Squirrels: The Return
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I'm Jason Alexander. And I'm Peter Tilden. And together, our mission on the Really Know Really podcast is to get the true answers to life's baffling questions like why the bathroom door doesn't go all the way to the floor, what's in the museum of failure, and does your dog truly love you? We have the answer. Go to reallyknowreally.com and register to win $500, a guest spot on our podcast, or a limited edition signed Jason bobblehead. The Really Know Really podcast. Follow us on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.

Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. Hey, welcome to Stuff to Blow Your Mind. My name is Robert Lamb. 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,

We what year was it was it in 2018 that we did a pair of episodes on squirrels that that turned out to be real fan favorites and I'll say host favorites too we we think about squirrels quite often and I've never really thought about them the same way ever since we did those those shows.

That's right. They were quite popular, talking about squirrels, their history, human and squirrel interactions, and what exactly squirrels eat. Yes. One of the big revelations from our research hall for those episodes was that

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 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 dead animals, attacking baby birds in their nests, maybe even preying on their own kind. Some kind sometimes just squirrels eating of the flesh.

Yeah, yeah. And a lot of this breaks down just to the basic idea that squirrels are more complex than 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 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, 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 our appreciation that grew out of that is we busted out, I think, two different T-shirt designs for our T-shirt store. Wow.

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 TeePublic store, you can find a link at StuffToBlowYourMind.com or check out the link tree on our Instagram at STBYMPodcast.

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 Skug, 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 them.

Agreed. But there have been recent developments that caused us to return to the issue of squirrels 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 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. P.S. There's a Mountain Goats album called Beat the Champ, and it is entirely about Lucha Libre. No synth, though. Off 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. We may have heard from a few other listeners over the years, too, occasionally sending in some squirrel news. I have found in combing through the squirrel news since 2018 is that generally squirrels make headlines when there is blood involved. Yeah. So we'll be touching on a few different shades of this.

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, Joey E. Ingritson, McKenzie M. Miner, LSC Oestreicher, Mari L. Potas, Tia A. Rivara, Lissandra

Lupin ML Tellus Jada C. Wall Lucy M. Todd and Sonia Wilde and the paper is called vole hunting novel predatory and carnivorous behavior by California ground squirrels published in the Journal of Ethology 2024 as I said I think it was out just this month in December 2024.

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 some bigger theoretical framework about mammal behavior.

So 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 all of the other animals are, well, you know, they're not as smart 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 any climate or ecological situation. But I

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 can't do it at all. Yeah.

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 by the time I read this. But the concept is called the ecology of fear.

And this is a bit 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 Memology published in 1999 by Brown, Landre and Gurung called The Ecology of Fear, Optimal Foraging, Game Theory and Trophic Interactions.

What 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 like a little park area 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 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 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 the foxes. Now, how would that be? It would be because, as the authors of this 1999 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 from a jar. These are cookies that react. You know, they react to the fact that they are being eaten and they are to varying 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 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 the main variables are going to be like the number of predators and the number of prey, how many 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. Right.

So to 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 times of day they do things. They might change their foraging strategies.

They might hide more or move away from any suspected predator more 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 frightening them.

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 of the city. And yeah, that's going to potentially

potentially interfere with everything that was going on. It's going to change the local criminal ecology. Yes, yeah. It'll change 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. For another not-quite-perfect but I think interesting analogy, I was thinking just about supply and demand in human economies. Hmm.

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. 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. It's 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 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 1999 paper summarize the effect 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 into the study about squirrels? Well, the authors of this 2024 paper cite the ecology of fear as an example of how prey animals, including squirrels, are

are not well modeled by thinking of them as rigid, inflexible machines or as like a, you know, just an inert resource like cookies in a jar. Instead, we should understand that to 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 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 from 2018. The paper is called Squirrels as Pets.

Predators by J.R. Callahan, published in The Great Basin Naturalist, 1993. You remember this one, Rob? Oh, absolutely. Yeah. And of course, if you're reading any subsequent papers about squirrels as predators, they all cite this one. Yeah. This seemed to be a major publication in the world of squirrel predator research.

