Tough Nuts
Joel Brown '80 finds serious science in observing the underground economy of urban squirrels.

Story by David Scott / Illustrations by Steve Breen

Joel Brown ’80 has crossed the globe to study animal behavior—jerboas in Israel’s Negev Desert, springbok in South Africa, sambar deer in Malaysia—but the métier of the man is something far less exotic. Brown is an expert in the ecological economics of the urban squirrel.

“I’ve worked with everything from snow leopards to black rhinoceroses,” he says of his 20 years of research in evolutionary ecology as a professor of biology at the University of Illinois at Chicago. “But just left to my own devices, I tend to gravitate toward rodents.”

He offers up one of those “what can I say?” smiles and adds, “I like rodents. That’s due to Bill Wirtz.”

Wirtz, a recently retired Pomona biology professor, taught Brown the finer points of handling ground squirrels when he hired the then-sophomore to help with summer work at the San Dimas Experimental Forest and the Bernard Field Station. After a couple of false starts in finding his major—Brown found the indoor labs of organic chemistry too confining and dress code of economics too preppy—he settled on biology and ecology.

Brown’s diverse academic interests coalesced in graduate school at the University of Arizona, where he began to use models more common to economics to assess animal behavior as an indicator of ecological systems. He determined that the population density of a species could be predicted by contingencies such as the prevalence of food or predators. Further, he could use the same information to predict behaviors, which in turn could help explain a species’ ecology.

An illustrative experiment Brown uses with his students involves mixing nuts into dirt to create a feeding patch. Students monitor the patch to chart the rate of the animals’ return as the seeds diminish. “The animals eventually reach a point where they’re not finding food fast enough and they give up,” Brown notes. “We refer to that as the giving-up density. We can go in and measure the seed dregs that are left and from that we can estimate the metabolic cost of foraging.”

That information can then be applied to other ecological and environmental factors. For instance, how attractive is a well-seeded food patch if it’s in an area rife with predators or far away from the safety of trees? “It’s like combat pay,” says Brown, drawing a timely parallel. “Like, how much would you have to pay you or me to take a night drive to the airport in Baghdad versus how much would you or I be willing to pay to go to Paris just to have a nice dinner outside of Notre Dame?”

Brown found his ecological economic indicator of choice circa 1987 when he came to work in Chicago, where perhaps only the disillusioned-but-faithful Cubs fans outnumber squirrels.

The furry little foragers also turned out to be a classroom boon. “Squirrels are real,” Brown says, noting that when he first started teaching at UIC he would give students examples from his own research in Libya or Kenya. He soon discovered, however, that students were not likely to relate to these “not-so real world” examples.

“When I started using the squirrels to illustrate examples, there was an unbelievable transformation in the pedagogy,” he notes. “I’d have students come back to class and say, ‘Remember how you said last lecture that the squirrels do this, this and this? Well, my dad says you’re wrong. Squirrels don’t do that.’ I’d think, ‘How cool! That means their dinner table conversation was about ecology!’ I discovered that as soon as I started using the squirrels, I was pointing out ecology right outside the classroom.”

Brown also found, not surprisingly, that squirrels captured the interest of more than just his students and their families. Chicagoans had a real affinity for the gray and red rodents who shared their backyards, alleyways, trees, power lines and campus quads. He decided to use these potential “citizen scientists” to track the distribution and abundance of Chicago’s two main species, the Eastern fox squirrel (Sciurus niger) and the Eastern gray squirrel (Sciurus carolinensis), and in 1997 helped create Project Squirrel—an idea based on the urban bird studies conducted by the Cornell University Lab of Ornithology. Squirrel watchers are encouraged to log onto www.uic.edu/labs/squirrel to chart their findings. More than a decade’s worth of data has allowed Brown and Project Squirrel to track shifts in squirrel populations and hone their findings on behavioral difference between the species (see the sidebar below).

An unexpected outcome of Project Squirrel is that it can offer as much insight into the observer as the observed. Brown likens that aspect of Project Squirrel to another Chicago institution by referring to it as “The Squirrel Oprah Winfrey Show.” Brown says he has heard everything from “‘I can’t believe there’s a Website devoted to this thing! People who love squirrels have a serious problem’ to ‘I spend $150 a week feeding squirrels because my mother survived invasion in the Ukraine by eating squirrels.’”

Brown’s subject matter and study techniques also have caught the imagination of the media. The Associated Press recently covered an experiment to analyze squirrels’ stockpiling behavior. To learn where and how their subjects stored food for the winter, Brown and his students glued strings to nuts. Then, to mark these “buried treasures” for later observation, they poked swizzle sticks in the ground. In a pilot study, Brown’s lab students “baited” 80 nuts with spools of thread and to their delight came back to discover what looked like a giant spider web. One intrepid hoarder had even managed to scurry across a very busy Chicago thoroughfare and hide his nut in a planter on the second floor of a parking garage.

The notion of impromptu squirrel string art has undeniable charm, but Brown sees it as just another method for measuring the animals’ behavior via an economic principle. He is fascinated by this act of “caching” and what it says about how the squirrel has evolved. “It’s the idea of squirrels having a futures market,” Brown says. “A squirrel has this nut in hand, and it has future value. The squirrel has a decision: ‘I can cache it, or I can eat it right now.’ What’s interesting, or course, is that the squirrel is making a choice.”

