The Rat Paths of New York

How the city’s animals get where they’re going.
By RYAN BRADLEY
Most New York animals stay close to home. Yes, itinerant coyotes will traverse the parks by night, and raccoons might travel half a mile in search of better trash, skunks a little less. But feral cats won’t stray three blocks beyond where they were born, and few mice will venture more than a hundred feet from their burrows in a lifetime. Rats seldom stray far from home, either. But they get where they’re going more easily than other New York animals, because they are more like us. The city suits them.
“With rats, the map is almost three-dimensional: the surface, the buildings, everything underneath,” Jason Munshi-South told me. We were rat-spotting in Lower Manhattan, and Munshi-South, an urban ecologist who is an associate professor at Fordham, was explaining what he’d discovered after studying New York rats, also known as Norway rats or brown rats, for three years. They cannot, as legend has it, collapse their skeletons to fit through cracks, nor are they especially bold; indeed, they’re “neophobic,” which means they won’t touch a new object, even unfamiliar food, for at least two days and sometimes as long as a week. They nearly always follow the same routes to their food sources. They sleep, on and off, for about 10 hours a day, and the rest of the time they travel in tight, well-worn paths. Munshi-South’s back-of-the-envelope estimate is that they take at least 2,800 steps a day, compared with the average American human’s 5,000 or so.
Rats live in colonies of 40 or 50 and sometimes relocate to new homes, but over the course of their one-year life span they rarely walk more than 600 feet from their birthplace. When they do, they seem to move north and south, with the subways, but, Munshi-South emphasized, no one is sure exactly how they do it. “We don’t even know if they move between stations, under- or above-ground,” he said. “That’s something we hope to figure out.”
Illustration by Louise Zergaeng Pomeroy 
We walked north from City Hall Park into the southern edge of Chinatown. Munshi-South was confident we’d see some rat activity, even on this bright, crisp morning. In the city, rats hug structural edges (“feeling” the walls with whiskers), and their routes are marked by sebum, oil from their hair that rubs off and darkens the concrete landscape. Pay attention, and you’ll see these lines on walls, an inch or so above the sidewalk, sometimes smattered with little clumps of fur. Rats build their colonies wherever they can burrow: in dirt, certainly, but really anywhere crumbly and close to constant food, usually in the form of trash, which is more or less everywhere. (A few pockets of the Upper East Side are free of large permanent rat colonies, but that’s about it.) Every few minutes, Munshi-South pointed to a lumpy mound, usually under a bush or near a trash can, pocked by silver-dollar-size holes. Rats tend to use just one entry and exit, but they like to build extra escape routes just in case.
“This is insane,” Munshi-South said. “It looks like a prairie-dog town.” We had reached Columbus Park, an asphalt playground near the original Five Points, the slum where men would pay up to $5 during the 1870s to watch fox terriers battle rats in the backs of saloons. Now a few seniors practiced tai chi, while others set out bowls of rice as offerings to passing spirits. What small patches of green remained had been scraped flat by rats. They weren’t eating the grass, Munshi-South explained, just dragging a lot of trash across it. “I bet if we just wait, they’ll come out,” he said.
Not more than a minute passed before a big rat emerged from under a bush and approached a woman who was putting out rice bowls. He inched forward slightly — it was a male; we could see his testicles — then rested, waiting. A minute passed, and a bigger rat emerged, also a male. He ignored the rice, though, and instead ambled from one rathole to the next, occasionally snapping up a loose crumb. There was a practiced efficiency to his movements, but he was old and missing an eye. “He’s making the rounds,” Munshi-South said — looking for the scraps that more successful rats had discarded. “He’ll probably be dead in a few days.” For now, though, the city would provide.
New York is the rat’s ideal habitat. Our idea of what a park or public space should look like mirrors its native environment, which, contrary to the animal’s common name, was almost certainly the grassy Asian steppe. We mow grass, plant a few shrubs and low bushes, a line of trees. Then we improve on nature by adding a constant source of food, our trash. Now at least two million rats live here, maybe millions more, depending on which scientist you ask. If we’d like fewer of them around, we might start thinking about how to make the city more attractive to other animals.
