Squirrels: The Return

In this episode of Stuff to Blow Your Mind, Robert and Joe return to the world of squirrels and their curious carnivorous ways…

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind, the production of iHeartRadio.

Speaker 2 (00:13):
Hey, welcome to Stuff to Blow your Mind.

Speaker 3 (00:15):
My name is Robert liamb and I am Joe McCormick.
And today we are coming at you with the return
of Squirrels to Stuff to Blow your Mind. If you
are newer to the show and your memory does not
go back this far, what year was it? Was it
in twenty eighteen that we did a pair of episodes
on squirrels that turned out to be real fan favorites,

(00:36):
and I'll say host favorites too. We think about squirrels
quite often, and I've never really thought about them the
same way ever since we did those shows.

Speaker 2 (00:45):
That's right. They were quite popular talking about squirrels, their history,
human and squirrel interactions, and what exactly squirrels eat.

Speaker 3 (00:56):
Yes, one of the big revelations from our research hall
for those episodes it was about well, I don't know.
I was going to say the darker side of squirrels,
but I don't know. It's not dark, it's just nature.
It's the more violent side of squirrels, the more carnivorous
side of squirrels. The thing most people don't think of
when they think of squirrels, which is scavenging meat from

(01:19):
dead animals, attacking baby birds in their nests, maybe even
preying on their own kind some kind, sometimes just squirrels
eating of the flesh.

Speaker 2 (01:29):
Yeah, yeah, I know a lot of this breaks down
just to the basic idea that squirrels are more complex
then a lot of people give them credit for. You know,
it's easy to look at a squirrel and think, oh,
that's cute, without of course realizing that this is a
wild animal. And yeah, they're not pure herbivores either, as

(01:52):
we discussed in those episodes. But the thing about those
episodes is that I think for many of us they
made squirrels a lot cooler because if you did kind
of dismiss squirrels as just, oh, well, they're the these
who we see them every day. They're mundane. You know,
they're out there trying to eat the bird seed. They're annoying,
but that's it. You know. It gave us maybe a
little more room to appreciate them. And a part of

(02:16):
our appreciation that grew out of that is we busted
out i think two different T shirt designs for our
T shirt store. We don't promote our T shirt store
as much as our T shirt store would like us to,
in part because we don't depend upon it. It's just
for fun. But if you go to our tea public
store you can find a link at stuff to Blow
your Mind dot com or check out the link tree

(02:36):
on our Instagram. At STBYM podcast you'll see I moved
them up to the top so you can see them
rather easily. We have one that is the squirrels are
Not what they seem and the other one is scug
King of Rats. These are both squirrel shirts. They're both
kind of metal looking. They're pretty good designs. I think
people had some fun with.

Speaker 3 (02:54):
Them, agree. But there have been recent developments that caused
us to return to the issue of squirrel once again.
Multiple listeners over the past few weeks have excitedly gotten
in touch to share news reports about a scientific paper
out just this month in the Journal of Ethology, which
returns to the topic of squirrels eating meat, and not

(03:17):
just eating meat, but hunting and killing prey. So one
of these messages, for example, came from our listener Daniel.
He provided a link to the paper and said predatory
carnivorous squirrels observed for the first time love the show. Ps,
there's a Mountain Goats album called Beat the Champ and
it is entirely about lucha libre no synth though off

(03:39):
topic for today, but good to know. Nonetheless, Thank you,
Thank you, Daniel. So if you are Daniel or any
of the other listeners who sent this news our way,
thanks for letting us know. And yep, you got your
way here we are talking about it.

Speaker 2 (03:53):
We may have heard from a few other listeners over
the years too, occasionally sending in some squirrel news I
have found in homing through the squirrel news since twenty
eighteen is that generally squirrels make headlines when there is
blood involved. Yeah, so we'll be touching on a few
different shades of this.

Speaker 3 (04:12):
Yeah. Warning that today's episode will include some gory details.
But it's all nature, folks, and we got to face
nature at some point, that's right. So what was found
in this new predatory squirrel research. Well, let's go straight
to the paper and have a look. So this paper
has a long list of authors, but I'm going to
read their names today. So this is by Jennifer E. Smith,

(04:33):
Joey E. Ingbritson, Mackenzie m Minor, lc O Striker, Mari L. Podas,
Tia A. Rivara, Lupen, mL tell Us, Jada C. Wall,
Lucy M. Todd, and Sonya Wild And the paper is
called Vole Hunting Novel, Predatory and Carnivorous Behavior by California
Ground Squirrels, published in the Journal of Ethology twenty twenty four.

(04:56):
As I said, I think it was out just this month,
in December twenty twenty four. And so actually, I think
this paper is really interesting because it's not just a
documentation of a surprisingly violent behavior being carried out by squirrels.
I mean, that's kind of that would be an interesting
thing if that's all it were, But it actually places
it within some bigger theoretical framework about mammal behavior. So

(05:18):
the authors begin by talking about ways that animals adapt
to their behavior to respond to changes within their environment.
Sometimes we can have this misconception that humans are really
the only animals that can adapt substantially to changing pressures
in the world around them, and that all of the
other animals are well, you know, they're not as smart

(05:39):
as us, and their behavior is produced by a system
of fixed instincts that are fundamentally rigid, so they just
can't really change very much, even if it would benefit
them to do so. Now, I think it's true that
humans are especially adaptable. The flexibility of human behavior is
really one of the things that makes us special in
the animal kingdom and allows us to survive in basically

(06:01):
any climate or ecological situation. But I think sometimes the
knowledge of our specialness in this regard can lead us
to underestimate the fascinating behavioral flexibility of other animals, especially
other mammals, even superficially unassuming mammals like squirrels. So just
because we're really good at something doesn't mean other animals

(06:22):
can't do it at all. And as one kind of
illustration here, early in the introduction of the paper, the
authors bring up a really interesting animal behavior concept that
I don't believe I had ever heard of before. If
I had heard of it, I'd forgotten about it, and
by the time I read this. But the concept is
called the ecology of fear. And this is a bit

