Inside the Bat Cave (2020) - full transcript

Hello and welcome.

I'm Lucy Cooke, and I'm going
to be taking you into the hidden

world of one of Britain's
most endangered and least

understood animals, bats.

Bats are mammals like us.

Yet they're as alien
as they could possibly be.

They're the only ones that can fly.

They see the world using sound...

and spend most of their life
in total darkness.

They're hard enough to spot,
let alone study.

So we're going to use the latest
science to uncover



their surprising secrets.

We've come to Bryanston, in Dorset,

which is home to one of the UK's

most important bat roosts.

Inside this old building is a colony
of greater horseshoe bats,

one of our rarest species.

And we've been following
it for half a year.

We've seen the arrival
of a new generation.

Discovered how their extraordinary
bodies work...

That seems incredible that
it's able to function

at such a low temperature...

and enter their strange
and complex social world.

Just so fantastically weird.

Today, we've brought together
scientists and conservationists



for an event vital to the
survival of the roost.

Later on, we're hoping to witness
the crucial moment when some

of the baby bats born here
over the last few weeks,

leave the roost and fly out
for the first time.

This is Bryanston in Dorset.

A former country estate that's now
home to far more bats than people.

Our greater horseshoe colony
has taken over what was once

the kitchens of an 18th century mansion.

It's now protected, part
of a nationwide drive

to save this bat from extinction.

Earlier in the year, we installed
a night vision camera

in the heart of the roost.

And today we're monitoring it from
our marquee headquarters close by.

With me to take a first look
inside is Dr Anita Glover,

of the Vincent Wildlife Trust,
who takes care of this roost.

Anita, is that a cluster
of pups in the bottom?

Yeah, so that darker cluster
that you can see at the bottom

is all young bats kind of crushed
together, which is something

that the mothers do when they
go out to forage,

is they'll put the bats into this huddle.

Oh, look, here we go, this
is the mum testing her wings.

And you really get a sense of that
40 centimetre wingspan.

The mothers teach their pups
the skills they need

to fly in the safety of the roost.

Now, this is one of the young pups
that's hanging onto the head

of its mother and practising
flapping its wings.

I don't know about you, but I don't
know how the mother

is holding on.

This is the very, very first
inkling of flight,

and I just love these images.

I think they're fantastic.

Tonight, we hope to see
some of these pups take

their first flight outside.

It's a vital milestone,
because the future of the roost

depends on this next generation.

And Bryanston is one of only 35
greater horseshoe breeding colonies

in the whole of Britain.

Both their range and their numbers
have shrunk drastically

compared to a century ago.

I've heard that in the UK,
populations have actually crashed

of greater horseshoe bats by up to 90%.

I'm assuming that humans
are involved in this somehow?

Yeah, sadly, yes.

Agricultural intensification,
land-use change the use

of pesticides, which has affected
food availability for them.

But also the destruction of their roosts.

Bats need a safe, dark space
away from predators.

The attic here is ideal,
and in one section,

Anita's team have built an enclosure
that's specially heated

for mothers to have their young,

a wire mesh makes it easy
for the pups to grip on.

You've had some success here,
haven't you?

We have, so we took this building
on in 1994,

and there was less than 100 bats
in the roost at that point.

And over time, through protection
of the site,

we've actually seen that number
increase to over 300 now.

This evening, Anita will count
them as they fly out,

to monitor how the colony's doing.

But greater horseshoes aren't
the only bats we're following here.

You might be surprised to know
that bats make up a quarter

of all mammal species in Britain.

There are 17 different types.

From tiny pipistrelles, as small
as a pound coin...

to noctules, as big as a starling.

Bryanston is a hot spot.

It's thought that over half our
native species live here,

each with its own unique place
in the ecosystem.

To study them, we've brought in
a battery of technology,

cutting edge cameras to capture
their behaviour, and ultrasonic

recording devices, audio
moths that detect back calls

beyond the range of our hearing.

Conservationist, Ajay Tegala,
is installing them

in places where we hope to find
significant bat traffic.

First one's going by the clock
tower, where it's suspected

there might be a roost of pipistrelles.

There's speculation as to whether
bats roost in this clock tower,

but nobody knows for sure.

So this wonderful device will record
the sounds emitted by the bats here.

And then, to a reasonable degree
of accuracy,

it will be able to tell us what
species have been here.

Some types of bat forage close to water,

so he's putting another audio
off by the river.

We'll look at the results later,
and if we find any new roosts,

they can be protected.

It's largely thanks
to its protected status

that our greater horseshoe
roost has thrived.

We began following it long
before the new generation

of pups was born.

I first came here five months ago
on a cold March morning.

Because of its conservation status,

we needed a special license
in order to enter.

Of all the animals I've studied
and written about, from sloths

to frogs, bats are among
the most otherworldly.

So what do you think
the temperature is today?

It's pretty chilly, I think.

Well, I think it's probably
about eight or nine degrees,

but the wind chill is probably
making it feel a bit colder. Yeah.

Winter is a dangerous time for our
bats as there are so few

insects to eat.

