Studying the White-Faced Capuchins

a howler monkey

Studying a species of new world primate has proven to be greatly different than the African primates I am accustomed to (namely, gorillas and baboons). To start with, white-faced capuchin monkeys are arboreal monkeys that spend their days in the mid-level forest or high in the canopy. This makes this species, by default, more challenging to locate, track, and study. Of the week I have spent researching the capuchins on Barro Colorado Island in Panama, two entire days consisted of wandering the forest perpetually for hours without ever encountering the capuchins. On the other hand, we chance upon troops of howler monkeys just about every half hour. If the howlers weren’t so resolutely lazy, I would switch to that species. This is not to complain, fieldwork in the African jungle can be infinitely worse, and I still enjoy the rainforest, with or without capuchin monkeys.

a large capuchin male threatening me

         To find these monkeys, myself and Lucia (my advisor’s wonderful Nicaraguan field assistant) walk gently through the forest paths that dissect the home range of several monkey groups. We stop occasionally to listen to the abundant noises pulsating around us. Capuchin monkey movement in the trees makes a distinctive crashing sound. And typically the infants in a group make piercing little screams that are unmistakable. However, during the heat of the day when the monkeys are resting, you can walk right by them without any clue of their presence. Once you’ve found a group of capuchins, it takes just as much effort not to lose them. Lucia and I will go dashing off of the designated path directly into the dense understory. Sometimes, she will go one direction and I will go the opposite. We use a system of hoots to communicate our locations since you cannot see after about 2 meters in front of you. This week has been exceptionally arduous, for the only monkey groups we have contacted have been groups that are relatively un-habituated. This means upon seeing us, the monkeys have a tendency to go hurtling off in the other direction, barking alarm calls and sneering threats towards us. Meanwhile, us terrestrial humans have to stumble clumsily through the thicket of lianas, cobwebs, ant nests, and menacing spiny vines while craning our necks at ludicrous angles to track the monkey group. The larger males and juveniles sometimes have momentary audacity, and climb into a position directly above our heads to slam down branches and throw seeds at our skulls. Or they will shake vines in front of our faces and open their mouths in a clown-like frown, bobbing their heads back and forth. It’s actually quite hysterical, especially when several of them line up and squish all their heads together to threaten us. It’s no wonder why my advisor calls these guys “devil’s spawn.”

capuchin lying on the branch to relax

            When they are more comfortable with our presence in the forest, the monkeys are endlessly entertaining. When eating, they make soft ooo-ing contact calls back and forth. It’s perhaps the most adorable sound I’ve ever heard a monkey make. In the middle of eating, sometimes the monkey will flop down on a branch, legs and arms dangling and swinging effortlessly. Occasionally, another monkey will come up and the pair will snuggle up together. Intermittently, some of the monkeys will climb to the forest floor to eat insects or wrestle. While they are not nearly as social as the baboons I have studied, they still like to groom each other often. And the males are much more social with the infants, even carrying them around from tree to tree. 

grooming capuchins

            With the habituated groups, Lucia collects basic data on behavior. This first requires full identification of all the monkeys in a group. While I used noseprints to distinguish gorillas, and tails and ears for baboons, identifying capuchin monkey individuals consists of looking at the eyebrows and forehead hairlines. Then, 10-minute long focal samples are collected on each of the monkeys, focused on rudimentary behavior such as feeding, locomoting, and sociality. It’s much less in depth as my studies of the baboons, but still yields an excellent basis for behavioral allocation. Certain behaviors are recorded on an all-occurrence basis, such as intergroup interactions, grooming, and copulations. The current project with the capuchins is centered upon collective decision-making. For instance, what or who determines where a troop goes in the forest or what they eat? During intergroup (between different groups) encounters, how are decisions made and who initiates them? My advisor and a team are planning to collar several monkeys in different groups next week to enhance the tracking ability of the primates and facilitate better data collection.

While I have not yet decided if this will be the species I focus my Ph.D. on, they have proven to be both challenging and exhilarating. That is perhaps what I love most about studying primates. It is an unpredictable field, yet it is one that can be greatly rewarding.

To give those who are interested in knowing a little more information about white-faced capuchin monkey life history and ecology: they are a diurnal species of primate that live in tropical wet and dry forests ranging from Belize to Northwest Colombia and Ecuador. They are distinguished by their black bodies and white face and shoulders. They also have a semi-prehensile tail that coils into a spiral when not in use. They have one of the largest brain to body size ratios of any primate, indicating a high intelligence level. Capuchin adolescents mature around 5-6 years of age and mature females have an infant about every 2.2 years. Males disperse at the time of maturity to find new groups, while females remain in their natal troop. Capuchins live in patriarchal units that average around 10 individuals, typically one or two large adult males, several adult females, and several sub adults and juveniles. Both sexes have linear hierarchies of dominance, with the alpha male being dominant to the top-ranking female. These monkeys are omnivores, with diets that are selective for fruits and insects. They are highly territorial in their home range, making intergroup interactions highly interesting. They are very curious individuals, and have been seen grooming other species of monkey and traveling with peccaries and coatis. Some monkey groups have been shown to use tools to crack open seeds or clams, another sign of their increased intelligence level. 

infant capuchin

two capuchins threatening with their heads together