The Builders

In an episode first aired back in 2025 on our sister show, Terrestrials, we take you on a musical journey all about beavers. Few mammals have a bigger positive impact on the planet than the beaver. With its bright orange buck teeth, the creature is an expert engineer that brings life wherever it waddles and even fights fires. Our story begins in the Bronx river, once known as the “open sewer” of New York City. After some humans decide to clean it up, we meet one of the river’s residents - José the beaver. We learn about the US government parachuting beavers out of planes into the mountains. And finally head to California where we discover how one beaver family saved acres of land from burning.

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  Hey, it's Latif. Earth Day is coming up on April 22nd. So this week, I wanted to bring you a story that is just a wholehearted celebration of nature from Radiolab's spinoff, Terrestrials. We released it last fall in the Radiolab for Kids feed. But look, I am a card-carrying grownup, and I really enjoyed this one. And I think you will too, no matter how young or old you are. Lulu will tell you more in a second. So, without further ado...

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  Wait, you're listening?

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  Okay.

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  All right.

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  Okay.

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  All right.

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  You're listening to Radiolab. For kids!

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  Radiolab.

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  From...

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  WNYC.

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  See?

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  Yep.

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  Three, two, one. Imagine...

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  You wake up in the dark.

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  Your eyes dart around to see...

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  A little circle of blue shimmering light.

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  You waddle over on your webbed feet and realize it's water.

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  So you dive in, headfirst.

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  As you kick and glide, you grow fur.

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  Really thick fur.

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  And an extra set of eyelids.

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  That act like goggles underwater.

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  And then you look behind you to find...

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  A big, black, scaly paddle.

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  It's your tail, which you can slap on the water with a nice, loud... You have become...

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  A beaver.

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  Okay, now is the part where I make you sing the theme song with me.

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  Okay, I'm ready. Terrestrials, terrestrials. We are not the worst, we are the... First.

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  Try again, opposite of worst is?

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  The best. Bestrials.

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  Yeah, you got it!

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  Okay, I like it.

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  Terrestrials is a show where we uncover the strangeness waiting right here on Earth. I am your host, Lulu Miller, joined as always by my song bud...

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  Take me to the river.

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  Alan. Swimming with the beavers.

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  So here we are kicking off this brand new season of Terrestrials. Well, all around us, really hard things are going on. Wildfires, wars, climate change. And so we wanted, in this moment, to look to creatures that might give us hope. Creatures that actually mend the world around them. And there is maybe no mammal that has such an outsized positive effect on the planet than beavers. Yep, those buck-toothed, waddling, funny-looking rodents. By the end of the episode, you will see how a single family of beavers can have such a positive impact on the world around them, you can literally

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  see it from space.

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  So our story today is going to center around one little beaver named Jose. He will rise out of murky waters in a place where no one expected he could survive. And to tell us his tale is producer Bud Anna.

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  Yep, that's me.

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  Yeah, you know, Jose is this incredible symbol.

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  And here to help me is Ben Goldfarb, who's a writer.

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  And beaver believer.

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  Don't stop bee believing. So Jose, he waddles out into the world with little webbed feet and whiskers and very large buck teeth that are bright orange. Because apparently...

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  Beaver's teeth actually contain iron.

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  Whoa, metal teeth?

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  Yeah, like a chisel.

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  The iron makes their teeth excellent for chopping down trees. Because beavers have one single obsessive hobby. It's not drawing or knitting or doing puzzles.

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  The classic beaver behavior that most people know about is they build dams.

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  A dam is basically a wall in the water that beavers build by dragging the trees that they chomp down across a flowing stream, blocking the water. And sometimes adding mud or other stuff to keep that wall sealed up tight.

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  And you see them sometimes carrying rocks around and their little front paws waddling on their hind legs. It's like the cutest thing ever.

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  A beaver dam makes water accumulate behind the barricade, turning a trickling stream into a new pond in the middle of the forest.

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  Ah, time for a shrimp.

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  Anna, can I just interrupt to ask why? Like, I've always wondered this about beavers. Like, a beaver like Jose, why is it driven to go through all this work to chop down trees and make a wall that creates pools? It just feels so random?

