The hidden world that birds see

Birds navigate using Earth’s magnetic field, but scientists still don’t know how they actually sense it. Called the holy grail of sensory biology, magnetoreception offers a window into the thousands of unique sensory worlds animals experience. To watch this episode on video, find us on Netflix! Guest: Ed Yong, author of An Immense World: How Animal Senses Reveal the Hidden Realms Around Us For show transcripts, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unxtranscripts⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ For more, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unexplainable⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ And please email us! ⁠⁠⁠⁠[email protected]⁠⁠⁠⁠ We read every email. Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/members⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ Thank you! Learn more about your ad choices. Visit podcastchoices.com/adchoices

• 0:00Speaker 00

  Support for the show comes from Google Gemini. You know that moment when curiosity strikes? You're exploring a new city with the family and a sculpture catches your daughter's eye. What is that? Who made it? With Gemini, you can snap a picture and get a fully interactive breakdown of its history, architecture, and even hidden secrets. Gemini is built for moments like that. Whether you're learning something new, solving a problem, or looking for your next favorite thing, Google Gemini is here to help. Download Gemini, Google's AI app, or visit gemini.google.com to learn more.

• 0:39Speaker 01

  This episode is brought to you by Michelob Ultra. Good times mean competitions between you and your friends, like seeing who can throw some pigskin the farthest or rush the field the fastest. Winner gets an Ultra. Because it's not just a superior-like beer, it's also giving fans superior access to their favorite sporting events. Superior is worth playing for. Visit michelobultra.com/superioraccess to enter. Enjoy responsibly. Copyright 2026 Anheuser-Busch InBev Michelob Ultra Beer, St. Louis, Missouri.

• 1:10Speaker 02

  There's this bird that kind of blows my mind.

• 1:16Speaker 02

  It's called the bar-tailed godwit, and it migrates from Alaska all the way to Australia or New Zealand. A few years ago, scientists put a tracker on it, and they found that it flew for 11 straight days, so over 8,000 miles. And it was just in the air the whole time, flying over the Pacific Ocean. Scientists used to think birds were using the sun, or the stars, or some kind of vague, undefined instinct. But it seems like birds are also sensing Earth's magnetic field. They're sensing magnetism. Magnetism is this fundamental force of the universe that we can't see or feel, but it's

• 2:00Speaker 02

  powerful enough to shape stars, it protects planets, it moves compass needles, and somehow it guides birds across entire oceans. But magnetoreception is the only sense where we don't know what part of the body is doing the sensing. One researcher called it the holy grail of sensory biology. I wanted to figure out how much we don't know about all this, how much is still unexplainable. So I called up Ed Yon. Ed's one of the best science writers working today. He won a Pulitzer Prize for his work covering COVID and public health during the pandemic. But more recently, he wrote a very different kind of book.

• 2:41Speaker 02

  It's called An Immense World: How Animal Senses Reveal the Hidden Realms Around Us. It's about birds that might see magnetism, dogs that can smell time, fish that can sense electric fields, and all the ways animals live inside realities we can barely imagine. And if we grapple with that, if we really try to take that understanding seriously, it might change the way we see ourselves.

• 3:23Speaker 02

  Hi, Ed. Thanks for coming on the show.

• 3:25Speaker 03

  Hi, thanks for having me.

• 3:26Speaker 02

  So you won a Pulitzer for your reporting during the pandemic. How'd you get into animals?

• 3:31Speaker 03

  It's actually the other way around, really. I was into animals for as long as I was into anything. As a child, I went to zoos and watched nature documentaries and read books about wildlife that were way too advanced for me but had very beautiful pictures. So I've loved the natural world for my entire life.

• 3:55Speaker 02

  So you wrote this book called An Immense World. It's all about the various diverse ways that animals perceive the world we live in. I really want to focus on birds in particular.

• 4:06Speaker 03

  Great.

• 4:07Speaker 02

  How did scientists figure out birds weren't just using the sun or weren't just remembering where to go? Like, how did they realize this was an actual sensory system that could sense magnetism?

