Why These Squirrels Are Eating Meat

In pop culture, squirrels are often seen as jerky, excited critters on the hunt for nuts to stuff themselves with and tuck away for later. But squirrels are on the hunt for something a bit meatier in the California Bay Area. Their target: local voles. The entire process — from hunt to kill — was captured on video. Want to hear more biology stories? Let us know by emailing [email protected] mailto:[email protected]! Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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  Hey, Short Wavers. Jessica Young here. And Regina Barber. With our biweekly science news roundup, featuring the hosts of All Things Considered. And today, we have Juana Summers. Hello. Thanks for having me. I hear today we're talking about carnivorous squirrels hunting in California. Yeah, yes. And also, a new study charting the biodiversity on ancient Earth. And new insights into how humans and dogs became friends. All that on this episode of Short Wave, the science podcast from NPR.

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• 3:57Regina Barber?

  OK, Juana, where do you want to start?

• 3:59Emily Kwong?

  OK, we got to start off with these squirrels. I thought squirrels ate nuts.

• 4:03Regina Barber?

  Yeah, so a study that was just published in the Journal of Ethology shows a group of California ground squirrels hunting, killing, and eating a vole, like a little mouse. And I talked with the lead researcher and a behavioral ecologist, Jennifer Smith. She's at the University of Wisconsin Eau Claire.

• 4:18Speaker 05

  We have one squirrel approaching a vole, targeting that vole, biting it at the neck, and take- Taking it down, eventually crunching through the skull and then eating the meat from the bones.

• 4:33Regina Barber?

  Wow, I am suddenly not hungry anymore. Okay, this really sounds like serious predator behavior. Is this a new phenomenon?

• 4:39Speaker 01

  Well, Jennifer says that if you look through the literature, there are other accounts of this.

• 4:43Speaker 05

  There's been accumulating evidence of one or two events within a species of a red squirrel taking a sparrow. They tend to try to take chickens?

• 4:57Regina Barber?

  There's also accounts of squirrels eating like roadkill or insects. But what's new here is that they've documented the whole process from start to finish with video, the hunt, the kill, and then the consumption. And they've shown that this isn't just like a one-off, but part of these squirrels' behavior.

• 5:12Speaker 06

  And where exactly do these fiercely predatory squirrels live?

• 5:17Speaker 01

  So this study is only looking at two populations of squirrels in a regional park in the Bay Area in California. They actually saw this during the 12th year of a long-term study.

• 5:27Speaker 06

  Okay, so we're talking about just two sets of squirrels in the Bay. But do these researchers think it's common, like, are all the squirrels out there that we see when we're going to work or going to the park or out on a run, are they just eating meat all the time? And like, we just haven't noticed?

• 5:40Speaker 01

  So Jennifer says that squirrels are actually like raccoons, bears, coyotes. They're just really flexible animals. And this vole population had a huge increase this year, you know, five to six times higher than normal. So the squirrels just took advantage of that.

• 5:54Regina Barber?

  Yeah, and Jennifer said the next big thing is to find out like how these squirrels learn this behavior. Are they teaching each other? Does this abundance of vole meat like lead to more squirrel babies? There's like so much to explore.

• 6:05Speaker 06

  All right, speaking of animals undergoing change, let's talk about this new study of species on early Earth. What's going on there?

• 6:12Speaker 01

  Okay, so first, just for context, if you look back at all the fossil evidence we have of life on Earth, we have an abundance of fossils starting around 540 million years ago. It's called the Cambrian explosion, which is when suddenly there are fossils of ancient mollusks and stuff. But before that, things are really more of a mystery.

• 6:32Regina Barber?

  So there's a few reasons. One researcher said that the time period is just less studied. And also, it's generally harder for organisms from this time to become fossils because their bodies were so soft and like they had no shells, no skeletons.

• 6:43Speaker 07

  They are not only soft, but also they are small. They are microscopic. So making it very difficult to accumulate enough data to have a meaningful analysis.

• 6:57Speaker 01

  OK, that is Shu Hai Xiao, a geologist from Virginia Tech. He's tried to find and study new fossils from this period. And now he's trying to make sense of it all and draw lessons about how biodiversity has changed throughout Earth's history, including in that early period.

• 7:11Regina Barber?

  Interesting. How's he doing that? So Shu Hai and his team use the existing fossil record, even though it's small, as a sample of all the species at different times in history.

