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

 

 

The Good and The Bad

There is a good side and a bad side to fieldwork. It is a game of trade-offs: is the good side enough to outweigh the bad? Is it worth it to endure the negative aspects of a field site to procure the positive? I’m not the first to admit that fieldwork is not just for anyone. Furthermore, having studied as a field biologist for four years and undertaking fieldwork in five different countries at multiple habitats and locations, I can tell you right away that fieldwork in the rainforest is perhaps the most strenuous of all. I will give you my perspective on the good and the bad of working in the jungle and you can judge for yourself if you would choose to endure. 

The Bad

            Let me begin with a story. My first day on Barro Colorado Island in Panama began quite well. I ventured off into the forest early in the morning with my graduate advisor to search for white-faced capuchin monkeys (my research species for the time being). My advisor insightfully pointed out the various fruits adorning the ground and explained which ones the monkeys eat. I was immediately intrigued by everything around me- the plants, the smells, the animals, the insects. We encountered the monkeys after only a couple hours in the forest and watched as they effortlessly brachiated through the trees and stared curiously down at us. It was a lovely hike and we returned for lunch.

This is where the atmosphere of the jungle shifted. I had the afternoon available and was ushered off into the jungle alone. Completely and utterly alone. In fact, I was the only person that went out at all that afternoon on the entire island. My advisor vaguely pointed out a trail on a creased map and after some confusion as to where I was supposed to find the trailhead (which consisted of me shuffling around awkwardly in circles for a few moments), I was off into el bosque!

A golden orb weaver spider, very similar to the one I found on my stomach

Almost immediately I encountered a troop of howler monkeys. One female and her infant attempted to lob a heavy branch in my direction, perhaps irritated by my presence. Ah well, I’ve had monkeys throw worse things at me before. So I continued on, clutching my map. For those who aren’t aware, I don’t have the best sense of direction. It didn’t help any that my map was worn and half of the trails were unmarked. Keep that in mind for later. As I’m confusedly staring at my map and marching along a steep, slippery trail, I run face first into a gigantic spider web. Not just any spider web, mind you, but a golden orb weaver’s web. The golden orb spider is known for weaving one of the largest and most intricate webs in the world, complete with a sticky anti-repellant substance. After peeling the cobwebs out of my eyelashes, I look down to discover that the spider was sitting directly on my stomach. Now this particular female spider, which was approximately the size of my hand, was not thrilled with her situation and, as such, she was raised up menacingly on her legs. Mass panic. So, my first reaction was to whimper and spin in perhaps fifty circles in the middle of the forest in an attempt to get her and the cobwebs off my body. This wasn’t the only time I found spiders or insects crawling on my body that day.

I continued on through the rainforest. It became more and more apparent as my distance increased from the research buildings that this trail has not been used or maintained for quite some time. More than once I lost the trail in the dense vegetation. At one point, the trail descended into an extensive ravine with a river winding through the base. A tropical storm event the week prior had caused several colossal emergent trees to fall into the chasm, obscuring the trail entirely. I slid down the muddy cliff and clambered up the opposite side around the tree calamity. But where was the trail… I searched and searched. Sunset was an hour away and the forest was already growing dark. Each patch of leaf litter mildly resembled a trail, but nothing was definitive. I eventually resorted to following the path of the river (and praying). With some divine providence, I found a trail cutting through the forest and fervently followed it for several kilometers until I recognized an area near camp. That was much worse than the spider. And to top off the experience, it began to rain, stirring up the molds and the pollens in the air so I sneezed repetitively. That day I learned that the forest can be hostile.

