In Our Time - Echolocation

Episode Date: June 21, 2018

Melvyn Bragg and guests discuss how some bats, dolphins and other animals emit sounds at high frequencies to explore their environments, rather than sight. This was such an unlikely possibility, to natural historians from C18th onwards, that discoveries were met with disbelief even into the C20th; it was assumed that bats found their way in the dark by touch. Not all bats use echolocation, but those that do have a range of frequencies for different purposes and techniques for preventing themselves becoming deafened by their own sounds. Some prey have evolved ways of detecting when bats are emitting high frequencies in their direction, and some fish have adapted to detect the sounds dolphins use to find them. With Kate Jones Professor of Ecology and Biodiversity at University College LondonGareth Jones Professor of Biological Sciences at the University of BristolAndDean Waters Lecturer in the Environment Department at the University of YorkProducer: Simon Tillotson.

This is the BBC. Thanks for downloading this episode of In Our Time. There's a reading list to go with it on our website, and you can get news about our programs if you follow us on Twitter at BBC In Our Time. I hope you enjoy the programmes. Hello, if you could hear bats flying at night, they were deafness. They make louder sounds on almost any animal, equivalent to a pneumatic drill or jet engine,

but at higher frequencies than we can detect, thankfully. Many bats use echoes from the sounds they make to locate. their prey and avoid obstacles in the dark. Dolphins and tooth whales, they too do that, and the techniques are being found in more and more animals. It's so sensitive, it's been likened to hearing in colour. Natural historians have had suspicions

that bats were echolocating since the 18th century, but it was so far outside human experience that even into the 20th century, anyone advancing the theory had to contend with ridicule from other scientists. Will me to discuss echolocation are Kate Jones, Professor of Ecology and Biodiversity at University of College London, Gareth Jones, Professor of Biological Sciences at the University of Bristol,

and Dean Waters, lecturer in the Environmental Department at the University of York. Dean Waters, who first suggested that bats might have this skill? Well, for that, we have to go back to 1793, and an Italian priest, Laceros Spalanzani. And Spalanzani, he had a pet owl, which predates Harry Potter, by some considerable margin. But Spalanzanianii noticed that when the candle was blown out, his owl just blundered into the walls. He said, well, owls probably need vision and light to be able to navigate at night. But he also observed bats, and he found that bats, even in complete darkness, could still orientate and navigate.

So he was sort of interested in how bats got around without using vision. He did all sorts of experiments by covering up their eyes with little cloths and so on. but he still found that they could find their way around, navigate very accurately. They would come back having had a good meal after being out at night. So in a sort of spirit of experimentation, he did something which is rather gruesome. So if anybody is perhaps of a sensitive disposition, they might want to kind of listen away. But he blinded some bats. And he found that the bats, which were blind, could still navigate and find their way around.

So he knew then that vision wasn't necessary for bats. And at the same time, a chap in Geneva called Charles Jureen was also doing some experiments, but he was plugging the ears of bats with wax. And he found that if you plugged a bat's ears, then it just bumped into things. So Jureen knew then that it was the ears that were necessary for bats to navigate. Spalanzani originally was fairly skeptical once he'd heard about Jureen's findings. But he repeated the experiments and found that if you plug bat's ears, then they can't navigate.

So hearing was necessary. These two men were on the track. They're on the trail then, but it took about until the 1930s for this to be taken of it anywhere that persons like yourselves could take seriously. Well, it did. The famous French zoologist, Cuvier, was very skeptical of these experiments. And so nothing really happened for about 120 or years or so. Then Hamilton Hartridge, who was a physiologist at Cambridge,

published a paper suggesting that it was high-frequency sounds that the bats were using. and there was a graduate student at Harvard called Donald Griffin who was working on bat migration and he had some bats and he heard that a scientist, a physicist called GW. Pierce had developed a microphone which could detect ultrasonics. And so Griffin took his bats along to Pierce's laboratory. They put them in front of the microphones, which are these little salt crystals that produced an electric current

when they were vibrated by sound. And within perhaps a minute, all of a sudden these little trace were coming out from the oscilloscope. You could hear the pulses because they were using a technique called heterodyoning, which was developed for radar. And so it must have been a fantastic eureka moment that within the space of a minute, this 130-year-old mystery had been solved

that bats use ultrasound for navigating. And can you just explain what ultrasound is? So ultrasound, by convention, is anything above our normal range of hearing. Which is what? 18 kilohertz. If you are young, female, and haven't been to too many nightclubs,

which I'm not sure really kind of applies to many of us here. But, so it's ultrasonic's above the range of hearing. And what a bats get up to? Well, they produce very high intensity ultrasonic pulses. What's very high? Very high is up to about 200 kHz. Normally bats, they have a range of echolocation calls,

but from about 18 kHz up to about 200 kilohertz or 200,000 cycles per second. So it's much higher frequency than we can hear, much higher frequency than dogs and cats can hear as well. This is key to their success as finding their prey and so on. Well, it allows them to exploit nocturnal insects, which is a fairly unique food supply, so flying nocturnal insects,

because there's nothing really out there that can exploit these. So it allows them to multiply and propagate and evolve and occupy pretty much every continent on Earth apart from Antarctica. Thank you very much. Garretz Jones, can you explain, can we just talk a little bit more about high-frequency sounds and why we can't hear them. Right, okay.