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  That's a great question. There, I mean, a beaver out on land is basically a fat, slow package of meat. Think about wolves and mountain lions and bears and coyotes. All of those big animals are gonna want to eat a beaver.

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  According to Ben, it all stems from the fact that beavers are super awkward on land. With their webbed feet and huge tail that drags on the ground, beavers are not good at running, making them easy pickings for land predators.

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  So if you're a beaver, you want to spend as little time on land as possible.

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  So?

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  By making dams, they create deep pools of water, which allows them to transform from wobbly wolf snacks into elegant professional swimmers who can spin and twirl and...

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  Can hold their breath for up to 15 minutes.

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  15 minutes?

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  Yeah, they're like a magical animal. Yeah, they're just incredible.

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  Pretty epic hiding place. Now, hundreds of years ago, in the time of Jose's great, great, great, great, great, great, great grandparents, the woods of North America was full of beavers.

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  There were probably several hundred million beavers.

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  Making dams and ponds everywhere, even in New York City.

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  There would have been beavers all over New York City.

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  That's right. The Big Apple was once...

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  The Beaver City.

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  And the beavers of Beaver City would wake up every evening, that's right, beavers are mostly nocturnal, in their beaver homes and hit the road, or the stream, I guess, and get to work.

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  Hey, I'm waddling here.

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  Hauling stones and sticks and redirecting water and finishing off each day with a nightcap of sweet wood juice.

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  Manhattan Island was one of the most lush, incredible ecosystems on the eastern seaboard, and beavers were part of what made it that way.

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  But about 400 years ago, all of that would change because of the arrival of Europeans and their insatiable desire for...

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  Hats.

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  Hats?

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  Top hats and cocked hats. Trapper hats with ear flaps, Wellingtons and sugar loaves. That's another name for witch hats.

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  Made of beaver fur. Sorry, guys. They killed them off by the millions for the fur trade. And as the beavers began to be killed off, the land and waterways began to change, pretty dramatically. Like, take the river that slides through the northern part of New York City, winding beside train tracks and beneath highways today. It's called the Bronx River.

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  It was described as an open sewer.

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  That's Christian Murphy. He works on the Bronx River today.

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  It was really just an elongated landfill.

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  And over the centuries, more and more animals disappeared from the river, including the few remaining beavers. And by the 1970s...

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  Parents told their kids, "Don't go down there. It's not safe."

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  Because for decades, companies all along the river used it as a convenient dump for their waste. And people had just given up on the Bronx River. They thought it was just too polluted to care about.

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  In many places, you couldn't see the water because of how thick the trash was.

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  Until one day, someone said...

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  "You know what? This river does not need to look like this. This river could be beautiful. This river could be full of life."

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  Inspired in part by the first Earth Day in 1970, a couple of folks from the neighborhood, like a lady named Ruth and a guy named Fred, they put on gloves and boots and began picking up the trash, bag by bag, day by day. And at first, people kind of laughed. They thought, "What good is a couple of bags of trash gonna do? This whole river's polluted." But then some kids joined in.

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  "Let's do this." "High five."

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  Scooping out trash by the huge garbage bag full. And eventually, someone very powerful joined in too.

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  "Hello, hello."

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  Congressman. His name was Jose Serrano, with a big friendly smile and a bigger bushy mustache. "Let's roll up our sleeves." And start to clean. Who directed millions of dollars to the cleanup project, ordering in trucks with big cranes to fish out refrigerators in cars and helping to change the rules over where factories could dump their toxic waste. And soon.

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  The river began to respond.

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  The water got cleaner and the forest began to regrow around it, bringing in more bugs and birds until

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  a little creature popped its whiskered head out of the water.

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  And it was a beaver.

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  Jose!

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  After an absence of more than 200 years, the beaver has come back to New York City.

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  And so they named him Jose in honor of that congressman who'd been an early bee believer that a little awkward human effort could make a big difference.

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  What an honor!