I’ve also discovered that the jungle can be invasive. The insects are particularly nasty. At the present, I have a lovely red necklace of mosquito bites. I am also the proud owner of a colony of chiggers that are currently munching away at the skin on my stomach. Chiggers are miniscule red arachnids (like ticks) that latch onto skin and utilize a chemical in their saliva to kill cells and then consume them. They are irritatingly impossible to remove because they are so infinitesimal. I consider chiggers to be preferable to the ticks, though. BCI is notorious for tick infestations during the dry season. Apparently there are “tick bombs” that house literally hundreds of ticks. If one such bomb detonates above you, you are showered with the arachnids. One guy here claims to have had over 110 burrowed ticks in his skin at one time. And there are bullet ants here: the bite of a bullet ant is said to be the most painful insect bite in the world, equivalent to being shot. There are also botflies in this particular section of forest. You know, those flies that lay eggs on your skin and then the larvae burrow underneath and eventually explode from your skin when mature. Or there are all the intestinal parasites you can contract. And let’s not get into tropical diseases.

The jungle can also be somewhat aggressive. You have to be exceedingly careful where you step and where you place your hands. Many of the palms are covered in slender spines that can stab right through your hand. Some of the fungi and plants are poisonous if touched. There is a vine called the fire vine which causes chemical burns when touched that leave permanent marks on your skin (most people here have scars). There are obscure holes in the forest floor that can cause you to fall or worse, break your ankle. The animals are not always friendly either. There are vipers with both hemotoxic and neurotoxic venom. The monkeys deliberately throw branches and other debris down if they want you to go away. When a gigantic branch lands a few inches from your foot, you realize how dangerous this can be.

Furthermore, this is a true wet tropical rainforest. The thunderstorms that occur here in Panama are unlike any I have ever experienced, including when my hometown in Boulder had a 1000-year flood. Yesterday, we got caught in a storm while watching the monkeys. First, the understory becomes very dark as clouds roll in. Then, there is a momentary delay as it begins to rain but the ground below stays dry. When the leaves above are eventually laden with water, it starts to pour and you feel like you are standing under a waterfall. In a matter of seconds my entire body was soaked and my boots were filled with water. The trees trembled with the deafening thunder and the trails became small rivers. It was sort of exhilarating, until we lost the monkeys and started to shiver from the sudden cold.

These are just some of the negative aspects of fieldwork in the jungle.

The Good

A white-faced capuchin male

            The good part of working in the rainforest is quite simply really. It’s when you catch yourself smiling as soft rays of sunlight embellish the leaf litter with golden hues. When you find flowers and fruits with colors so vibrant, you’re not sure if they are genuine. When you find a small frog cleverly disguised as a leaf sitting beside your boot. When you gaze up into the canopy at a family of monkeys cavorting along the branches. When you stop for a moment to listen to the rustles, chirps, hoots, croaks, twitters, and whispers that echo between the trees. When you see an extraordinary array of insects of every size, shape, color, and pattern. When you watch a colony of thousands of ants build a miniature kingdom with ordinary dirt. When you encounter an animal unexpectedly and have the opportunity to watch behavior you have never seen. When you look at the vast diversity of life all around you and realize what an incredibly complex ecosystem the jungle is. These moments seem to erase all the negative, making the forest both enchanting and invigorating. For me, the abundance of life in the tropical forest is enough to counteract the “bad.” Indeed, simply the opportunity to study primates in the wild is more than sufficient.

Geoffrey's tamarin monkey: these guys like to peer down at you and bounce around on the branches, squeaking hysterically

Tamarin

Male howler monkey with an albino tail

An anteater

Find the frog in this photo

Beautiful fungi

The Next Adventure: Panama and Barro Colorado Island (Capuchin Monkeys)

I consider the jungle to be louder at night. Well past sunset into total darkness, a cacophony of noises erupts, enveloping the forest in the calls and echoes of a million creatures. The high-frequency vibrations of insect wings persist at the top of the jungle chorus, piercing through the air until your ears ring. Bats echolocate to find prey, creating shrill vocalizations that harmonize with the buzzing insects. Then comes the dissonance of frog calls as each species bellows acrimonious notes to attract mates. Beneath the dominant sounds of the insects and bats and frogs, you can hear a thousand other noises. The heavy plunk of water droplets falling onto leaves. The rustle of leaves as coatis forage in the canopy. The chirp of a gecko. The staccato hoots of a monkey. Each animal call or movement contributes to a symphony of nature that reverberates incessantly throughout the night.

