Reflections
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It's a hot, sunny day in the African bushveld. A pride of lions rests under the shelter of some trees. While the females care for their cubs, a large male lounges a short distance away. He rests. Occasionally, swatting flies away with his tail, and all is calm until, out of the corner of his eye, he spies another tail, also swatting flies away.

He gets up to investigate further, and in perfect sync, the owner of the other swatting tail jumps up to its feet too. It's another male. The lions freeze, staring at each other intently. One takes a step forward, and so does the other. One cocks their head, and so does the other.

Ready to defend his pride, our male charges this intruder. Both run towards each other. The distance between them closes. But instead of coming teeth to teeth, both lions crash into a pane of reflective glass. Their nose is pushed up against a mirror. Our brave, courageous male lion doesn't realize, but the stranger he's ready to stand up to is none other than his own glorious reflection.

I'm Rutendo Shackleton. And I'm Sebastian Echeverry. And this is the BBC Earth Podcast.

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LinkedIn, the place to be, to be. In this episode, we're talking about reflections. We've got disoriented bats, fiber optic fish, and the bird that does incredible impressions. ♪

So this lion was taking part in one of science's favorite experiments, the mirror test. Yes, he was. This experiment was actually an activity that I did when I was an intern at the Lion Rewilding Program in Zimbabwe. We got a very long mirror and put it against the lion's enclosures. And what we do was wait and see what the lions did once they noticed their reflections. So what did you see with these lions? They were very, very big.

They were really interesting. So for the younger lions, they were really unsure, you know, if this reflection they were seeing, this other lion they were seeing was friend or foe. So they were crouched down, approaching the mirror really slowly, you know, unsure, sniffing this air around them to try and figure out who this stranger was.

But then you had the large males who were just guns blazing. They were ready to defend their territory. And so they'd come and they'd charge the mirror and they'd be growling and roaring. And they were spraying so much urine everywhere. Like we had to make sure that we were not in the splash zone. We didn't expect that. But they were really like... Oh, that's an image. I know, right? Yeah.

You cannot get lion urine out of anything very easily. So we made sure that we step back a lot. But then we have the older lions who were a bit more chilled and relaxed. They were so interesting because they saw their reflection and then started rubbing their faces and their heads and their bodies open.

So even though it sounds like none of the lions figured out that they were looking at themselves, you still got a little bit of insight into how they deal with strangers. Yeah. But...

It's probably the first time they've ever seen a mirror, right? Mirrors are not a thing that most animals will ever see in their entire lives. So it's got to be like this fundamentally strange experience of seeing your reflection for the first time. You've seen other lions, but never one quite like this. Yeah, not one that you can't smell, that you can't see the back of, right? For sure. Cheers.

But while mirrors might be rare, that doesn't mean that reflection itself is not important in the animal kingdom. There's quite a few animals that use the reflection and refraction of light in mind-blowing ways. Animals whose very survival depends on how they can shape light that hits them.

For example, the very shiny marine hatchet fish that does some incredibly cool things with light. Just in room light, they really look like standard kitchen aluminum foil. Super consistent, exactly the same amount silvery over every little square millimeter block.

That's Allison Sweeney, an evolutionary biologist at Yale University. They're just really visually striking. Now, is that a common thing for, like, fish? Because I feel like my mental image of fish in the ocean is that they've got these silvery, shiny sides. Is that reflectiveness a common adaptation out there? Not when you're fishing at 600 meters.

They live in this zone of the ocean called the midwater, which tends to be deeper than where photosynthesis can happen. So there's not enough light to power plants and algae or bacteria anymore. But you're not fully in the true, like, abyss where it really is super black. We would be able to see. So it turns out their first major task is just don't get eaten.

All right, so I'm a hatchet fish. I'm hanging out with a dozen of my best friends. We're just flicking around a little bit, standing mostly still in an empty giant void. And we're looking for predators. Who is out there and how are they hunting me? So there's going to be squids and other bigger fish. Is this like gulper eel territory? Yeah, giant moths that just sort of swallow you down whole and eyes that sort of sit in the top of their heads looking directly upward. All right.

So right now, the hatchet fish seems to be in a really tricky situation. From below, they're contrasted against the bright background of the sky, and these giant fish with giant jaws are looking straight up at them.