(06:43):
of a tangent from the main paper here, But I
thought this was so interesting I wanted to get into
it in some detail. So one of the references they
cite introducing this idea of the ecology of fear is
a paper from the Journal of Mammalogy published in nineteen
ninety nine by Brown, Landree, and Gurung called the Ecology
of Fear, Optimal Foraging, Game Theory, and Trophic Interactions. What

(07:05):
the authors of this paper point out is that it's
easy to have an oversimplified view of how the presence
of a predator can impact prey availability within an area.
So I'm going to make up an example, and this
scenario might not be perfectly valid in nature for the
specific animals I'm using, but this is just to illustrate
the principle. So imagine you've got a little park area

(07:28):
and a bunch of rabbits living spread out across it,
and they are being preyed on by a band of
local foxes, and you're studying the predator prey interaction between
the rabbits and the foxes. And then suddenly a new
predator is introduced into this local environment. It's a cougar,
and the cougar eats rabbits too. The foxes and the

(07:50):
cougar both compete for the rabbits, So how does the
cougar affect the availability of food for the foxes? A
simple way of thinking is that the cougar kills and
eats some of the rabbits. Thus some of the rabbits
are removed from the population. Thus the number of rabbits
available for the foxes to hunt is reduced. But the

(08:11):
authors here point out that reality is more complicated than that.
In the example I made up, the cougar might eat
some of the rabbits, but the actual number that it
kills and consumes compared to the total number of rabbits
is relatively small. And yet the presence of the cougar
could still greatly impact the availability of rabbit prey for

(08:31):
the foxes. Now how would that be. It would be because,
as the authors of this nineteen ninety nine paper say, quote,
mammalian predator prey systems are behaviorally sophisticated games of stealth
and fear. So what they're saying here is that prey
mammals are not inert resources that are consumed like cookies

(08:52):
from a jar. These are cookies that react. You know,
they react to the fact that they are being eaten,
and they are too very carrying degrees. Depending on the
species adaptable, they can change their behavior in response to
a threat. So the authors say that when studying predator
prey interactions. In nature, there's actually a spectrum of different

(09:14):
kinds of systems. So at one end of the spectrum
you would have what the authors call population driven systems,
and then at the other end of the spectrum you
have what the authors call fear driven systems. In population
driven systems, the main dynamic is predators killing prey, So

(09:34):
the main variables are going to be like the number
of predators and the number of prey, how many prey
animals the predators eat, Whereas in fear driven systems, the
presence of predators creates a condition of fear among prey,
which causes prey to become harder to catch. So to

(09:55):
go back to our example, if you have a cougar
suddenly show up in this park, it could cause the
rabbits to become significantly less available as prey, not just
because they're literally disappearing from the population by being eaten,
but because the rabbits are becoming more vigilant and more cautious.
They're venturing out of shelter less. They might change what

(10:15):
times of day they do things, they might change their
foraging strategies. They might hide more or move away from
any suspected predator earlier, earlier in possible detection. So in reality,
a predator can functionally deplete the supply of prey animals
in an area, not just by eating them, but by

(10:36):
frightening them.

Speaker 2 (10:37):
Huh. I can't help but imagine a scenario where it's
Gotham City, right, yeah, and maybe you're the local police force,
and you have various stakeouts in place, you have various
pending cases and so forth, and then there's a batman,
essentially a new super predator preying on the criminal population

(10:59):
of this and yeah, this's going to potentially interfere with
everything that was going on. It's going to change the
local criminal ecology.

Speaker 3 (11:09):
Yes, yeah, it'll change like police joker interactions. Not just
because all of your local jokers and riddlers have been
put in Arkham Asylum, but they might actually stop doing
crimes or something, or do them in a less easy
to detect way. Yeah, for another not quite perfect, but
I think interesting analogy. I was thinking just about supply

(11:29):
and demand in human economies. When you have a lot
of people who want to buy the same product and
that product is in limited supply, the buyers can end
up limiting access to that product, not just by literally
buying up and hoarding all of the products that exist,
but by the secondary effect of driving up the price.

(11:51):
Sellers realize demand is high, They're like, oh, a lot
of people want to buy this, So the sellers raise
their prices as much as they can, and this limits
access to the product, even though the product doesn't actually
vanish from the market, is just too expensive for a
lot of the people who want it. Similarly, I think
you could think of a predator as a predator by

(12:11):
its presence bidding up the price of prey. It's not
that the prey animals no longer exist. Some of them
don't exist anymore, but for most of them they're still there,
but they are increasingly expensive to acquire because they adjusted
their behavior in response to a predator. And so the
authors of this nineteen ninety nine paper summarize the effect

(12:32):
by saying behavior buffers the system. A reduction in predator
numbers should rapidly engender less vigilant and more catchable prey.
The ecology of fear explains why big, fierce carnivores should
be and can be rare in carnivore systems ignore the
behavioral game at one's peril. So how does this tie

(12:54):
into the study about squirrels where well, the authors of
this twenty twenty four paper cite the ecology of fear
as an example of how prey animals, including squirrels, are
not well modeled by thinking of them as rigid, inflexible
machines or as like a just an innert resource like
cookies in a jar. Instead, we should understand that, to

(13:17):
varying extents, squirrel species and other mammalian prey can change
their behavior patterns when different pressures appear in surprising or
perhaps even alarming ways. But mammals like squirrels don't only
change their behavior in response to the threat of a predator,
they also alter their behavior in response to changes in

(13:38):
the availability of food. So from here the authors go
into a big catalog of let's talk about all the
documented instances of squirrels, specifically, in their case, the California
ground squirrel eating meat. That's where they're going from here,
and so they end up citing a paper that we
talked about extensively in our older series on squirrels from

(14:01):
twenty eighteen. The paper is called Squirrels as Predators by J. R.
Callahan published in The Great Basin Naturalist nineteen ninety three.
You remember this one, Rob Oh, absolutely, yeah.

Speaker 2 (14:12):
And of course if you're reading any subsequent papers about
squirrels as predators, they all cited this one.

Speaker 3 (14:18):
Yeah, this seemed to be.

Speaker 2 (14:19):
A major publication in the world of squirrel predator research.

