Intro to Woolly Monkey Identification

Written by R. Ellis

When I first arrived at Tiputini Biodiversity Station, I was confronted with a daunting reality: I was responsible for being able to individually recognize all 80 or so monkeys we observe. Of course, I knew this information coming in, but l didn’t understand how much of a challenge it would prove to be until the first time we followed a group. A recurring thought kept running through my head:  all of these monkeys look exactly the same! Telling the males apart from the females was easy enough, but distinguishing between individuals of the same sex seemed utterly impossible. To compound my fears, that first group was G, our largest group, with about 30 individuals. Briefly, I wondered what I had gotten myself into.

Chromeo has a broken finger on his left hand that remains straight at all times, helping us identify him from other large males in surrounding groups

Chromeo has a broken finger on his right hand that remains straight at all times, helping us identify him from other large males in surrounding groups.

Fortunately, Kelsey had faith that learning all the individuals could be done, as she, along with her other field assistants, had achieved it the season prior. This gave me some respite, but I was still anxious that I would never be able to tell these monkeys apart.

Months later, I look back and smile at my self-doubt. Though it took quite a while, we can all confidently identify most of the members of our woolly groups, an impressive feat many other primatologists believed not possible.

So how do we do it? Though the notion might make some blush, the best way to tell our monkeys apart is actually by staring at their genitals.  Males have visible testicles that get larger and become covered in fur of varying thickness and color as they get older. Females have conspicuous clitorides that vary slightly in size, shape, and color. To the casual observer, these differences may seem minute, but through careful and conscious observation, they become beacons of differentiation to those of us who study them. Many a dinner conversation has slowly turned into a discussion (and sometimes a debate) about the features of a particular monkey’s genitals.

However, monkey balls alone aren’t always enough, and we’ve learned to pick up on other differences. Another helpful identifier with the females is which juvenile follows her. In many of our groups, there is only one juvenile per age/sex class. For example, Group D has only one very young female juvenile, one medium sized juvenile female, and one newborn male. So if we see a monkey carrying a newborn in that group, we know it must be Darlene carrying her baby, Dax, because no other monkey in that group has offspring that fits in that age/sex class. We also look for identifying genital characteristics in the juveniles.

We even use more subtle differences to aid in their identification, such as their build, the way they walk, and presence of defined crests or jowls. These features are great for distinguishing males from females when we can’t see their behinds, but we also use them to differentiate males from other males. With Group G, we have to put our powers of observation to the test. As mentioned above, they are our largest group, and there are several juveniles in the same age/sex class.  In addition to all of the above, we gather information on the tiniest of differences, such as how hair grows on their head, amount of chest shagginess, and weight. We strike gold when an individual has an easily recognizable feature such as a broken finger or a patch of fur missing. Some of our monkeys have even been fitted with radio collars with little charms that let us know who they are.

All these tiny differences seemed overwhelming at first, but through practice, we’ve become confident* in our identification skills. Knowing who our monkeys are allows us to have a much more intimate and, in my opinion, worthwhile relationship with them, seeing interactions in a way we never would have if we didn’t know who they were.

This is the backside of Chai. Her clitoris is very large and globular and often appears pale in color.

This is the backside of Chai. Her clitoris is very large and globular and often appears pale in color.

Cali's clitoris/labia on the other hand can appear long and flacid. Due to some darker pigmentation, her clitoris can sometimes look like a very droopy 8.

Cali’s clitoris/labia, on the other hand, can appear long and flacid. Due to some darker pigmentation, her clitoris can sometimes look like a very droopy 8.

*Of course, to make sure our confidence is appropriately placed, we collect multiple fecal samples from each monkey for DNA analysis.

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