But most animals have a hard time getting around the city. When Munshi-South first moved to New York eight years ago, he studied white-footed mice, which live in heavily wooded parks, where there are many fewer rats. (Rats eat baby mice.) He took genetic samples from hundreds of mice that had been trapped in 15 parks, on a hunch there might be some differences among them. A mouse in Pelham Bay, after all, would rarely if ever interbreed with a mouse in Central Park; the journey would simply prove too daunting. His results confirmed the disconnection: White-footed mice so rarely leave their forested home territories that, over time, each population of city mouse became for practical purposes marooned, and genetically distinct. A white-footed mouse from the Bronx, indeed, never makes it to Manhattan or any other borough.
Still, new animals do show up from time to time — turkeys, red foxes, coyotes. Leslie Day has been watching them come and go most of her life. She lived on a houseboat at the West 79th Street Boat Basin for nearly 40 years, falling in love with the wilder aspects of this urban space. A middle-school science teacher, she eventually got her Ph.D. in science education and wrote three books drawing on her observations and research, including the “Field Guide to the Natural World of New York City,” with entries on, among other city animals common and uncommon, Eastern gray squirrels, rabid wolf spiders, opossums, red-backed salamanders, cabbage white butterflies, common snapping turtles, the Northern rock barnacle, the double-crested cormorant, little brown bats, big brown bats, the American eel, the pyralis firefly and, inclusively, earthworms, which, she notes, “were brought to North America by the early European settlers.”
Illustration by Louise Zergaeng Pomeroy 
Day recently moved to land, in Washington Heights, near the George Washington Bridge. Down at the basin she watched raccoons and squirrels, but up in Washington Heights she follows skunks. “Oh, my God, we have a million of them,” she said when we met at her apartment. Skunks have terrible eyesight and live their lives low to the ground, smelling, smelling and being startled. One had taken up residence under Day’s front stoop, she said, and we went out to take a look. There were hundreds of tiny, perfect divots in the lawns surrounding her apartment building, where skunks had stuck their noses into the soil, rooting for bugs.
We walked over to the Heather Garden in Fort Tryon Park. Day pointed to a gap along the terrace — last summer, she said, she had been walking past this very spot with her friend Mike Feller, who worked as the chief naturalist for the city’s Parks Department for 31 years, and they noticed something unusual: a mound of brilliant white sand pierced by a pinhole leading down into the earth. Day thought it might be a sand trap made by an ant lion, a predatory insect, but Feller told her no, it was probably just plain ants. He’d bet anything, he continued, that it was sand someone dredged from the Rockaways and trucked up long ago to make this terrace. The ants go down and excavate it, reminding us of our past. Like the rats, and the woodchucks, and the skunks, and all the burrowing creatures, even us, the ants don’t just walk back and forth, but up and down, through time.
When I got home I called Feller, and he told me about another small but significant journey that happens each spring, one that has been happening since not long after the glaciers retreated thousands of years ago. It isn’t historic, Feller said. Just beautiful.
“On warm, rainy nights, the spotted salamanders emerge from underground and walk 100 yards down to vernal ponds — wetlands that only exist in the spring and beginning of summer — to breed,” he said. “It’s a highly ritualized, synchronized thing that they do: Coming up out of the forest floor, they amble down to the water’s edge, and a male and female do this very intricate nose rubbing. They swim together, then apart, and the male swims down and leaves a little mushroom, a sperm-containing sack, and the female dives down, picks it up and implants it in her. It is a bizarre, aquatic ballet. In a few small spots in the city, it’s happening, right now.”
