuchins create, apparently for the purpose of testing their social bonds. These are variable in their content, but there is a fairly high degree of consistency in the way each pair of monkeys performs its ritual. Here are two examples of capuchin rituals:
In this first clip, immigrant adult males BL and QJ are passing a piece of bark back and forth, each gently but firmly attempting to retrieve the object from the other’s hand or mouth. This sort of ritual (with much mutual engagement and reciprocity in roles) is typical of this pair of monkeys. Because they were born outside the study area, we do not know their exact ages, but they appear to be the same age (within a year of one another); BL joined Flakes in September 2004, group 5.5 months after QJ joined. They started devising rituals together in May 2005, initially giving one another “dental exams” which involved inserting their fingers in one another’s mouths. In February 2006 they started using one another’s hair as an object to pass back and forth, and by March 2006 they were also using “toys” such as the bark used in this example. They were mutually enthusiastic practitioners of these rituals until BL emigrated in November 2009. At the time of this particular interaction, QJ is the 2nd ranked male and BL the 3rd-ranked male in the group.
In the second clip, we see Minstrel (‘MI’, the alpha female) and her maternal half-sister Mead (‘ME’, who is two years younger), performing a ritual that is highly typical of their relationship. Minstrel, on the left, is clutching Mead’s hand and inserting it in her (Minstrel’s) mouth. Mead reclines, passively accepting this. Minstrel readjusts Mead’s finger, inserting it deeper into her mouth on the other side, and then switches back to the original position. This is just one of multiple clips from this ritual, but the behaviors and lack of symmetry is fairly typical both of this bout and of the relationship more generally.
The research described on this site is based in part upon work supported by the National Science Foundation under grants No. SBR-9870429, SBR-0613226, BCS-0848360, BCS-1638428, BCS-1919649, several grants from the Leakey Foundation and National Geographic Society, and funding from the Templeton World Charity Foundation and Max Planck Institute. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or other funding agencies.
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