
The Squirrel Census Answers a Question You Weren’t Asking - danso
https://www.citylab.com/life/2019/06/squirrel-census-results-population-central-park-nyc/592162/
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scott_s
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/](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.

~~~
sdenton4
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/](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.

~~~
autoexec
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.

~~~
forgotmypwd123
_I_ still excitedly point out squirrels everywhere I go, and I'm over 30...

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bnjmn
A potentially less labor-intensive way to estimate animal population is to
capture a sample, tag them, release them back into the wild, and then later
take a second sample and see how many of those animals are tagged:
[https://en.wikipedia.org/wiki/Mark_and_recapture](https://en.wikipedia.org/wiki/Mark_and_recapture)

I was hoping this article would say something about improving the margin of
error for this kind of statistical estimate, or at least provide a critique of
mark-and-recapture statistics for counting squirrels (maybe they are just
too... squirrely), but alas it sounds like they threw a bunch of volunteers at
the problem:

> The trick is to divide and conquer. They drew a grid of 350 hectares—plots
> of land measuring 10,000 square meters—over Central Park. Think of them as
> something like Census tracts. Volunteers then fanned out and conducted two
> counts, one in the morning and another at night. The Squirrel Sighters, as
> they were called, spent 20 minutes per count searching for furry subjects,
> looking up in the trees and down in the bushes, and listening to the clawing
> and clucking sounds they make. Allen likens it to an Easter egg hunt; some
> volunteers found many squirrels, others saw none.

~~~
sdenton4
I was talking to a bird person who used to participate in various population
studies with the national park service. There exist species for which tag-and-
release doesn't work at all: jays and corvids in particular are verrrry good
at avoiding the places and types of traps where they've been captured before.

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simonw
I bought the report from the website, which includes two maps, a booklet,
postcards and (I'm not kidding) a vinyl record with the audio version of the
report.

The whole package is BEAUTIFUL. It's some of the most delightful information
design I've seen in a very long time. Totally worth the $75.

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sushisource
> The city used LIDAR technology, in which a drone or airplane shoots a light
> at the ground and the length of light is measured to determine elevation.
> The “phantom hills” are recorded when the drone or airplane mistakes, say, a
> building’s shadow as a hill.

Uhhh... No? Lidar definitely wouldn't have that problem.

~~~
farisjarrah
Would you mind educating us why? I cant seem to find info online immediately
about shadows affects on lidar?

~~~
saltcured
LIDAR doesn't really depend on any other illumination, so there are no shadows
as such. If there is too much other illumination in the same wavelengths (or
too little returned reflection) it might not register a return at all and this
would appear as a hole in the data.

If not shining straight down, it might have an error for the horizontal
positioning of a building's roof, but it will still measure a discontinuity
like a cliff edge where one measurement hits the roof elevation and the next
hits the ground adjacent to the building.

If measuring through a tree canopy, there will be multiple levels of returns
as beams penetrate to different elevations before reflecting. These levels may
include some measurement of the true ground level, unless the canopy is so
dense that all beams hit a tree. So, a dense mass of trees or brush might
obscure the true ground level beneath them. Perhaps the original article
author conflated this with the idea of shadows.

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jordan801
Did a census bureau employee knock on their trees, driving them utterly nuts
with redundant and intrusive questions? Questions like, "Did you gather nuts
full time last week?", "Do you believe you've been given ample opportunity to
gather nuts?" and "How many squirrels do you live with? Do they also gather
nuts?".

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KineticLensman
TL;DR: There are an estimated 2,373 eastern gray squirrels in Central Park.

Link to the (somewhat uninformative) census website:
[https://www.thesquirrelcensus.com/](https://www.thesquirrelcensus.com/)

~~~
danso
Yeah I was going to submit the project homepage but currently it’s mostly a
page for advertising the book

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mncharity
Before reading the article, you can have fun doing a rough quantitative
estimate. A Fermi question.

How many squirrels live in NYC's Central Park?

Is it more like 1, 10, 100, 1000, 10k, 100k, 1M, 10M, or 100M? What hard "no
way is it more/less than" lower and upper bounds are you comfortable with and
why? What about soft "I'd be surprised if it was more/less than" bounds and
why? Doing iterative bounding and discussion, is a far more fruitful way to
use the common estimation problems of education, than the traditional point
estimates.

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AstroJetson
This makes sense, the Audubon Society does this with birds.
[https://www.audubon.org/conservation/about-great-backyard-
bi...](https://www.audubon.org/conservation/about-great-backyard-bird-count)

Everyone counts their "back yards" and they compile all the data. About the
same difficulty as the squirrel count, but you are trying to identify what
kind of bird.

On the other hand, I don't think that number is right. Based on my trips to
NYC, and the amount of squirrels I've seen I think it's way low. But I may be
skewed by the number of pigeons that are also in the park.

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tropo
The census question not asked: are these squirrels native or invasive?

In most of the world the answer would be "invasive", particularly in the UK
where they are wiping out the natives, but they appear to be native to New
York.

~~~
gerbilly
They are native to New York yes, the eastern grey squirrel is a north american
species.¹

However, the squirrels in Central Park, were deliberately introduced.

It's unclear whether they were absent from Manhattan naturally, or whether
they were extirpated due to urbanization, and the re-introduced later.

And about the invasive status of the grey squirrel in Britain, it's sad that
they were deliberately released in Britain, because it's not as if they swam
across the Atlantic or hopped a freighter.

Now you guys are fighting an extermination campaign with all the regrettable
suffering it causes to both squirrels and humans.

1: The Urbanization of the Eastern Gray Squirrel in the United States Etienne
Benson J Am Hist (2013) 100 (3): 691-710.

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Cactus2018
North Carolina State University white squirrel report:

Website - [https://untamedscience.com/biodiversity/white-
squirrel/](https://untamedscience.com/biodiversity/white-squirrel/)

Article - [https://www.washingtonpost.com/local/ever-seen-a-white-
squir...](https://www.washingtonpost.com/local/ever-seen-a-white-squirrel-
meet-the-guy-whos-keeping-tabs-on-them-
nationwide/2019/04/14/c38e4822-5c7e-11e9-9625-01d48d50ef75_story.html)

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ericnkatz
So there was an episode on 99% invisible podcast about this topic, not sure if
related to this census or not but it's an interesting listen for those who are
curious: [https://99percentinvisible.org/episode/uptown-
squirrel/](https://99percentinvisible.org/episode/uptown-squirrel/)

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firstinstinct
Put a lot of false food for the squirrels and estimate the squirrel population
by how much false food they try to eat.

False food: It looks like fruit but taste very bad, it is suppose only one
bite for each animal.

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mattnumbers
I really hope that this becomes an annual effort so that we can finally study
the effects of black hole mergers on the Central Park squirrel count.

