Flying Squirrels? NYC’s Got ‘Em

Late last fall, I installed a bird feeder (okay, two bird feeders) on my fire escape. I had moved into an apartment in Washington Heights perched next to a rocky slope covered in trees, which looked like decent wildlife habitat—undeveloped and inaccessible to pedestrians, if somewhat neglected and trash-strewn. I put up the bird feeders expecting to see, well, birds.

But a few days later, in the middle of the night, I heard a loud metallic thwang, followed by another. I rushed to the window to discover…bats? Rats? A bizarre hybrid of the two? It took me a moment to realize that it was southern flying squirrels that were munching away at the suet and birdseed I'd set out. The next night, when another flying squirrel glided to the fire escape, I was ready with a headlamp and a camera.

New Yorkers know squirrels, at least we think we do—they're gray, with big bushy tails, and have an affable if mischievous presence in parks and backyards around the city. (I once watched one steal a sandwich, foil and all, from a woman's purse in Madison Square Park.) But eastern gray squirrels aren't the only squirrels in town. In the last vestiges of New York City's old growth forests, flying squirrels still glide through the canopy at night.

Until they started visiting my fire escape, I had counted southern flying squirrels among the animals that I was unlikely to ever see in the city. They're nocturnal, for one, spending the daylight hours nestled into cavities high up in trees. When they are active, they spend a good deal of their time in the upper forest canopy. They're also small, about half the size of their larger gray cousins. 

And then there's the fact that the forests they prefer—old woodlands with lots of dead trees—have been virtually eliminated from the city over the last 350 years. But there's still some good flying squirrel habitat left, most of which is under the jurisdiction of the Parks Department and protected from further development. Manhattan's Inwood Hill Park and Alley Pond Park in Queens has some, as does the New York Botanical Garden and Van Cortlandt Park in the Bronx and a few of Staten Island's larger green spaces. 

I'd always assumed that if I did see a flying squirrel, it would be a brief encounter, a shadow passing between branches after sundown. I'd tried to look for them a few times, squinting up at the tops of trees at dusk, but I never had any luck. Now, suddenly, they were eating sunflower seeds on my fire escape.

"They're probably pretty common, but we just don't know," said Jason Munshi-South, a biologist who studies urban wildlife at Fordham University, with an emphasis on rodents. "We don't see them, because we're not out at night as much. They're kind of this hidden biodiversity in the city."

The southern flying squirrel is one of four squirrel species that can be found in New York City (the other three are the aforementioned eastern gray squirrel, the eastern chipmunk, and, surprisingly, the groundhog). "Flying" is a bit of a misnomer—southern flying squirrels glide on their patagia, membranous flaps that connect their fore and hind legs and keep them aloft. These squirrels make tricky research subjects, but Munshi-South has had the opportunity to observe them a few times over the years. Ten years ago, a group of southern flying squirrels began appearing at one of his camera traps in the Bronx and putting on a show.

"They kind of launch themselves off a tree trunk," he said.

He hadn't been looking for them; their relative obscurity means that there are only a few southern flying squirrel specialists in the country. Even for a mammalogist focusing on rodents in flying squirrel territory, a sighting like that is relatively rare. And the scientists who do study them are still making discoveries. As recently as 2019, a researcher in Wisconsin discovered that the southern flying squirrel glows neon pink under ultraviolet light, an adaptation that they think might help them evade owls, or perhaps attract mates. 

If eastern gray squirrels are right at home in an urban environment, stealing sandwiches and climbing power lines, southern flying squirrels are probably a little less comfortable with the enormous footprint of the human city. "The extent to which they're using street trees is hard to know, but they're probably not going to be blocks away from the forest," Munshi-South said. While it's unlikely that you'll see a flying squirrel in Midtown, they manage to get by here, nesting in tree cavities and sometimes even gaps in the roofs of buildings.

But these rodents face increasing challenges in New York's crowded natural spaces. While the last swathes of old growth forest are mostly protected, New York City's southern flying squirrels are up against a serious nest shortage. The cavities they need in those woodlands—small, squirrel-sized holes—are in high demand here, due in large part to competition from invasive birds such as European starlings and house sparrows, which thrive in the city. Like many New Yorkers, flying squirrels cope with a tight housing market by taking on roommates. More social than other squirrel species, they're willing to pack together into nests, sharing the precious real estate during cold winters.

And they're adaptable, a necessity for any New Yorker. Behavioral plasticity—the ability to adjust behavior to accommodate environmental changes—is a trait of highly successful urban animals, from gulls to raccoons to rats. While flying squirrels can't exactly hang up their patagia and give up their canopy-soaring ways, their varied diet might help them get by in a place like New York. "We think of squirrels as seed eaters, but they're really omnivorous," Munshi-South explained. "They'll even eat small animals, raid the nests of birds and things like that. They're opportunistic."

When the squirrels first appeared on my fire escape, I was immediately taken by their extraordinarily large eyes; if the bodies of southern flying squirrels are smaller than eastern gray squirrels, their eyes look double the size. Many nocturnal animals have big eyes, which help them see in the dark, but flying squirrels stake their lives on theirs, navigating dense branches in mid-air at speeds of up to 35 miles per hour. What's more—they glowed! In the footage from the trail camera I eventually installed on the fire escape, the eyes resembled headlights on a car, an effect Munshi-South attributed to a structure behind the retina called a tapetum lucideum, a tissue layer that helps some nocturnal animals collect light to see.

My girlfriend's cats were also transfixed by the squirrels, passing entire nights at the windowsill to watch them zip back and forth. For such snack-sized animals, the squirrels seemed pretty unskittish about their spectators, despite the fact that cats in the United States kill somewhere in the range of 6.3 to 22.3 billion small mammals every year. In the forest, these squirrels have to watch out for formidable nocturnal predators like owls, but one of the perks of adapting to a life in the upper-canopy might be not having to worry so much about cats. 

Still, I keep the window tightly shut.