Longtime Manhattan residents who remain fiercely loyal to their respective neighborhoods are a dime a dozen.

You know the type: dyed-in-the-wool downtown denizens who only venture north of 14th Street for dermatologist appointments, pilgrimages to the Met or visits to their elderly great aunts who live in the East 90s. And then there are the uptown old-timers who venture downtown only rarely, usually to check out a hot new restaurant that so-and-so told them about.

New York City and its neighborhoods are constantly evolving, but this stereotype holds true. And as it turns out, it applies to rats as well.

According to newly published findings by Fordham University Ph.D. student Matthew Combs, Manhattan’s preponderance of plain slice-loving rats are just as wary about leaving their respective neighborhoods as some residents are. Following two years of extensive trapping and DNA testing across the borough, Combs and his colleagues concluded that uptown rats and downtown rats are genetically distinct and very rarely mate — let along co-mingle — with their neighbors.

“We know that related rats, rats in the same colony, tend to stay within about 200 to 400 meters of each other, even over multiple generations," Combs tells NPR. “That tells us that most rats actually stay right very close to where they were born.”

Combs found that within these two large geographic areas of Manhattan, colonies of rats — specifically the brown rat (Rattus norvegicus) — stick to individual neighborhoods and rarely venture more than a couple of blocks — or even a single block — from their established turf. For example, Upper West Side rats are genetically distinct from Upper East Side rats while rats hailing from, let’s say, Chinatown and the West Village, also have dissimilar DNA.

“They’re actually unique little rat neighborhoods,” Combs tells the Atlantic, noting that the rat-defined boundaries of these neighborhoods are surprisingly congruous with the human-defined boundaries.

So what about Midtown Manhattan and its neighborhoods — Times Square, Chelsea, Murray Hill, Hell’s Kitchen and on? If uptown rats don’t travel south and downtown rats don’t travel north, what kind of rats, if any, live in the middle?

Combs and his colleagues found that midtown, which serves as a geographic barrier between uptown and downtown rats, is still teeming with rodents. No surprise there. But given that larges swaths of skyscraper-laden midtown are commercial-oriented and tourist-driven (read: fewer trees, backyards and scrumptious household trash), rat colonies here were found to be sparser but also more susceptible to inbreeding compared to uptown and downtown rats.

European rats: a NYC tradition since the 1700s

Rat on NYC subway platform According to new research, Manhattan rats are the same kind that arrived from Europe centuries ago. And as it turns out, they like to stick close to the neighborhoods where they were born. (Photo: Ludovic Berton/flickr)

In addition to tracking the uptown and downtown divide between Manhattan rats, another key finding of Combs' research touches down on the remarkable longevity of Manhattan’s rat population.

Brown rats first arrived on the island in the mid-1700s via ships originating from Western Europe, particularly France and England. Centuries later, the DNA of Manhattan rats — both of the uptown and downtown variety — still most closely resemble the DNA of European rats. This is fascinating when you consider New York City’s status as a global hub of trade and immigration. Rats, just like people, have arrived in Manhattan from points all across the world. Yet it’s the direct descendants of 18th century European rats that continue to dominate the streets of the Big Apple today.

Combs and his team conducted their research over the summer months, starting at the northern tip of Manhattan in Inwood and gradually working their way down. With the permission from the New York City Department of Parks and Recreation, traps were set in public parks and green spaces; local residents also were more than happy to identify other popular neighborhood rat hangouts. “Almost every time you say you’re studying rats to someone in New York City, they have stories for you,” Combs tells Popular Science.

Although rats are clever critters, the strategic placement of traps — an oh-so-tempting combination of peanut butter, bacon and oats was used as bait — helped to yield over 250 rat specimens. Once collected, Combs trimmed an inch or so off the rats’ tails for DNA analysis. It's a very useful piece of tissue," he tells PopSci. "We could have also taken an organ or a toe."

According to Combs, the small percentage (about 5 percent) of New York City rats that do abandon their colonies and stray further away from their home-base neighborhoods (i.e. midtown rats) are the most problematic. "Those are the rats — those dispersing rats — that can actually move genetic information and move even their pathogens, and lead to that spread of disease and that gene flow we detected," Combs explains to NPR.

And then there are the rats who decide to travel very long distances via public transportation ...

Understanding the enemy

Through insight gleaned from his own in-the-field research, Combs, who is at work completing a dissertation on the spatial population genomic of New York City rats, hopes to help the city manage its world-famous rodent problem.

In 2015, Mayor Bill de Blasio — no friend of large rodents — pledged $3 million to the so-called Rat Reservoir Program, a track-and-eradicate scheme that targeted large colonies in particularly rat-plagued neighborhoods across the city. (Originally launched a year prior as a smaller pilot initiative, the program shouldn’t be confused with a separate 2013 scheme launched by the Metropolitan Transit Authority that strictly aims to sterilize mamma subway rats.)

Building off the successes of the expanded Rat Reservoir Program, in July de Blasio announced the launch of an even larger, more expensive — $32 million! — plan to reduce rat activity in the three most rat-infested sections of the city by 70 percent: Manhattan's East Village/Chinatown/Lower East Side; Bushwick and Bedford-Stuyvesant neighborhoods in Brooklyn and the Grand Concourse section of the Bronx.

While widespread rat eradication will continue as normal, the new plan primarily focuses on nipping the problem in the bud by eliminating food sources and preferred habitats of rats. Planned actions will include increasing curbside trash pickup in targeted areas, replacing rat-friendly public trash cans with harder to access ones; and ramping up enforcement of rat-rated violations. Various city agencies including the Department of Sanitation and the New York City Housing Authority will join together in the effort.

“All New Yorkers deserve to live in clean and healthy neighborhoods,” says de Blasio in a press statement. “We refuse to accept rats as a normal part of living in New York City. This $32 million investment is a multi-pronged attack to dramatically reduce the rat population in the city’s most infested areas and improve the quality of life for residents.”

As for Combs, it's understandable that he feels some admiration for these defiant neighborhood-loyal New Yorkers. “They are, quote-unquote, vermin, and definitely pests we need to get rid of,” he tells the Atlantic. “But they are extraordinary in their own ways.”

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.