So, as Dean mentioned, our hearing is restricted to around about 18 to 20 kilohertz. There's no real need for us to hear really high frequencies. Whereas if you're a bat, well, first of all, you're flying around at night, you need to work out where obstacles are. Critically, for many bats,

you have to detect very, very small targets, things like tiny insects. To detect small targets, you have to produce very high-frequency sounds, frequencies with very, very short wavelength. Can you just explain a bit more what the high-frequency sound is? What it consists of, the wave, how is the wave-shaped? Okay, so if you just think of a series of peaks and troughs

forming waves, if you think in terms of a stone being thrown into water, for instance, the waves that emanate from that stone going into the water, there are similar waves going on in air when we speak at the moment. So I'm talking to you. There are sound waves propagating through the room. But these bats need to produce really, really high-frequency sounds. They need to do this because they need to get echoes from very small targets.

High frequencies are really necessary to get these strong echoes back. So one of the reasons why bats use ultrasound is to get strong echoes from small targets. However, there are costs as well associated with producing these very high frequencies. All sound spreads spherically away from a sound source, and it spreads according to the square of the distance from the source. So the sound attenureate very, very rapidly. Ultrasound, very high frequencies, the short wavelengths are absorbed. It's absorbed by particles in the atmosphere.

So ultrasound not only falls away in intensity because of this so-called spherical spreading, which applies to all sound frequencies, it also is subject to atmospheric attenuation. So the really high frequencies do not travel very far. So the frequencies that bats use tend to be typically in the range between about 20 and 60 hillyhertz. Still out of our hearing.

Out of our hearing range. So there are a few bat species that echolocate, one that echolocates around about 80 hertz. kilohertz. We can hear it tick, ticking as it flies in Mediterranean habitats, for instance. There's one bat species that goes as high as 212 kilohertz.

But because of the need to use high frequencies to detect small targets, and the costs of these sounds not travelling very, very far at high frequencies there's this sort of window of ideal frequencies that bats tend to use. What do we

need to know about the speed of sound to help us understand what bats are doing. Okay, so the speed of sound is really important. So bats really have to work out the positions of objects around them. And to do this, they can work out how far a target is away from them by measuring the time delay between producing the sound and receiving the echo. So the speed of sound is pretty constant. Typically, it's around about 340 metres a second.

It varies a little bit according to temperature, according to humidity. But it's this time delay that's critical in how a bat sort of translates a time delay into the distance and object is away. So bats making a very, I mean, an extraordinarily rapid mathematical calculation.

The echo comes back. It has to work out the time is taken to go and to come back. It's to work out, divide that by two and then go in the direction. So it's moving very quickly inside its brain? Yes, I mean the sort of neural processing that's going on must be happening very, very quickly. It's not just the distance of the target that the bat has to work out either.

It also needs to work out where the object is in the vertical plane and where it is in the horizontal plane. And it does it in the vertical plane by having a little structure in its year called a tragus. And there are sort of interference patterns of sounds that are created by the tragus. And scientists have shown that if you tape down the tragus of a bat, the bat's ability to work out where a target is in the vertical plane diminishes. And then in the horizontal plane, the bat is using intensity differences from one year to the other year.

So these three features, target range, the vertical position, and the azimuth, the horizontal position of the target. The bats have different mechanisms for working out these positions. Thank you very much. Kate Jones, can we go on with what they can detect? So we know how they're doing it. You know the speed at which they're doing it. We're still, as I read from my notes here,

it's quite a lot of where you don't know. But what you do know is the things they can detect. Can you just tell the listeners what they can pick up? Yeah, so, I mean, as Dean and Gareth have said, they try to detect, localise, and find objects. So they use that for navigation, but also eating prey. so a huge proportion of bat species eat insects. So they're trying to find these quite small insects in the pitch dark.

So they use frequency, a range of different frequencies, to find these insects. So when a bat's starting to find insects, they will start the series of pulses. So they're a bit like tweets, so it'll be like, like in a search call. So the bats will figure out where all these insects are and they're kind of searching around in space.