Speaker 3 (14:23):
Callahan really seemed to do the legworking cataloging all these
different examples not just of squirrels eating meat, but actually
functioning as predators. Now, there's an important distinction to make here,
which is the difference between what you might call it
just standard predation versus what is called facultative predation. An

(14:44):
animal is generally categorized as a predator if it needs
to be a predator, if it can be expected to
catch and kill prey as a regular part of its
behavior across its geographic range.

Speaker 2 (14:56):
Yeah, especially in the case of obligate carnivores. You know,
where this creature has to hunt. Meat is what it eats.

Speaker 3 (15:03):
But also, I think you can think of some omnivores
as just straight up predators if predation is a regular
part of their acquisition of food. Meanwhile, a facultative predator
is an animal that can sometimes optionally engage in predation
if the circumstances are right, and that's typically what we're

(15:24):
looking at with squirrels. I'm not aware of any squirrels
that are consistent obligate predators, but there are a bunch
of squirrels where the evidence is pretty good that while
they are primarily herbivores, they will be omnivores when they
need to be. And that's you know, the occasions might
be rare, but many of them will shift strategies to

(15:45):
eat foraged meat and sometimes even actively catch and kill
live prey on an as needed or as available basis.
Now this came up in our older episodes, but Callahan
lists a bunch of different squirrel prey animals for the literature,
just to gloss over them quickly. This includes birds, frogs, rats, lizards, rabbits, gophers, moles, snakes, fish, voles, ducks,

(16:11):
wild turkeys, turtles, crabs, and salamanders. And sometimes this would
this eating would involve the eating of the flesh, eating
the meat. Sometimes it seems to be focused more on
bones or joints, possibly for mineral supplementation in some squirrel species.
But if you look at all of the previous research
on squirrel predation. Taken together, it emphasized that the vast

(16:35):
majority of the hunting done by squirrels was targeted at
first of all insects or invertebrates, and then if you're
looking at vertebrate prey, it would be relatively helpless juvenile
prey such as actually eggs like bird eggs or bird
hatchlings in the nest.

Speaker 2 (16:53):
Yeah, so memory serves this paper and also a paper
that I'll be referring to later, looked at the fact
that when you're studying all this, yeah, you do have
reports of squirrel predation and squirrels eating meat and and
and so forth. But then also you have a lot
of data that has arrived at via analyzing the stomach
contents of harvest squirrels. And of course that data doesn't

(17:17):
all provide a lot of context. Like you you can
look at it and say, well, they still mostly eat
seeds or plants or whatever, but there is a certain
amount of meat. As to how that meat was obtained,
you have to draw conclusions sometimes because yeah, there's there there.
Of course, you can scavenge, you can take out prey
that are just weak or helpless, juvenile and so forth.

(17:41):
But then there is that threshold, right that you cross
into potentially actively hunting prey, actively hunting something that is
that is not like wounded or dying, but is to
some degree like a like a valid, healthy prey creature.

Speaker 3 (17:59):
That's right, And to some extent this ambiguity remained up
until the time of this new paper. So the authors
describe the landscape of squirrel meat eating research before their
paper as follows. They write, quote, despite the growing consensus
that many squirrel species opportunistically consume meat, much of the
early evidence for predation is based on stomach contents or

(18:23):
the killing of heterospecifics in captive settings eg. Zoos or traps.
This makes it challenging to distinguish between scavenging and direct predation.
So this is what you're saying, Rob, We're in this
situation where you can find squirrels and like cut open
their stomachs and say, oh, there's some meat in there,
but we can't tell did it actually kill something, or

(18:44):
did it just find something dead and eat part of it,
or in these other cases, you might have evidence that
the squirrel did kill and eat an animal, but it
was an animal that was caught in a trap or something.

Speaker 2 (18:57):
Right, And I want to add an important caveat here
about predation. I don't want to make it sound like
true predation is a fair fight. We've covered enough examples
of predation in the past to know that there are
plenty of obligate carnivores, obligate predators who are still They're
obviously not going to go out and say, all right,
show me the strongest of the pack. No, the one

(19:17):
I shall fight today. No, no, no, They're still they're
still going after off you know, weekend, young, old, and
so forth, because they're inherent increased risks involved in going
after stronger prey.

Speaker 3 (19:30):
Predators use their coupons, they are looking for the super
saver options. Yes, oh, but anyway, the authors here continue
quote the direct study of hunting behavior by squirrels remains rare,
and most reports in field settings are still limited to
a single depredation event. So one thing this does bring up.
I've seen a few people kind of comment that like, oh,

(19:53):
you know, this isn't new. We have examples from before
of squirrels eating meat, or squirrels, you know, report isolated
reports of squirrels killing and eating animals. That is true,
We do have these reports But what this new study
contributes is extensive direct documentation, including video footage, of a
specific species of squirrel, in this case, the California ground

(20:16):
squirrel or Odospermophilus beachyi, hunting, killing, and eating adult vertebrate
prey animals, specifically voles in the study. So how is
this different than what we had before. Well, it's just
a lot more observations of the predation behavior compared to
the previous reports that were usually fairly isolated, and we

(20:37):
have video evidence here. And they're not just going after
juveniles or something that's caught in a trap or whatever.
They're going after adult vertebrate prey animals. So a little sidebar,

(20:58):
who are these California round squirrels the Odospermophylis beachy I.
First of all, yes, they're cute. According to me, at
least that's that's my opinion, Rob. I don't know if
you share it, but yeah, they're cute little guys.

Speaker 2 (21:11):
I mean, yeah, I guess, I don't know. I feel
like I'm you know, I'm not used to being around
these California squirrels, but the squirrels i'm around here in Georgia,
I think of them as I just know too much
about them, and I see them too often. I think
of them as like, it's hard for me to imagine
someone thinking they're straight up adorable, because like I hear

(21:34):
them on the fence, I see the effects of their
claws on the fence. They're like furry grappling hooks, you know,
like they're they're clearly tough creatures. I saw one fight
off a hawk once in my backyard. Oh yeah, it's
they're they're rough and tumble. So yes, cute, but with
a number of caveats as far as my opinion of

(21:54):
them goes.

