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What Happened to NYC's Subway Rats?

After miles of subway tunnels flooded during the storm, many expected the rats to appear on the city’s streets.

The New York City subway tunnels are home to thousands, if not hundreds of thousands of rats, a big portion of whom needed to find higher ground when Hurricane Sandy slammed into downtown Manhattan earlier this week. After miles of subway tunnels flooded during the storm, many expected the rats to appear on the city’s streets. After all, they’re great swimmers. They could just follow the water up to the surface, right? By most accounts of what really happened to the rats, that’s wrong. The rats did not show up on the surface or anywhere else. Why not? Because they’re dead.

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“Most of the rats that are living there will actually drown,” said Herwig Leirs, a rodentologist at the University of Antwerp in Belgium. “Rats will be carried away by the current and won’t be strong enough to swim to the surface and breathe, or they’ll be pushed to grates, they will get stuck there and they won’t be strong enough to swim against the current.” A rodentologist in New York backed up Leirs’ theory, adding that young rats are particularly vulnerable and would surely drown if they weren’t carried out by their mothers.

But not all of the rats will fall victim to the disaster. Those that make it out of the flooding will be treated to a veritable feast of garbage and debris that washed into the tunnels during the hurricane. Meanwhile, with humans out of the subway, they can roam free and mate at will. This is where disease becomes a concern. Rats are notorious for spreading disease, and as they’re displaced by flood waters, the rats that survive will venture into new areas where humans might be living and bring their infections with them.

It might not have been as bad as it seems, thanks to rats’ social behavior. As Bora Zivkovic from Scientific American pointed out in a great column:

There is a rule of thumb – if you see a rat on the surface during the daylight time, this means that the underground population is enormous. And I see them every month I go up to New York. When the rats are crowded, dominant rats take the best spots. If the population forages on the surface, dominant rats forage during the night. Subdominant (or submissive) rats are temporally displaced to the daytime shift. This is important. If Sandy started to flood the tunnels during the day (and nobody knows, or makes public, this information as the subway was already closed to people by then), it will be the non-dominant rats who are on the surface, and thus more likely to survive. If the flooding started at night, it will be dominant rats on the surface, floating away into safety. Dominant rats are more likely to be able to relocate and survive in other places where they have to compete with locals. Non-dominant rats would have a much harder time finding a new home.

If the flooding happened after dominant rats took to the surface and drove the weaklings underground to die, New York’s rat population may have just gotten stronger. (That’s just one of many potential outcomes, and it’ll be interesting to see if anyone will — or even can — study it.) But the basic equation is still there: If subway flooding happened slowly, some rats were likely able to escape to the surface, where they had a better chance of surviving. And not all of the tunnels flooded, which means a whole lot of rats — soon to have more space and trash to eat — survived to breed. But in those tunnels that flooded? Expect a whole lot of dead rats.

Image via Flickr