Bats The Wonder of Animals

Planet Earth.

Millions of species.

But a few are special.

Born to thrive.

The key to their success lies in their opportunism.

For others, it's down to their ability to collaborate

and, for some, it's all about

surviving where others can't.

So, what is their secret?

In this series, we'll delve deep beneath the skin to reveal

the unique features that set some species apart.

New behaviour and the very

latest scientific discoveries will offer fresh insight into

the wonder of animals.

New Zealand...

..over 1,000 miles from the nearest continent.

Every mammal on these islands was brought here by humans.

All, that is, except one.

The bat.

These remarkable animals have colonised some of the remotest

places on our planet...

..becoming one of the most widespread of all mammals on Earth.

And there are three key ingredients to their success.

First, an incredible anatomy.

One which has enabled them not to just take to the air...

..but to master it like no other animal can.

Second, a raft of unrivalled senses

that's allowed them to feed in some extraordinary ways.

And finally, their sophisticated physiology,

which means that they've been able to survive

in some of the most surprising places.

In this episode, we will take a closer look at these three

key factors to uncover the incredible abilities of bats.

Having taken to the skies around 60 million years ago,

bats are the only mammals that can truly fly.

But the way their anatomy has evolved to do this is completely

different to any other flying animal.

Whereas birds' wings evolved by extending the forearms

and shortening the fingers, bats' wings are different.

The arms are still important, but it's the bones in the hand

that offer additional dexterity.

The thumbs became claws and the four, bony fingers

on each hand have elongated.

It's this that allows bats to change

their wing shape in an instant.

The result is an unprecedented manoeuvrability.

They can make a 180-degree turn

in less than half the length of their wing-span.

And this wing pattern comes in all shapes and sizes.

Short, wide wings are perfectly suited for hunting

mobile prey in dense environments.

While long, narrow wings of the larger bats, like flying foxes,

help in long-distance flights...

..allowing them to travel up to 40km in a single night.

To fly such distances, it's important to minimise weight.

So, a bat's wing bones are bound together by a super-thin,

lightweight membrane.

It's so thin that it can be susceptible to tearing.

But bats have a solution.

It's one of the fastest healing tissues of any mammal,

repairing itself ten times quicker than human skin.

Even a hole this size can be completely healed

in just a few weeks.

But although the surface of this membrane looks smooth,

it's actually covered in thousands of tiny hairs.

Almost invisible to the naked eye,

they can be as short as a tenth of a millimetre

and 12 times thinner than a human hair.

But they're not here to keep the bats warm.

At the base of each hair are minute sensory cells.

These give the bats a detailed and instant airflow map during flight.

The position of the hairs

across the wing surface monitor the precise direction of air currents.

Bats can then calculate when to accelerate and when to decelerate...

..and also detect turbulence that might otherwise

cause them to stall.

This amazing anatomy from lightweight bones to

super-thin, hair-covered membranes

has enabled bats to conquer the skies.

But although crucial to their ability to colonise the planet,

this unique system of flying also presents bats

with their single greatest challenge.

In terms of energy, bat flight is incredibly expensive.

When they're flying, they burn up twice as much energy per second as

a similar sized mammal would if it were running.

And some bat species have to

beat their wings at 14 times a second just to stay airborne

and this can drive their heart rate

up to an astonishing 800 beats per minute!

A single hour of flight can use up 10% of their total supply of energy.

So, after a busy night's hunting,

they're practically running on empty.

The bats need to recover their energy

and to do this they must feed.

They've got to find the richest food available

in the most efficient way possible.

That's where their astounding senses come in.

In temperate climates like the UK, the most energy-rich food source

for bats is very small...

..and always on the move.

Like all insect-eating bats,

the Natterer's uses echolocation to hunt its prey.

BAT CHIRPS

By emitting a series of high-pitched calls

and interpreting what bounces back,

it can pinpoint its prey's precise location.

But the problem for most echolocating animals is that

emitting these calls means using even more energy.

But scientists have discovered that bats have evolved a solution.

The muscles that move their wings are the same muscles that

operate their lungs.

So during flight, every breath

coincides with every wing beat.

They breathe in on the down stroke

and out on the up stroke.

So when the bat is breathing out...

..it takes almost no extra energy to emit an

echolocation pulse at the same time.

A bat will only break this arrangement

when it closes in on its target.

Then it emits a frenzy of pulses...

FAST CLICKING SOUND

..to give it a much more detailed picture of its prey.

This energy-saving technique

is so effective that a single bat can stay airborne long enough

to consume one third of its own body weight in insects every night.

Hundreds in a single feeding session!

In Belize, however, there's a bat that uses echolocation

to get all of its energy in just one go.

This is the greater bulldog bat and, rather than fly around

all night looking for small prey,

it targets a much bigger meal.

It uses echolocation to sense movement on the surface

of the river.

Then it's time to go fishing.

It's after a high-protein catch using minimal energy.

Now, echolocation is all very well...