And then when they hone in on the target, they find them off. They'll speed up the rate that they're making these pulses. So they get much more information about the environment. Why? Because the thing is moving away or it's moving down or it's taking evasive action. It needs a lot more information about where this object is. So it'll speed up its call rate. So it'll start going, and then it will end with a what's called a terminal buzz,

which is like someone blowing a raspberry like this. So it will try and, it will find the insect and catch it. So there's a, as Gareth said, there's a huge variation in types of calls and frequencies that they use. And it's all down to this problem with frequencies, like frequencies don't, high frequencies, don't travel very far in air so that if you want to see quite far you need a lower frequency. So think

about elephant rumbles so they can hear for miles because it's a low infrasonic call but with high frequency it doesn't travel very far at all so it would be a few metres at most. So the problem is you've got to trade off

between seeing far and seeing in detail. You use the were seeing several times. How does a bat see? It's in the dark. And then just from the notes that you give me what they can, they know that this

is a very little insect, but they also know it's furry. They know they have an enormous amount of information about it before they attempt to eat it. So how does this mass of information come in at that speed and when that's more? Well, the wavelength of

sound, so if the higher frequencies have got short wavelength, so short peaks and troughs between the different cycles. So if you imagine like a wave coming towards you as I'm speaking to you, if you've got high-wave, high-frequency, you've got these very short wavelengths. So if I have this wave coming towards you, then the chances of me hitting a really tiny object

or furry or an antennae are much higher because you've got such a high frequency. And so you get this bounce back of all this fine detail. So it's like you're trying to see with sound with this really short wavelength of call. But the problem is you can't see very far. So over across evolutionary time, bats have tried to optimise their calls for the environment that are in and the prey that they eat. So, for example, bats which have high frequencies, they don't travel very far,

so they make them really loud so that they can kind of get them across the, air. So this means, as you said in your introduction, the bats are really loud. So they're really, really loud. I mean, I said in my introduction, but you said in your notes. Would it would a bad sound if I could hear it now? Would it be as loud as a pneumatic drill? One little bat. It's some, one bat in South America has been recorded at 160 decibels. That's 20 decibels higher than a rock concert and 15 decibels higher than our pain threshold. So it's just one back.

Yes. So how do they do that? I mean they... We're going to come. We are certainly going to come to that. So thank you very much for all that. And that's due, Dean. How do they make these sounds? They make the sounds in the same way that we do.

So they have vocal cords. The only difference really is that bat vocal cords are they're much stronger and more robust than ours. But they've got a couple of kind of special properties. So if you imagine the bat's vocal cords, if you imagine a kettle drum with a slit down the centre, and so you have two vocal cords on either side, and if you pull that tight, that kettle drum,

and the slit will then close, and what the bat does is then compresses its air in its lungs, and it compresses it to the point almost to blood pressure, so the bat is almost switching off the blood supply to its lungs because the pressure is so high. What it then does is it then releases the vocal cords, and that they contract under elastic energy. The vocal cords open,

and they start to vibrate. And because it's high tension at the beginning, it's a very high frequency that comes out. So if you tune a guitar string, the tighter it becomes the higher the frequency. But as they relax under elastic recoil, the frequency then becomes lower. So Bats produce this signal that starts off very high

and ends up very low. So it's a sound. But the other really interesting adaptation is they have special muscles that retention the vocal cords. They're about 100 times faster than human muscles. In fact, they're about 100 times fast than the fastest mammalian muscles. You have to go to invertebrates or some snakes to have muscles which are that fast.

And they need to be that fast because these bats are producing signals 10 times a second. When they go, as Kate said, into approach and search phase, you can be up to 200 calls per second. So they have to retension these vocal cords 200 times in order to get the signals out. That must be exhausting. So how do they get help from the... the rest of their tiny frames with fragile bones and all the rest of it? They do.

I mean, essentially, they're lucky because they get echolocation for free. As Kate said, this is incredibly loud. It's an enormous amount of energy that comes out. They're producing 120 decibels of calls, 10 times a second, eight hours a night, enormous amounts of metabolic energy. But they get it for free because the muscles, the muscles that contract the lungs are coupled to the flight muscles. So as the bats raise their wings on the upstroke, the muscles compress the lungs and the animal exhales and produces its echolocation call.

So one wing beat, one echolocation call. So they can couple the two mechanisms together. Garrett, this is an obvious question. I like asking obvious questions. Why don't they deafen themselves? Okay, there are a couple of ways that don't deffin themselves. A couple of mechanisms involved. One of them involves the middle ear muscles.

So the little bones in the middle ear, I think it's the hammer and the stirrup essentially, have muscles attached to them. And when these muscles contract, the bat essentially almost becomes death while it's calling. So one of the really important things for bats as well is the closer they get to targets, the more they have to shorten the call.

