Scientists Map Nightlife and Communication of NYC Rats to Help Urban Planning and Pest Control

Here in New York City, we humans crown ourselves rulers of the five boroughs—but the kingdom is split. We cohabit with a parallel society that commutes along subway rails, picnics in parks and patronizes trash cans like they’re Restaurant Row. A new field study watched them the way New Yorkers often watch each other: from a respectful distance and with digital tech. The findings shed light on how rats have adapted to city life—and how chatty they are. “There’s this kind of secret language that rats are communicating in with each other that we don’t hear,” says Emily Mackevicius, a neuroscientist and a co-author of the study. “They’re very social,” adds Ralph Peterson, another study co-author. “They’re rugged, and they’re New Yorkers themselves: persistent and resilient and able to thrive in a very extreme environment.”

At three Manhattan locations—a park, a subway platform and a sidewalk—the team used a specialized wireless recorder to eavesdrop on the rats’ ultrasonic conversations, which humans can’t hear. They placed thermal cameras on tripods or held them by hand to record the warm bodies moving like glowing, otherworldly specters along the cooler ground. Dmitry Batenkov, a team member who works with machine learning and computational modeling, then converted the two-dimensional videos into three dimensions because 2D recordings distort the size and movement of animals, making rats closer to the camera appear larger.

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New York City is home to an estimated three million rats—approximately one for every three humans. Virtually all of these are Rattus norvegicus—the brown rat, aka the Norway rat—a larger and more robust species than the black rat (Rattus rattus), which arrived first on ships in the 1600s but was displaced by the brown rat in the 1700s. Since then about 500 generations of brown rats have lived here and have developed unique genetic adaptations related to metabolism, diet, nervous system and locomotion. Even the shape of their heads has changed. And to survive, they need a single daily ounce of water and food, the latter of which we provide in abundance, often processed.

Over this past summer in New York City, the research team—Mackevicius, Peterson, Batenkov and Ahmed El Hady, a neuroscientist who has studied rats and collective behavior—came together with a simple yet powerful idea: take what is known about rats from lab research and see how it holds up in the places we share with them. They wanted to do so not just to understand the animals’ behavior and cognition in the urban wild but also so that city planners, building managers and public‑health teams could craft decisions with real data to make city life a little less—squeaky. If scientists can more precisely measure rats’ complex habits and predilections, they can apply those data to trash pickup timing, building design, disease risk near burrows and even the question of which blocks attract big, bold rats versus skittish juveniles. Peterson, a computational neuroscientist, sums the concept up succinctly. “It’s like Sun Tzu says in The Art of War: to defeat your enemy, you have to understand your enemy.”

“To defeat your enemy, you have to understand your enemy.”

In 1944 Joseph Mitchell, the legendary New Yorker writer who chronicled the city’s overlooked characters, wrote about the metropolis’s shadow mascot: “Anyone who has been confronted by a rat in the bleakness of a Manhattan dawn and has seen it whirl and slink away, its claws rasping against the pavement, thereafter understands fully why this beast has been for centuries a symbol of the Judas and the stool pigeon, of soullessness in general.”

But maybe Mitchell was wrong about the soulless part. Rats are the dolphins of the sewage system; they chatter constantly as they run along the sidewalk in packs, peeking from holes, scavenging beneath grates or slipping into human-audible squeaks during scuffles by the dumpsters. One of the rats that the team recorded even soliloquized alone inside a garbage bag—perhaps offering a Yelp review for passing comrades.

Rats are the dolphins of the sewage system.

The study, which was released as a preprint paper that has not yet been peer-reviewed, also revealed that the rats modulated their ultrasonic squeaking based on ambient sound. In the subway system, which was louder than parks and sidewalks, rats communicated more loudly. But the moment that truly surprised Mackevicius was in the street. “There was an ambulance going by, and you could look at that in the spectrogram, and the rat vocalizations were louder than the ambulance,” she says. “They’re just kind of screaming to each other, but we just don’t hear it.” Peterson, who has studied rodent vocalizations in the lab, was struck by how talkative the vermin were. “Why would you vocalize if not to some end?” he asks. “The fact that we don’t understand that yet—this is one of the questions that really keeps me up.”