As I listen to this rainforest music through the screens on my windows, I’m sitting in a bedroom at the Smithsonian Tropical Research Institute on Barro Colorado Island. Termed BCI for short, this island sits in a large artificial lake at the center of the Panama Canal (Gatun Lake). Gatun Lake was formed during the building of the canal when the Chagres River was dammed in 1913. Consequently, the large hill that originally was connected to the greater forest became the largest island in the lake (BCI). Set aside in 1923 for research, this 1600-hectare island remains one of the best-preserved forests in the world and has been studied by rainforest scientists for over 90 years. I’ll be spending the next week at BCI, studying white-faced capuchin monkeys under the direction of my PhD advisor Dr. Meg Crofoot at UC Davis. 

Panama City (about half of it, the rest was hidden behind a tree)

Needless to say, these past couple days have been a whirlwind of introductions to Panama, Panama City, the Canal, and most of all the jungle. I knew very little about Panama City prior to entering this country. I spent a semester abroad in San Jose, Costa Rica and inadvertently assumed that Panama City would be quite similar to its neighboring country. Not so. The matrix of 12-lane freeways carving a labyrinth through profuse skyscrapers and the array of enormous ships in the harbor told me otherwise. Situated directly on the mouth of the most famous canal in the world, Panama City is rapidly booming. In part due to profits from the canal, in part due to illicit drug cartels. Anyways... despite the glittering buildings rising into the clouds, the city appears somewhat illogical. There are tin-roofed shacks crowded off to sides of the high-rise buildings. There are random jungle hillsides rising from portions of the city. There are hundreds of old military bunkers and buildings scattered throughout the city, remnants of the American influence on the canal. And if you look closely, half of the towering buildings are only partially built and appear abandoned. Regardless, Panama City presents an imposing metropolis welcoming in the thousands of ships using the canal.

The Panama Canal

I had a few hours in the city before heading to the island and the monkeys. We drove up a large forested hill on the city’s edge to overlook the view of the canal and the towering buildings. The canal was magnificent, with literally hundreds of ships hovering at the mouth to wait for their turn to cross. While I understand little of the engineering background, it certainly appears to be a marvel of technology and innovation. It cuts a deep scar through the center of the country, bridging the Pacific and Atlantic Oceans in less than 80 kilometers. My environmental conscience was pleased to see that the canal is flanked by large swaths of untouched forest on either side, both curtailing canal erosion and preserving the native landscape. The sprawling city with copious high-rise structures at the mouth of the canal was remarkable in a different way, considering that less than a million people reside there. All a part of global recognition, I suppose. 

The Bridge of the Americas- one of only two brides connecting the two sides of Panama

Panama City Panorama

A ship going through the canal

Ready to head towards the island, we drove along a road parallel to the canal towards the interior of the country. We passed some of the canal locks which were working to lift a massive cargo ship up above sea level to cross Gatun Lake. We left our car at a boating dock and took a small speed boat into the canal and across the lake towards BCI. 

As we rounded the shore of the island, saturated stumps—remnants of the forest that is now buried beneath the canal and lake—emerged from the thick, shimmering green water. The surviving forest on the island formed a thick wall of emerald foliage, tumbling into the water. We docked just below the research center buildings scattered up the hill and disappearing into the jungle. BCI reminds me of La Selva research station in Costa Rica, except the forest seems slightly wilder. I was left for a few moments before dinner at 6:30 in the dining hall. BCI is large enough of a research station to have an on-staff chef. There is little to do at night once the sun sets in the jungle and so once dinner was completed, I departed to my room where I sit now, listening to the forest come alive around me with the sounds of the night.

The view from my bedroom balcony