And it gets worse. The same fish with the underslung jaws and the eyes pointing straight up often have headlamps, basically. So fish have evolved headlamps for hunting around for prey. And if you think about it, being a mirror seems like a pretty bad adaptation for hiding from something looking for you with a headlamp. I think I can see that. So you've got these...

giant fish hunting around and they've got headlamps as well. And if you're a hatchet fish, you're basically a mirror to them. So when they flash their big headlamps, then they'll just reflect and they'll find you and they'll eat you, right? That is the dangerous situation these fish find themselves in. There's predators from below, there's predators from the side. What are they going to do? But the hatchet fish, they do have something going for them.

They are very narrow, and they've got a really clever trick up their sleeve. Or should I say, on their bellies.

Yeah, so there will be really harsh shadows coming straight down. And the direction that you'll get the best visual contrast is by looking straight up. Because now the background is the brightest thing there is. And so you make yourself as tiny as possible in the vertical direction. And then they go one step further and they put light bulbs on their belly. That is awesome. Let me get this straight. If I've got it right...

Allison has just said that these fish have light bulbs in their bellies. Allison's talking about these special organs on the bottom of the hatchet fish called photophores, which, you know, they don't have glass, but they basically behave like a light bulb, except that they're on the bottom of a fish.

These little organs on the belly light up with both the correct color and the correct angular distribution of downwelling light. So it's actually like a cloaking device that replaces the light that goes missing because there's a fish in the way. In other words, the hatchetfish are hiding in plain sight. When a predator is looking up from below, it's searching for the silhouette of the hatchetfish against the bright sky.

But thanks to the photophores on the belly of the hatchet fish mimicking the light from the sky, it makes them appear basically invisible to the predator. And the way that it works is actually really, really cool. It all begins with these super shiny scales on the side of the hatchet fish.

Allison and her team spotted something really strange. We actually noticed that if you shine a flashlight on the side of the fish, the light comes out the photophores on the belly. It turns out the skin is doing something pretty clever with light that hits it that is different than just, you know, aluminum foil or a mirror. Allison discovered the shiny outer layer of the fish's skin is actually very thin.

And under that, you have these bundles that are long and skinny and run from the back to the belly of the fish that in cross-section look a lot like fiber optic cables. Hold up. Did Allison just say fiber optic cables as in the cables that carry light to bring me high-speed internet? Yeah, that is 100% right. So these fish not only have light bulbs or, you know, the photophores on their bellies...

Those are actually powered by fiber optic cables. I asked her how it works. Okay, like try to take me through like the journey of like a beam of light. I'm coming out of the predator's headlamp. I'm hitting the side of a fish and is it the photons of light? Are they like bouncing through these bundles in the fish's skin and they like the light bounces all the way down out of the belly? Is that what's happening?

Yeah, that's exactly what happened. So if I am a beam of light coming in, I first hit this mirrored structure, and a little bit of me bounces off as if I were a mirror, but most of me penetrates into this fiber optic structure, and so it seems to just sort of randomly bounce around in there until it finds its way out the photophores in the bottom. So if I'm this predator, if it was a mirror, I'd see like this bright light

light bouncing right back at me, I'd be like, aha, go there. But because they've got skin that reflects light in this really special way, the light's all spread out, so it's just like a faint little thing that I might not even notice. Exactly. So the hatchet fish have got fiber optic cables in their skin, but they don't quite work like the ones that we use to carry our internet connection.

We've engineered our cables to ensure that they don't lose any of the signal. But the hatchet fish actually kind of want them to be a little leaky.

Allison says that's not as bad as it sounds. You know, at first glance, you look at the structures and they look sort of sloppy and it's like, oh, how cute. They tried to make fiber optics, but they didn't quite get there. But then if you look at it for like just a little bit longer, you notice like, wait a minute, making it a little bit leaky. And actually exactly that amount leaky gets you to this much cooler, fancier, more sophisticated function in context.

I love that idea, right? That we kind of have this perception of, oh, everything needs to be just perfect, right? For what humans think it's going to be. But evolution has slightly different goals. And so what looks imperfect to us is just a reflection of what the animal needs to survive. Yeah, exactly. That's super cool.

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You know, Sebastian, it reminds me of, and this is a Star Wars reference, two TIE fighters. Of course. Entangled in an intergalactic battle, fighting through the galaxy, fighting through the stars. And the

They're shooting at each other. And you think about cloaking technology that you see in those sci-fi films. And these two spaceships are like fighting and fighting. And then one of them wants to get away. And so it lands in a nearby planet, gets really low, and then turns on its cloaking device. And so it's invisible all of a sudden. And then its enemy just flies past it, not even detecting it.