• 7:20Speaker 07

  Kind of like in an election, right? So the pollster would take a small sample of the voters and they get an idea what their voting result will look like.

• 7:32Regina Barber?

  So from this small number of fossil samples, they can make some big picture inferences about the history of life on Earth.

• 7:38Speaker 06

  OK, that makes sense. Tell us what they found.

• 7:41Speaker 01

  So their data published this month in the journal Science has finally provided quantitative confirmation of some hunches scientists have already had. For example, there's this period called the Boring Billion. This is a time span of a billion years, starting around 1.8 billion years ago, in which paleontologists have guessed that there was probably very little diversity of life and pretty low turnover of species. And according to the paper's data, that's true.

• 8:05Regina Barber?

  And they also found that like right after the Boring Billion, there were ice ages that were followed by super rapid species turnover and like a boom of diversity, which has made Shu Hai wonder if ice ages reset evolution.

• 8:17Speaker 01

  And that's definitely one thing he wants to look into. And other researchers I talked to also told me that they just want more research and fossil data about the Boring Billion era in general. Because honestly, like this kind of work on early life is just really important to understand not only how life started, but how life adapts to environmental changes, like thinking about climate change now and in the future.

• 8:36Speaker 06

  All right, let's go from one ancient era to another. Now, we're going to talk about our ancient relationship with dogs. I have a very present day relationship with my dog, Bromo, who's kind of like my best friend.

• 8:45Regina Barber?

  Oh.

• 8:46Speaker 01

  Totally. I mean, I think our relationship with dogs as humans is just very longstanding. Researchers think canids, which include wolves and dogs, were probably first domesticated in Eurasia between 19,000 to 12,000 years ago. And new archaeological evidence, published in Science Advances, gets a closer look at that relationship in Alaska, in a window of time 12,000 years ago.

• 9:09Speaker 06

  OK, so just paint me a picture of what Earth was like in that time and how this relationship played out.

• 9:14Speaker 01

  Well, with the end of the last Ice Age, people had begun to cross the land bridge between Asia and North America. Researchers believe those people likely came with canid companions.

• 9:24Regina Barber?

  And new evidence of canid bones from Alaska supports that theory. Their paper analyzes more than 100 specimens, but the most interesting bone was excavated in 2018 outside of Fairbanks. There, researchers found a single tibia or lower leg bone, and DNA evidence suggests the bone belonged to some kind of ancient wolf or like proto-dog, and dated the bone to 12,000 years ago.

• 9:45Speaker 06

  Interesting. What made that leg bone such a fascinating find?

• 9:49Speaker 01

  The clues inside the bone. The team sought permission to analyze the bones from the Healy Lake Village Council, which represents the indigenous people of the area. And when the scientists did a chemical analysis of the bones, they found substantial traces of salmon proteins, meaning these canids regularly ate fish.

• 10:06Speaker 06

  That's very Alaskan of them, but I mean, how do we know that these canids weren't just out there hunting salmon themselves?

• 10:13Regina Barber?

  So salmon is not naturally available in big quantities in Fairbanks, which is why researchers think they were probably getting salmon from humans, like proof of domestication, at least for this one ancient wolf.

• 10:23Speaker 01

  An archaeologist, Angela Perry, who was not a part of the study, agrees with this conclusion, that this 12,000-year-old wolf with a salmon diet was either intentionally fed by humans or was heavily reliant on scraps, which suggests that this wolf lived in close, constant contact with human communities.

• 10:39Speaker 06

  Sounds just like my dog when he sits under my kitchen table and begs for scraps.

• 10:44Speaker 01

  Juana, thank you so much for letting us just babble about science.

• 10:48Regina Barber?

  Yeah, you're one of our favorites.

• 10:50Speaker 06

  Wow, what an honor. Please let me come back. I love this.

• 10:57Speaker 01

  You can hear more of Wana on Consider This, NPR's afternoon podcast about what the news means for you.

• 11:05Speaker 01

  This episode was produced by Rachel Carlson and Jordan Marie Smith. It was edited by Rebecca Ramirez, Christopher Intagliata, and Ashley Brown.

• 11:15Regina Barber?

  Tyler Jones checked the facts. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber.

• 11:23Speaker 01

  And I'm Jessica Young. Thanks for listening to Short Wave, the science podcast from NPR.

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