To survive it, they have to hibernate.

Do we need to whisper?

No, but we'll just talk quietly.

Talk quietly, OK.

I'll do my best, it's not one
of my special specialities.

In cold conditions, bats enter
a state called torpor.

Their body temperature drops
and their vital systems slow down,

reducing their need for food.

Gosh, it's like a maze in here.

There is this one.

It would be fascinating to know the
temperature of the bat, wouldn't it?

It would.

Ruud is here and he's got
a thermal imaging camera

that's going to enable us to see
what temperature that bat is.

Is that really...

The bat is only eight and a half
degrees centigrade?

Wow, that's pretty much
the temperature of the room.

That seems incredible that it's able
to function at such

a low temperature.

When active, bats need to maintain
a body temperature

of around 37 degrees centigrade,
like most mammals, including us.

But in torpor, this can fall
to as low as five degrees

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

It's just absolutely mind-blowing
to think about what's

going on inside the body
of that animal right now.

How they managed to pull
off that physiological feat

of allowing themselves to survive
that degree of hypothermia.

In here, you've got relatively
stable, cool, humid temperatures.

And that's what the bats are looking
for in hibernation.

Chilly, though. I know, my nose
is cold. Mine is.

My nose keeps running, it's so cold.

Bats are thought to have evolved
in the tropics.

To adapt to colder climates,

they hibernate often
in extraordinary ways.

In Japan, the tube-nosed bat makes
itself a little igloo in the snow,

where it hides away for the winter.

In this footage, the spring thaw
has melted the roof off its snow den

and the bat is coming out of torpor.

In cities, bats can be even
more ingenious.

These pipistrelles in Holland
are hibernating

in the cavity walls of a tower
block, like living insulation.

At Bryanston, Anita and I search
for more hibernating bats,

moving softly so as not to disturb them.

Gosh, it's a bit of a mission
to get up here isn't it?

Definitely hidden themselves away.

Wow!

There's a lot more in here, aren't there?

There are, there are, it's difficult
to say how many there are.

Just so fantastically weird.

I love bats, so cool.

What makes all this especially
bizarre is that many

of the hibernating females have
a sperm bank inside them.

They mated back in autumn,
but haven't yet

started their pregnancy.

Instead, they keep the sperm alive
in their body through the winter.

When spring comes, they use
it to fertilise an egg

and the pregnancy finally begins.

Since the winter, our cameras
in the attic

have continued to follow
the colony's progress.

We've captured remarkable footage
of pregnant females

and the arrival of their pups,
which has never

been witnessed here before.

Joining me to take a look are Anita
and leading bat scientist,

Professor Kate Jones.

So here we have a few weeks ago
when the mums are still pregnant.

And I think it's just astonishing
to see how large they are, really.

I mean, look at that, looks like
a fluffy tennis ball, it's huge.

You can now see just how big
her abdomen is.

And inside is a baby that when it's born,

is going to be up to a third
of its mother's body weight.

Normally in mammals, it's only
about a fifth of its body size.

So that's an enormous weight
on the mother.

The females will have just one pup
a year, but can have many

over a lifetime, as they sometimes
live as long as 30 years.

Anita hopes there'll be at least
100 new pups this year,

to ensure the roost continues to grow.

Here, we've got a baby. Oh,
wow, that's cool.

That looks like it's pretty young.

It's like a mini dragon.

Yeah, it is, that that's
quite a young one.

When they're in their first few
days, they just have huge wings

and a huge nose leaf and it doesn't
seem to be much

in the way of a head and body,
so they got, sort of,

some growing into their appendages
to do over time.

This footage shows a pup
in the earliest days of life.

They're born naked and blind...

but develop rapidly.

This pup is about a week old.

Its eyes are now open and it has
a light covering of fur.

That seems to make two
babies on this one.

That's really uncommon for most
UK bat species

to actually have twins.

So it's just possible that it was
another pup that clambered

on and the mother tolerated it.

The pups have only two or three
weeks to grow and develop,

ready for their first flight.

It's the most dangerous
moment of their young lives.

And Kate's been finding out why.

In this quiet suburban street in Kent,

there's a most unusual home.

Here, Hazel Ryan looks after
lost and injured bats.

Today, she's returning a pup to his
roost at the top of a chimney.

Found close to death, Hazel's
nurtured him back to health.

Still too young to fly, the pup
climbs up towards the sounds

and the smells of his colony.

Just one of the 100 or so bats
Hazel has cared for this year.

So this is one of my best
rehabilitation rooms,

and it's a bit full at the moment,
it's a really busy time of year.

We have 34 bats at the moment.
34? Wow!

This little one here, Yorkletts,
he's one we've had...

Yorkletts? Yeah.

Well, we named them after where
they came from,

so he came from a village
called Yorkletts. He is tiny.

It's a bit sad really, because
he was caught by cat.

We think he was probably only
on his first or second flight out.

He's just at the stage where
he's learning to fly

and a cat caught him and injured
his wings.

We've had him for a little
while and you'll see the holes

are actually beginning to heal.