• 4:19Speaker 03

  Yeah, so this goes back to the 1950s, when some German ornithologists were watching birds at the time when they're about getting ready to migrate. Birds show this restlessness, this anxiety that in German is called Zugendrueche. And scientists just looked at these birds and realized that their restlessness wasn't just random. They tended to hop in a particular direction, like they had this sort of sense of which direction to go in.

• 4:50Speaker 02

  They're like hopping in the direction that they kind of want to migrate?

• 4:55Speaker 03

  Totally, yeah. You could put them in a cage, you could put the cage in a room that's completely isolated, so dark, no view of any landmarks, you can't see outside, much less the sun or the stars, and the birds are still hopping in basically the right direction. And then you can take wires and create an artificial magnetic field around the bird that basically flips the Earth's natural one. And now they start hopping in the opposite direction.

• 5:25Speaker 02

  Ah, so you can like control which way they want to go by controlling the magnetic field?

• 5:30Speaker 03

  Around them, yes, exactly.

• 5:32Speaker 02

  I think I want to just take a second to make sure I understand what exactly a magnetic field is.

• 5:39Speaker 03

  I don't know if I can define that exactly for you. I mean, I'm not sure I can define it for you exactly either. This is actually a very difficult thing to do, but I think, you know, the vision of magnetic fields that we get in the high school textbook will do for these purposes. So you have a bar magnet with north and a south pole, and you have lines that curve out from one pole and go back to the other. And these lines represent this field around the magnet that magnetic objects are influenced by. It just so happens that the entire planet is basically one of these magnets.

• 6:21Speaker 03

  The Earth has a solid iron core, and it's got a churning layer of liquid iron around that, and that turns it into basically a gigantic bar magnet with the same kind of field lines enveloping it. And so when I hold a compass and look at it, the needle on the compass is being influenced by the planet's field, and that's how we can tell a direction. Now, it seems that animals, migrating songbirds, sea turtles, possibly giant whales, many more, a lot of the ones that do these arduous, long-distance migrations, have these inbuilt biological compasses.

• 6:59Speaker 02

  I guess, I guess my question then is like, I'm looking at you with my eyes, right? I'm listening to you with my ears.

• 7:08Speaker 03

  Yep.

• 7:08Speaker 02

  What are birds sensing magnetism with?

• 7:12Speaker 03

  Great. Also, I love the way that you're asking these questions with a slightly confused tone. That is the right, that is the right tone, just to be clear.

• 7:21Speaker 02

  I have no idea how to even like wrap my, I'm gonna let you have the magnetic field thing without asking like 15 more questions on it.

• 7:28Speaker 03

  Yes.

• 7:28Speaker 02

  But, but yeah, I, what is in the bird that is getting them this information?

• 7:36Speaker 03

  The short answer is, we don't know.

• 7:39Speaker 02

  Perfect.

• 7:40Speaker 03

  And that's kind of astonishing. Just take vision. My eyes see. I can tell you exactly which molecules inside my eye are responsible for reacting to light and transforming that into an electrical signal that goes to my brain. That's all really worked out.

• 7:58Speaker 02

  Right.

• 7:59Speaker 03

  We don't have that for magnetoreception, and there are many reasons for that. One of the reasons is that with light, the stuff that we see, we know that light is blocked by living matter, and so any organ that detects light should be on the surface of the body or, you know, connect, exposed to it by some kind of hole. The problem is that magnetic fields permeate living matter. So they just go through my body, and they're not impeded by skin or bone or anything like that. And so a sensor that detects a magnetic field could be absolutely anywhere. It could be in one place, it could be, say, in a bird, it could be in their head, could be in their eye, could be in their butt, could be in their wings.

• 8:44Speaker 02

  Like, we just don't even know where to start looking, is what you're saying?