Callahan really seemed to do the legwork in 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 just standard predation versus what is called facultative predation.

An 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. Yeah, especially in the case of obligate carnivores, you know, where this creature has to hunt. Meat is what it eats. 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. Mm-hmm.

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 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 eat foraged meat and sometimes even actively catch and kill live prey when

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 from the literature. Just to gloss over them quickly, this includes birds, frogs, rats, lizards, rabbits, gophers, moles, snakes, fish, voles,

ducks, 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 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. Right.

Yeah. So if 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 so forth. But then also you have a lot of data that is arrived at via analyzing the stomach contents of harvest squirrels. And of course, that data

doesn't provide a lot of context. Like, you can look at it and say, well, they still mostly eat seeds or plants or whatever, but there's a certain amount of meat. As to how that meat was obtained, you have to draw conclusions sometimes because, yeah, there's...

Of course, you can scavenge. You can take out prey that are just weak or helpless, juvenile, and so forth. But then there is that threshold, right, that you cross into potentially actively hunting prey.

prey, actively hunting something that is not like wounded or dying, but is to some degree like a valid, healthy prey creature. 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, the

Despite the growing consensus that many squirrel species opportunistically consume meat, much of the early evidence for predation is based on stomach contents or the killing of heterospecifics in captive settings, e.g. 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 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 like caught in a trap or something. 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. Certainly we've covered enough examples of predation in the past to know that there are plenty of obligate carnivores, obligate predators around.

Who are still there. They're obviously not going to go out and say, all right, show me the strongest of the pack. No, that is the one I should buy today. No, no, no. They're still they're still going after off, you know, weekend, young, old and so forth because they're in inherent increased risks involved in going after stronger prey. Predators use their coupons. They're 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, 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 squirrel or Otospermophilus beechii, 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 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. ♪

I'm Jason Alexander and I'm Peter Tilden and together on the really no really podcast our mission is to get the true answers to life's baffling questions like why they refuse to make the bathroom door go all the way to the floor we got the answer will space junk block your cell signal the astronaut who almost drowned during a spacewalk gives us the answer we talk with the scientist who figured out if your dog truly loves you and the one bringing back the woolly mammoth plus is

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So a little sidebar, who are these California ground squirrels, the Otospermophilus beechii?

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. 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,

I think of them as... I just know too much about them. And I see them too often. I think of them as... It's hard for me to imagine someone thinking they're straight-up adorable because I hear them on the fence. I see the effects of their claws on the fence. They're like furry grappling hooks. They're clearly tough creatures. I saw one fight off a hawk once in my backyard. Oh. Yeah. It's...

They're rough and tumble. So, yes, cute, but with a number of caveats as far as my opinion of them goes. Well, I think it's going to be all caveats from here on out. So, yes, they're cute. But Rob, 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 that

And I thought this picture was, I don't know, it 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. Yeah, I have a real visceral reaction to this. There's something heartbreaking about a potentially wasted avocado.

I feel like this one is savable. I think I could get in there with a knife, cut off the part that's been fouled by the squirrel, and have plenty left over for sandwiches and whatnot. You better do a good job because you don't know what the squirrel's been eating before the avocado. Well, I think it's only going to seep in so far. I'm going to cut that part off and spread the rest.

So these California ground squirrels, the adults typically grow to around 20 to 30 centimeters long in the body, plus another half body length or so again with the tail. They have a mottled 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 not as bushy as the common tree squirrels that you'll see, but it is bushy nonetheless. Medium bushy maybe.

They are natives to the western part of North America, found today in U.S. states of California, Oregon, Washington, and Nevada, and extending south into Baja, California. They generally inhabit grasslands 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 and 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 mentioned that 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 100 different species of plants that 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. 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 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 eating insects and other invertebrates and eggs and nestlings of numerous birds, including killdeer, California quail, bobwhite quail, ring-necked pheasant, morning dove, dark-eyed junco, and American robin.