Oh, I see, those are the holes.

You can see the little puncture wounds.

Bat wings have many blood vessels
allowing their skin to heal

amazingly quickly, ten times
faster than human skin.

While the bats are recovering,
Hazel has to hand feed them.

The older ones munch on mealworms.

The younger bats, like Yorkletts,
are fed with milk.

I'm testing the temperature.

Yeah, I just touch my top lip...

as you would with a baby's bottle.

OK, so... It should feel warm
but not hot. OK.

And then if you try... It's kind
of the treating though, you know.

The side of the mouth. Hello.

Come on, Dude.

Once they get the hang of it,
they will just latch onto the end

of the pipette.

Because, of course,
they're mammals, just like us,

So they're feeding on milk.
He's so tiny that...

Yeah, you're worried.

I'm worried that I'm going
to drown him in milk.

As they recover, Hazel gives
her bats flight training.

She does it here
in a specially-built cage.

It's a rare opportunity for us
to bring in specialist cameras

to observe bat flight and detail.

Today, Hazel has two bats
of different species

with different flying techniques.

First, the aptly-named brown
long-eared bat.

It's short, wide wings make flight
slow but manoeuvrable.

Essential to navigate through foliage,

to snatch insects from leaves.

Those ears are incredible and
therefore picking up tiny, tiny

insect sounds that are
around the cluttered forest.

Next, a pipistrelle
Britain's commonest bat.

Slimmer wings give it a
smoother, faster flight.

It can reach speeds
of up to 30km an hour,

ideal for capturing insects
out in the open.

It's fascinating how the wing shape
and the speed of the bat

can tell you so much about its
biology and what it's feeding on

and where its foraging.

But the pipistrelle is a slow coach
compared to the fastest bat

in the world.

The Brazilian freestyle has been clocked

at an astonishing 160km an hour.

Speedier in level flight
than the fastest bird.

But what makes bats such
accomplished flyers

is their extraordinary wings.

This is X-ray footage of a bat in flight,

filmed in a lab in the States.

It reveals how their wings are based
on the same anatomy as our hands,

but with massively elongated fingers.

The forefingers make
up most of the wing...

while the thumb has evolved into
a claw sticking out the front.

Before a bat can take off, its wing
muscles need to be warmed up.

To find out how, ecologist Dr Liat Wicks

uses a thermal camera
to record the temperature.

This bat's been inactive for a while,

so it's appearing
cooler against the hand.

To be able to fly and sort
of kick start their muscles,

they need to warm up quite quickly.

So what they have is
something called brown fat.

This brown fat is concentrated
between the shoulder blades

and it can be burned to
produce extra internal heat.

So it'll take some minutes,
and once it's warmed up

to its optimum flight
temperature, it'll then become

more active and possibly take off.

Once in the air, bats have
the opposite problem...

cooling down.

Because they flap their
wings up to 12 times a second,

their muscles produce so
much heat it puts the bat

at risk of overheating.

The bat's body appears very,
very hot, sometimes hotter

than a human face
on the infrared. Wow!

Whereas the wings are relatively cool.

So where are they losing energy from?

So... How are they not exploding?

A recent study showed that they
lose the majority of their heat

from their body, but it's still
how - how are they doing that?

Right. So we're looking at how
maybe it's radiating through

the fur itself. We're very
early stages with baseline

data collection, but we
are testing those theories.

Research like this is revealing
the intricate natural engineering

that makes bats such amazing flyers.

Back at Bryanston,
our greater horseshoe pups

are progressing through flight school.

They have to work their way
up through a number of stages

before they can fly solo.

First, the wings stretch.

Next, the frenetic flap.

This exercises their flight muscles.

Here, a large pup is flexing its wings

while still clinging to its mother.

Finally, they attempt
the micro test flight

in the safety of the roost.

This aerial debut lasts just six seconds.

To take off, our young pups
simply have to let go.

It's a key advantage
of hanging upside down.

The tendons in the bats'
claws make them clamp shut

when bearing its body weight.

This means no energy is required to hang,

and they can do so for hours,

even months at a time,

until they need to take flight.

Recent research, in America,
has been revealing

the remarkable ways
different bats take off.

Most bats, really, they
kind of take off from height

and they kind of just fall,
and then start... Fall and fly.

Fall and fly. Yeah.

But there's also the vampire bats.

So, this one feeds on blood,
but it's usually on cattle,

and so it needs to be
running around on the ground.

So, it's learnt to leap
from a standing point

up about three feet in the air.

Have a look at this.

Wow, that's amazing!
It's like a Harrier jump jet.

Presumably, if you've been sucking
the blood from a cow's foot,

you've got to make a quick escape.

Their muscles are so large,

and it's using its claws
there to propel itself up,

and also giving it direction
once it's left the ground.

That's take off. That's impressive.

Now, landing, that's
really counterintuitive.

Landing is my favourite,
this is the coolest part.

Bats have got to land on
surfaces that are above it,

so it's got to try and somehow
hook itself onto the ceiling.