So imagine you're getting to the ball. and closer and closer to an object. The sound is coming back faster and faster. So you really want to hear these faint, very, very faint echoes that are coming back. So you need to reactivate your hearing, to hear these faint echoes from close objects. So you have a sort of send-received system, a bit like occurs in radar, actually.

So the sound is sent out, the middle of the muscles contract, the bats don't deafen themselves by these really, really intense sounds. and then they have a listening period that the echoes come back in. But as they come closer and closer to objects, the sounds have to get shorter and shorter so that the outgoing sound, which is really, really intense, doesn't overlap with the very, very faint echo that's returning. So what do they do?

Did I read that they displaced an eardrum or something? I think it's more to do with these muscles attaching to the tiny bones in the middle of the mechanism. is the mechanism by which this self-deafning is voided. I mean, horseshoe bats do it in a different way, and maybe we'll talk about that. Well, there are a thousand species. We haven't turned to talk about a thousand.

But the horseshoe seem to be quite. Yes, I mean, it's quite. So they don't deafen themselves, and they're moving in. Can we go back to seeing? It's not, I didn't quite get it. What do you mean by sea? You're all talking what they see. What do they see, and how do they see?

Dean, you're going to tell us what they're sick. If you think about what vision really is, you generate a map. Inside your auditory, sorry, your visual cortex, I get the two mixed up now, because they are essentially the same. The visual cortex, you generate a map of where everything is. So you can reach out and you can touch something because you've seen it. Your touch map is the same. It's a map.

If you touch something, you know where that object is. If you reach for a glass of water at night, you know where it is. The auditory map is exactly the same. So bats build up a map, but rather than using... vision or touch. They use their auditory senses. They build up a picture of echo delays and how big objects are within their auditory field. So they just generate a map picture inside their heads. Okay, so there's a really famous philosophical essay by Thomas Nagel called What Is It Like to Be a Bat? And Nagel was essentially interested in, you know, the question, can we ever get our heads inside the

head of another human being? But there's an extremely. extreme example of trying to work out what it must be like to be something else. He chose a bat. He thought bats were really, really alien creatures. And I'm not sure we will ever, you know, be able to understand, picture the world as a bat sees it. But there are some things that we can get some ideas about. I imagine they're seeing the picture of the world in quite a sort of stroboscopic way. So they're getting these pulses coming back maybe 10 times a second that builds up a picture of the world around them perhaps in the way that we see stroboscopic light at a disco

or something similar as well. So I think we can get, you know, some sort of picture of how bats are seeing the world, but getting ourselves inside the heads of a bat and picturing exactly how they process things, how they see textural detail and everything, that's a real challenge. Kate Jones, so we can't hear bats.

Are some of their prey in a better position than we are As this stealth bomber homes in Are they thinking, whoops, now can we take avoiding action? Well, bats evolved around 60 to 95 million years ago And so they evolved later than a lot of their prey that they eat So insects evolved much earlier So, you know, one of the reasons for their massive success in the mammalian kingdom is that they've tapped in to unsuspecting prey.

So the vast majority of pray that batsy don't hear them and they sneak up and do a great job. But there are some. A great job? Not if you're an insect. Well, you know, but I'm a bad expert. I mean, you're not a great job, are you really? No, you're not much of your dinner.

You're a midnight snack. A midnight snack. So there are a few insects that have devout. these anti-bat devices. So a lot of these are kind of bat-detecting ears. So hearing in insects has evolved in at least six different orders of insects. And also within butterflies and moths, epidopter. It's also evolved independently around six times.

So it's a really good adaptation to listening for bats and we think for some insect groups it was a kind of co-opted affair so that they could they could hear movement anyway or they hear noises anyway in some of these organs on their body but in lepidopter we think they've evolved

these bat hearing ears and they take avoiding action can you tell us about the tiger moats and sort of anti-aircraft yeah so so so some bats when they when they hear these ultrasonic calls, they're very sensitive to particular types of calls. So I talked about that search phase call before. So if a moth with these ears, here's a search phase calls,

they might not be that bothered because the bats far away. It hasn't seen them yet. But when it starts to speed up, they start panicking and then think, okay, I've got to take a voided, avoid, you know, defensive action. So they can maneuver, they're really maneuverable so they can drop out the sky or take different turns and twists so they behave really erratically so that the bats don't see them. And then some moths have even evolved this ability, as you said, this tiger moth to make clicks. So they are actually producing sound. And we don't exactly know what the function of this is, but the tiger moths are also poisonous so that the bats can't eat them. So it could be a warning.

Or it could be that it's a startle response. So for naive bats, like, wow, what's this? You know, I can't eat that. Or it could be that they're jamming. They're jamming them. So they get really confused. I don't know where this thing is. I don't know what it's doing.