• 8:47Speaker 03

  Totally. One scientist described this to me as looking for a needle in a needle stack. And I don't think that beautifully conveys the challenge here. A lot of our intuitions about how sensing works just doesn't really apply here. And the other problem here is that theoretically, you shouldn't be able to sense a magnetic field, like, they're really, really weak. So right now, the molecules in my body are just kind of jiggling about on their own, and those tiny little movements pack billions of times more energy than the Earth's magnetic field. And the idea that something biological, something alive, should detect that is kind of preposterous.

• 9:32Speaker 03

  It's why, for a long time, scientists didn't believe that this was even possible.

• 9:37Speaker 02

  It's interesting, because my instinct would be like, okay, maybe they aren't sensing magnetism then, but we have pretty good evidence that if you flipped the magnetic field, they hopped in a different direction. They definitely are sensing magnetism. We don't know what the organ is.

• 9:52Speaker 03

  Yep.

• 9:53Speaker 02

  Do we have any guesses?

• 9:55Speaker 03

  Yeah, we have three reasonable guesses. So one involves this iron mineral called magnetite, and the crystals of magnetite basically work like a compass needle. So just picture that. You have cells with these crystals inside them that are moving in, depending on their relationship to the Earth's magnetic field.

• 10:17Speaker 02

  Almost like an inbuilt compass or something like that?

• 10:19Speaker 03

  Almost like an inbuilt compass. The second involves electromagnetic induction. So as a bird flies, its inner ear has these canals full of fluid that conduct electricity. And as those move through the planet's magnetic field, they get small electric currents induced in them. And maybe the bird can then sense those currents. We know that there are animals that can sense electric fields. That's a little bit easier than sensing the really weak magnetic field.

• 10:52Speaker 02

  Got it. Okay, so it could be magnetite, it could be...

• 10:56Speaker 03

  Induction.

• 10:57Speaker 02

  Induction.

• 10:58Speaker 03

  And then the third possibility, arguably is some of the strongest evidence backing it up, but it's also the most complicated. It kind of involves quantum physics, and I don't think we should go there, but I can explain it a bit more simply.

• 11:12Speaker 02

  I never think we should go there. Let's just write.

• 11:15Speaker 03

  Okay.

• 11:16Speaker 02

  Stay away.

• 11:16Speaker 03

  Let's imagine you've got a pair of molecules.

• 11:19Speaker 02

  Okay.

• 11:20Speaker 03

  That are locked in a partnership. Think of two dancers.

• 11:24Speaker 02

  Okay.

• 11:25Speaker 03

  When light hits those molecules, when a spotlight shines on the dancers, they start getting excited. They take hold, they begin the dance. And when they're in that excited state, they can be influenced by even something as weak as the planet's magnetic field.

• 11:43Speaker 02

  Ah, okay.

• 11:44Speaker 03

  And so by sensing those chemicals, we can get a sense of where the bird is relative to the planet. The chemicals in question exist in a bird's eye. And this raises the really, really tantalizing possibility that birds might actually be able to see the Earth's magnetic field.

• 12:09Speaker 02

  Wait, hold on, hold on. Okay, hold on. What is that? What is that? What? I don't even have a good question. What does that mean?

• 12:17Speaker 03

  Right.

• 12:17Speaker 02

  What would that be?

• 12:18Speaker 03

  It's good that you don't have a good question because I don't have any answers. So it's a match made in heaven. Look, we really don't know. We don't know which of these ideas is correct. And even if this one is correct, we absolutely don't know what it might be like. I like to imagine maybe it's a kind of like heads up display. Like maybe part of the bird's visual world has a different quality to it, maybe in terms of brightness or contrast or something that allows it to know over there, that's where I should go. But I really want to stress, this is completely made up. All of these possibilities are on the table.

• 13:03Speaker 03

  What does magneto-reception feel like to a bird? We have absolutely no idea. And I think that's kind of wonderful because it does open up the space to just freely imagine, right? Like when it comes to things like vision, we have a good starting place because we, most of us do it. But with magneto-reception, it's so strange, it's so alien that you really have no choice but to just let your mind go wild.