So, it slows down,

it flips around,

and then lands.

So, this is the most amazing
acrobatics I've ever seen.

It closes one of its wings -
that makes it roll -

and then it uses its inertia to grab
on to the ceiling with its feet.

So, it's using the speed of
its flight to create the inertia

to then land. That's called
a two-point landing.

But where exactly do
bats go when they fly out

of their roosts at night?

Some of the most innovative
research is happening in Bulgaria,

which has more types of bat
than almost anywhere in Europe.

These limestone caves are home
to 3,000 greater mouse-eared bats.

Dr Stefan Greif and Laura Stussholt
are investigating exactly

where they go hunting and
what insects they eat.

At dusk, they assemble a special trap

to catch some bats without harming them.

This is a harp trap.

The bat flies into these
nylon strings, and then,

like in a cartoon... Well, sort of.

it glides down and falls into this bag.

Next, they're going to take a bat

and attach a sophisticated GPS
tag that can track its movements.

Now we put some glue
on the back of the bat.

So, this is medical glue, skin glue,
that they also use on humans,

so it's not harmful to the
bat, and it actually dissolves

after a few days again. So the
tag would fall off by itself.

We prefer to recapture
the bat with the tag on,

so we know we really
can get our tag back.

So, now this guy is finished
and we can actually release him.

The tag also contains a tiny microphone

to record the sounds of the bat feeding,

and from that they can tell
what insects it's eating.

But to retrieve all this
information, Stefan and Laura

need to recapture the bats.

Now they're going to seek out
one they tagged last night,

a single bat amongst 3,000.

It can get quite busy in here.

It's like a little bat circus
when they fly all around your head.

It's over here.

You got it?

Got it.

Yay!

There we go.

Back at the research station, Stefan
and Laura download the GPS data.

They discover the bat flew 22km nonstop,

touched down for 90 minutes in a
wheat field to refuel on insects,

then returned home to the cave.

By using these GPS tracks,
we can find out

where the bats are hunting
and their feeding grounds.

Which means it's important for us

to make sure that these feeding
grounds are kept preserved.

So, these GPS tracks
can help in conservation.

Next, they listen to the audio
recordings of the bat feeding.

First, it chomps its way
through a hard shelled beetle.

They're a little bit crunchy,
and they go on for a long time.

So, we've got a big meal this time.

Then, something a bit softer - a moth.

So, this is the sound of
the chewing of the moth.

They're a little bit weaker

and they're not as
crunchy as the beetles.

We get a good sense of the numbers
of the prey that they're eating.

How many insects per night,
on the ground and in the air.

That gives us a very good estimate
of the intake, basically.

So, that means that we can
start to quantify the impact

they have in the ecosystem.

Research like this shows
the important role bats play

in keeping insect populations in check.

The more we learn, the more
we can appreciate bats.

But it hasn't always been this way.

Bats have been feared throughout history,

and even today they're shrouded in myths.

When I say I study bats, people
go, "Oh, bats get in your hair."

And when they say that to me, I say,
"Well, they've got a sophisticated

echolocation system. What would
they be doing in your hair?"

I think it's that thing of
them being slightly in-between

creatures, aren't they? They're kind
of neither one thing or another,

and that's a bit
creepy in a way. Yes.

Even in the Bible, in the Book
of Leviticus in the Old Testament,

bats are described as being unclean.
Yeah, that's true.

In the Middle Ages, there was,
you know, that was a sort of...

European artists were
depicting the devil as a bat.

In Dante's Inferno, when talking
about the wings of Satan,

he says, "They're not feathered
as a bird's wings are.

"They're bat-like and leathery,
each fanned away the air."

In the black and white world
of Christian morality -

angels had bird wings.

Demons, bat wings.

The nail in the coffin was
when bats that drink blood

were discovered in the 17th century.

The author Bram Stoker kept
among his papers an article

that mentioned these "vampire bats,"
now thought to have influenced

his famous creation - Count Dracula.

Bats became fully associated with evil,

and I think it's just incredibly
unfair, isn't it, Kate?

Well, I love bats, so I would say that.

But they have all these services
that they provide to us.

So, they have this huge
role in insect control.

So, they eat thousands of insects.

There's a study in Texas
where they were looking at

how well the bats were controlling
the insects on this cotton crop,

and they estimated it was about
a third of the value of the crop

was saved by the farmer by
not having to apply pesticides.

Exactly, yeah. Another benefit -
seed dispersal, as well,

they're really valuable at doing that,

and also as pollinators, too.

Am I right in thinking that the
bat is one of the pollinators

of the agave plant - which would mean...

no bats, no tequila?

So, there's obviously a big vote
for why we should love bats.

Perhaps the tide is turning.

Every year, more and more
volunteers from all walks of life,

are getting involved in protecting bats.

Ajay went to Scotland to discover how.

This is Linlithgow Palace,
near Edinburgh.

Once the residence of
Mary Queen of Scots,

it's now home to hundreds of bats.

Today, the Lothians Bat Group,
one of over 90 in the UK,

has come to survey them.