The study also suggested that the city rats’ size and behavior were linked. Younger rats were more likely to venture out together; the team saw groups of up to 20. “The smaller ones are likely juvenile rats, so they’re kind of learning how to forage, and they tend to move a bit more slowly and a bit less in coordination, with bursts of movement,” Mackevicius says. But sometimes the researchers also saw lone rats. “These are big, honking, huge rats,” Peterson says. “This seems like some sort of role that this single rat has, to go out into the environment and assay its surroundings and bring food back or relay information back to the rest of the colony. It had me asking a lot of questions about social hierarchy and delegation of roles and tasks.” Mitchell’s 1944 article said exterminators called old rats “Moby Dicks,” a reference to the giant white whale in Herman Melville’s classic novel. “Rats that survive to the age of four are the wisest and the most cynical beasts on earth,” Mitchell quoted an exterminator as saying—which matches Peterson’s observation about the big, solo scavengers: “They kind of know what they’re doing out there,” he says.

“Rats that survive to the age of four are the wisest and the most cynical beasts on earth.”

In Mitchell’s article, one New York exterminator argued that buildings had to be rat-proofed, that killing rodents was a waste of time. “It’s like taking aspirin for a cancer,” he said. Some contemporary research concurs, noting that poison can endanger pets and the ecosystem and that rats reproduce too quickly for poisoning to work. They become sexually mature in just two to three months, with females going into heat every few days and able to conceive within a day after giving birth. Pregnancies last only about three weeks, producing litters of six to 12 pups—and sometimes up to 20. Under ideal conditions, a single pair could theoretically generate thousands of descendants in a year, though survival rates keep numbers much lower.

“What you need to do is create environments that they don’t like,” Mackevicius says. At a city rat-mitigation-training event for community gardens, she learned that rats avoid open space—a tendency confirmed by lab experiments. For instance, community gardeners in New York City often remove clutter to make use of this aversion. Similarly, trash cans tucked into an alley might look like a romantic dinner for two in a dim alcove, but the same cans in an open space could feel like a picnic on the Cross Bronx Expressway. This acute awareness that rats have of open and protected spaces was the other reason that Batenkov converted the 2D videos into 3D: to precisely measure the rats’ behaviors in relationship to their settings. This data could someday even be used to generate rat’s‑eye simulations to show exactly how they navigate the city.

“Rat-mitigation strategies have been the same for a long time, but the rat numbers are rising,” Peterson says. “I don’t think putting a box with a little piece of cheese in it is going to do anything…. People underestimate how smart the species is.” He believes we should at least consider more futuristic solutions, even if they might sound zany. For instance, research on gerbils—another highly social rodent—has shown that they will respond to recorded gerbil vocalizations played on speakers. “We can build little robotic systems that sense [rat] movement and shine light at them or sense their movement and play certain vocalizations back at them,” he suggests, “and do this in a very dynamic way that addresses this issue of how to mitigate a smart species.” At very least, the city could use the team’s surveillance system to create a low-cost network that detects rat hot spots and infestation spikes—a real-time rodent weather report that would allow city officials to target their responses. This humane, data-driven pest control would be safer for people, pets, and the ecosystem and could even be generalized to deal with other urban cotenants, from raccoons to stray dogs.

The study left the team with tantalizing questions: What are rats really saying? How smart are they? What are their burrows like? Peterson recalls watching a battle-scarred rat on the subway tracks as a train came through. “The train left… and we saw the rat flopped over in a seemingly dead posture. It must have been a minute. Then it popped back up and started running away. It’s perhaps evidence of a rat playing dead in the wild, which we know that other species do.”

Mackevicius had previously been studying birds in central park, and when she started on rats, she was surprised by how friends reacted. “More people asked to go out on fieldwork with me for rats than for birds,” she says. Many passing New Yorkers also approached the researchers as they worked, asking what they were doing and getting excited upon learning they were studying rats. “Then they would offer their own personal rat story,” Peterson recalls. “‘Oh, if you want to see rats, come to this place. I see them. They’re as big as cats. They do this. They do that. They chew through steel.’ There’s this kind of childlike intrigue that everyone in the city has, which feels interesting, especially in a very divisive time. It’s like rats are bringing people together.”