And that's what I think of when I think about the hatchet fish. They're redirecting light in a way that makes them invisible to the eye of a predator. Absolutely. It is...

This thing that humans are like enamored with, right? We keep writing stories about the ability to disappear. And like these hatchet fish, you know, when you first look at them, they kind of look like a mirror. But go in a little deeper, see what's going on underneath the skin. And they're working completely differently. They're bending light. They're bouncing it around them to just fade into the waters. It's super cool.

And, you know, now we've covered actual mirrors with the lions I've studied. And then we've covered animals that look like mirrors, but actually redirect light so that they look invisible. Yeah.

There is another really important way that animals use reflections, and that's for navigation, which is also known as echolocation. Of course. So bats use reflections of sound as a means to orient and navigate in their environments.

And what's really interesting is that a small amount of scientific tinkering can make a huge and very strange difference to their ability to navigate. Here's Yossi Yovel from the Bat Lab for Neuroecology at Tel Aviv University.

Let me start with saying that, you know, bats use sound. Most bats, I should say, use sound to orient. And when doing so, the assumption was always that they measured distance through time. They emit sounds. Sounds travel through air. Basically, they hit objects. They are reflected back.

The bat's brain will measure the time passing between the emission and the reception. And then the hypothesis was that they can translate this into distance based on the speed of sound. Basic physics, if you know how much time passed, and if you know the speed, you know something about the distance. So this assumes, right, this description assumes that the bat's brain knows something about the speed of sound.

So assuming this, we said, okay, is this innate or do bats learn it? We take newborn pups. Are they already familiar with the speed of sound? Is their brain wired to know the speed of sound when they are born? Or do they have to learn it by experience? The way that we tested it, the idea was that we will change the speed of sound. How do you change the speed of sound? You enrich air with helium, for example.

Helium is an inert gas, so you can breathe it as long as there's enough oxygen. And we simply took small echolocating bats and we reared them in an environment that is always enriched in helium. And then we look at their response. We examine whether they now perceive objects according to the regular speed of sound or did they learn a new speed of sound.

So how do we assess this? Our bats, they take off and they have to land in order to eat. So they need to leave their roost and land on an object in order to get food. And if the air is enriched with helium, this means that the speed of sound is faster. And the echo will return faster than in normal air. They will perceive objects as being closer than they really are.

which means that they will try to land on an object that does not exist. They will undershoot. So if they can learn a new speed of sound, you expect them to land on the target at the right spot. And if they do not, then you expect them to undershoot or to land before the target. And this is exactly what we saw. Bats in a helium-enriched environment landed before the target,

whether they were born to a helium environment or not. So you would see them opening their tail membranes. This is what a bat does when it lands and stretching their legs and everything was just too early and they would just land just before the target. I think that the bat is simply surprised. It expected a target and suddenly it's on the ground. My only anthropomorphic interpretation would be that the bat is really surprised by what just happened.

So this suggests that they are born with a knowledge, pre-wired, if you wish, knowledge of the speed of sound.

If they do not adjust to the speed of sound, it basically says, you could say this differently, and as I said, it's a bit hard, it's philosophical, you could say that they actually don't measure distance. Because without the speed of sound, there is no distance, there is only time. And this is my conclusion, actually. As I said, it's a bit philosophical, it's like going into the bat's brain. But my conclusion is that the bats perceive the world...

when using echolocation, because I should say bats also see, and that's a different story. But when using, let's say, in complete darkness, bats perceive the world in terms of time.

The other thing that changes is that they also change their echolocation. Bats constantly adjust their sounds. So, for example, they will change the intervals between the sounds. And they will do this based on the distance of the target. For example, let's say if the target is far, then the bat will emit sounds with a longer interval. So like...

Something like this. But if the target is closer, it will increase the rate. So the intervals will become shorter. Something like this. So based on the intervals, this is like a window into the bat's brain. We know what the bat thinks, what it perceives the object's distance to be. And this way we see that they always perceive the targets being closer in helium, whether they were born in helium or not. It doesn't matter. It's exactly the same.

Every student, first year philosophy student, they read a paper by Nagel, a very famous paper, What is it like to be a bat? And the whole point of this paper is that we will never know. And of course, I agree, we will never know. But I think this study actually took us one step closer to understanding what it is like to be a bat. ♪

So there's a major question. What knowledge should we be born with and what should we learn? And it's a trade-off, right? On the one hand, let's be born with everything. This will save time. But on the other hand, this will prevent us from any flexibility, right? If something changes in the world, we will not be able to adjust. On the other hand, why not be born with full flexibility? Why not just learn everything, right? And the answer is yes.

