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April 16, 2024 6 mins

It turns out that some tree squirrels have complex organization systems for their stashes. Learn how they hide and find exactly what they want in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/mammals/squirrels-really-organize-nuts.htm

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Speaker 1 (00:01):
Welcome to brain Stuff production of iHeartRadio. Hey brain Stuff,
Lauren Vogelbaum Here. Tree squirrels are pretty common in cities, neighborhoods,
and wooded spaces around the world. But how much do
you really know about them? I'm not saying that they're
planning something big. There's a misconception that tree squirrels hibernate

(00:23):
during the winter. Trust me from looking out my kitchen window,
they are plenty active. Hibernation is an evolutionary trick some
animals use to conserve energy when food is scarce. Tree
squirrels don't need it because they store enough away to
keep themselves fed. However, their cousins, the ground squirrels, which
have a less bushy tail, burrow underground and are common

(00:43):
in the American West, do hibernate during colder months. Another
misconception is that tree squirrels store that food they've collected
during the summer and fall, like for example, acorns directly
in their nests are dens for easy access during the winter.
But the process by which tree squirrels keep themselves fed
during the lean months turns out to be way more

(01:04):
complex and active than stalking a pantry at home. Researchers
are learning that it suggests some advanced memory skills. A
group out of the Department of Psychology at UC Berkeley
published a study about this back in twenty seventeen. In it,
they lay out how tree squirrels use a mnemonic technique
called spatial chunking to sort out and hide their nuts

(01:25):
scores by size, type, and perhaps even nutritional value and taste.
When they're hungry later, it's theorized they can remember where
to find what they want. But let's back up a little.
The tree squirrels are a diverse group of squirrels that
live primarily in trees instead of burrowing in the ground.
They'll eat pretty much anything seeds, nuts, tree buds, berries, leaves,

(01:48):
parts of pine cones, bird eggs, nestlings, and the occasional
slice of found pizza. Some of that stuff they eat
right away and the rest they well squirrel away for later.
But as winter approaches, squirrels are faced with a challenge.
They know instinctively that food sources will soon be scarce,
so they gather all the food they'll need for a

(02:09):
few months while also keeping themselves fed day to day.
That's why they're so busy in the fall, when nuts
like acorns have all fallen from their trees. Some squirrels,
like red squirrels, tend to hide their food in a
single stash, but others are what's known as scatter hoarders,
which means pretty much what it sounds like. They hoard
their food and scatter it in several different locations where

(02:31):
they can easily access it. That's usually close to the
tree holding their nest or done, but they often expand
into areas of around seven acres or three hectors. Rather
than leaving their goods above ground where other squirrels might
steal them, they bury them. This is called caching about
an inch under the soil that's around two to three centimeters.
Squirrels are even known to crack open nuts before burying

(02:53):
them to prevent them from germinating, though not always and
actually squirrels accidentally plant a lot of trees trease. Anyway,
when it comes time to eat, they forage for the
nuts they buried. Squirrels do possess a strong sense of smell,
which allows them to sniff out nuts from under a
blanket of dirt, especially if the squirrels marked its nuts
with their own scent, usually from glands on their face,

(03:15):
but researchers have long noticed evidence of strategic intelligence in
the placement of their food. For instance, one study in
two thousand and eight reported that Eastern gray squirrels engage
in deceptive caching, That is, they dig a hole, pretend
to throw in an acorn while holding it in their mouth,
cover up the empty hole, and then run off to
another secret stash place. They do this, it was suggested,

(03:39):
to fool other squirrels who might be watching, and the
study from twenty seventeen indicates even more complex thinking behind
the caching. In field experiments conducted over nineteen months from
twenty twelve to twenty fourteen, researchers fed forty five marked
free ranging Eastern fox squirrels one nut at a time,
as sixteen total for each squirrel, varying the type of

(04:01):
nut almonds, hazelnuts, pecans, and walnuts. If the squirrels didn't
eat the nuts right away, the researchers tracked through GPS
where the squirrels subsequently buried their prizes. What they found
showed evidence of spatial chunking, meaning that the squirrels put
specific nuts in similar places to apparently help them remember
which nuts were ware, So for example, a given animal

(04:24):
would place almonds in one general area and hazel nuts
in another. We can only assume that had pizza been involved,
it would have gotten its own location too. This mneumonic
strategy has also been seen in rats. The researchers explained
that the strategy could make it easier for squirrels to
find not just any stash, but the specific type of
stash they're looking for, and use less brain space to

(04:47):
do it. For the article this Episodes based on How
Stuff Works, spoke via email with Michael A. Steel, a
biology professor at Wilkes University in Pennsylvania and the guy
who first described the deceptive cas us mentioned above. He said,
I find the results consistent with some of my studies
and those of others in which we are learning how

(05:08):
involved the scatter hoarding process is for tree squirrels. Squirrels
are certainly well adapted to solve foraging and caching problems,
well beyond most people's greatest expectations. We know that gray
squirrels selectively move more valuable seeds or nuts to sites
in the open where predation risks are higher, but pilfridge
risks from other squirrels are lower. This means squirrels cess

(05:31):
seed and nut quality and trade off some risk of
predation to secure seeds and sights. The twenty seventeen study
took into account, among other variables, the sex of the
squirrels in the experiment, the order in which the nuts
were received by the squirrels, and the weight and nutritional
value of each nut. They appeared to be organizing nuts
by size in addition to type, so the next time

(05:54):
you see a squirrel digging up a nut, know that
she might have found the exact one she was looking for.
Today's episode is based on the article squirrels actually organize
their net hoard Here's Why on HowStuffWorks dot Com, written
by Jamie Allen. Green Stuff is production of by Heart

(06:15):
Radio in partnership with how stuffworks dot Com, and it
is produced by Tyler Klang. Four more podcasts from my
heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.

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