Speaker 3 (21:54):
Well, I think it's going to be all caveats from
here on out. So yes, they're cute. But I included
for you to look at here in our outline. I
found a picture hosted on the University of California Integrated
Pest Management Program website. It's a picture of an avocado
that has been gnawed on by a California ground squirrel.
And I thought this picture was I don't know, it

(22:16):
just struck me. It looks both beautiful the pattern that
emerges and the different colors of the avocado flesh as
it has been gouged and carved out by the rodent's teeth.
But also I think it's hauntingly sad.

Speaker 2 (22:29):
Yeah, I have a real visceral reaction to this. There
is something heartbreaking about it, potentially wasted avocado. I feel
this one, like this one is saveable. I think I
could get in there with a with a with a
with a knife, cut off the part that's been fouled
by the squirrel and you know, have plenty leftover for
sandwiches and whatnot.

Speaker 3 (22:48):
You better do a good job because you don't know
what the squirrel has been eating before. The avocado.

Speaker 2 (22:53):
Well, I think it's only going to seep in so far,
and I'm gonna cut that part off and spread the rest.

Speaker 1 (22:59):
So.

Speaker 3 (22:59):
These California ground squirrels, the adults typically grow to around
twenty two thirty centimeters long in the body, plus another
half body length or so again with the tail. They
have a modeled gray and brown fur on their backs
and on the flanks, with usually lighter colored fur on
the underside. They have a bushy tail. A couple of
the sources I looked at mentioned that the tail is

(23:21):
not as bushy as the common tree squirrels that you'll see,
but it is bushy nonetheless, I don't know, medium bushy.
Maybe there are natives to the western part of North America,
found today in US states of California, Oregon, Washington, and Nevada,
and extending south into Baja California. They generally inhabit grasslands

(23:41):
where they dig out burrows in the earth that are
sometimes shared by a bunch of different squirrels. They hide
out and brood their young in the burrows. They typically
forage during the day. They and they use these burrows
because in part they are a common prey species to snakes,
predatory birds, and larger carnivorous mammals. So to be super clear,
California ground squirrels mostly eat plants. The authors mention that

(24:05):
they forage most often for seeds that come from grasses
and oaks, and during the growing season they will eat
green vegetable matter, including quote leaves, flowers, buds, stems, shoots, roots, tubers, twigs,
and bark from a wide variety of different plants. The
authors mention over one hundred different species of plants that

(24:26):
they eat from. So as herbivores, they are also very
flexible foragers, as the avocado art we just talked about
would indicate. They are a common agricultural pest within their range.
If farmers have to deal with these things a lot,
especially if you're growing I think, like fruits or nuts.
But while those foraging strategies are the rule, we also
get the exceptions, and quite a number of exceptions have

(24:48):
been observed, maybe to the point where we should question
whether they become a rule of their own. These observations
include occasional carnivory, and while the reports are more isolated
and sporadic, the authors found published accounts of the ground
squirrels eating invertebrates. Of course, they're going to be eaten,
you know, insects and other invertebrates, and eggs and nestlings

(25:11):
of numerous birds, including kill deer, California quail, bob, white quail,
ring necked pheasant, mourning dove, dark eyed junco, and American robin.
Continuing the agricultural pest theme, they have been documented chomping
ride on into domestic chicken eggs. They have been documented
to eat fish. I think there's just one occasion of this,

(25:33):
but eating a small silvery fish called the California grunion.
And then finally the author's note quote Fitch, nineteen forty
eight observed the California ground squirrel consuming, but not directly killing,
young desert cottontails, adult pocket gophers, and kangaroo rats, so
eating several of its cousins here. But again to emphasize,

(25:56):
just because a squirrel is eating a rabbit, that doesn't
mean it caught and killed the rabbit. It might have
found a dead one free meal. And there have been,
as we alluded to earlier, observations of the California ground
squirrel eating meat in non natural conditions, for example, scavenging
on human trapped fish and rodents, songbirds, and on other

(26:18):
California ground squirrels. And there have also sometimes been observed
instances of these ground squirrels cannibalizing juveniles of their own species.
But again, what has long been elusive is much evidence,
extensive evidence of these animals actively hunting and killing adult
vertebrate prey. Well, this study found, oh yeah, under the

(26:41):
right conditions they will absolutely do plenty of that. The
specific prey here was the California vole or microtus Ce californicus.
And if you look up this paper, it provides links
to video that you can watch of these attacks of
the squirrel just ruthlessly snatching a vole behind the base
of its skull in its jaws, and I thought in

(27:05):
this one particular video I saw it was fascinating how
much it resembled traditional predator behavior, like what you would
see with a wolf or a dog grabbing a squirrel,
so like clamp the jaws at the back of the
neck and shake. But while this did show up in
the video I was looking at, the authors say that
this was not the most common type of attack with

(27:27):
the shaking like this. They characterized the squirrel on vole
attacks as follows. In three documented hunting attempts from this study,
squirrels engaged in typical predator stalking behavior, meaning that they
flattened out their bodies low to the ground, and then
attempted to minimize the sound produced as they approached prey

(27:50):
before leaping into a sudden attack. That was the minority
of cases. Nineteen of the documented hunting attempts involved chasing
just a squirrel flat out run chasing a single vole
across the ground. When the squirrel was able to come
within range, it would pounce on top of the vole
and then hold it down with its front paws and jaws.

(28:11):
Then it would begin biting, most often at the neck,
but also at other body parts. A bite shaking was
observed in one attack, and squirrels occasionally but did not usually,
engage in sit and wait ambush strategies, hiding behind tall grass. Quote. Instead,
hunting attempts were best characterized by squirrels opportunistically chasing a

(28:34):
single vole over a short distance in open areas across
dirt substrate. And I thought that was interesting that, like,
perhaps I'm taking the wrong thing away from this, but
that just read to me as like, huh, you know,
they don't maybe they don't have a super refined strategy
like a lot of obligate predators would. They're just sort

(28:56):
of winging it.