Most animals make city living better, or more interesting, but animals that eat rats might be especially welcome. Coyotes from the Bronx have devoured many rats in Riverside Park and Central Park, and in April a coyote was sighted all the way down in Chelsea. Smaller rat catchers, like foxes, are not uncommon in London, but they are rare in New York. We don’t make it easy for them. If you’re a fox or a coyote coming in from the countryside, you might try to stick with what you know: dirt, low cover, bushes that hug the ground. You would follow the rail lines, which are open to the air but still overgrown in places, or the parkways, the great green strips that Robert Moses built, or even the older, abandoned Long Island Motor Parkway, between Alley Pond Park and Cunningham Park, in eastern Queens. You would follow them until the concrete takes over completely. And then? Well, it gets harder. (It’s worth noting that probably the greatest predator of rats in Manhattan right now is the red-tailed hawk, which of course moves with far more freedom.)
In Central Park, I met Timon McPhearson, a professor of urban ecology at the New School. McPhearson studies how animals and plants get from one place to the next; for the last 10 years, he has been thinking about how to connect big “reservoirs of biodiversity,” like Central Park, to everything else. Even things as small as the walled-in tree pits all along the sidewalk outside the park. “That’s a dot,” he said, pointing to one. “I want to connect the dots.”
Illustration by Louise Zergaeng Pomeroy 
Sometimes, as in the case of the tree pits, connecting the dots can be as simple as adding a green strip between them. Open up the sidewalk a little, add some dirt, pull a few benches apart and, presto, all kinds of animals suddenly have a space for darting and hiding. Or run a pipe under the road, maybe put some soil in there to make it slightly more comfortable. “It’s all open,” McPhearson said. “You just need to start thinking about negative spaces, spaces that aren’t being used for anything else.”
Most of McPhearson’s proposals for building a connected city are modest (“If you can imagine where to put a bike rack, you could imagine where to put a green element”). But he has a larger vision of what the city might be, which begins with turning five blocks of Midtown into a pedestrian plaza with a natural, historic creek running through the middle. “That would be the new, future park,” McPhearson said. “The whole world would gasp.” It wouldn’t be cheap, but the countervailing revenue potential in real estate is huge; according to McPhearson, a tree in front of a house increases that house’s value by as much as 15 percent.
A new ecological infrastructure could have an impact worth billions of dollars, not just in the form of pricier lofts and storefronts but in the form of better mental and physical health. We are fundamentally natural beings, as McPhearson points out, and we are drawn inexorably to wild spaces, no matter how small — an affinity that E. O. Wilson, drawing from Erich Fromm, called biophilia. (“Mysterious and little-known organisms live within walking distance of where you sit,” Wilson wrote in 1984. “Splendor awaits in minute proportions.”) McPhearson’s fundamental point is that spaces where animals can move freely are good for people too.
The animals will come if we let them. Northern Manhattan alone has six large parks, and it is connected by five bridges to substantial woodlands in New Jersey, the Bronx and the forested suburbs beyond. In recent years, woodchucks have begun to make their way into Manhattan from the north. They are leaving the suburbs for the same reason rats began heading uptown long ago: overpopulation. As farming near the city has subsided, the woods have returned, and with the woods the wildlife. It’s natural dispersal, driving the woodland creatures to follow the landscape into the city.
Soon, thanks to a series of city- and state-sponsored greenway projects, the woods in the highlands that spill down to the Hudson will be interconnected, and a path will run along the river from the northernmost point of Manhattan down to the Battery — a great route for a bike ride or run, and a new, complete byway for the wild things coming down from the north. A fisher, a sort of weasel that preys on rodents, was seen in the Bronx last summer. That was unusual, but there could be more, moving farther south, as the paths into the city ease.
When I was walking with Leslie Day through Fort Tryon Park, the heath was beginning to come in, shades of purple and lavender against the brown and gray. We stared out at the great gray river, treetops tumbling down to its shore, and I mentioned how it was interesting that all these animals would come into the city, and that so many would choose to stay. “Oh, but just look at what’s here!” Day said, and she swept her arm across the vernal land.
Ryan Bradley is a writer living in Los Angeles.
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A version of this article appears in print on April 26, 2015, on page MM36 of the Sunday Magazine with the headline: Creatures of Habit. Today's Paper|Subscribe