Amazing key, Bob.

I can't wait to see through this door.

Surveys like these feed into the
National Bat Monitoring Programme,

an annual bat census to find out
which species are most at risk.

Wow, what an incredible place.

We're on the lookout for a rare bat...

the Nathusius' pipistrelle.

This tiny bat has been found
to fly almost 2,000km,

from Latvia to Western Europe,

the longest known migration
of any small mammal.

The group here wants to find out
if there are any in the palace.

Leading them is Natalie Todman.

The Nathusius' pipistrelle,
we've never recorded up here

in the palace, so we're really
keen to see if we can find it.

And that's really quite rare, isn't it?

It is, yes, it's probably one
of the rarest species in Britain.

But we don't know if they're
actually roosting here,

so it'll be very interesting
to see whether we're going to

record them here inside.

In the Great Hall of the palace,
we spot our first bats.

To recognise the species, we all
have detectors which can pick up

their ultrasonic calls and
make them audible to us.

The frequency of the call is key.

This one's coming through at
around about 55 kilohertz.

And that tells us?

Which tells us this this
is a soprano pipistrelle.

What we really would like to hear
is something coming in below 40,

which would make it a Nathusius'
pipistrelle. Absolutely.

Oh, I just love the sound,
it's fantastic. Yeah.

I'm sort of torn, because
I'm so fixed to the screen,

and yet I feel like I'm missing
out on them flying above my head.

I know, that's the problem.

When you have a screen like this
telling you so many good things,

it's such a temptation
to watch this when,

really, what we want
to do is watch the bats.

The dark nooks and crannies of
the palace make it a great place

for other species to roost.

We're looking at a
Daubenton's bat which is clinging

to the wall, and we've got a
really good view of it there.

Oh, yeah, it's lovely
to see them like this.

It feels almost like
we're intruders here,

because we're seeing it
at such an intimate moment.

When you see bats on the wing,
they look so powerful

and so, sort of, fearless.

But when you see just how small
they are, they look very vulnerable.

Suddenly, there's
exciting news from elsewhere.

Ooh...!

Natalie's got a Nathusius'.
Got a Nathusius'?

We've just picked up our
first Nathusius' pipistrelle

of the evening. Fantastic!

There's a couple up there,
there's a Nathusius'

and there's a soprano
pipistrelle, as well. Gosh.

You can actually see the Nathusius'
is just slightly bigger.

A much lower frequency, coming in
just around about 40, or just under.

It's actually really exciting to
actually find them IN the palace,

not just around about.

Tonight is the first time
the Nathusius' pipistrelle

has been spotted in Linlithgow Palace.

Did you all pick it up?
Did you get it on your detectors?

Yes. Yes. Fantastic.

They're putting on a good show tonight.

It's too early to say if there's
a Nathusius' roost here,

but this first sighting
will prompt more research.

This is important conservation
work that feeds in to

this national database.
Yes, that's right.

The National Bat Monitoring
Programme runs various surveys

throughout the summer,
at various levels of expertise,

so anyone and everyone
can get involved in them.

I've never been involved in
something like this before.

So, to know that there's so
many different kinds of bats

just a stone's throw from my
house, but also that we have

rare bats here, it just makes
it all the more exciting.

Back at Bryanston, the detectors
we've placed around the site

will tell us which
species are hunting here,

and perhaps even roosting.

While at the greater horseshoe
roost, our cameras are uncovering

a fascinating and complex social world.

There's just a lot of activity all
the time, day and night it seems.

They're grooming, and also you
can see this lovely interaction

between those two, where
they're almost lip touching.

I don't know whether they're
sniffing each other for recognition

of individuals through smell,
but we see quite a lot of that.

So, yeah, just constant activity.

The colony is matriarchal.

The adults are mostly female
and often closely related -

mothers and daughters, aunts and nieces.

At this time of year,
adult males tend to roost elsewhere.

For the pups, the roost
is relatively safe -

but when they fly outside tonight,
they'll encounter a raft of dangers.

They're out for the first time.

They don't really know,
instinctively, what's outside.

Their mothers will know this landscape

like the back of their hands.

But for those young bats,
they're going to have to stick with

other colony members,
you know, just to be safe.

For pups who do get lost or injured,

a helping human hand can
sometimes be a life-saver -

as Kate's been finding out.

I've come back to Kent to
catch up with Hazel Ryan,

who rescues injured bats.

We've returned to the flight cage
where the bats test their wings.

Previously, she introduced me
to Yorkletts the pipistrelle pup.

Sadly, it didn't survive.

Her injuries were just
too extensive from the cat

and she didn't make it,
unfortunately. It's really sad.

It is. And, unfortunately, you
know, a lot of young bats do die

because of cats. Yeah,
it must be really difficult

when you're taking
such great care of them.

But every one that does survive
sort of makes up for that.

That makes the difference.
Like Sheppey.

That's one of the bats that
I've got to flight test today,

which I'm hoping we'll be
able to release really soon.

You gave me Sheppey to keep warm.

That's right. He's getting
warmed up, ready to fly!