Speaker 2 (28:59):
On an level you could say, it's like they also
kind of know how to do it as well.

Speaker 3 (29:04):
Yeh yeah, yeah, they do know. I mean they know
how to bite, to like bite and subdue the prey
with the four paws and the jaws. Where does that
knowledge come from? Interesting question? The authors summarized, saying, quote,
hunters successfully captured and killed a vole in seventeen of
the thirty one observed hunting attempts, which is fifty five percent.

(29:27):
So they observed thirty one cases of a squirrel trying
to kill a vole. Seventeen of the thirty one worked.
The other fourteen attempts failed. Prey either got away during pursuit,
or escaped after being initially captured by a squirrel. Close quote.
Another interesting thing is that in seventy percent of these
kills the squirrel would not eat the vole directly at

(29:51):
the kill site, but instead carry it away to a
second location, sometimes even into its burrow or out of view,
but other times just carrying it away to some different place.
And I don't know for sure the reason for this,
but I wonder if this is because the squirrel is
prey itself and it might not be comfortable being out

(30:11):
in the open. If this is, if this place is
the place where the vole was vulnerable to the squirrel,
that's also probably a place where the squirrel is vulnerable
to one of its predators.

Speaker 2 (30:23):
Right, and now you're presenting a two for one deal,
So you got to get out of there.

Speaker 3 (30:28):
Oh man, if you're like a hawk right here or something,
and you can get two animals out of a single catch.
Oh and one more detail from this part about the
attacks is apparently these ground squirrels, you know what, they
love to rip off the head quote In eleven of
the events for which consumption of an intact carcass was observed,
squirrels first removed the head of the vole, so that's

(30:50):
just procedure. Head remove head first. Next, they either directly
pulled meat out of the torso or first stripped fur
from each of these body parts before can assuming the
exposed meat, organs and cartilage. So an interesting thing about
these gory observations is the context that came in because

(31:10):
these observations were made within the context of a larger
project known as the Long Term Behavioral Ecology of California
Ground Squirrels Project, which had been going on for years.
This has been carried out at a place called I'm
not sure I'm pronouncing this correctly, but I think it's
Brionas Regional Park in California, Brio Nes Regional Park, sort

(31:35):
of northeast of Oakland and Berkeley. Interestingly, the project was
in its twelfth year before these instances of squirrels killing
and eating voles were first observed. And that doesn't mean
it never happened before, but these squirrels have been studied
intensely for twelve years in this region before anybody observed

(31:56):
them doing this, and then once it was observed, they
were observed doing it all the time, basically every day
after the first observation, for a period of a couple
of months. I was reading a press release about this
paper that was giving some narrative about how the scientists
came to these observations, and they interview the lead author,
Jennifer E. Smith, who is an associate professor of biology

(32:19):
at University of Wisconsin eau Claire, who ends up saying
in this press release quote, this was shocking. We had
never seen this behavior before, and emphasized she emphasizes how
strange it is that like squirrels are, they're just such
a familiar animal to people. People just see them in
their yards in the park all the time. And here suddenly,

(32:41):
after twelve years of intensive observation, we're seeing this predation
behavior happening all over the place within the range of
this particular study, and it's like what it's like out
of nowhere. Apparently there were some undergraduate researchers who had
been doing field work for the study, and they came

(33:02):
in one day and just you know, ask one of
the professors on the project about it. They're like, yeah,
we saw squirrels hunting and killing voles. And the professor
was like what no, no, no, no, But then saw the
footage and it's right there.

Speaker 2 (33:16):
Yeah, yeah, you can't argue with this footage, some of
these grizzly photos.

Speaker 3 (33:20):
And as I said, after the first instance, they began
to see this behavior basically every day, so they observed
it as a summer behavior throughout June and July twenty
twenty four. And the researchers did not during this period
observe the ground squirrels hunting and killing other animals, only voles.
That's kind of interesting. So it's previously unobserved behavior suddenly

(33:44):
seems to be happening all over the place at least
that they're noticing, and it's only targeting one prey species.
They don't generally become predators. Why would this be Well,
they ended up pairing this with a with an interesting observe,
which was a massive increase in a documentation of voles

(34:06):
logged by local citizen scientists in the area on an
app called eye Naturalist, which is sort of a biological
and wildlife social media platform kind of a place being
log Wildlife and the Citizen Science app. Yeah, yeah, and
so they noticed, h that's interesting. So we're seeing suddenly
ground squirrels showing this thing we've never noticed before where

(34:29):
they're hunting and killing voles. And also people are saying, whoa,
there's tons of voles out here. Where did all these
voles come from? And the authors compare the number of
vole sidings reported on this app to the ten year
average from before and found that the peak of vole
sidings in the summer of twenty twenty four there were

(34:49):
roughly seven times more vole observations than the previous ten
year average. So suddenly all these voles coming out of nowhere.

Speaker 2 (34:58):
Yeah, and what are you going to do? Right, what
are you going to do when there's that many voles around?

Speaker 3 (35:02):
Exactly. So, according to the authors, it is normal for
some vole populations to kind of boom and bust. They
cycle through these population density patterns, and they tend to
kind of peak every three to five years. But the
peak achieved in the summer of twenty twenty four, rob
you can see from a chart I've included, was like

(35:24):
way way more than the normal peaks, even the previous
peaks from like you can see in kind of twenty
twenty or so.

Speaker 2 (35:31):
It's such a peak that it doesn't make you judge
the squirrel the squirrels at all. You're like, maybe we
should have been eating vowles as well. Clearly it's out
of control, right.

Speaker 3 (35:41):
This brings us back to the idea from earlier about
behavioral flexibility in response to changes in the environment. So,
like the ecology of fear, there can also be an
ecology of food abundance. So these two patterns are observed
and they seem to line up in time. One of
them is suddenly a big surge in vole populations, and

(36:01):
the second one is squirrels shift their foraging strategy from
let's mostly focus on grains and other plant matter to
if you see a vole, chase it and kill it.

Speaker 2 (36:13):
I mean it's in season exactly. Yeah.