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  And the fact that Jose the Beaver showed up in the Bronx River wasn't just a sign that the water was getting cleaner, because beavers clean the river too, just by being there and being beavers. See, there's a hidden power to beaver dams. They actually make everything around them healthier.

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  And that happens in a few different ways.

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  So first, there's the water. The dams act like purifiers that filter out pollution like trash and even.

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  Chemicals from agriculture.

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  Which get trapped in the dam and drop down into the soil instead of getting carried out to sea. Second, dams cool the air.

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  Because the pools that dams create mean more water is being evaporated into the air. And so when it's hot, it's kind of like a mini air conditioning unit, making it more hospitable to all kinds of creatures. Third, dams enrich the soil. Nutrients in the water get stuck and drop down into the earth, which creates more fertile ground.

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  And fourth, the real biggie. All of this combined allows new life to sprout. Algies, grasses, cattails and flowers, which attract...

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  Baby trout and salmon.

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  And dragonflies and butterflies and...

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  And frogs and salamanders.

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  And then birds come.

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  Woodpeckers and herons.

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  And pretty soon, coyotes and foxes and in some regions...

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  Moose will come down there to eat all of the aquatic vegetation growing in the ponds.

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  Thank you, Beavs!

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  And in Jose's case, after just a few years of him hanging out in the Bronx River...

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  Somebody looked and squinted their eyes and said, "Wait a minute. There's a second beaver there. There are two beavers."

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  Sacre beave! Another beaver!

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  And so Jose and the second beaver, they were roommates.

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  Classic New Yorkers.

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  Sharing rent on the river, sharing groceries, you know, cutting down the same trees together. And it gets better.

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  I can't imagine it getting any better. But it does. Because you've maybe heard of a little-known pop star named Justin Bieber? Well, they held a naming contest and...

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  And the second beaver was named Justin Beaver.

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  Thank you, Alan. Jose and Justin lived together for years. Munching on wood, swimming with their eyes peeking out of the water, and slowly but surely increasing the biodiversity of the river and the forest around it. And as time has ticked on, the river has only grown healthier, welcoming back snapping turtles and sunfish and even, as was spotted in 2023...

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  Two dolphins swimming around in the Bronx River.

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  No. Yes. Dolphins? Uh huh. Yep.

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  Okay. Go beavers. I can't, I mean, imagine if like, everywhere you walked, you just sprouted flowers and life followed you.

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  That would be nuts.

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  I mean, how long does it actually take? Like, once a dam goes in, is it years before you start seeing this greening effect?

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  No, that's the thing. It's super fast. Like, within a couple of months, there'll be cattails and lily pads and swamp roses blooming.

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  Wow. Okay, so just to recap everything these funky little guys are doing to the world around them. Their dams are cleaning the water, cooling the air, making the soil richer, and increasing biodiversity in these pretty dramatic ways.

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  Yep.

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  But that's it, right? Like, there's no, there can't be anything else.

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  There's so much more.

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  Our next storyteller thinks beavers can even fight fire.

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  Find out how after this break.

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  Pollsters are gearing up to get a bad rap yet again, but they do more than sometimes miss on election outcomes. People want to raise taxes on the rich. I can tell you that definitively because we know it from polling. And if we lose trust in polls, we have no way to understand what Americans want to be done. On this week's On the Media from WNYC.

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  Find On the Media wherever you get your podcasts.

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  Look, up in the sky, it's a bird, it's a plane, no, it's beavers parachuting down from the clouds? Crates full of beavers, part of a shipment to be dropped from an airplane. No, this is not an old-fashioned cartoon. It's something that our governments actually did in the 1940s and 50s. Some folks in a couple of different states put them in boxes and then...

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  And drop those boxes out of airplanes with parachutes on them and let them land in the mountains to do good for us, like move them from the cities to the mountains.

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  You're kidding right now, right?

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  They literally pushed them out of planes. Idaho did this, California did this.

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  This is Dr. Emily Fairfax, and she explains that this was the government's weird idea for pest control. They took beavers that were being nuisances, turning people's yards and farmlands to swamps, and then just dropped them off in the mountains.