I think he is pretty warm.

Can you feel him wriggling around?

He's actually in here...

which is quite odd.

OK, thank you.

Aw! He's a juvenile male,

and unfortunately he
got trapped in a house.

As a juvenile, I guess
they can't fly as well,

they get a bit confused,
and got in a house,

and then got completely
trapped? Yeah.

They're like all youngsters.

They go exploring, they don't
really know what they're doing.

Not very competent, you know,
like teenage drivers!

But, luckily, he wasn't injured.
Oh, OK.

He was just really starving.

He needed rehydrating, feeding up.

So we've been feeding him for a
couple of weeks. He's really nice

and fat now - he's about doubled
his body weight, I think.

That's brilliant.

Really, today is just the
final test to make sure

that he can be released,
hopefully, tonight.

Oh, that's brilliant.

We can let him go to the end
of my fingers. Oh, my goodness.

Oh, there he goes!

So, this is how a bat with
no injuries should be.

You can see how fast he's flying.

And he's coming round really fast...

right over our heads.
Just over our heads!

He's already an accomplished
flyer now, so... Wow!

There he is. Whoa!
See, he just heads for our heads.

That's brilliant.

So, we're going to go and release
him back to the roost tonight? Yes!

And the family are really excited,
the people who found him.

Oh, that's brilliant.

Are they going to be
there tonight? They are.

They're so pleased that
he's made a full recovery.

Hi, guys. Hello! Hi!

I heard you found a bat!

Yes!

My dad and my stepmum were on
holiday, and I said that I'd come

over, put some milk in the fridge,
get them some bread and things.

And I just looked at the sink in
the kitchen, and it was just there.

So, how did you know who to call?

Google.

I just Googled, "What to do if
you find a bat in the house."

Was it the Bat Helpline
that you called? Yes.

Yeah, National Bat Helpline. Yeah,
the Bat Conservation Trust website.

Yeah. That's it, yeah.

And you did all the right things -
put it in the box with the water,

making sure the lid was on tight.

So, Jessica, I heard that you
really wanted to see this bat...

Mm-hm... and you didn't
get to see it before.

No. I've been keeping him warm.

Because to fly, he has to
have really warm wings.

Oh.

This is the smallest type of
bat that we have in this country.

Oh, blimey. Yeah?

Was it all OK? He's fine now, yeah.

He's doing really well. He was just
really hungry and really thirsty.

But now he's quite chubby cos
we've given him lots to eat.

They look like elf ears.

They do, don't they? Yeah.

How do you feel about little
Sheppey being released tonight?

I feel happy because it's going
to be with its family and friends.

Aw, that's really sweet.
Yeah, that's it.

I think that's true.

We've got plenty of space,

and we can see where he goes
because he's going to, hopefully,

circle around for a little bit.

So, it's a really good
evening to release a bat,

cos see how calm it is here?

Would you like to say goodbye to him?

Bye-bye, Sheppey.

I wasn't sure when we found him
if he was going to make it at all,

so I'm really pleased
that he's ready to go back.

If it wasn't for you,
he wouldn't have survived.

Well, I think if it
wasn't for you, Hazel,

he wouldn't have survived either!

So, the both of you, really, I
think, need to take credit for this.

It's really brilliant.

OK, he's flapping...

Ooh, away he goes!

He's going to circle around
a little... Where did he go?

Oh, he went that way, off
and over... Oh, my goodness.

Well, he didn't seem to be...
Over there, on the floor!

No, it's on the floor.

I thought he went that way! Yeah.

Well done, Jessica.

Well done! Flippin' heck.

Once Sheppey is warmed up more,
we can try to release him again.

The delay is fortunate as
another bat's shown up.

There's a bat flying just over there.

That's good news.

I think he wants to go.

There he is, he's circling round.
That's brilliant!

He's with the other one, there he is.

He's following the other bat.
There he is.

That's him and his friend
going round and round.

It's really nice to see him
flying around with another one.

I don't think he could
have found a better house

to get trapped in,
actually, to be honest.

There!

Brilliant. Bye-bye, Sheppey!

For bats, getting airborne
is only part of the challenge.

To navigate in the dark,
they have to echolocate.

As they fly, they emit many shrill calls.

They're incredibly loud,
up to 140 decibels,

noisier than a pneumatic drill.

Yet they're so high pitched,
we can't hear them.

Here, we've slowed the calls down.

The sound waves travel outwards,
hit objects in the environment,

and bounce back as faint echoes.

These allow the bat to sense
what's ahead and how far away it is,

anything from a tree to a tiny insect.

Remarkably, humans can
learn to echolocate, too.

At Durham University,
Dr Laura Thaler works with

visually impaired people who use
echolocation to help them navigate.

But today she's going
to teach me the basics.

I can't really imagine that
I'm going to be able to navigate

using sound rather than vision today,

but I am very much looking
forward to trying it out.

First, Laura's going to show me
how sound bounces off objects.

The goal is... that I do this
well enough so that you can

actually hear the difference.

Shh...!

OK, that works. Good.