Speaker 3 (36:16):
So to come back to kind of the crude human
economics analogy I used earlier, you can think of this like,
you know, I don't normally buy vole meat at the store,
but you go to the store and vole meat is
so so cheap they're practically giving it away, so why not.

Speaker 2 (36:30):
Yeah.

Speaker 3 (36:31):
One of the authors of the paper. Sonia Wilde off
UC Davis gave a quote to that press release I mentioned, saying, quote,
the fact that California ground squirrels are behaviorally flexible and
can respond to changes in food availability might help them
persist in environments rapidly changing due to the presence of humans. Oh,

(36:51):
And I thought that was kind of interesting because on
one hand, you could just say, well, you know, these squirrels,
this squirrel species has a certain amount of behavioral flexibility.
That's part of its natural repertoire. You know, it can adapt,
and that's just part of what kind of animal it is.
And that's totally possible. But I also wonder if humans
could have, inadvertently, by our presence, helped create populations of

(37:17):
more behaviorally flexible squirrels. You know, if we're going around
wherever we go, changing the nature of the environment, We're
changing the you know, the very topography of the landscape,
we're changing what kind of food is available, We're changing
all sorts of things wherever we go, does that as
sort of in our wake cause the secondary effects where

(37:37):
we select for more behaviorally flexible populations of animals in
the areas with proximity to human civilization.

Speaker 2 (37:47):
Yeah, yeah, absolutely, yeah, we even changes that we might
not think of being that drastic. They have these ripple
effects in the environment. And yeah, next thing, you know,
it's squirrels ripping heads off.

Speaker 3 (38:00):
Now, plenty of unanswered questions remain, like how common? Is this?

Speaker 2 (38:04):
Really?

Speaker 3 (38:05):
Unclear? Fascinating question we don't fully have the answers to,
But how do the squirrels actually make this shift? Like
where does the hunting behavior come from? Is it a
learned behavior that's passed down from from parent offspring or
is it a kind of instinctual ingrained behavior, In which case,

(38:25):
what sort of instincts are harnessed from the normal foraging
strategies and repurposed for hunting If it is instinctual? Another
how like how does it get triggered? You know, how
does the squirrel know to shift? It's it's say like okay,
it is time to hunt now? And another interesting thing
are like what are the secondary dynamics that emerge? We
were talking earlier about secondary dynamics that you might not

(38:48):
always envision that come out of animals changing their behavior.
Does this change what the voles do? And does that
have secondary effects?

Speaker 2 (38:57):
You know this I can't help but think about it's
hard to really set aside this idea that squirrels are
breaking bad here by eating meat, and like they have
this really dramatic moment where they say, now I embrace
death or something, you know, But I maybe the better
way to think of it is to remind ourselves, perhaps

(39:17):
that the squirrel doesn't see a difference between ultimately between
the food that is obtained from seed or a shoot
from a plant and from the body of a vowel.
You know. It's like these are all like distinctions of
vegetation and animal like. Yes, they're at present in the

(39:38):
strategy that is employed, the methodology of obtaining that food,
but in terms of like seeing this big divide between
plant world and animal world, between plant food and animal
food is maybe more of a human construct, and we
bring that baggage into examining these creatures.

Speaker 3 (39:56):
What are these big furry nuts that run away from me?
They're sure are delicious?

Speaker 2 (40:00):
Yeah, all right, So I was looking around as well
for some articles from the past several years on squirrels
in general, but also squirrels eating meat. And yeah, another

(40:22):
one that came to light since we last recorded the
blood dripping mos of squirrels. This is one that was
published in twenty twenty two. It was published in the
journal Acta Ethologica and it's titled first Evidence for active
carnivorous predation in the European ground squirrel by Kachamakova. At all, So,
the European ground squirrel is Spermophilus setellus. Now did we

(40:46):
already mentioned the genus Spermophulus close?

Speaker 3 (40:50):
The California ground squirrels are in the genus otto Spermophilus.

Speaker 2 (40:54):
Okay, so some similarities here in the naming. Anyway, some
of you might be wondering what why are they thought
of as spermophiles? Well, the translation to fixate on here
is seed love. So they are seed lovers as in
European ground squirrels sure do love to eat plant seeds. Yeah. So,
the endangered squirrel species in question here is native to

(41:17):
Eastern and Central Europe, and indeed a huge part of
its diet consists of seeds, plant shoots, also roots and
flightless invertebrates or in the mix as well. But this
paper presented evidence for active predation by the European ground squirrel,
in particular the hunting, killing, and eating of active animals,

(41:38):
so not merely the weaken, the dead and the so forth,
as we've been discussing, but actually going after I don't know,
more formidable prey. You might say, I don't know with
all the caveats of predation that we mentioned earlier. Now,
to be sure, European ground squirrels are still mostly eating seeds,
but in the spring they supplement their diet with bugs

(42:00):
consisting of quote considerable amount of animal components, and researchers
have also known for a while that they'll eat voles,
they'll eat green lizards. These have been found in their
stomach contents, which is a lot of the previous findings
that we've had to go on. Ground nesting birds are
also seem to be on the menu, and like many

(42:22):
other animals, European ground squirrels are also opportunistic cannibals. If
there is an opportunity to munch on a dead number
of your own species, or perhaps there's there also scenarios
where one might feast upon the young. That sort of
thing is totally on the table, you know, it comes
down to basic economy of energy.

Speaker 3 (42:41):
Yeah, and as we said, California ground squirrel does the
same thing occasionally if the opportunity presents itself, they'll eat
their own kind.

Speaker 2 (42:48):
Right, So, as has been the case with these other studies,
a lot of the past evidence was based on stomach
contents and observations of squirrels feeding on carcasses, but questions
remain actively pursue live prey, hunting and killing them, or
where they mirror you know, basically scavengers and at times

(43:09):
very opportunistic carnivores. Well, the authors point out that there
was no previous evidence of European ground squirrel's killing prey,
hunting and killing prey until now and that was the
that's the big finding of this paper. And getting into
the observation portion of the study, they share the following

(43:29):
on two six, twenty twenty at nineteen twenty seven, that's
the time in the area of the town of Schumann,
and they include of very detailed information about exactly where
this occurs. A young learning to fly Eurasian tree sparrow
Passer montanas was caught by an adult European ground squirrel.