I love the vocabulary all this. How on earth you distinguish a naive bats? You, 10, naive. Go to the back of the cane. Just saying, sorry, finish off. But then bats have got all these countermeasures. So it's like an arms race. So bats have got...

There's some evidence that bats can change their frequencies so they go much higher. And we've talked about problems of high frequency calls that they don't travel very far, but some have gone higher to avoid moths hearing them, all lower. So it's all they go into stealth mode and they don't make echolocation calls.

It's all action out there, isn't it? It's crazy. Yeah, and if you're in Texas and 20 million come out of a cave at the same time, time. Anyway, never mind, let's not... Well, we must think about it, but it's very difficult to think about, really. You wanted to get in, Dean.

Well, I was just going to say that this is actually a nice experiment that you can do at home. It is that you can demonstrate your moth defense mechanisms. All you need is a bunch of keys. Keys produce a lot of ultrasound when you jangle them. And if you have an outside light that you have moths gathering around, particularly at this time of year, it works

really well, is you sneak up on your moth with your bunch of keys very, very carefully. And then you take your keys and you jangle them very violently. And what you'll see the moth doing is it will do a whole series of loops and dives it might fly off from the opposite direction and sometimes they even just drop to the ground and hide up in the grass.

Because as far as they're concerned, they've got very simple ears, is those keys produce enough ultra-tenthsound just like a bat, cry key, it's time to get out of here. So you can actually see this co-evolutionary arms race in action at home. As we have a moth invasion of London I can see quite a few people reaching for their keys

rushing upstairs. Obviously if moths are not your thing and you're scared, just take a bunch of keys, you'll be fine. Yeah. So it's not just insects that can hear bats or respond to this acoustic attack, but plants not can hear bats, but they also respond to bats acoustic calls. So some bats pollinate and sped seeds of lots of different plants,

are important pollinators. And some plants can have a, adapted their leaves to be a parabolic dish so that they can advertise really to bats to say, come here, there's a free snack and you can pollinate my plant as well. So that it's like a bat beacon, which I think is absolutely incredible. Well, we ought to swerve off slightly to dolphins in the echolocation,

but this is so intense. I'd rather stay here for a while if you don't mind. Can we, Gareth, can you tell us about the horseshoe bat? Yeah, horseshoe bats are amazing. I mean, I'm an evolutionary biologist, I'm interested in. in adaptation. And for me, the echolocation calls horseshoe bats. One of the best examples of adaptation out there. So essentially bats with echololosh...

Sorry, when you said adaptation, we've been told they've been going for about 90 million years. So they've adapted over that long time, or just in the last 50 million or what? We don't. Well, the fossil record of bats is not great. There's a big argument about whether the first fossil bats were capable. of echolocation or not. It's one of the big sort of questions in echolocation research at the moment. But there have almost certainly been evolutionary modifications over time of the calls. Okay, back to the horseshoe bat.

So the horseshoe back call, the horseshoe back call lasts about 50 milliseconds, 50 thousandths of a second. It's absolutely pure tone core. It doesn't waver in frequency at all. This gives the, so echolocation has to work in three ways. First of all, you have to, have to detect a target, you have to then localise the target and then you can classify the target. These long, long calls are very, very good at detecting targets. They're also very good at classifying targets. So something like a mosquito might be flapping its wings at say several hundred times per second. A beetle might be flapping its wings, perhaps four times a second. So from the little acoustic glints, as we call them,

come back during these long calls, these bats can tell a mosquito from a beetle. They can classify prey types, and they can choose their dinner accordingly. That's very, very smart. Not only do they have this ability to classify targets, they also put little sweeps at the end of the core, and this allows them to localise targets as well.

They also do something remarkable called Doppler shift compensation. So these very long constant frequency calls are very susceptible to Doppler shifts. So the classic example of doppler shifts is when you're standing on a road in central London and an ambulance comes towards you, the sound waves get compressed. The frequency goes up as the ambulance moves away, the sound waves stretch out and the frequency goes down. These long calls are very, very susceptible to Doppler shifts. So what the horses you're doing is they learn. the frequency of the call from call to call in relation to the speed that they're flying,

so they're compensating for the Doppler shifts incurred by their flight speed. This means that the call they send out and the echo that they receive are on different frequencies. So they don't have this problem of self-deafning. They're separating the pulse and the echo in frequency rather than in time. So horseshoe bats are amazing in that they can produce these calls that are adapted for all these functions of echolocation, detection, classification, localisation, and they can do it by this remarkable Doppler shift compensation. It's a fantastic example of adaptation.