I did hear a difference. Yeah.

But to get an echo back that you can use,

you need a much shorter, sharper sound.

A mouth click...

is a very brief sound.

That's better, isn't it? Yeah.

Now I'll try to use
my clicks to help me find

the edges of an obstacle
while I'm blindfolded.

What I would like you to do
is click and move sidewards,

so that you can use your own
sound feedback to determine

once you've passed the obstacle.

So, you want me to walk sideways
like a crab whilst clicking...?

Yes.

...to see if I can judge
where the obstacle is?

Yes, yes.

I got it right! I thought that's
where the change was! Brilliant.

Someone who's taken part in
Laura's research is Kerrie Brown.

She lost her sight to
eye cancer as a child,

and is one of an estimated
5% of blind people in the UK

who've learned to use
a form of echolocation.

Bye! Bye!

Just doing that just now,
I can definitely pick up

a hedge there, or a tree.

It's a sparser sound and maybe
bouncing back from a solid object.

It's quite open here at the moment.

She uses her stick to warn her
what's on the ground just ahead,

and echolocation for obstacles
in the wider environment.

There's something there,
which is probably a pole,

cos it's a good sharp sound that
comes from it but it's quite thin.

Obviously, you don't get
the echo for very long.

A car would be longer and lower,

so you can start to get a vague shape.

If I really want to hone in
on something and I need to be

quite accurate, I'll start
doing faster clicks.

And that lamppost there is a
good one that I've hit before

when I'm not concentrating
on echolocation.

So it's a good one to try and
hone in on with the clicks.

Back at the research lab,
Laura is exploring how

echolocation compares to vision
as a means of navigating.

She's kitting me out with
motion capture technology.

So, Lucy, move your feet.

Move your shoulders.
Yep, there you go.

That's you. Yeah...!

That is really cool!

I have to navigate round
an obstacle course twice.

First, using echolocation...

then with my eyes open.

Laura is now going to show me how
my attempts compare with Kerrie's.

Kerrie did the same task as you did.

She actually...

walks quite fast.

That's amazing.

She walks really fast
and really confidently. Yes.

And not doing the same sort
of shuffling and dithering

that I did. No.

Compared to when you walked
with your eyes open, though,

when she started avoiding
the obstacle is a bit later.

But in terms of, you know,
how swiftly she actually moves...

you know, we couldn't really tell.

Seriously impressive.

Laura's been investigating
what it is that makes people

like Kerrie so skilful.

So, effectively, these people
are using echolocation to see.

What's happening in the brain?

So, one thing we have done
to get at this question is,

is to put people into an MRI scanner.

We found that people who
are trained in echolocation,

they process echolocation sounds
in a part that we refer to

as primary visual cortex.

So, it's the part of
the brain that receives

direct input from the retinas.

So, you're saying that people
who are using echolocation

are using their visual cortex
in the same way that people

who have sight use to navigate?

So they... Or a similar way?

Yes, yeah.

That has blown my mind.

Seeing sound is something
Kerrie has experienced.

When I was doing my training,
I had a bit of an "Ah-ha" moment,

which was when I echolocated
a flight of steps going up.

I felt like I saw the graduation of
the steps going up in front of me.

So, that's interesting when
something like that happens.

What's interesting for me
is how far I can push myself

and how much I can do that
I didn't think was possible.

Echolocation is a relatively
new and rare skill for humans...

but bats have had over
50 million years to perfect it.

Their mastery is most
apparent when they hunt.

This pipistrelle, in total darkness,

is honing in on a tiny midge
just a millimetre long.

Returning echoes allow
the bat to pinpoint it,

and within a tenth of a second,
the midge is doomed.

Back at Bryanston, our pups
are just learning to echolocate.

Most bats make these calls
through their mouth,

but the horseshoes
actually use their nose.

The horseshoe-shaped folds
of skin act as a megaphone

to boost the sound and
give this bat its name.

But our pups' echolocation isn't yet
good enough to hunt down insects.

For the next few weeks,

they'll continue to feed
on their mother's milk.

Here, a large pup is suckling.

I've read that the lactating mothers,

they'll eat their lean body
mass every night in insects.

Yeah, I mean, the thing is that they...

It's hugely demanding in terms
of energy, the gestation period,

and then producing the milk,
and making sure that those pups

are well fed and grow quickly.

So they really have to
either take very large prey,

or consume, you know,
huge numbers of smaller prey

to be able to produce
the milk for the pups.

At the greater horseshoe roost,
it's the moment we've been

waiting for - the maiden flight
of many of the young pups.

First, they'll leave the
protection of the attic roost.

Then, fly down into a large semi
open space on the ground floor

for some final flight practice.

I'm going inside with
specialist cameraman

and bat enthusiast Ian Baker.

Fantastic.
So, we're in the old kitchen

Get that camera on.

And would you expect to see bats
flying around now, Ian?

Probably another five minutes.
Five minutes to go?

We've cut it a bit fine,
but we're in position.

Here they come, pouring out.

This is the perfect place for
us to observe the bats up close

before they leave the building.