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  They are live trapped and moved to distant mountain lakes and streams where their efforts will aid to conserve water, provide fishing pools. Instead of like taking them out on a horseback or a car, they trapped them out of planes, but you know, I give them credit for trying. Now into the air and down they swing, down to the ground near a stream or a lake.

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  Emily gives them credit because she too is trying to bring more beavers out into the wild where they might be able to do some good for the planet. Although that did not used to be her job, far from it. She used to be an engineer who worked on?

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  Weapons.

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  Weapons?

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  Nuclear weapons.

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  Whoa.

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  Very different career path.

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  But she happened to turn on the TV one night and catch a nature documentary.

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  And they were showing all these aerial shots of beaver dams and wetlands in the desert, and they were bright green. And I was like, what? Beavers live in the desert? How can they keep it green when everything's so dry?

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  And she realized that just like her, beavers were engineers.

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  Using all of their engineering to live a good life.

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  And mend the world around them.

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  And I wanted that for myself, so I started studying beavers and I haven't looked back since.

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  Emily hung up her nuclear weapons coat and put on some rubber overalls for a new job, following beavers through wetlands to try to learn how they do what they do. And eventually she came to focus on this one little family of beavers that lived up high in a mountain in northern California in a creek.

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  It's called Little Last Chance Creek.

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  So she called the family the Little Last Chance Beavers. There was a mom, a dad, and?

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  There were definitely three to four babies there.

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  Aww. And she started watching them literally taking notes as they?

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  Timber!

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  Constructed their intricate dams and lodges.

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  We're logging a busy day at work.

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  And she discovered that on really hot, sweaty days inside a beaver's house.

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  It's cold in there.

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  You've been in a beaver lodge?

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  I have.

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  And on super cold days outside? It's super toasty.

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  So the beavers sleep in a big snuggle pile in like one room.

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  Oh.

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  It's very sweet.

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  That's really sweet.

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  They kind of snore sometimes. It's extremely cute.

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  And Emily learned that their family members weren't the only ones staying warm in there.

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  They might have mice that want to come live inside the lodge with them. They might have muskrats that want to live inside the lodge with them. They might have little snakes that want to live inside the lodge with them.

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  Ugh, they allow this? They allow these trespassers?

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  Oh, absolutely. It's kind of like they're running a little bed and breakfast, which I call a bee and beef.

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  Ah, there we go.

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  Winter turned to spring, spring to summer, and then one day, there was a spark. And the dry grasslands and forests around the little last chance beaver family caught fire and began burning and burning.

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  It was a really devastating fire. It burned a lot of forests.

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  This was back in the summer of 2021, and it became one of those mega fires we're seeing more and more of because of climate change. Thousands of people had to be evacuated, hundreds of houses burned down. And as for the plants and critters of the mountains?

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  It seems like absolutely everything has burned.

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  By October, humans were finally able to extinguish the fire, but Emily had no idea what happened to those beavers.

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  Could they have survived the fire?

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  So one day, she began the long drive up the mountain.

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  And the drive up is very disheartening because everything is just blackened and it's silent.

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  Which was the creepiest and strangest part to me.

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  So I'm not feeling like super confident.

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  But she keeps driving.

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  And we find a route in.

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  They get out of the car and begin walking. And suddenly?

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  It is loud. It is splashing water. There's all sorts of birds. There's lots of bugs. There's a lot of wind in the trees and the grasses and the rustling you expect.

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  Oh, wait. And even there being wind in the trees means there's still trees standing?

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  There's still trees. The pine trees that were near it are fine. The trees that are in the wetland are fine.

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  It was completely green.

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  Completely unburnt. Not even just like a little burnt. Like they were unburnt. And When I got there, like honestly, it was like tears in my eyes.

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  Why tears?

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  Because I drove past the burned houses coming up and the burned roads and all the things that we wanted to protect and couldn't. And thinking about the future of climate change and knowing that this is the future that's coming, that's a really difficult reality to wrap your head around. I was living in California at the time. Like, I was seeing my future there. And then getting up to the beaver wetland, it was a very hopeful moment because sometimes it feels like we're all out of ideas and it's not working. But then, right in front of me, something is clearly working. And even if we don't know exactly why or how yet, we can learn from it.

