Erin Vogel

Biological Anthropologist and Behavioral Ecologist

Every night, an orangutan builds a new nest to sleep in. And each morning, shortly after waking up, s/he comes out of the nest and pees.

Imagine yourself standing under a tree, in the Indonesian part of the island of Borneo. An orangutan wakes up and prepares to release his morning urine. That’s part of why you are up so early: to catch that pee, so you can use it to learn about the orangutan’s health. But … how will you do that without making a wet, smelly mess?

This problem was an important one for Behavioral Ecologist Erin Vogel, orangutan expert. Read on to find out about how she and her colleagues solved it.

Orangutans spend a good deal of time alone or looking for food with their infants. Vogel and her colleagues follow orangutans for whole days, studying “how primates make a living in the forest.”

Erin’s parents probably weren’t surprised when she studied ornithology (“bird biology”) in college, went into behavioral ecology, and began observing birds and then capuchin monkeys, in Costa Rica. “My parents have told me that when I was a little girl, they used to take me to the Bronx zoo. I used to sit in front of all of the enclosures. I was just fascinated by the animals.”

This fascination continued as she got older:

In my senior year of high school, in my AP biology class, I had a teacher named Mrs Pasteur. One day, … a bee had gotten cut in half by the window, but it was still moving, and she pulled out its abdominal muscle [probably one of the thorax muscles which bees use to fly]. And it was still moving! I was fascinated by that — that it could still be triggering, even though the bee was clearly decapitated.

Vogel has a strong sense of curiosity … and a strong stomach.

“I don’t eat the bugs, no: I put my foot down there.” But Vogel does try most of the food items her orangutan subjects eat, from mangosteen-like fruits and rambutan (tropical fruits available at Trader Joe’s) to durian, which has such a strong smell that you cannot bring it on buses or airplanes in Indonesia. “I try all of the fruits they eat in the forest; the leaves as well.” One fruit (Genus Mezettia) has a very hard seed inside of it. Orangutans use their powerful jaws to crack it open and obtain the protein-rich seeds.

What food is available to wild orangutans? What do they eat? How healthy are they? These are some of the questions that drive the research Vogel does.

She and her colleagues estimate the number of fruits in each tree where their orangutans stop for a meal. “We use log [logarithm]-based categories (1-10; 11-100; 101-999 fruits; and so on) to estimate how much fruit is in the tree.” They also count how much fruit the orangutans eat. And they collect the different foods, dry them, and weigh 10-15 grams of each one. “Then we send these [samples] to a lab in Indonesia, where they look at the percentage of protein, fats, carbohydrates, and fiber in the food.”

Using those percentages and their observations about how much food the orangutans eat, the scientists calculate how much energy that amount of food produces. They can do this because they know that “You get about nine kilocalories per gram of fat.” “We can use these data to look at the relationship between energy coming in and the health of the animals themselves.

Orangutans “have a really diverse diet: they eat fruit that’s ripe and unripe, leaves, bark, insects, and all sorts of vegetation.” But their favorite food is fruit: when it’s available, fruit makes up 50-80% of their diet. “But there are periods when they only get four to 10% fruit.” This depends on the different seasons and the weather. “When it’s really dry, we get a lot of fires where I work; we think the smoke cover inhibits the trees from flowering and fruiting in the year after big fires.” This is “unique about these forests in Southeast Asia.” At times, the orangutans only manage to eat 300-500 calories a day. But when there’s plenty of fruit, their caloric intake might range from 1,000 to 4,000-5,000 and sometimes even 7,000 calories a day. Surprisingly, they spend about the same amount of time eating in these different seasons of more and less food. But when the fruit is scarce, orangutans spend their time “feeding on leaves, which give them much less energy back.”

If animal behavior sounds as fascinating to you as it does to us at Math4Science, you might want to check out some of the resources Vogel enjoyed when she was younger, from Jane Goodall’s books to David Attenborough’s BBC films to National Geographic magazine. Or the book by Robert Sapolsky that “opened up a whole new world” for Vogel, A Primate’s Memoir. Sapolsky “combined behavioral research with physiology and I thought that was a great way to find out how primates deal with their ecology.”

So, what about the pee? The scientists collect five to 10 milliliters of urine from each orangutan they watch, every day. They try to gather several samples in the morning, pipette the pee into one-milliliter vials, which they put in a solar freezer, and send them back to their lab at Rutgers University. Back in New Jersey, they analyze the urine to figure out how healthy the orangutans are. Hormones like cortisol, testosterone, and c-peptides of insulin tell them something about the stress the animals experience. Urea concentrations and nitrogen isotopes indicate protein balances. And cytokines tell them how well the primates’ immune systems are working. (Vogel explains that “when you cut your arm, there are certain cytokines you will produce.”)

Apparently her conversation with Math4Science was not the first one in which Vogel was asked many questions about … pee. “Everybody asks how we collect the urine.”

At first, they tried spreading large plastic sheets on the ground under the trees where the orangutans slept. “That got really messy and smelly because you’d have to carry the plastic sheet covered in pee” with you all day.

Next they took umbrellas, turned them upside down, and put them under the trees to catch the pee. But that turned out to be nearly as messy a method as the plastic sheets.

Finally, Vogel’s Indonesian assistants “took a small branch of a tree with a V-split at the end, so it was Y shaped.” They set up a plastic bag, held open by the branch, forming a “make-shift plastic basket.” Standing under the tree, they were now able to catch and contain the pee. “And then we only had to pipette the pee from the plastic bag into the collection vials in the forest.” Voila! Cleaner, happier scientists, able to study their orangutan subjects without getting too close for comfort.