(43:51):
The ground squirrel ripped out the sparrow's abdominal cavity and
started to feed on the bird's internal organs while still alive.
And waving its wings.

Speaker 3 (44:00):
Oh, and they got a photo.

Speaker 2 (44:03):
Yes, this is the photographic evidence of what they refer
to as the predation event. And yeah, you can see
this little guy again very arguably cute creature. And you
can also see that it is munching on the body
of a bird and there is blood flowing from the
mouth or look, I'm getting the sense of blood flowing

(44:24):
from the mouth of the squirrel.

Speaker 3 (44:25):
I have to share you included in the outline here
at the painting by Goya of Saturn devouring his son,
and the resemblance is striking. Yes, this is absolutely a
prelude to the witch's sabbath.

Speaker 2 (44:40):
Now as to why this particular European ground squirrel turned
to the meat of the living, they suspect that it
is a quote seasonal increase in the energetic needs of
the European ground squirrel. So again, this photo was taken
on June second. Interesting that our previous example was also
more or less than the same window with the voles. Yeah, July,

(45:04):
so the June second and the author's site that this
is a crucial and delicate time for the European ground squirrel.
So what's been happening in the European ground squirrel world
at this point is the males have just finished fiercely
competing with each other for mates, and so many of
them are weakened or even injured from those ensuing battles,
and just also just the energy expenditure of the whole endeavor. Meanwhile,

(45:27):
the females have already given birth and they are nursing
their young all right, which of course also requires a
lot of energy. On top of all of this, highly
nutritious seeds are not yet numerous in the environment, and
what is available is ravaged by overgrazing. Meanwhile, in the
bird world, juvenile birds have left their nests, so they're vulnerable.

(45:51):
They're not ready for this cruel world. And so these
seed loving rodents turn their ravenous attention to these available
riches of the flesh. The way they're analyzing it and
writing about it in the paper we have. Part of
it is the fact that there is suddenly this in
this case, a feathered fruit or nut that is available,
that is presenting itself, is on the menu. But also

(46:14):
on top of that, some of the seeds they really
depend upon are not yet available, and they're you know,
they're worn out and have increased nutritional needs, and so
it just leads right to the blood feast.

Speaker 3 (46:28):
So the situation is, we just finished some strenuous activity,
We're ravenously hungry. All the restaurants are closed. What what
are we going to do? Here's something, here's something with
feathers on it. It keeps flapping its wings. I'm just just
trying to eat the seeds. Yeah, yeah, the seeds out
of its belly. So another example here. And then you
know there's the added importance that they discussed in the

(46:50):
paper too, that this is an endangered species, and so
you know there's there's even added there's added incentive to
understand it and help us figure out, you know, how
to protect now. In looking I was looking through various
squirrel related news items from the past several years. Inevitably,
there have been a number of news stories dealing with squirrels,

(47:11):
generally in urban environments, behaving aggressively or even attacking human beings.
I may be remembering this wrong, but I sort of
think like they were the kind of reports that were like,
you couldn't totally discount them, but you also weren't sure
you should believe them either.

Speaker 2 (47:25):
Yeah. Yeah, a lot of these are, you know, anecdotal,
and I don't know. It's one of those things where
when squirrels are going about their normal business, nobody is
writing about it in the local newspaper, but there's one
attack and it gets written up. So I don't want
to present the idea that these attacks are common, but
they apparently did occur. So just a brief example of

(47:50):
some of the headlines I ran across. Here's one from
the Guardian from January twenty twenty one. It was angry
vicious spate of squirrel attacks leaves New York City neighborhood
in fear. At least three people in Rego Park and
Queens have been jumped upon and bitten by a possibly
deranged squirrel.

Speaker 3 (48:08):
Okay, I apologize for laughing. Squirrel attacks are in one
sense inherently funny, but now I'm thinking about it like
if a squirrel did jump on you and start biting you,
that would be scary.

Speaker 2 (48:17):
It would be terrifying.

Speaker 3 (48:18):
Okay, sorry, sorry, sorry for laughing.

Speaker 2 (48:20):
But still it just drives home the fact that we
often just totally disregard them or think they're cute and amusing,
and then when we encounter the savage side of the squirrel.
It is shocking and terrifying. Here's another one. This one's
from BBC News December twenty twenty one. Squirrel injures eighteen
people in two days of attacks in Buckley. A gray
squirrel which attacked and injured eighteen people has been captured

(48:42):
and put down.

Speaker 3 (48:43):
I'm gonna flag that one for later and go see
how the eighteen people were chained together. Here.

Speaker 2 (48:49):
Yeah, apologies, but I'm not going to respond to individual articles.
You were going to do more generally.

Speaker 3 (48:56):
I'm not taking questions on these squirrel attacks.

Speaker 2 (48:59):
Yeah, and here's another one. This was from NBC fifteen
News September eighteenth, twenty twenty four. Squirrels on a train.
Train ride canceled due to attacking squirrels Gomshal Suri. So
these are just a taste of some of the headlines
I ran across many more squirrel attack stories regarding isolated
incidents which seemed to regularly get picked up by the
media and sort of passed up the media chain. Now,

(49:31):
these incidents don't necessarily represent anything new. I don't want
to suggest that. That Guardian article, for example, by Oliver Millman,
points out that the two most likely causes for this
sort of behavior are, unsurprisingly disease on one hand, and
on the other hand, becoming overly accustomed to feeding by humans.
Ah yes, yeah, So on the disease front, of course,

(49:53):
Raby's which we've talked about on the show before. It's
apparently rare in squirrels, but it does happen according to
DC Sea Health, and that source, which is undated on
the DC Health website, claims that no person in the
US has ever contracted rabies from a squirrel, but it
is obviously possible for someone to contract rabies from a squirrel,

(50:14):
as they can carry rabies. Rabies concern, they point out,
is warranted, especially if the squirrel is behaving abnormally when
it bites you. And I did look up some of
this on the CDC website. Centers of Disease Control Prevention
says it's extremely rare for squirrels to have rabies or
to pass rabies to pets or humans in the United States. Now,

(50:36):
on the other end of the spectrum, the idea that
people are feeding squirrels that are getting close to squirrels,
and in doing so they are eroding the healthy fear
of humans that squirrels have. That is obviously a major issue. Squirrels,
no matter how cute they are in your eyes, they
should remain afraid of human beings and practices like feeding

(51:00):
them by hand is certainly just asking for a bite.
And also if they feel threatened it all, they will
also attack you, which it comes into the scenario as
well if you have already either you or other people
have done something to erode that distance between you and
the wild squirrel.