• 13:35Speaker 02

  Okay, I mean, you know where I have to go now because I know you're saying that we don't know and we can't know right now. But if we can freely imagine for a second, I don't know. What could that mean to see magnetism? Like if there are magnetic field lines, would that mean that everything a bird sees is like striped? How can we even try to conceptualize what this kind of sense would be like for a bird? What its internal experience could be?

• 14:09Speaker 03

  Yeah, with great difficulty, right? Like you'll notice that these hypotheses that I've put forward really involve converting magnetic fields into things that we're more familiar with.

• 14:19Speaker 02

  Yeah.

• 14:20Speaker 03

  Like something to do with vision or something to do with touch, right? And I think that's part of the challenge. It's not only that we don't have the sense, but we also really have no way of talking about it.

• 14:35Speaker 02

  Yeah, we don't have words.

• 14:36Speaker 03

  Right, we don't have a vocabulary. You know, with vision, we have brightness and image and dimming and all of this rich descriptive language. We have that for smell.

• 14:46Speaker 02

  Yeah, it'd be like asking what a song smells like or something.

• 14:51Speaker 03

  Right, like we just don't even have the starting place for describing what a bird might sense on its way.

• 15:04Speaker 03

  I think that's kind of wild, right? Because here, you know, you've talked about bar-tailed godwits, but like probably all migrating birds are using this to some extent. You know, it's the summer, like I just spent two months watching this glorious parade of species flying past me. In a couple of months, I'll see them coming back down south in the other way. They're all probably detecting magnetic fields. The sense that is so omnipresent around us, we can't describe, we find it really hard to study, we don't understand. We just know that it exists, which is kind of great.

• 15:48Speaker 02

  So what is it actually like to be a bird? Or a dog? Or a bat?

• 15:55Speaker 02

  We'll give it our best shot in just a minute.

• 16:07Speaker 01

  This episode is brought to you by Michelob Ultra. Good times mean competitions between you and your friends, like seeing who can throw some pigskin the farthest or rush the field the fastest. Winner gets an ultra. Because it's not just a superior light beer, it's also giving fans superior access to their favorite sporting events. Superior is worth playing for. Visit michelobultra.com/superioraccess to enter. Enjoy responsibly. Copyright 2026 Anheuser-Busch InBev Michelob Ultra Beer, St. Louis, Missouri.

• 16:35Speaker 04

  College football is back. So Hilton called to me, the superstition concierge, to make your fan rituals a reality. Need a room to match your lucky number? We got you. Want to make sure our team doesn't wash your lucky jersey? Oh, that smells lucky. Hilton's unmatched hospitality can keep up with any superstition. Even a marching band wake up call at 5:55 in 55 seconds. Hit it! When you need a team that will do whatever it takes on game day, it matters where you stay. Hilton, for the stay.

• 17:06Speaker 05

  When you need to build up your team to handle the growing chaos at work, use Indeed sponsored jobs. It gives your job post the boost it needs to be seen and helps reach people with the right skills, certifications, and more. Spend less time searching and more time actually interviewing candidates who check all your boxes. Listeners of this show will get a $75 sponsored job credit at indeed.com/podcast. That's indeed.com/podcast. Terms and conditions apply. Need a hiring hero? This is a job for Indeed sponsored jobs.

• 17:39Speaker 06

  You should be Professor X. And you should be Magneto.

• 17:45Speaker 02

  So this is really why I wanted to talk to you. More than the birds, more than magneto-reception. It's because of what we can get by imagining how all kinds of animals experience the world. And this is what your book, An Immense World, in large part is about.

• 18:03Speaker 03

  Yeah.

• 18:03Speaker 02

  But I wonder if you can tell me about the concept of an umwelt? This is sort of a central theme running through your book. What does that mean? Why is that relevant here?