Continuing the agricultural pest theme, they have been documented chomping right on into domestic chicken eggs. They have been documented to eat fish. I think there's just one occasion of this, but eating a small silvery fish called the California grunion.

And then finally, the authors note, quote, Fitch, 1948, 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, just because a squirrel is eating a rabbit, that doesn't mean it caught and killed a rabbit. It might have found a dead one. Free meal. Right.

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 California ground squirrels. And there have also sometimes been observed species.

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 right conditions, they will absolutely do plenty of that.

The specific prey here was the California vole or Microtus C. 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 this paper,

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 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 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. 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 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 is 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 of winging it. But on another level, you could say it's like they also kind of know how to do it as well. 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. Yeah.

The authors summarized saying, quote, hunters successfully captured and killed a vole in 17 of the 31 observed hunting attempts, which is 55 percent. So they observed 31 cases of a squirrel trying to kill a vole. 17 of the 31 worked. The other 14 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 70% of these kills, the squirrel would not eat the vole directly at 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 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. Right. And now you're presenting a two for one deal. So you get out of there. Oh, man. If you're like a hawk right here or something, 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 11 of the events for which consumption of an intact carcass was observed, squirrels first removed the head of the vole. So that's just procedure. Head remove, remove head first. Next, they either directly pulled meat out of the torso or first stripped fur from each of these body parts before consuming the exposed meat organs and cartilage.

So an interesting thing about these gory observations is that is the context they came in because these observations were made within the context of a larger project known as the long term behavioral ecology of California ground squirrels project.

which have 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 Briones Regional Park in California, B-R-I-O-N-E-S, Regional Park, sort of northeast of Oakland and Berkeley.

Interestingly, the project was in its 12th year before these instances of squirrels killing and eating voles were first observed. And that doesn't mean it never happened before. But the squirrels have been studied intensely for 12 years in this region before anybody observed 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. Hmm.

I was reading a press release about this paper that was giving some narrative about how the scientists came to these observations. And they interviewed the lead author, Jennifer E. Smith, who is an associate professor of biology 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 she emphasizes how strange it is that squirrels are just such a familiar animal to people. People just see them in their yards, in the park all the time. And here suddenly, after 12 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 students

researchers who had been doing field work for the study and they came 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 but then saw the footage and it's right there yeah

Yeah, you can't argue with this footage, some of these grisly photos. 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 2024.

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 previously unobserved behavior suddenly 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 observation, which was a massive increase in documentation of voles logged by local citizen scientists in the area on an app called iNaturalist, which is sort of a biological and wildlife social media platform kind of place reading log wildlife and citizen science app. Yeah, yeah.

And so they notice, huh, that's interesting. So we're seeing suddenly ground squirrels showing this thing we've never noticed before where they're 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 compared the number of vole sightings reported on this app to the 10-year average from before and found that the peak of vole sightings in the summer of 2024, there were roughly seven times more vole observations than the previous 10-year average. So suddenly all these voles coming out of nowhere.

Yeah. And what, and what are you going to do? Right. What are you going to do when there are that many voles around? Exactly. So, um, uh, according to the authors, it is normal for some vole populations to kind of boom and bust. They cycle through these, uh, these population density, uh,

And they tend to kind of peak every three to five years. But the peak achieved in the summer of 2024, Rob, you can see from a chart I've included, was like way, way more than the normal peaks, even the previous peaks from like you can see in kind of 2020 or so. It's such a peak that it doesn't make you judge the squirrels at all. You're like, maybe we should have been eating voles as well. Yeah.

Clearly, it's out of control. Right. 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 the second one is squirrels shift their foraging strategy from, oh, let's mostly focus on grains and other plant matter to if you see a vole, chase it and kill it. I mean, it's in season.

Exactly. Yeah. 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? Yeah.

