From the Vault: More Squirrels Eating Meat

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.

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 pre 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. We don't promote our T shirts store or 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 Yourmind dot com or check out the link

tree 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.

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 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 this news our way, thanks for letting us know. And yep, you got your way here we are talking about it.

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. 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 some bigger theoretical framework about mammal behavior. So the authors begin by talking about ways that animals adapt to their behavior to respond it 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 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 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. 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 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, Landrei, 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

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 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 from a jar.

These are cookies that react. You know, they react to the fact that they are being eaten, and they are two 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 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 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.

supply 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.

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 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 a qui because they adjusted their behavior in response to a predator, and so the authors of this nineteen ninety nine 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 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 you know, just an innert

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 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.

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.

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

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.

there's a 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. 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.

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.

I shall fight today. No no, no, there's still they're still going after off weekend, young old and so forth, because they are inherent increased risks involved in going after stronger prey.

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 Odospermophilus beachyi, hunting, killing and eating adult vertebrate prey animals 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. So a little sidebar, who are these California ground squirrels the Odospermophylis BEACHYI. First

of all, yes, they're cute. According to me, at least that's my opinion, Rob, I don't know if you share it, but yeah, they're cute little guys.

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.

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 it's it's hauntingly sad.

squirrels that you see, but it is bushy. Nonetheless, I don't know medium bushy.

predatory birds, and larger carnivorous mammals. So to be super clear, California ground squirrels mostly eat plants. The authors mention 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 or one hundred 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. 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 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 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 thing, 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, 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, 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. 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 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 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 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 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 in age 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 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 of winging it.

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 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.

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 consuming the exposed meat, organs, and cartilage. So an interesting thing about these gory observations is that is the context that 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 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, Briones Regional Park, sort 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 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 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 emphasize 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, after twelve years of intensive observation, we're seeing this this predation behavior happening all over the place within the range of this particular study, and it's it's like what it's like out of nowhere.

Apparently there were some undergraduate researchers who had been doing field work for this 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, no, But then saw the footage and it's right there.

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 a documentation of voles 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 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 roughly seven times more vole observations than the previous ten year average. So suddenly all these voles coming out of nowhere.

I mean it's in season exactly.

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 more behaviorally flexible squirrels. You know, if we're going around wherever we go, changing the nature of the environment, changing the you know, the very topography of the landscape, or 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 these secondary effects where we select for more behaviorally flexible populations of animals in the areas with proximity to human civilization.

Another how like how does it get triggered? You know, how does the squirrel know to shift? It's say like, okay, it is time to hunt now. And another interesting thing 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?

the European ground squirrel is Spermophilus setellus. Now, did we already mention the genus Spermophilus close?

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 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 seemed to be on the menu, and like many 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.

times very opportunistic carnivores. Well, the authors point out that there was no previous evidence of the European ground squirrels 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 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. 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.

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

its belly. So another example here. And then you know there's the added importance that they discussed in the paper too, that this is an endangered species, and so you know there's even added there's added incentive to understand it and help us figure out 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.

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.

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 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, 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 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.

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 was always struck stuck with us as a great example of why you don't feed wild animals, because again, you erode 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 disservice and potentially doing a great disservice to anyone that's going to be in contact with that animal.

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 Nation 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 they're they're natural 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

been reported to bite people just for pointing at them. So, again, this is not something that's 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.

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 rest of the days we fill in with some classic content of Vault episodes and so forth.