• 18:11Speaker 03

  Yeah, so umwelt is just German for environment. But in the context of animal senses, it has a very particular meaning. So my umwelt is the part of the world that I can perceive. It is that unique blend of sights and smells and textures and sounds that I have access to. And the crucial thing here is that it's going to be totally different if I was another animal or if I was another individual. So if we had a bar-tailed godwit here, sitting in my lap, its umwelt would be radically different from mine. It would be able to sense the Earth's magnetic field. I can't do that. It would see colors that I can't sense. It will probably smell things that I can't sense. It would feel the air currents around the room in a way that I can't feel.

• 18:56Speaker 03

  And even though we share the same physical space, we would have a very different experience of that space. And that's what the umwelt concept is. I happen to think it's one of the most delightful concepts in biology because it hints that, you know, even in these places that we feel like we understand, we're really only getting this tiny fraction of all there is to get.

• 19:20Speaker 02

  Yeah. I wonder if you can take me through a couple of your favorite umwelts that really illustrate just the expansive diversity of perceptual worlds that animals have.

• 19:36Speaker 03

  Yeah, sure. So birds see a much wider range of colors than we do. They see ultraviolet, which is a color we tend not to see. And this massive catalog of ultraviolet blended in with other colors and kind of a cocktail of purples and similar hues. This means that when they're looking out in the world, they are seeing things that we absolutely do not. Patterns on flowers on their own feathers that we miss because we don't live in a world that's quite as colorful. When you go into the water, you have fish that produce their own electricity, their

• 20:17Speaker 03

  own electric fields, and can sense the electric fields given off by each other and by other living things. You have seals that can detect the turbulent currents left behind by swimming fish that basically act as tracks left behind in the water. Closer to home, my dog, Typo, senses this world of smells that I am absolutely not privy to. Like when we go on walks, this is made clear to me by the way he intently sniffs the sidewalks and pavements that look completely nondescript to my eyes and yet are bursting with interest to his nose.

• 20:58Speaker 02

  And with dogs, I mean, I've done some of this reporting on the show that, you know, based on how much of a smell has faded, the dog can almost smell time.

• 21:09Speaker 03

  Right.

• 21:09Speaker 02

  Which is something that is hard to wrap my head around.

• 21:12Speaker 03

  Yeah, smells linger in a way that a lot of other stimuli don't. And because of that, when a dog is sniffing, it's sort of sniffing into the past and a little bit into the future. It's anticipating things that are going to happen based on smells that have drifted in its direction. And, you know, I love thinking about that, the different nature of the different senses and what your experience of the world is like if you have a different primary sense to the vision that most humans rely on.

• 21:42Speaker 02

  Yeah.

• 21:42Speaker 03

  Because I think that as much as I don't think like this, I think there are a lot of people who really think that humans are the shit. You know, that we are the greatest species.

• 21:55Speaker 02

  We've never messed up.

• 21:56Speaker 03

  We're doing, we're doing great, guys.

• 21:59Speaker 02

  We're doing it.

• 22:01Speaker 03

  You know, that for many reasons that are understandable, our intelligence, the technology at our disposal, that we really are at the top of this ladder of being. You know, that's an idea that dates back to Aristotle millennia ago. But I think that the umwelt idea is very equalizing. It's a little bit dethroning. It's humbling. It shows that for all of those things, you know, we are still missing out on so much.

• 22:32Speaker 02

  Yeah, I mean, I think about This line from Wittgenstein, I think he said something like, if a lion could speak, would we understand him?

• 22:39Speaker 03

  Right.

• 22:40Speaker 02

  And, you know, it, there's all this work being done on like translating whale song or trying to communicate with animals as if the way to communicate is just to convert the noises they make into the letters that we use.

• 22:55Speaker 03

  Yes, yes, thank you.

• 22:56Speaker 02

  Right. And it does feel like there's just.

• 22:58Speaker 03

  There's a lot bigger differences than just.

• 23:01Speaker 02

  A lot bigger difference.

• 23:02Speaker 03

  Translation, you can't Google translate the whales.