One of the authors of the paper, Sonia Wild of 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, and I thought that was kind of interesting because on one hand, you could just say, well, you know,

these squirrels, the 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

If humans could have inadvertently by our presence helped create populations of 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 sort of in our wake cause the secondary effects where we select for more behaviorally flexible populations of animals in the areas with proximity to human civilization? 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 it's squirrels ripping heads off.

Now, plenty of unanswered questions remain, like how common is this really 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 parent offspring? Or is it a kind of instinctual ingrained behavior? In which case, what sort of instincts are harnessed from the normal foraging strategies and repurposed for hunting if it is instinctual? How does it get triggered? How does the squirrel know to shift and say, OK, it is time to hunt now?

And another interesting thing, you're like, what are the secondary dynamics that emerge? We were talking earlier about secondary dynamics that you might not always envision that come out of animals changing their behavior. Does this change what the voles do? And does that have secondary effects?

You know, this I can't help but think about like it's hard to really set aside this idea that squirrels are breaking bad here by eating meat. And like they they have this really dramatic moment where they they say, now I embrace death or something, you know. But maybe the better way to think of it is to remind ourselves perhaps that the squirrel doesn't see a difference between death.

Ultimately, between the food that is obtained from seed or a shoot from a plant and from the body of a vole. You know, it's like these are all like distinctions of vegetation and animal. Like, yes, they're present in the 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. What are these big furry nuts that run away from me? They sure are delicious. Yeah. ♪

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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 one that came to light since we last recorded the blood dripping moths of squirrels. This is one that was published in 2022. It was published in the journal Acta Ethologica and it's titled First Evidence for Active Carnivorous Predation in the European Ground Squirrel by Kachimakova et al. So

The European ground squirrel is Spermophilus satellus.

Now, did we already mention the genus Spermophilus? Close. The California ground squirrels are in the genus Otospermophilus. Okay. So some similarities here in the naming anyway. Some of you might be wondering 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. Ah.

Yeah. So the endangered squirrel species in question here is native to Eastern and Central Europe. And indeed, a huge part of its diet consists of seeds, plant shoots, also roots, and flightless invertebrates are 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. So not merely the weakened, the dead, and the so forth, as we've been discussing, but

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, consisting of, quote, a 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 also seem to be on the menu. And...

And like many other animals, European ground squirrels are also opportunistic cannibals. If there is an opportunity to munch on a dead member of your own species, or perhaps there's 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. Yeah. And as we said, California ground squirrel does the same thing. Occasionally, if the opportunity presents itself, they'll eat their own kind. 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. Did they actively pursue live prey, hunting and killing them, or were they mere, you know, basically scavengers? And...

And at times very opportunistic carnivores. Well, the authors point out that there was no previous evidence of European ground squirrels killing prey, hunting and killing prey,

Until now. And that's the big finding of this paper. And getting into the observation portion of the study, they share the following. On 2-6-2020, at 1927, that's the time, in the area of the town of Schumann, and they include...

Very detailed information about exactly where this occurs. A young, learning to fly, Eurasian tree sparrow, Passer montanus, was caught by an adult European ground squirrel. 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. Oh!

Oh, and they got a photo. Yes. This is the photographic evidence of what they refer to as the predation event. And

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. Look, I'm getting the sense of blood flowing from the mouth of the squirrel. I have to share, you included in the outline here 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. 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 2nd. Interesting that our previous example was also more or less in the same window with the voles. June, yeah. June, July.

So the June 2nd, and the authors cite 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, the females have already given birth and they are nursing their young.

All right. Which, of course, also requires a lot of energy. Yeah. 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. 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. So the way they're analyzing it and writing about it in the paper, 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 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. So the situation is we just finished some strenuous activity. We're ravenously hungry. All the restaurants are closed. What are we going to do? Here's something. Here's something with feathers on it. It keeps flapping its wings. I'm just...

I'm just trying to eat the seeds. Yeah, yeah. The sticky seeds out of its belly. So another example here. And then, you know, there's the added importance that they discuss in the paper, too, that this is an endangered species. And so, you know, there's even added incentive to understand it and help us figure out, you know, how to protect it.