..but in a constant arms race between predator and prey...

..it's important for bats to stay one step ahead.

The tympanate moth has developed a remarkable response to

echolocation - a rudimentary ear.

If it senses an incoming sonic pulse,

it takes immediate evasive action.

But it may well have met its match.

This is the long-eared bat.

It still uses echolocation, but when it gets close to its prey,

it enters stealth mode.

It switches off its targeting mechanism and instead relies

on a far more conventional sense.

It's able to hear even the slightest movements

thanks to its enormous ears.

It's now a game of patience.

All the moth has to do is stay perfectly still.

One tiny move...

..and it's all over.

In New Zealand, these short-tailed bats can fly and echolocate

just like other species.

But here, the most energy-rich prey isn't in the air.

It's actually on the forest floor.

So that's where they hunt.

Mirroring the behaviour of the shrew-like animals

they evolved from.

They're hunting large insects called wetas,

using a combination of echolocation

and a highly developed sense of smell.

Their bodies have adapted, too.

They fold their wings away into special sheaths on their backs,

allowing them to walk on their elbows.

They also have particularly strong hind limbs

and a robust pelvis, just like their ground-living ancestors.

These bats have effectively turned the clock back 60 million years

in order to maximise the potential of their environment.

But there is one species that needs to find a much bigger victim

in order to survive.

Vampire bats are the only mammals to feed entirely on blood.

And it couldn't be achieved without some astonishing senses.

These bats only eat at night,

approaching their quarry

as quietly as possibly by crawling on the ground.

When they're close, their super-senses kick in.

Tiny heat receptors in their nose leaf can detect the most

blood-rich veins on an animal, from up to 20 centimetres away.

These highly specialised nerve cells are similar to the

pain-detecting cells found in the human tongue that warn us

when something's too hot.

Vampire bats may feed on a pig for up to 30 minutes

and they can consume 25ml of blood.

A highly effective anti-coagulant in

their saliva ensures that the blood keeps flowing.

There's only one problem.

When they've had their fill...

they weigh too much to fly.

But they've got ultra-efficient kidneys,

which, within a few minutes can process the blood,

so they can immediately urinate and rid themselves of the excess plasma.

Their load lightened, they can soon fly away.

Bats' sophisticated senses help them replenish their energy.

But then they have to find the fastest way home,

otherwise they're simply going to burn up all of that

energy they've just acquired.

And how bats find their way back to their roost, night after night,

has always been a mystery.

But now scientists think they might have located the answer.

A new study has found that, in order to do this,

bats are able to utilise a completely different sense.

They've discovered tiny iron oxide particles

inside some bats' brains.

These may give them an internal compass...

..which may help them find the most direct route back to their roosts.

Using magnetoreception in this way puts bats into a select

group of animals that are capable of using the Earth's natural magnetism

to navigate the planet.

So this could help them efficiently find their way back to their roost

and it's here that they've come up

with some neat tricks to conserve energy.

Most bats rest during the day...

..and sometimes in the most surprising places.

These Mexican free-tailed bats live under the

Congress Avenue Bridge in Austin, Texas.

Tent-making bats in Honduras seek sanctuary

by building a home under leaves.

Once they find a suitable leaf, they chew through

the midrib before folding it in half to create a tent-shaped shelter.

Perfect protection from sun, wind and rain.

In Borneo, caves provide a sanctuary where bats can roost,

safe from predators, as they rest after a night's flying.

Here, up to three million wrinkle-lipped bats might

live in a single colony.

The problem is,

it's cold and trying to keep warm uses up

valuable energy.

To combat this, the bats cluster tightly together,

sharing their body heat.

It's so effective that their huddles can actually raise

the ambient temperature of the cave

by up to ten degrees centigrade.

But huddling isn't enough for the bats living in Northern Canada,

where the temperature can drop to 20 degrees below zero.

Here, bats have to rely on their specialised physiology

to pull them through.

These brown bats have been here throughout the freezing winter.

As the thermal imaging camera shows,

their bodies are the same temperature as their

surroundings despite being warm-blooded animals.

This is because the bats

have shut down their bodies to preserve energy.

They switch off the blood supply to their limbs

and slow their heart rate to just ten beats a minute.

And in this deactivated state,

they can survive on a single breath every 90 minutes.

They've been known to stay in a state of torpor, like this,

for up to 140 days.

And when it's time to wake up, they begin a well-rehearsed ritual.

They raise their heart rate and then use a special patch of fat

above their shoulders to warm their blood, pumping it around their body.

So after just ten minutes, they are fully active again.

Even in the summer months,

they can conserve energy by entering what's known as daily torpor.

A crucial adaptation to survive when times are tough.

A unique combination of remarkable anatomy...

..amazing physiology...

..and surprising senses...

..has enabled bats to thrive wherever they live.

There are 1,240 species worldwide.

They are so successful, they represent

more than 20% of all the mammal species

we currently have on Earth.

And that's the wonder of bats!