• 23:04Speaker 02

  Or it'll be harder than we think.

• 23:05Speaker 03

  Thank you. Right. I think thinking about interspecies communication as just a matter of building a sufficiently advanced dictionary is the wrong way of thinking about it.

• 23:19Speaker 02

  Yeah.

• 23:20Speaker 03

  Because the deep mystery about the Umwalt idea is how does another animal perceive the world?

• 23:27Speaker 02

  Right.

• 23:28Speaker 03

  What does it feel like to be a bat, in the words of Thomas Nagel, a philosopher, or a bar tailed godwit, or my dog, or anything? And I think fundamentally, that is an unanswerable question.

• 23:39Speaker 02

  Yeah.

• 23:40Speaker 03

  There is always going to be this chasm, this divide between my subjective experience of the world and yours or that of another species. And that's okay. I think learning to sit with that unknowability and that discomfort of uncertainty is a big part of why I love this topic and why I love this idea, even if you know that you won't get the answer. It's the effort that matters and the effort that we should still make.

• 24:15Speaker 02

  Yeah, I mean, it does make me feel humble in the face of all of these species that we share the world with. And I think, I don't know, it also makes me think about you and me and every person I come into contact with. Because like, if this is the case with us and animals, you know, my friends and I, my family and I, my coworkers and I, we must be experiencing radically different versions of the world. And if we can accept at a certain level that we kind of are all experiencing something different, I feel like that humility has to extend to our relationships with each other.

• 24:59Speaker 03

  Yeah, you're absolutely right. If you do that, if you flex those muscles, you do start extending that to other people as well. And as well you should, because we all know that we are different from other people, right? We have different beliefs, values. But, but the Umwalt idea says that at a very, very fundamental level, simply the information that we can rest from the world, like the things that we perceive in our surroundings, even that is different. And, and I think it's a great base for thinking about how different we are from other people, trying to empathize with them. It's one thing to, to gawk and be amazed at bar tailed godwits and bats and dogs and

• 25:44Speaker 03

  even ticks, but I really hope that the values in the book help us be better people with other people, too.

• 25:52Speaker 02

  If you want to see this episode on video, head over to Netflix. This episode was produced by Valerie Schenkman and me, Noam Hassenfeld, it was edited by Joanna Solotaroff. Our video editors are Shelby Smith and Alex Coles. Our animator is Karim Kereya. Our fact checker is Melissa Hirsch. Our studio engineers are Devon Howard and Joe Nebrous. Mixing and sound design by Christian Ayala. Music from me. Meredith Hadnot runs the show. And Byrd Pinkerton watched as Flapton shaved down the sides of the guitar, pulling small

• 26:34Speaker 02

  pegs out from a pouch along his waist and hammering them in. "I still remember when I first made this for Platty," Flapton said. "She was the one that gave me the courage to fight back." Thanks as always to Brian Resnick for co-creating the show with Bird and me. And thanks to listener Daniel for writing in with a team I missed, the Anaheim Ducks, formerly the Mighty Ducks, a team I had forgotten about when I asked about teams named after works of art, especially galling because the Ducks are named after one of the greatest works of modern cinema. Love listeners who fact check. If you have thoughts about the show, we'd love to hear from you. Please email us at [email protected].

• 27:19Speaker 02

  Or if you'd like to support this show, join Vox. Become a member. Just go to vox.com/members. And if you signed up because of us, let us know. Unexplainable is part of the Vox Media Podcast Network, and we'll see you right back here next time.

• 27:35Speaker 07

  This episode is brought to you by Born in Roma Fragrances by Valentino Beauty, the iconic fragrance duo. Donna Born in Roma Eau de Parfum is a feminine fragrance featuring juicy black currant, central jasmine, woody cashmerin, and warm vanilla. Its masculine counterpart, Womo Born in Roma Eau de Toilette, has notes of fresh violet

• 28:20Speaker 07

  leaf, aromatic sage, green betever, spicy ginger, and mineral salt. Shop at macy's.com.