The way you're talking, I think we're going to take over quite soon. Kate, Kate, can we distinguish parts by the sound they make? You talk of distress calls. You talk of, I'd like to put it, a mother knowing a child, and that sort of thing. So you can distinguish them in those ways. Yeah, so we've, over the last few years, we've developed lots of technology sensors to hear bats so that, you know, most of them are above our frequency. So we have these little devices which we can now use to transform that sound down, lower it in frequency so we can hear. So one of the ways that we try to tell species apart, like humans try to tell species apart, is by listening.

listening to these calls on these senses. And bats' calls are really different from bird calls. So bird calls are like, here I am, I look fantastic. Don't you want to come and mate with me? That's a kind of a call that a bird makes or get off my territory. And bat calls are very functional, so they're how to find their way around so that they can be very variable. They're very tricky.

they change, they have different accents across space, across geographic space, and they've also got differences in sexes, so that it's very difficult to tell a species from its call. Dean Waters, some bats don't use echolocation. No, there's basically two groups or two. Bats are in the order Karoptera, which means chiro meaning hand and terror,

meaning wing as in your chiropractor and terror as in pterosaurs. So we have two sub-orders. We have the micro-caroptera or the small handwings and the mega-caroptera, which are the big handwings. And the big ones, the mega-corrupt terror, don't echolocate. There's only one group that echolocates, which is the Rosettus, which are some cave,

Egyptian fruit bats, they live in caves. And they produce a sort of tongue-click that goes in. But the microchroptera, they all ecolate or all can echolocate, but some of them choose not to, because these are the stealth bats. So these are the ones that are overcoming the insect defense mechanisms. So because insects, a lot of insects can hear bats,

is if you switch off your echolocation or make it very, very low intensity at the very end, is your insect can't detect you, so you can then you can catch it. You can listen by passive hearing. So some bats have got really big ears they just listen to the passive sounds that the insect are making either in flight or if they're crawling around on the ground

so they can listen rather than echolocate and that then doesn't alert its prey. Gareth Jones, which evolved first? Flight or echolocation? Right, the chicken and egg question. This again is not resolved at the moment. So my feeling is likely that echolocation evolved before flight, partly because if you're flying around at night time,

you need echolocation to find out where objects are. There's also we've forgotten the business, it so is not to bump into things either. Yes, that's right, that's right. So, yes, obstacle avoidance is really, really important. So there is a debate going on. So there is a fossil bat, on aniquinitress, it's called, and it dates to around about 53 million years ago.

And people have looked at the structure of the cochlear in the year of this fossil. And have argued that actually the structure of the cochlear suggests that it did not echolocate. Therefore, flight evolved before echolocation. However, scientists have also looked at other bones near the hyoid apparatus in the throat. And some of these bones are characteristic of echolocating bats.

So they've argued, well, actually, this bat did echolocate after all. It's a problem. This is a pancake fossil. It's really flat. so the structures can get distorted in it. My feeling is probably echolocation first, but also, as Dean mentioned earlier, there is this coupling between flapping the wings and producing the sounds,

so the bats can essentially produce echolocation sounds for cheap at no cost when they're flying. No energy cost. No energy cost. So this could mean that there's strong selective pressure for flight and echolocation to evolve in tandem together at the same time. There's also a really fascinating discovery that happened last year.

People have found a pygmy dormouse in Vietnam that produces sounds very much like the echolocation calls of bats. It's got ears very much like echolocating bats. The scientists have not conclusively shown that it echolocates, but the structure of the calls, the structure of the years suggests this could be a terrestrial echolocating species. It's not related to bats, not an ancestor, but it does show that, you know, echolocation can be effective on the ground.

So I'd like to come in with, there is a bit of controversy around this mega, megabat and microbat taxonomy, so that Dean was saying, and Gareth has been talking about the evolution of echolocation. So with megabats, they haven't got this ability to echolocate, and with microbats, they do have it. But new genetic evidence, and this is a little bit controversial, but new genetic evidence has shown that the megabats are firmly within the evolutionary tree of the microbat. So there isn't such a thing as megabats and microbats. They're all bats, which has got a fascinating implication for the evolution of echolocation.

So it's either evolved once at the base of this group and then lost in the megabats, or it's evolved independently twice. So those are really over. open question. So it's absolutely a fascinating area that, you know, not all chiroptologists agree on. Well, I think I'm going back to the evolution of echolocation is possibly evolve even more than twice. If you look at where the horseshoe bats now are placed with megabats, and you also have this crazionictrous thong longi, which is a fantastically long name for the world's smallest bat. That's also within that group as well. And that has a different type of echolocation.