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  And as for the little last chance beavers?

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  I did stay out in the evening and saw both mom and dad swimming. And when they were out swimming, I could hear three, maybe four, different young beaver wines coming from where the lodge was.

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  They made it.

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  Yeah.

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  And it wasn't just them. When Emily looked at the area from way high up in space from a satellite, she saw something incredible. This halo of green around the beavers' dams. She guessed that this one little family, these five or six awkward beings, had saved about seven and a half acres of land from burning.

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  Yeah, that effect is called making fire refugia. It's a patch that doesn't burn that other things can use.

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  Refugia is a fancy word, sort of like for refuge. It's just like place that is safe?

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  Mm-hmm.

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  Okay.

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  Exactly.

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  Refugia.

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  I love this word. I have not stopped thinking about it since Emily taught it to me. How might we all create a little refuge around us for the other beings of this world? Even if we are clumsy and awkward and waddling and tired? I think about the people in the Bronx, those first two or three people who started picking up trash.

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  We got this!

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  And eventually created a ripple effect that cleaned up the river. These things can happen. They do happen in the human world and in the animal world.

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  That day at the beaver dam, Emily saw frogs and birds and even a bear, creatures she suspects might not have survived the fire without that beaver family. And that's why she has come to see beavers as firefighters.

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  Yeah, they're spreading water out across the whole landscape that's keeping everything nice and green and healthy and stopping it from being easy to burn.

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  Emily has tested this effect in mountains and forests and deserts.

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  And so far, what we've seen is that they are really good at making fireproof patches pretty much everywhere.

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  Little rings of green that you can literally see from space.

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  You know, when we talk about restoring nature, we don't always know how to do that. But guess what? Beavers instinctively know what it's supposed to look like.

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  That's Beaver Believer Ben again. He and Emily both work in different ways to inspire and convince people to protect beavers.

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  One of the mantras of the Beaver Believer goes, "Let the rodent do the work. They'll store water for us. They'll capture pollution. They'll help us fight wildfires. They'll create habitat for all of the fish we like to eat and the birds we like to watch and so on. They do all of this stuff for us if we let them.

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  Another mantra: Be more beaver. What if we too worked to build structures that actually mended instead of harmed the land? As pie in the sky, or impossible as that may seem, there are people already out there doing just that, following in the beavers' footsteps, waddling awkwardly toward a better world, one step at a time.

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  Let me see that tail slap.

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  We're small and awkward, and the challenge is tough. If we work together, we can rise above. We waddle on until the job is done. So don't cry as a river. You know we'll just dam it up. I'm a beaver believer. Beaver, beaver.

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  You little overachiever. I'm a beaver believer. Beaver, beaver. Let's get to work. If you believe, roll up your sleeves and... Let me see that tail slap.

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  Even though they're kinda weird, the beaver's got it going on. Those little awkward engineers, sometimes it only takes just one. Maybe two, just a few little critters to chew what needs to be done. And change the world for everyone.

• 25:37Speaker 03

  Alan Gofinski, Gofinski, everybody. He used real beaver tail slaps as percussion in that. Uh, and that's it. There's nothing else cool about to happen.

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  What's that?

• 25:49Speaker 04

  Excuse me, I have a question. Me too. Me three. Me four.

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  The Badgers. Listeners with badgering questions for our experts. Are you ready?

• 25:58Speaker 05

  Absolutely.

• 26:00Speaker 07

  Hi, my name is Felix, and I'm six years old. Do baby beavers have baby teeth?

• 26:12Speaker 03

  Yep. Not the big buck teeth, but some of the side teeth, which are called cheek teeth. Cheek teeth, cheek teeth, cheek teeth. Say that 10 times fast.

• 26:19Speaker 07

  My name is Remy, and I'm six years old. Since beavers eat wood, what does...

• 26:25Speaker 03

  Does that poop look like?

• 26:27Speaker 05

  Well, they do the double poop.