There seems to be little
family groups that rotate

and circulate around and
occasionally come together.

This behaviour we can study
in great detail now,

and see things that
we've never seen before.

Do you think that was a pup?

Yes. It looks like
there's a piece of string

between the mum and the pup.

We've got two bats flying
in close formation,

and the leading bat
looks slightly larger.

This must be a mother
teaching her pup how to fly.

Some pups are still very much learners.

Here, two young bats
crash into each other.

Some bats refuse to come
out when they're told to

and just hang at the exit.

Rebellious teenagers.
Rebellious teenagers!

There's a lot of stuff
for them to learn. Yeah.

Flight, echolocation, spatial memory.

And where to get the food.
I mean, it's like their brain cells

are just firing and just growing.
It's just amazing, isn't it? Yeah.

To think of, kind of, what's
going on with these pups now.

Outside - Anita, Kate
and Ajay are setting up

with detectors and clickers,
ready to count the bats.

Ooh...! Oh! Ah!

We just had one fly out
and fly straight back in.

There'll be quite a bit of that early on.

Oh, there's one...

There we go.

Uh, this is quite stressful.

This is amazing!

So, this is one of the first times
that their babies are flying.

Whoa! Oh, my goodness.

Do you think they get a
bit scared by being left,

and then they're trying their
best to follow their mums out?

We can make assumptions if we see
pairs of bats emerging together

and one of them appears to be
a larger, more competent flyer.

How are you getting on?
Oh, hey! Hey.

How many do you think have
come out? Over 100, so far.

Over 100, yeah, wow. OK.

I just think it's such a thrilling
thing to think that some of these

pups are flying for the first time.

Close to the roost, badgers,
owls and foxes are on the hunt

for an easy meal, so it's crucial
the pups don't crash land.

I just saw one come out
and just circle around,

so that could be a
training flight, couldn't it?

Could be...! Could be,
could be, could be...!

A tree next to the building
seems a favourite training ground.

Mothers and pups circle it continuously.

They're doing practice flights.

They're coming in, out,
flying around the building,

flying around these trees,
just in amongst the vegetation.

That bat there keeps doing
circles around the tree,

and then goes off that way.
Maybe it's going back in again.

That's what's so thrilling
for me today to be here,

to see all of these bats sort
of flooding out of this building.

You know, we live at a
time with insect apocalypse

and environmental degradation,
and it's such doom and gloom.

But this just really
just lifts your spirits.

Before long, it's all quiet again.

The outpouring of bats
is over for tonight.

It was quite frenetic there for a while.

It was fast, it was exciting.

I don't want to say it's the end,
but it is, I think it's the end.

So, that's their first flight!

Wahey! Brilliant. I don't
think they did too badly.

None of them crashed into us, so...
No. They definitely didn't.

We've seen pups coming out
and flexing their wings

and experimenting with
flying in this space.

It's just totally thrilling, isn't it?

Yeah. It's a real privilege,
actually, to be able to watch this.

Now the numbers have been gathered
from our count here at the roost,

and from the detectors that
will tell us about other bats

around Bryanston, it's
time to find out the results.

First, the all important census
of our greater horseshoe bats.

The final count was around 400 bats.

So well done on the clickers.

Yay! Very good.

And I think that feels
like a positive result.

Yeah, it shows that the colony
is continuing to increase here.

In the last 25 years,
it's literally tripled in size

in terms of the adult bats in there.

That's around about 100 of this
year's young that are already

leaving the roost in the evening,

which is really exciting
to have observed that.

And it kind of reflects
what's happening, nationally.

We're starting to see greater
horseshoe bats make a comeback,

but it's really important
to remember that that's

against a backdrop of a
massive historical decline.

And so they're definitely
not out of the woods.

Absolutely. But I can't help
feel a little bit inspired

by the work that you've done here,
because that is just a sort of

tremendous result, to feel that
you're having this success here,

and I think I'm going to take
some hope from it, for sure.

Kate's got some interesting
news, too, from the detectors

we placed by the river
and the clock tower.

We processed all the data
from the AudioMoths,

and by the river there
was about 12 species,

and up by the clock
tower there's about ten.

So, you've got a really
great population here

of different species.

Actually, one of the interesting
things is that there are

loads of soprano pipistrelles
around the clock tower.

There was a huge kind of dawn swarm.

So, that's where they're all
circling around their roost

before they go back in
and rest up for the day.

So, I think that, you know,
that's really consistent

with a soprano pipistrelle
roost, in the clock tower,

because of the timing of the
activity that we're seeing.

Anita, what was it like seeing
inside the roost with the cameras?

Having the opportunity to
be able to see something

that you've not seen before,
that's new to you,

despite the fact that you've
been working around these animals

for a long time - it's been brilliant.

And as the technology becomes
more available and more accessible,

more and more people can get
involved and contribute data,

and it just becomes
exponential, doesn't it?

We're going to learn
a lot more about bats

in the next few years,
I think. I hope so.

It's going to be the glory years,
hopefully, for the bat.

Let's hope.