So you're actually looking at echolocation styles or different types of calls arrangements like the horseshoe bats evolving multiple times within this lineage. You would like to that? Well, I think I would just add that I think my understanding is the evidence at the moment is favouring the single origin and then loss in the mega-corruption. It's partly because people have looked at the developmental history of year structures in these animals and they find similar developmental patterns in the non-ecolocating bats

to those in echolocating bats, and the argument has been made that this is support for a single origin and then subsequent loss, which is actually the most parsimonious, the most likely explanation in my mind. I think echolocation is such a sophisticated adaptation, especially in the way bats use it, that multiple origins is perhaps unlikely. Is it, Cades, our bad's having an effect. on the way insects are developing. Are they on the lookout over 60, 70 million years

and they've developed, they have evolved to meet the threat? Absolutely have. You know, you see this bat-moth evolution as a really good example of a predator prey arms race. So it's usually held up as a really interesting example of how evolution over time has adapted the moths to the presence of bats. so even, you know, not just the ears but behavioral adaptations.

So some moths have become a bit more diurnal because they're trying to avoid bats or they try to shift different seasons. So they come out before the bats come out of hibernation or after the bats have gone back into hibernation. So I think there's a really incredible kind of an arms race going on and adaptations back and forth. Dean, what areas in this research has been, quite a lot, obviously since you've got going

three, four decades. And you think are, A, not known and rather more worryingly, perhaps even not knowable? Well, I think there's, the big question for me is there's a big mismatch between these fantastically elegant behavioural experiments that you can do

on bats, where you can sit a bat on a platform, you can train it to listen to two different loudspeakers, and you gradually reduce the differences between the two calls you're producing until the bat can't tell one or the other. from one from the other. And then they'll walk towards a loudspeaker,

I think it's producing a call which is slightly later or has a slightly different structure. So they're telling us they can resolve incredible detail. But from what we understand about the physiology, the way that animals process auditory information, we know that's not possible. They shouldn't be able to do the things that they can. But they do.

So there's two things. Either there's something extra in the behavioural experiments that we don't understand, the bats are listening to different cues. And bats are very clever. so we might be training them to listen to the different things. So what we interpret the experiment is doing, the bats may not. Or there's something extra in the physiology that we don't yet understand.

I suspect they're doing something in the physiology that we don't understand what it is yet. Are we taking that on? How we take people like you taking that on, or your fellow academics in different disciplines, and saying, okay, we will try to use this or find this out how it applies to other things, including ourselves. Right. So, I mean, there's a huge amount of research in sonar and radar,

and the signals derived by sonar and radar engineers resemble those of bats very, very closely, except bats evolved them over 50 million years ago, probably. How bats ahead in this race between radar and bats? I think, given their miniature size, their ability to fly around very quickly, their adaptations have not necessarily... There are groups in America trying to do biomimimedes,

studies to try and mimic echolocating bats, but I think the bats are remarkable in these adaptations. What would you really like to know about bats before we're in this programme? I'm really interested in how to track bats over time and space, so to understand their populations and their conservation. And I am frustrated by the fact of how little we know about echolocation calls and we need to build up better libraries in our understanding of calls to be able to build better methods to identify bat, individual bats. So more to come back in a few years time with more bat talk.

I'm very sorry that we didn't get round to dolphins and toothed whales, but that's another time, another program. Next week we'll be to discuss the Mexican-American War of 1846 to 1848 and how it left Mexico with half its territory. Thank you very much for listening. Thanks to Kate Jones, Gareth Jones and Dean Waters. And the In Our Time podcast gets some extra time. now with a few minutes of bonus material from Melvin and his guests.

I mean going back to the sort of mega micro thing is that it's a great introduction to the Yanga Kroptera yintero Kharoptera argument. Whatever those names are. Because it leads very neatly into understanding about how we traditionally classified organisms based on their morphology, life history strategies versus the molecular genetic. The molecular genetics always throws some spanners into the works. I mean, obviously, the molecular genetics is not without problems and faults and interpretations. One question I didn't ask is how can they tell their sound,

20 million come bats out of the cave in Texas. How can bat number one tell it, distinguish its sound from bat number 1900 million? Anyway, how can they distinct to their own particular sound? It's extraordinary. I've been to Bracken Cave in Texas. There are 20 million Mexican free-tail bats that come out. And if you try and make a recording, it's just noise. You can't even make out individual calls.

It is extraordinary. But bats have this sort of temporal expectation. So when they produce a call, they have an expectation window when that call's going to come back. So they can change the gain in their auditory system so they can ignore anything until they get to the window where they're expecting that signal to come back. And at that point, they will then ramp up the gain

and listen for their own. $20 million? Yeah, that is a bit crazy. Can you work out how they manage to do it? Well, we think also that they recognise their own calls, and that's really another area, which is credibly interesting that we don't know anything about. We think that they can recognise their own voice.

