The Empire State building, pizza and Broadway are just a few things synonymous with New York City — and then there's the rats.
Like many other major metropolitan areas, New York City has a rat problem. But that doesn't mean that all the rats are the same.
"Despite the fact that rats live right in our cities and under our feet, under our noses, there's actually quite little knowledge about how they behave in the cities, how they move around," Combs says.
And that lack of knowledge is a problem, just like the vermin themselves.
"They are a serious public health threat," he says. "They carry several zoonotic diseases that we are worried about. So the more we know about how they move, how these colonies interact, the better we can create management strategies to stop them."
Combs and other researchers spent two years going around the city and trapping rats. After extracting and analyzing their DNA, he determined that the rats that live in uptown, north of 59th Street, are distinct from those living in downtown, south of 14th Street. The Midtown area is more sparsely populated — by rats, anyway — presenting a barrier to genetic mixing.
Much like people, New York City's rats have their own home areas and generally stick to those neighborhoods, the study found.
"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 says. "That tells us that most rats actually stay right very close to where they were born."
While a majority of the rats stick to their home turf, Combs says about five percent do leave their colonies and go to different blocks, parks or even farther — up to 2,000 meters. It's those rats, he says, that present the biggest problem.
"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 says.
While it may seem like it is good news that these rats generally stay in the same area, Combs says it's not that easy of a matter.
"It's not a good thing if your neighbor has rats, because it means that you have rats as well," he says. "That's not quite in line with the way that we deal with rats."
Combs says that in New York if a person has rats, it's the property owner who has to deal with them, but really it's a community scale issue and should be dealt with that way. He's hoping that his research can change how rats are dealt with.
As for his personal feelings about rats, Combs says the pests are more complex than they seem.
"The more I learn and the more I read about rats, I think the more I'm able to respect them," he says. "I mean, they're remarkable creatures — they're able to change their movement patterns based on the things humans do, so they're very smart. They're also very social creatures."