• 26:29Speaker 03

  The double poop? What does that mean? They poop once and then what?

• 26:35Speaker 05

  They eat that again.

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  Bah.

• 26:36Speaker 05

  And then when it comes out, it looks like a sawdust marshmallow. And the little sawdust marshmallows, if you dry them out, they're actually great fire starters.

• 26:42Speaker 03

  What? Have you ever done that?

• 26:44Speaker 05

  I have burned one to see if it could burn, and it burned just fine.

• 26:47Speaker 03

  Now, that's what I call a useful nugget.

• 26:50Speaker 07

  Hi, my name is Tyler. I'm 39 years old. I am trying to figure out how do beavers raised in captivity know how to build a dam, even if they've never seen a river?

• 27:04Speaker 05

  They learn from their instincts and also from following around their parents and brothers and sisters and trying to do what they do.

• 27:10Speaker 03

  Wait, so are there regional differences in architectural style? Like how you get Swedish modernism or southwestern adobe?

• 27:19Speaker 05

  Anecdotally, yeah, there are. And some of them built some really weird dams.

• 27:23Speaker 03

  Really? Like, how so?

• 27:25Speaker 05

  Like, at like 90-degree angles from one another, like zigzagging instead of having nice curvy shapes.

• 27:30Speaker 03

  Huh.

• 27:31Speaker 05

  They like teach their kids what's available to build with. It could be garbage, mud. I have seen cow bones. I have seen all sorts of interesting things.

• 27:39Speaker 03

  Oh, spooky, a dam made out of bones? Like a skeleton dam?

• 27:43Speaker 05

  No joke, I saw that on a Halloween field tour, and I thought someone had like set it up for me.

• 27:47Speaker 03

  Haunted lodge, haunted dam.

• 27:49Speaker 05

  Just like cow knuckle bones and a femur, and they're just like integrated into this dam. It was like unreal.

• 27:56Speaker 03

  And that's where we gotta leave it with the Spawuuki Beaver Dam. And I won't tell you that vanilla ice cream, candy, yogurt, and many perfumes used to be made with an oil that came from the beaver's booty. It was called castorium. And that's true, if you used to eat like vanilla ice cream or certain candies back in the time of like your great-great-grandparents, you were actually tasting beaver bum. I won't tell you that because I'm nice, but I did learn it in Beaver Believer, Ben Goldfarb's great book called Eager: The Surprising Secret Life of Beavers and Why They Matter. Highly recommend you check it out. And that'll do it for today. Terrestial's with- Created by me, Lulu Miller, with WNYC Studios. Our executive producer is Sarah Samback.

• 28:40Speaker 03

  This episode was produced by the naughty gnawing-on-wood Anna Gonzalez. Tail-slappingly-good sound design by Mira Burtwin-Tonic. Our team also includes Alan Gofinski, Talia Chala, and Joe Plord. Fact-checking by Diane Kelly. She would not let us get anything wrong. "Wood" spelled W-O-O-D. Support for Terrestrials is provided by the Simons Foundation, the Arthur Reining-Davis Foundations, and the John Templeton Foundation. Thank you. We have got new episodes churning out every two weeks. We hope you'll listen and subscribe to the Radiolab for Kids feed, and tell your friends. It really helps our chances of getting to keep going. We also have social media, where Alan drops Frog Fact Friday videos every Friday. Frog Fact Friday.

• 29:26Speaker 03

  And we also have animated music videos contests, and just like me saying hello in various natural places, that's @terrestrialspodcast. And if you want to submit a badger's question, sign up for our newsletter or check out past episodes, just head on over to www.terrestrialspodcast.org. Okay, hopefully all those links would work for you. Would work? Would work? Nah. Okay, be very careful out there. Go sink your teeth into some good stuff. And see you in a couple spins of this dirty, old planet of ours. Woo, woo, woo, woo, woo. Bye.

• 30:06Speaker 04

  Hi, I'm Maddy, and I'm from Frederick, Maryland. Leadership support for Radiolab's science programming is provided by the Simmons Foundation and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.