Speaker 3 (51:17):
This is the sinister inverse of the ecology of fear.
This is the ecology of brazen This.

Speaker 2 (51:24):
Yeah, I probably shared this story in the last Squirrel episode.
I'm gonna tell it again anyway. I only have so
many stories, folks. But years ago, my wife and I
encountered a very aggressive rock squirrel in Grand Canyon National Park.
Luckily no one was bitten or injured. But we were
out on a rocky hike along this like outcropping and
we'd paused for a moment. My wife had pulled out

(51:45):
a snack bar, and that's when a rock squirrel appeared
and began to move in very close, ultimately jumping on
her leg. Luckily, I believe she was wearing jeans at
the time and then we drove the squirrel away with
a hat. Luckily, again no one was hurt, but it
is always struck stuck with us as a great example
of why you don't feed wild animals, because again, you

(52:06):
you erode that that healthy gap between you and the
wild and then that animal thinks you are a source
of food and it can come in closer, and you know,
obviously it gets even worse when you're dealing with larger animals,
more destructive animals, and potentially deadly animals. And you know,
mainly thinking of bears here, but even with something like
the squirrel, you're you are doing that squirrel a great

(52:29):
disservice and potentially doing a great disservice to anyone that's
going to be in contact with that animal.

Speaker 3 (52:35):
Yeah. Yeah, this is why they emphasize like the bearproof
garbage cans in relevant areas and things like that.

Speaker 2 (52:40):
Yeah yeah, yeah, you know, And that's that's another big
thing too, Like you go through areas like Yosemite, and
you know, you frequently pass signs to show, well, a
bear died here because it was hit by a car, which,
on one hand, you know, cut down on speeding obviously,
but one thing that the Grand Canyon National Park points
out about squirrels in particular, but also the supplies to
other animals is if you're feeding them from vehicles, this

(53:02):
too causes animals to congregate near roads and vehicles, So
Grand Canyon National Park sometimes goes as far as to
say the rock squirrel is the most dangerous animal in
the park. If you're not familiar with the environment of
the Grand Canyon National Park, you should know that. Of
course they're much larger creatures, and some of those too.
You can make a strong argument that their natural aversion

(53:24):
to humans has been somewhat eroded. But squirrel incidents with
rock squirrels do occur due to humans feeding them. They
end up congregating near the places humans gather, including outside
gift shops and snack bars, and as Joshua Bowling reported
in an asy Central article from twenty eighteen, they've also

(53:45):
been reported to bite people just for pointing at them.
So again, this is not something that is going to
get you bitten by a squirrel in the wild that
is like naturally removed from your vicinity. But once you've
eroded that healthy day distance, things like this apparently become possible.
It feels threatened, it bites and so forth.

Speaker 3 (54:06):
Yeah, So when parks and other places say don't feed
the animals, they mean it. They're not messing around. There's
a good reason.

Speaker 2 (54:12):
Yeah, I mean, there's the old saying a fed animal
is a dead animal for many reasons. Roads, cars, contact
with humans, threats to humans, and so forth. Grand Cash
and the Canyon National Park advises you keep a distance
from wildlife, including their squirrels, don't approach the wildlife, including
the squirrels, and if the wildlife approaches you, you report it. So, yeah,

(54:36):
I tattle on those squirrels. Yeah, yeah, squirrels are wild animals.
I just want to. I'm not going to. There are
other recent news items one could get into, and I'm
not going to. But squirrels are wild animals and they
should remain wild, and we should do whatever we can
to keep them that way. It's our responsibility to the
environment that we have shifted and changed, and not just

(54:57):
because they might bite us. But let's that be the
added a stick to the carrot.

Speaker 3 (55:03):
Well what do you think, Rob? Does that do it
for today?

Speaker 2 (55:05):
I think so? We'll see what another five years. This
full update the State of the Squirrel Kingdom.

Speaker 3 (55:11):
To another squirrel sequel, yeah, or.

Speaker 2 (55:14):
Sooner if they eat more interesting things, you never never know,
never know what's going to come up.

Speaker 3 (55:20):
How do they level up from this? I guess they
got to start eating things bigger than them and then
they'd really get our attention once more.

Speaker 2 (55:26):
Absolutely all right, we're going to go and close it out,
but we'd love to hear from everyone out there. Do
you have thoughts on squirrels, your encounters, your observations, how
this information that we've discussed here or this podcast itself
has changed your view of squirrels, Or maybe you're like
just nodding your head and saying, yeah, this is squirrels

(55:47):
to a t. This is what they do, this is
who they are.

Speaker 3 (55:49):
Whatever your thoughts off.

Speaker 2 (55:50):
Yes, yeah, either way, write in let us know we'd
love to hear from you. Just a reminder that Stuff
to Blow Your Mind is primarily a science and culture podcast,
with core episodes in Twouesdays and Thursdays, short form episodes
on Wednesdays. Let's see, we have a weird house cinema
on Fridays. That's our time to set aside most serious
concerns to just talk about weird films. And then the

(56:11):
rest of the days we fill in with some classic
content vault episodes and so forth.

Speaker 3 (56:16):
Huge thanks as always to our excellent audio producer JJ Possway.
If you would like to get in touch with us
with feedback on this episode or any other, to suggest
a topic for the future, or just to say hello,
you can email us at contact at stuff to Blow
your Mind dot com.

Speaker 1 (56:38):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from my heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you're listening to your favorite shows

(57:02):
had noted the pocop