Of late, Brown’s lab has been looking deeper into this act of caching. “We suspect that squirrels are very much aware of their bank accounts—jokingly, their 401(k) equivalents,” Brown says, “and this in turn influences their behavior.” He and his students alternately raided or salted squirrels’ caches to see what would happen. “We made squirrels go from riches to rags and rags to riches, and they immediately begin to behave accordingly. It was like a movie,” Brown says. When squirrels win the nut lottery, they immediately became more cautious about protecting their wealth and won’t take big risks in finding new food. When squirrels find themselves newly poor, Brown notes they show much greater interest in food for the future “so they’re not living from paycheck to paycheck anymore.”

The squirrels also adapt their behaviors in reaction to being observed. Brown tells how one graduate student had to stop raiding caches when a squirrel wised up to the swizzle sticks and got more than a little fussy, nipping the student on the rear. The team also has observed how squirrels modify their caching if they suspect there’s a rival (even a friendly grad student) nearby. “They will pretend to dig a divot, pretend to bury a nut—they fake it—and then go off and dig another divot. They will make up to five fake caches before they’ll actually bury it,” Brown says, also noting that the wily squirrels can effectively fake out their human observers 90 percent of the time.

Squirrel behavior can affect the actions of humans as well. Brown is delighted that Project Squirrel and his work have the power to turn nature lovers into full-fledged ecologists. Sara Emerson, a Ph.D. candidate in biology at UIC, came to Chicago from California with a B.A. in psychology from Humboldt State as well as “a desire for adventure without clear direction.” She found the project to be so much fun that she applied to Brown’s program and began her Ph.D. studying foraging of fox squirrels. “Any number of scientific principles can be tested with squirrels and then extrapolated to other, harder-to-study animals,” she says. For Emerson, that next step involved studying the ecology and coexistence of samango and vervet monkeys in the Soutpansberg Mountains of South Africa.

Emerson’s story gets at the heart of Brown’s educational agenda. He’s proud that many of his students have gone on to use his principles of ecology and economics to study population densities and animal behavior around the world and that the foraging habits of gray squirrels on a campus quad south of the Chicago Loop have had impact far beyond their habitat. To that end, he offers the following tidbit about a “bizarre cosmic connection—totally coincidental.”

“Chicago has a really nice mix of Eastern fox squirrels and Eastern gray squirrels,” he explains, “so right here on UIC’s campus we have two species of tree squirrels. I now have the pleasure of knowing that Pomona College has the same mix right on its campus, and they likely distribute themselves on campus according to exactly the same rules as they do in Chicago.”

How does he know? Last spring, he returned to visit Pomona and, of course, he just had to take the time to watch the squirrels at work and play on Marston Quad.

Secrets of the Urban Squirrel
Data, schmata … in the time of TMZ titillation, inquiring minds want the “dirt” that Joel Brown and Project Squirrel can dish on our wild little friends. Well, turns out most cities host turf wars between fox and gray squirrels. Says Brown: “Gray squirrels seem like city folks. Fox squirrels seem more like country folk,” which is to say that the smarter-but-more-contemplative gray is likely to be seen hanging out on a college campus where food is plentiful and students eat pizza, not rodent ratatouille. Fox squirrels, on the other hand, survive on instinct and are more likely to be found in areas prone to predatory attacks from pit bulls, rottweilers or even coyotes.

The distinction is true of their temperaments as well. “Gray squirrels are better at managing their competitive environment," says Brown. “Fox squirrels are better at managing their fear environment. Fox squirrels are in-your-face with some predators. They will scream at dogs. They will climb up trees and scream at a redtail hawk.” Brown further observes, “I’ve seen gray squirrels stand back while fox squirrels are being fed by somebody. The fox squirrel will bury the peanut and run off to get another one. The gray squirrel just comes over and steals the buried peanut.”

Given their penchants for futures speculation and nut savings accounts, how would Brown typify squirrels as socio-political animals? “They vote Libertarian,” he says. “It’s basically every squirrel for itself.”

When it comes to the urban squirrel as party animal, it’s all about season and location. Brown says, “The squirrels tell us there’s nothing more fun than being a summertime squirrel in the city, probably because garbage cans are overflowing and people eat outside.” He likens it to the Roaring ’20s … until winter hits. “It’s a great party, but the hangover’s horrible.” Savvy squirrel revelers know that a nature preserve like Chicago’s Morton Arboretum is the place to be come first snowfall, thanks to nature’s swag bags filled with acorns and such. Come summer, however, Brown likens the squirrel social life at the arboretum to something akin to a Temperance Society.

But enough about cribs, acorn 401(k)s and social scenes. Let’s talk squirrel hanky-panky. Do fox squirrels and gray squirrels interbreed? “Ah, we would love to know that!” says Brown. “That’s one of the reasons why, whenever we get a chance, we try to collect a little blood sample from what we call the FLSes—funny looking squirrels. There is reported interspecies courting behavior.”

Brown also notes that urban grays will co-den as a way to combat the cold Chicago winters while fox squirrels would never do such a thing. But get this: There are reports of gray squirrels denning with fox squirrels. “I don’t think a fox squirrel has it in him to say, ‘Okay maybe during the day I have to watch you so you don’t steal my food, but maybe at night it’s okay to pile in with you to stay warm,’” says Brown. “If you see a gray squirrel denning with a fox squirrel, you can be sure it was the gray squirrel’s idea.”