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Comment by scott_s | Hacker News Reader

I encountered this last week as well, spurred on by the thought: where did the squirrels in NYC's Central Park come from? According to this article, they were introduced by humans in 1877: http://nymag.com/news/features/squirrels-2014-2/

But, I wonder if there's more natural migration going on now, or if Central Park is isolated enough from other green spaces that this population is cutoff from others. If that sounds absurd, remember: Manhattan is an island! I think squirrels are more free-roaming in the Bronx (with a bunch in the Botanical Gardens), but there's a river between them, and lots of paved concrete. Squirrels will swim, but there's quite a few blocks of mostly paved concrete between the river banks and Central Park. A squirrel could make the trip, but there may not be much cause to.

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Although the squirrels in that park were introduced by humans, it should be noted (as mentioned in the article you cite) that those squirrels, Eastern Grays, are native to that area. They just were no longer in that particular place because we destroyed their habitat to make room for our cities there.

So in a sense introducing them to parks in those cities was just putting back what we had driven off.

It's interesting that the Eastern Gray squirrel was also introduced to parks in Seattle. The Eastern Gray is not native out here. The native squirrels out here are the Western Gray, the Douglas, the Red, and the Northern Flying squirrels.

That raises the question of why when they decided they wanted squirrels in the parks that they went to the trouble of importing Eastern Grays from the other side of the country, instead of just sending someone out to trap a few Western Grays and release them in the parks.

It turns out that the reason is that a lot of the parks feature non-native trees. Western Grays really want to live off of native trees, and so don't do well in those parks. Eastern Grays either are native to the same places the non-native trees are native to, or are happy with them anyway, so they do fine in Washington parks, regardless of whether or not those parks feature native plants or non-native plants.

That also means the Eastern Grays did fine when they left the parks, and they have pretty much completely replaced the Western Gray. There's now only three isolated populations in the state, where once they were widespread and common.

There's a lovely 99% Invisible episode about the squirrel census, that includes a LOT more on history of squirrels in america: https://99percentinvisible.org/episode/uptown-squirrel/

In short, they started to be introduced into parks in the 1850's or so, and were a bit of a national craze.

I once knew a girl who was visiting the US from a city in Brazil and she was shocked by squirrels and the fact that we just let them run around our cities and do whatever they do.

She was a little worried about attacks or food theft, but eventually she saw they were harmless. Even then she'd still excitedly point them out everywhere she went.

I still excitedly point out squirrels everywhere I go, and I'm over 30...

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