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The Squirrels Next Door

Student scientists study human impact on urban wildlife

They swipe your stuff, leave food everywhere, chatter incessantly — and if you give them the opportunity, they’ll walk all over you.

Bad freshman year roommates? Close.

For Suffolk University students, the Boston Common is like an extension of campus, an enormous quad stretching out between their classrooms and dorms. Right next door is the Boston Public Garden, home of the famous swan boats, Make Way for Ducklings statues, towering trees, and hundreds of noisy neighbors: a thriving population of gray squirrels.

Just how much does city life — from tourists and food trucks to barking dogs and busy streets — affect these bushy-tailed Bostonians? A group of Suffolk biology students braved rain, snow, and stolen snacks to find out.

Mutual curiosity

During the first day of fieldwork in the Boston Public Garden for his ecology course, biology major Majeed Ghazi felt a strange sensation.

“I was just watching the squirrels, taking notes, and I felt one climbing me! It happened right from the beginning,” he says.

Another ripped a pencil out of classmate Nicoleen Boyle’s hands as she recorded her observations.

The Garden’s squirrels are so accustomed to people — and the food they often bring — that many have lost their natural diffidence. In order to maintain a scientific detachment, students developed a protocol for brushing the more curious critters off of each other. They also learned to avoid eating during observation.

“I took out a granola bar once,” says biology major Ixchel Lopez. “The squirrels recognized the wrapper sound and came running.”

Clips from the Field

Videos by student Christine Vlahos

The ideal environment

Most of Professor Lauren Nolfo-Clements’ small-mammal research takes place during the summer on Boston’s more remote Harbor Islands, where she and a few hardcore students don boots and waders and spend long steamy days handling rodents and brushing off ticks. It’s a far cry from the manicured lawns and tulip-bordered walking paths of the city’s iconic park.

Established in 1837, the Boston Public Garden was the nation’s first public botanical garden. It includes plants and trees from all over the world — each tree meticulously labeled, from the Japanese larch to the California redwood.

“The Public Garden is a dream ‘introduction to fieldwork’ site,” says Nolfo-Clements, whose ecology class took on the squirrel research project. “Trees are easy to classify and return to; the squirrel population is booming; and there’s great visibility for animal and human behavior.”

The urban fieldwork assignment allows students to explore an entire ecosystem that most people never even consider, and it’s steps away from campus.

“I never thought about the squirrels and what they do,” says Lopez, Class of 2019. “I’d never noticed their nests. I’d never even noticed all the labels on the trees in the Public Garden.”

In January, Lopez and 39 other ecology students started gathering weekly observations about the squirrels, their habitat — and the human impact on both.

White SquirrelPhoto by student Christine Vlahos

The White Squirrel

The Boston Public Garden’s most famous rodent resident is the white squirrel. He’s not an albino, explains Nolfo-Clements, but a genetic variation makes his fur very light in color. According to student observations, the white squirrel – who is regularly approached by curious humans – is more fearful of people and seems to weigh less than other squirrels. Although his coloring makes him popular, it also makes him a more obvious target for predators and prevents him from retaining as much heat as the darker squirrels in cold weather.

Human impact

As students observed visitors feeding the squirrels, they noticed that other squirrels would gather around and watch, learning the behavior from their braver counterparts.

Despite that conditioning, Lopez estimates that for every squirrel begging there are three or four looking for food on their own.

Ghazi agrees, noting that he’s observed most squirrels foraging for food. “They might take a peanut from a tourist,” he says, “but then they bury it like normal squirrels would.”

That’s a good thing, says Boyle, a class of 2019 biology major and big data minor who hopes to go on to earn a master’s degree in epidemiology.

“I feel protective toward the squirrels,” says Boyle. “I feel defensive when people are feeding them because they’re getting fat, and that makes them bigger and easier targets for predators like cats and hawks.”

By the numbers

40

student scientists

18-20

hours of fieldwork each

24

acres of land in the Boston Public Garden

200

squirrels in the Public Garden (approximately!)

230

trees of usable size for climbing and nesting

100-200

calories burned by each squirrel every day, more if they’re very active or the weather is cold

4%

of squirrel time spent begging vs. 27% foraging in grassy areas and 15% digging

Open-ended assignment

“This course was very independent and student-led. We were sent out with a notebook, not a set protocol. We had the freedom to develop questions and be in charge of our research in a way I haven’t been before in a classroom or lab,” says Boyle.

One of the questions that Boyle’s group explored was whether the squirrels choose their habitats based more on human interaction or on ecological factors like access to trees that produce more food or offer better shelter.

“We found it’s an even mix,” she says. “Humans represent a reliable food source but also a potential danger from kids and dogs.”

Willow trees near the pond were the most popular habitat, Boyle found. They’re easy to hollow out, easy to climb, and attract many regular visitors who feed the squirrels consistently.

Boyle’s team reasoned that space, rather than food, is the limiting factor in how many squirrels inhabit the Public Garden. Man-made barriers — busy streets, clusters of houses — make venturing to nearby green spaces like the Charles River dangerous.

Lopez and Ghazi focused on communication among the squirrels.

“Squirrels play a lot, but not on the trees where they live,” says Ghazi. “They use a lot of vocal communication. They bark, yell, and they use tail movements, too, especially when they’re scared by loud trucks, sports cars, or aggressive dogs. When they’re frightened they yell and jump in and out of trees.”

Nolfo-Clements will continue the research with students in coming years. Though permission through Boston Parks & Recreation and the university’s animal care and use policies prevent her and her students from tagging or marking the squirrels, she hopes to eventually gain permission for genetic testing through hair sampling.

For now, they’ve learned to keep track of individuals based on their colors and the shapes of their tails, says Lopez. They’ve even named some — and she can point out Eli, Marcus, Scott, and Red as she walks through the park.

Boyle identifies her subjects by their homes:

“One tree is very syrupy, so we can always spot the squirrels that live there by their messy fur,” she says.

In or out?

Gray squirrels don’t hibernate. That made it possible to study them through the snowy winter and often-bitter rains of early spring. For Baghdad native Ghazi, the conditions were challenging at first.

“It was hard to write notes with gloves on, and our phones would stop working in the cold,” he says.

But after a while, Ghazi and Lopez, who hails from Cancun, adapted. Some students even embraced the winter wonderland.

“The cold was fun,” says Boyle. “It was peaceful in the snow, spending silent hours observing. You don’t get that often in the middle of the city.”

The most important takeaway for the students wasn’t about the squirrels’ biology or behavior, but about their own futures as scientists.

“It’s important to find out whether you’re an indoor or outdoor scientist while you’re still in school and can explore different fields. Fieldwork isn’t for everyone. It can be messy and unglamorous,” says Nolfo-Clements.

“I’ve worked in labs before and it’s easier. It’s predictable. Working in the field has taught me that things go wrong. You have to modify your plans and be flexible,” says Boyle.

Lopez wants to pursue a career in medicine or nutrition. Before taking the ecology course, she never thought about doing fieldwork. Now she knows she loves working outdoors, which could open up new potential scientific careers.

Ghazi discovered that he feels the same.

“I took biology in high school but never had fun with it,” he says. “Being exposed to fieldwork was eye-opening. When you work directly with nature you gain more respect.”

–Andrea Gimler