Mapping the Rats in New York City

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Michael Mills, a veteran health inspector in New York City, helps create a map of the city you won't find in any guidebook: a rat map. That's right, a map of the New York neighborhoods that rodent populations call home.

The city's rat map was first introduced a year ago, with an intensive pilot program in the Bronx. Mills and other inspectors scoured the streets, building by building, cataloging rat hot spots — places that show so-called active rat signs, such as lived-in burrows, fresh droppings, telltale gnaw marks on plastic garbage bags — in an effort to target rodent-control measures more effectively. That geocoding information was entered into each inspector's handheld indexing computer and aggregated with similar data from all across the borough. (See the top 10 animal stories of 2008.)

Today, rodent complaints by residents from all over New York are electronically pinpointed on the city's computerized rat map, which allows inspectors to track complaints and hot spots over time and determine how well rat-control efforts are working. The results, after just one year, should be music to the ears of most New Yorkers: when the pilot study began in the Bronx, inspectors found active rat signs on 3,100 of the borough's 39,000 properties. Preliminary results now show that 1,250 of those properties are rat-free. That's a 40% drop-off in infestations.

Without that initiative, the rat numbers would be expected to stay the same or even go up, says Dan Kass, an assistant commissioner in the city's department of health and mental hygiene.

The only species of rat (of the four-legged variety, anyway) that lives in New York City is the Rattus norvegicus, also known as the Norway rat or the brown rat. Nobody knows exactly how many live here, but everyone agrees that the population has exploded in recent years — thanks to warmer winters, ever more wasteful food habits and, in part, the city's crippling fiscal problems in the 1970s.

The problem had gotten so bad in parts of the city — who can forget last year's overtaking of a KFC/Taco Bell in Greenwich Village by a pack of rats? — that a change in tactics was clearly necessary.

For years, the city government has dealt with rodent complaints on an individual basis. Citizens called up the health department, which sent out inspectors and, if need be, exterminators, who got rid of the immediate problem. But that left rats in nearby nests untouched, allowing them to repopulate the area. (See pictures of animals in love.)

What was needed was a more coordinated effort — one that targeted all the nests on a block or in a neighborhood. Just as important, the strategy had to involve all the relevant government agencies. Rats found on the edge of Central Park, for example, might be living in a nearby subway station and dining on garbage left on the sidewalk by a grocery store or restaurant. Getting rid of that rat population would require collaboration between the three city agencies that govern the subway, the park and the sidewalks — an endeavor that has gotten easier since the mayor's office set up the Rodent Task Force, which meets weekly to coordinate work.

The effort doesn't end there. After the cleanup, local residents and businesses are responsible for plugging up the vacant rat holes and keeping their garbage covered. To do all that, however, they have to know exactly where the rats are to begin with.

Enter the rat map. On a recent patrol, Mills and his colleague Bobby Corrigan, a doctor of rodentology who also works for the New York City health department, were back in the Bronx, on West 184th Street. The target was an abandoned house sprayed over with graffiti — a vestige of the way much of New York used to look 20 years ago.

The holes in the front yard were obvious rat burrows, and there were lots of them. Mills pointed out freshly dug dirt from one of them — evidence that the hole had probably been active the night before. Further confirmation: tiny droppings in the corner where the chain-link fence meets the front wall of the house. "I've been trying to get into that house for the past three to four months," Mills says of the boarded-up building.

He wants to set poisoned baits inside — winter is the best time to exterminate, since rat populations are already reduced by the cold and relative lack of food. "But don't worry. We'll find a way to get in there," he says.

Some homeowners have put out poisoned blue pellets on their own — a real no-no, says Mills, since dogs, cats and small children often mistakenly eat the poison. It's much safer to get bait boxes, which are anchored in place and contain poison, which only rats can get to. Even so, it makes no sense to put out poison if you don't also tidy up your garbage, since rats will ignore baited food in favor of tastier leftovers.

Mills enters data in his tablet computer and moves on to the vacant lot next door. Rats like to scurry under things when they're out in the open. Sure enough, we find rat burrows under several scattered pieces of concrete. He points out a distinct musty odor — more evidence of rats. It all goes into the computer, which contains a detailed map, including the outlines of buildings.

So it goes, building by building, lot by lot. Every garbage can without a lid, every window screen that had been nudged aside just enough to let a rat slip by, grease marks from rat hair along a concrete wall — it all gets noted and pinpointed on the map. "We train our inspectors to see what everyone overlooks," says Corrigan, echoing Sherlock Holmes. "This is a living laboratory. There's probably 100 variations in rat colonies in New York as to how they behave."

Under the old pen-and-paper system, inspectors could check out about 20 properties a day, according to Mills. The computerized geocoded map allows them to catalog 10 times as many.

Last November, a version of New York City's rat map was made public (first-time visitors may not be able to access the map immediately; send an e-mail to to learn the workaround). You can search by zip code or exact address for information about the number of inspections or notices of violation at a given property. The interface of the public map is a bit clunky and hard to navigate, which may be why the city is sponsoring training sessions for community groups and other interested organizations. "We do hope to make this a bit more friendly in the future," Kass says.

New Yorkers have really taken to the rat map, says Corrigan. "Once they realize you are not blaming them for the problems, they have really gotten into it," he says. It's amazing the things that New Yorkers can bond over.

Christine Gorman blogs about rats and other public health matters on Global Health Report.