How many of the NYC rats survived hurricane Sandy? This question has been asked in the wake of Sandy's flooding of lower and east Manhattan. See, for example, articles in Huffington Post Green, Forbes, National Geographic, Business Insider, Mother Nature Network and NYMag.
Floodwaters enter Hugh L. Carey Tunnel. MTA photo
The short answer is: some rats drowned, some survived.
The complicated question, how many drowned and how many survived, is probably impossible to answer. But we can speculate using the information and knowledge we have in our possession. But things we really need to know, we don't - information is just not available (and some of it never will be).
How many rats are in NYC?
Nobody knows. Nobody seems to even be attempting to estimate.
Beware of the myth that there is one rat per person. That is a very old myth. It started in 1909 when W.R.Boelter published a study of rats in England. He asked farmers (but never bothered to look in the cities) to estimate how many rats they have in their fields. From that informal survey, Boelter came up with an average of one rat per acre (yes, of agricultural land). At that time, there were 40 million cultivated acres in England. From that, he estimated the total population of rats on agricultural land to be about 40 million. Completely coincidentally, England in 1909 also had a population of 40 million people. So, the 1:1 ratio stuck. And it has been repeated for more than a century, by media, by scientists, by United Nations, by pest control companies, by health departments, and apparently everyone else.
In 1949, Dave Davis did a systematic study of rats, by trapping and capturing them, and estimated that rat population in New York City was only about 250,000. Not even close to 8 million.
An aside - I have an indirect personal connection to Davis. For a while he was a professor in the Department of Zoology at NCSU, that is, in my own department. At the time he was ready to retire, in the 1970s, he was actively working on daily and seasonal rhythms in various animals. He used to work with Curt Richter before, at Johns Hopkins, and Curt is one of the pioneers of chronobiology. David sent some woodchucks on a ship from Philadelphia to Australia. While on the ship, rats kept EST time, but quickly re-entrained to the Australian local time once they arrived there and were exposed to ambient light. Although the field was still very young, Davis' work made the rest of the department aware of it (they did not think it was Biorrhythms silliness, as many assumed at the time), so they were interested in hiring a replacement who was doing something similar. So they hired this bright, young lad from Texas in his spot - two Science papers already published and he took only 3.5 years to get both MS and PhD. The new faculty's name was Herbert Underwood. Two decades later I joined the Underwood lab. The rest is history.
Anyway, back to rat population. Estimates vary wildly, to as high as 32 million. Nobody really knows.
New York City is old. It was built and rebuilt. New buildings were built on top of the old ones. There are old, buried tunnels, rooms, chambers, now not accessible to humans but perfectly accessible to rats. Gradually, the city dug out more and more sewers, more and more various pipes, more subways and other tunnels. Thus more places for rats to nest. We gradually built comfortable homes for more and more rats.
The rat population is not evenly distributed either. They tend to be where poor people live, and where the restaurants are. That's where there is food.
And not all rats go to the surface. Rats are pretty loyal to the place of birth, and rarely venture more than about 60 feet from it, throughout their lives. If displaced, they can find their way home from as far as 4 miles, but for a foot-long animal, that is an extremely long distance.
If they can get food down under, e.g., from subway passengers throwing out uneaten food onto the tracks (which they do), rats never need to go up to the surface. They never get captured and counted in surface surveys.
Can rats swim?
Yes, rats are strong swimmers. They can even dive for a little while - see this video: if a domesticated rat can be trained to dive (and enjoy it), I assume that a wild rat can do it when its life is threatened.
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