The hidden world that birds see

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1:20There's this bird that kind of blows my mind.

1:26It's called the Bartailed 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 powerful enough to shape stars.

2:13It 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 Yong. 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. It's called An Immense World, How Animal Senses Reveal the Hidden Realms Around Us.

2:58It'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.

3:34Hi, Ed. Thanks for coming on the show. Hi, thanks for having me. So you won a Pulitzer for your reporting during the pandemic. How'd you get into animals? 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. 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.

4:18How 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?

4:30Ed Yong: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 Zügenruhe. And these 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. They're like hopping in the direction that they kind of want to migrate? Totally, yeah. You could put them in a cage. You could put the cage in a room that's completely isolated.

5:13Ed Yong: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. Ah, so you can like control which way they want to go by controlling the magnetic field. Around them. Yes, exactly. I think I want to just take a second to make sure I understand what exactly a magnetic field is. I don't know if I can define that exactly for you.

5:56I 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 a 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.

6:19Ed Yong: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. 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 in 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.

7:10I guess my question then is like, I'm looking at you with my eyes, right? I'm listening to you with my ears. Yeah. What are birds sensing magnetism with? Great. Also, I love the way that you're asking these questions with a slightly confused tone. That is the right tone. Just to be clear. I have no idea how to even wrap my—I'm going to let you have the magnetic field thing without asking 15 more questions on it. But yeah, what is in the bird that is getting them this information? The short answer is we don't know. Perfect.

7:50Ed Yong: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. 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, exposed to it by some kind of hole. The problem is that magnetic fields permeate living matter.

8:37Ed Yong: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. It could be in their eye. It could be in their butt. It could be in their wings. Like we just don't even know where to start looking is what you're saying. Totally. One scientist described this to me as looking for a needle in a needle stack. And I think that beautifully conveys the challenge here. A lot of our intuitions about how sensing works just doesn't really apply here.

9:15Ed Yong: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. It's why for a long time scientists didn't believe that this was even possible. 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 flip the magnetic field, they hopped in a different direction.

9:59They definitely are sensing magnetism. We don't know what the organ is. Do we have any guesses? Yeah, we have three reasonable guesses. Okay.

10:10Ed Yong: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. Almost like an inbuilt compass or something like that. Almost like an inbuilt compass. Okay. 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.

10:54Ed Yong: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. Got it. Okay, so it could be magnetite. It could be induction. And then the third possibility, arguably, are 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. I never think we should go there. Let's just stay away. Let's imagine you've got a pair of molecules that are locked in a partnership.

11:34Ed Yong:Think of two dancers. Okay. 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. And so by sensing those chemicals, we can get a sense of where the bird is relative to the planet. it. 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. Wait, hold on. Okay, hold on. What is that?

12:24What is that? What? I don't even have a good question. What does that mean? What would that be? 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

12:42Ed Yong: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 of 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. What does magnetoreception 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?

13:29Like when it comes to things like vision, we have a good starting place because most of us do it. But with Magnetic Reception, it's so strange, it's so alien that you really have no choice but to just let your

13:43Ed Yong:mind go wild. 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. 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, like something to do with vision or something to do with touch, right?

14:35Ed Yong: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. Yeah, we don't have words. 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. Yeah, it'd be like asking what a song smells like or something. Right. Like we just don't even have the starting place for describing what a bird might sense on its way.

15:15I 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 and 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.

15:59So what is it actually like to be a bird or a dog or a bat? we'll give it our best shot in just a minute

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18:23You should be Professor X and you should be Magneto. So this is really why I wanted to talk to you. More than the birds, more than magnetoreception. 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. 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? Yeah.

18:56Ed Yong: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.

19:33Ed Yong:It would 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. And even though we share the same physical space, we would have a very different experience of that space. And that's what the Umbold 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. 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.

20:20Yeah, 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 cues.

20:40Ed Yong: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 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.

21:28When 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. 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. Right. Which is something that is hard to wrap my head around. 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.

22:14Ed Yong: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. 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. We've never messed up. We're doing great, guys. We're doing it. 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.

22:56You 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. 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? Right. And, you know, 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.

23:39Yes. Yes. Thank you. Right. And it does feel like there's just a lot bigger differences than just translation. You can't Google translate the whales or it'll be harder than we think. Thank you. Right.

23:51Ed Yong:I think thinking about interspecies communication as just a matter of building a sufficiently advanced dictionary is the wrong way of thinking about it. Because the deep mystery about the Umwald idea is, how does another animal perceive the world? Like, 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. 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.