Brilliant bats!

Bats use echolocation - ultrasound sonar - to find their way around and to hunt down prey. But how do they do it?
21 May 2015

Interview with 

Jade-Lauren Cawthray, Natural History Museum, London


This week we're asking what's the most amazing animal. Talking to Ginny Smith, Jade Lauren Cawthray is an ecologist, citizen science practitioner and bat enthusiast...

Lauren - Well, some of my competitors this evening have already mentioned how their amazing animals should kind of have similar powers or interesting features that super heroes have. But my amazing animal actually has a super hero named after it which makes it especially cool - batman. And they are found across the world in every single type of habitat or part of the world except for the Polar Regions, where it's too cold and there aren't any insects that they can eat. Now I'm particularly fond of the British bats here in the UK and we have 18 species of bat here in the UK and 7 within Cambridge City. There are two major groups, two major types of bats. We've got the mega bats which are humongous bats with dog-like faces, big eyes and little ears. Most of them are eating fruits. Some of them like to eat nectar from plants and then we have the micro bats which are usually the smaller bats. They have big ears, little eyes, and are often insect eaters. And all the bats here in the UK are the micro bats. They're all insect eaters. Now, the size of bats varies hugely. The biggest bat in the world is a flying fox and it has a wingspan of 2 meters. So put your arms out, stick your arms out side to side. The flying fox is bigger than your arm span. It's humongous and it can fly straight out into oceans for long, long distances. The smallest bat in the world was relatively recently discovered and it's called the bumblebee bat and it is as small as your thumbnail.

Here in the UK, of our 18 species, our smallest bat, the pipistrelle bats, we've got a common pipistrelle and a soprano pipistrelle. They're about 23 centimetres wide and the biggest bat in the UK is the noctule bat which has a 40-centimetre wingspan. So, it's quite substantial and you see them flying high across hedgerows and treelines here in the UK. Bats do some incredible things. Some of the most amazing things includes hibernation and echolocation. So, hibernation is particularly important for bats that live in temperate environments, like ours here in the UK, where you have seasons, you have a hot summer; you have cooler autumn; really cold winter; and then a lighter spring. And because during that winter period, there aren't any insects available for them to eat, they need to go to sleep. And they need to get their body temperature really, really, really low so that they're not using energy because there's no food to replace that energy. So, they slow their heart rate down to 4 beats per minute. And this means that they can get their metabolism down and make sure their body temperature is the same as the air temperature and that means then they're not losing energy by heat into the atmosphere, and can save as much fat through the winter to try to get them back through until the spring comes. Certainly here in the UK, they'll start to go into hibernation about October time and they'll hibernate all the way through until about March time. So, our bats have started to fly around again and started to feed again.

Now, here in the UK, once the insects start coming, they can start getting out again and the females are really, really hungry because inside the females, they are now starting to grow baby bats inside of them. So they have to start eating lots and lots of food. A colony of about 100 pipistrelle bats can eat up to 1 ton of insects in a single evening. The female bats, the baby inside of them can grow to 50% of their body weight. In about August time, it gets quite exciting because then the babies are born. The babies at first, they drink milk from their mothers. They have milk teeth first and those milk teeth will drop out and they'll replace them with insect eating teeth and then they'll start to come out and fly and feed with the other adult bats. At that point, the mums and dads start to socialise again. They've been keeping themselves separate. Mum's been busy looking after the babies and then the mums and dads start to get together. They start to go and have a nice dinner for two over in a branch and a tree somewhere and then something very exciting happens. The male bat gives the female bat a special cell. The female bat keeps that cell in her body throughout the whole of the winter. The egg cell and sperm cell aren't joined yet. They stay separate in her body. And when the temperature rises again, she then makes fertilisation occur in her body and the sperm cell and the egg cell meet. It's at that point that then she's able to grow the baby. This is a really important strategy for survival because during that winter period, there is no food available for her to grow that baby bat. So, she needs to stave off that process of growing a new young bat inside her until there's food available, which I think is an incredible strategy. So, just a couple of amazing things. I should probably also mention that bats are the only true flying mammal in the whole world which makes them pretty cool. But they also have another extra special feature which we've got an audio recording of...

Now, you might just have heard that crackling then popping sound. Now, that is the sound of a bat. What we've done with that recording is we've taken a bat detector out into the field and the bat detectors recorded the noise that the bat is making. But then the bat detector does a special calculation to turn that noise into something we can hear because bats, their echolocation calls and many of their social calls are really high pitched, at a frequency our human ears can't hear. And so, that noise is the right pattern that is actually going on outside all of the time, but something scaled down to what we can hear. What the bats are doing is they're giving humongous shouts out to their environment and the shouts are so loud that they can deafen themselves. So, they actually have to detach their ears so that they don't deafen themselves when they shout. And then that noise bounces off the environment and depending on how far away an object is from them, that depends on how quickly the sound comes back and then their brains make a calculation about the distance to the nearest tree, the distance to the nearest wall. But the sound and the complexity of those soundwaves is so fine that they're able to determine shapes and features as well which means that a pipistrelle bat, our 23-centimetre long bat is able to find tiny little gnats and mosquitoes in a whole field of trees and leaves and other insects and moths flying around.

Ginny - Those are some amazing abilities - to be able to fly, to be able to see in the dark with sound. I think bats have a good chance of giving the other animals we've talked about tonight a run for their money. But let's go over to the judges to see what they think.

Georgia - Thanks, Jade. You mentioned batman. I love this idea of an actual batman like, think how much better Ben Affleck would be if he was fluffy, squeaked loads and could detach his own ears. I would watch that film.

Max - I just wanted to ask you a little bit more about detaching their own ears. Just how?

Jade - You know like within our ears, we have three little bones. Well, they've got the ability to separate those for a fraction of a second while that shout goes out.

Ginny - In our human ears, to conduct the sound from outside to inside, as Jade says, there are three bones which connect to each other. The air pushes our eardrum, that pushes one bone, and pushes the next bone, pushes the next bone, and that's transmitted off into our brains. So, if you separate two of those bones, that information can't get from the outside through to the brain. So, I think that's right. That's how that works.

It's time for our judges to give their final scores of the night. Over to you guys...

Max - 8

George - 8

Georgia - 10


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