It takes energy and time to learn, right? So it wastes time. And if you think of a bat that is born in summer and in certain regions,

Four or eight weeks later, it has to start hibernating. So there's a very short period in which it has to learn to hunt, feed and be ready for hibernation, migrate or hibernate. So there's not much time. And it's also it takes a lot of energy to learn. So things that are rather fixed in the world, maybe it's better to be born with this knowledge. It's probably better. That's what evolution decided, right? That it's better to be born with this knowledge.

Another case of scientists playing pranks on animals to learn about them. I love this kind of research, as I've said many times. I know you like these kind of studies. It does make me just think of fun houses at a carnival full of trick mirrors.

It's really hard to tell where anything is, right? You get really dizzy because it's really warped, you know, inside there. And it is so hard to navigate. You can't tell where anything is. You don't know what's near, what's far. It makes me kind of feel for the bat in the experiment. Even though, like Yossi said, they did get a treat no matter what. It still must be a really disorienting experience.

All right, I got one more type of reflection I want to make sure we definitely talk about, and that is the brilliant diversity of mimicry, right? Ooh, yes, yeah. Where one species is evolved to look kind of like the mirror image of a completely unrelated species. This happens so much in nature, and it's really, really cool.

One of my favorite examples is hoverflies. These are flies, so they don't have a stinger, and they're not, you know, they can't really, like, bite or harm you in any way. But they look a lot like bees and wasps, which have stingers. So things that confuse them won't attack the hoverflies. But the mimicry is so good that...

One of entomologists' favorite hobbies is anytime a newspaper article or something is doing a story about a bee, everyone checks to see if they actually got a photo of a bee.

I'm not going to lie to you. I have been fooled by many a hoverfly. They're quite good at what they do. My favorite mimicking animal is the mimic octopus. Oh, that's a good one. And some people, including myself,

would call it the ocean's mystique. So, you know, mystique from X-Men, you know, would change rapidly. She could turn into anyone. And so this octopus can actually impersonate up to 15 different deadly marine species. Things like flatfish, jellyfish, sea snakes, lionfish. It is able to just transform anything.

before your very eyes, it's really cool to see. Yeah, the mystique is like the perfect comparison point. And for some animals, it's not just visuals, right? It's sound, too, that they're using in their mimicry. Right. There's a genus of Australian ground-dwelling birds called the lyrebird. There's two species of them, and they are so good at mimicking sounds. They're

They can sample up to 20 to 25 bird species in their song. So they can include a yellow-tailed cockatoo call, a kookaburra call, an eastern whipbird call. And they're also able to mimic non-bird sounds like chainsaws, drills, car alarms, shooting from video games, and camera shutters. The lyrebird communicates his sexual prowess by...

by basically having a sampled composition. It is his love mixtape to whatever female is in the vicinity. So we'll leave you with this to finish up today's episode. And when you're checking out this Lyrebirds Spotify playlist or mixtape, think of it as a reminder that animals can be their own kind of reflection.

of their environments, of the challenges they've evolved to overcome, and of the richness of life around them.

The BBC Earth podcast was hosted by me, Rotendo Shackleton. And me, Sebastian Echeverry. Our interviewees were Alison Sweeney and Yossi Yovil. And the Lyrebird soundscape was provided by Mark Anderson of Wild Ambience. Our producers are Jeff Marsh and Rachel Byrne. The researchers are Dawood Qureshi and Seb Masters. Podcast theme music was written by Axel Kakoutier. And mixing and additional sound design was by Peregrine Andrews.

The production manager is Catherine Stringer, and the production coordinator is Gemma Woodson. The associate producer is Kristen Kane, and the executive producer is Deborah Dudgeon. The BBC Earth podcast is a BBC Studios production for BBC Earth. My dad works in B2B marketing. He came by my school for career day and said he was a big ROAS man. Then he told everyone how much he loved calculating his return on ad spend.

My friend's still laughing at me to this day. Not everyone gets B2B, but with LinkedIn, you'll be able to reach people who do. Get $100 credit on your next ad campaign. Go to linkedin.com slash results to claim your credit. That's linkedin.com slash results. Terms and conditions apply. LinkedIn, the place to be, to be.