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, 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. Yeah.

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 some of the headlines I ran across. Here's one from The Guardian from January 2021.

It was angry, vicious. Spate of squirrel attacks leaves New York City neighborhood in fear. At least three people in Rego Park in Queens have been jumped upon and bitten by a possibly deranged squirrel. OK, 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. It would be terrifying. So sorry. Sorry. Sorry for laughing.

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 2021.

A squirrel injures 18 people in two days of attacks in Buckley. A gray squirrel, which attacked and injured 18 people, has been captured and put down. I'm going to flag that one for later. I'm going to go through how the 18 people were chained together here. Yeah. Apologies, but I'm not going to respond to individual articles. We're going to do more generally. I'm not taking questions on these squirrel attacks. Yeah.

And here's another one. This one's from NBC 15 News, September 18th, 2024. Squirrels on a train. Train ride canceled due to attacking squirrels. Gamjol Suri. So these are just a taste of some of the headlines. I ran across many more squirrel attack stories regarding isolated incidents, which seem to regularly get picked up by the media and sort of passed up the media chain. Mm-hmm.

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Now, 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, rabies, which we've talked about on the show before, it's apparently rare in squirrels, but it does happen, according to D.C. Health. And that source, which is undated on the D.C. Health website, claims that no person in the U.S. has ever contracted rabies from a squirrel. But it is obviously possible for someone to contract rabies from a squirrel, 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 for 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, 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 them by hand is certainly just asking for a bite. And also, if they feel threatened at all, they will also attack you, which 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. This is the sinister inverse of the ecology of fear. This is the ecology of brazenness. Yeah.

I probably shared this story in the last Squirrel episode, but I'm going to 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 paused for a moment. My wife had pulled out 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 has always struck, stuck with us as a great example of why you don't feed wild animals. Because again, you, 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, I mean,

I'm mainly thinking of bears here. But even with something like the squirrel, you are doing that squirrel a great disservice and potentially doing a great disservice to anyone that's going to be in contact with that animal. Yeah, yeah. This is why they emphasize like the bear-proof garbage cans in relevant areas and things like that.

Yeah, yeah, yeah. You know, and that's another big thing, too. Like, you go through areas like Yosemite and, you know, you'll frequently pass signs that show, well, a bear died here because it was hit by a car, which on one hand, yeah, cut down on speeding, obviously. But one thing the Grand Canyon National Park points out about squirrels in particular, but also this applies to other animals, is if you're feeding them from vehicles, this, 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 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 AZ Central article from 2018, they've also 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 distance, things like this apparently become possible. It feels threatened, it bites and so forth.

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. 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 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, I'd

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 because they might bite us, but let that be the added stick to the carrot. Well, what do you think, Rob? Does that do it for today?

I think so. We'll see, what, another five years, this full update, the state of the squirrel kingdom. Do another squirrel sequel. Yeah. Or sooner if they eat more interesting things. You never know. Never know what's going to come up. 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. Absolutely.

all right we're going to go and close it out but uh we'd love to hear from everyone out there do you have thoughts on squirrels your encounters your observations um 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 to a t this is what they do this is who they are uh whatever your thoughts off yeah yes

Either way, write in and 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 on Tuesdays and Thursdays, short form episodes on Wednesdays. Let's see, we have Weird House Cinema on Fridays. That's our time to set aside most serious concerns to just talk about weird films and

And then the rest of the days we fill in with some classic content, vault episodes and so forth. Huge thanks, as always, to our excellent audio producer, JJ Posway. 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 stufftoblowyourmind.com. Thank you.

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I'm Jason Alexander. And I'm Peter Tilden. And together, our mission on the Really Know Really podcast is to get the true answers to life's baffling questions like why the bathroom door doesn't go all the way to the floor, what's in the museum of failure, and does your dog truly love you? We have the answer. Go to reallyknowreally.com and register to win $500, a guest spot on our podcast, or a limited edition signed Jason bobblehead. The Really Know Really podcast. Follow us on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.