I can recognise my own voice, so can you. So why can't bats do that? We think they probably can. So like infant bats are left in this Bracken Cave in a big nursery, in a little crush, well, a big crush. and the bat mums go back and feed and then come back and find their own pup so they can find their own pup in thousands of pups so at the beginning of this research we thought that was totally impossible that they'd find

their own pup and we thought that they were aloe feeding they were aloe nursing so they were just nursing any pup that was there and everybody was very excited about this whole idea of aloe nursing that was crazy idea you know how did that evolve but actually they recognise their own pup in a whole bunch of pups, a mass of pups, they can do it. I think that's incredible. It is, isn't it? I mean, for me, some of the big, exciting, well, two really exciting areas to explore in echolocation research at the moment are, one, the use of little miniature devices that are being fitted to bats. So you can put these tiny tags on bats, work out where they are from their GPS coordinates, but also record their echolocation calls.

So this is giving us an unprecedented view of echolocation behavior in the wild on these tiny animals. You get the tags back, you can download their echolocation calls as they fly around. And the other area that's really exciting for me is molecular genetics. And what is it that what are the genes involved that make bats, give bats this amazing ability to echlocate? And there are some amazing examples of convergent evolution at the gene layer. So whales and dolphins have evolved hearing genes that have undergone similar mutations to those in bats to cope with dealing with high-frequency echolocation calls. So I think there are some really exciting new discoveries awaiting us in the world of genetics. I think we kind of have this idea that echolocation somehow is difficult.

I mean, flight we know has evolved multiple times, lots of animals climb up trees and chuck themselves out and glide. So the evolution to powered flight is probably not that difficult. But somehow the idea that that echolocation is this sort of holy grail. But we all echolocate to some extent. We perceive the space around us by the reflection of our own echoes. So he put somebody into an anachic chamber that absorbs all sound around. There's a fantastic big one down at Southampton University, the sort of size of it almost a concert hall.

Really disorientating experience because everything, even the rustling of your clothing, you can't pick up the echoes. You have no idea how big the space is. Whereas you walk down a corridor, you pick up the sounds of your own, your feet, your clothes rustling, you know how big that space is. So all human beings will echoicate to some extent. It's just kind of the activity about doing it actively and processing it really quickly. For me, the really exciting research is on, I don't disagree with Gareth,

but I think it's on about how we interpret these echoes. So bats are leaking information about themselves into the environment all the time. And we can use that to monitor their populations so that, we can start to build up, you know, new technologies and new sensors so that they can go through all these recordings and pull out different species of bats, tell if there's a bat there and what species it is. And it also is a way of really engaging with the public as well

because you can give them these detectors and then the whole sky becomes alive with bats because you can't hear them normally. And then you get these detectors and then it's an amazing experience for people they're just flying over their heads and they didn't recognize, didn't notice. And it's like a whole new world

of ecology and nature and conservation that they just didn't know about. I think that's really powerful for me. Yeah, just some more points really about these echolocation humans because it is remarkable. And people have recently analyzed the sound clicks that echolocating humans make. So several visually impaired people echolocate.

There's some very famous people that guy called Daniel Kish in America, who rides bikes by using echolocation, etc. And the cliques that these humans are producing around about 3 milliseconds long, which is about the same duration as the calls of bats sometimes. They're much lower in frequency, so they typically have most energy between 2 and 4 kilohertz. But they can still be used to build up a remarkable picture of surroundings. But the humans using these clicks are actually using the visual cortex in the brain,

which we use for understanding the world by sight, to process the echoes. In the bats, it's the auditory cortex that's become really, really specialized for processing echoes. So there are these quite remarkable differences between how humans are doing it and how bats are doing it. But echolocating humans, amazing. And it is being developed by people making things, turning, actually basically cutting to the chase, turning them into bats really. Yeah, yeah, absolutely. I mean, sort of going back

to Thomas Nagel's essay of what does it like to be a bat. So there's a couple of things you can do. You can use sonar technology. I mean, we all use sonar technology almost now. Every car has got reversing alarms on it. As you're going towards an object, your alarm will go

beep beep beep beep beep beep. It gets sort of louder and faster. So that's just mapping distance onto sound frequency. You can develop devices for helping people with visual impairments that many years ago we helped develop a cane which send out ultrasonic pulses, picked up those pulses and relayed those to a little vibrating button on the handle that would vibrate faster the closer you got to objects. But also we're looking

at ways of taking radar imagery rather than seeing it visually is mapping that onto your auditory space so that this idea about visual maps and auditory maps is rather than having a radar image, which is on a screen, is you take that radar signals and you turn it into sonar and you listen in three-dimensional virtual audio space to where objects are around you. So it's incredibly versatile. We can learn an awful lot from how bats use their location.

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