Original subtitles

66 million years ago,

an asteroid was on a direct collision course

with the Earth.

Its impact was to dramatically change

the course of life on our planet...

...leading to a mass extinction

that wiped out three-quarters of all animal life.

Out of the darkness that followed,

emerged a group that went on to dominate the world.

That group is the mammals.

Highly adaptable and remarkably widespread,

they are now found in every ocean

and on every continent,

in the air and underground.

In this series,

we'll reveal the secrets behind their success

and the challenges they now face

in a world dominated

by the most successful mammal of all -

us.

Evening in the forests of central Africa.

A family of chimpanzees is looking

for somewhere to spend the night.

Like us, they have excellent daytime vision...

...but at night, they could be caught unawares.

As the light fades,

they climb up into the canopy,

where it's safer.

There, they start to make beds for themselves.

Here, in the treetops,

the whole family will be able to sleep soundly

through the darkest hours.

But sleeping at night is unusual among mammals.

More than two thirds of them only become active

after the sun has set.

So, while you and I and chimpanzees

are fast asleep...

...most mammals the world over

are as active as they will ever be.

Zambia.

It's evening, and the light is fading.

A female leopard is starting to think about hunting.

She can see there is plenty of possible prey.

But, in daylight,

they can see her just as easily as she can see them.

That, however, is all about to change...

...when her remarkable night vision will give her

a crucial advantage.

The leopard's eyes have a reflective structure

behind the retina, called a tapetum,

that amplifies even the tiniest amount of light.

That now becomes very valuable,

because, tonight, it is particularly dark.

Impala have learnt to be wary.

With her prey so alert...

...she has little chance of catching one here.

But there are other opportunities nearby.

20 metres above the forest floor,

a troop of yellow baboons

are settling down for the night.

Even on such a dark night as this...

...a leopard can pick out the most vulnerable.

Baboons have poor night vision.

Their hearing, though, is excellent.

The closer she gets,

the greater the risk of waking them.

The troop is now fully alarmed...

...so she becomes bolder.

In all the commotion,

a mother and baby take a wrong turn...

...and now they are trapped at the end of a branch.

There seems to be no escape.

The thinnest of branches offers the mother and baby a lifeline.

With the baboons so alarmed,

she will need all her power and agility now.

The troop scatters again,

and one makes a fatal mistake.

Many nocturnal mammals, like the leopard,

have extremely sensitive night vision.

But how do you find your prey

if it is completely out of sight?

The Sahara.

Under a moonlit sky,

it's one of the quietest places on Earth.

In the cool air of night,

sound travels further

than it does in the heat of the day.

And one mammal uses that to its advantage.

It's a creature that's rarely seen...

...because it can hear us coming.

A fennec fox.

Its body is scarcely bigger than that of a guinea pig.

But those ears are huge.

If anyone can hear a pin drop,

a fennec fox can.

And in this vast open space,

it's listening for the tiny footsteps of its prey.

A gerbil.

But, at the first sign of danger,

gerbils hide underground.

The fox searches dune...

...after dune,

listening for the faintest of audible clues.

Those enormous ears are so sensitive,

they can even hear the movements of prey hiding underground.

But then they have to be dug out.

There is no gerbil.

But those ears help pinpoint

all sorts of other smaller creatures under the sand.

Such as beetles and lizards.

And they don't only help to find food.

This fox can hear...

...a distant call

echoing across the dunes.

It's January.

The beginning of the breeding season.

But for this pair...

...perhaps it's just a little too early.

To meet the challenges brought by darkness,

nocturnal mammals have sharpened their senses

in extraordinary ways.

And that's all been possible...

...because mammals started their journeys into night

a very long time ago.

200 million years ago,

the land was dominated by dinosaurs

and other great reptilian hunters,

but they were mostly active during the warmth of the day.

So the early mammals kept out of their way

by only emerging to feed at night.

They were very small,

they had hairy coats which kept them warm...

...and they found their way around by using

one of the most ancient senses of all.

Touch.

In fact,

they were probably very like this little creature,

a tiny Etruscan shrew.

This one is a mother.

And she's taking her young family

for their first night-time walk.

To ensure they don't get lost in the darkness,

they, literally, keep in touch.

The babies hold on tight...

...until they reach the safety of a new nest.

Touch not only helps them find their way...

...they use it when hunting.

Weighing less than a ping-pong ball,

Etruscan shrews are the world's smallest terrestrial mammal.

But they're still formidable predators.

Some of the hairs on the end of their noses

have become enlarged into whiskers,

that are especially sensitive to touch.

Like an extra pair of hands,

they guide them

on a never-ending search for a meal.

To fuel their frenetic lifestyle,

they feed every few hours.

A bush cricket.

It's almost as big as she is...

...and well able to make a quick getaway.

She will need the lightest of touches

if she's to catch it.

So she switches to whisker mode.

To prevent it escaping,

she must grab one of its jumping legs.

She won't get a second chance.

It's a relatively enormous meal.

But she must eat a lot

to feed her ever-growing family

and fuel her fast-paced lifestyle.

So she'll soon be out hunting again.

Feeling their way by touch is not the only method

by which mammals deal with the problems of darkness.

In Argentina, as night falls,

life starts to stir in an abandoned farm building.

There are all kinds of smells drifting through the air -

some powerful...

...some faint.

And one nocturnal mammal has

an extraordinarily sensitive way of detecting

even the faintest of them.

An armadillo.

There are 21 species in the Americas.

This one is the large...

...hairy...

...armadillo.

After dark,

he heads out into the surrounding pasture...

...guided by a highly sensitive nose.

This male has detected a smell

that he finds especially enticing...

...and soon locates the source.

A female in season...

...and she's producing an irresistible perfume.

He's fallen for her.

But she is not so sure about him.

So she takes the lead.

The male has to keep up, as best he can.

Back in the abandoned building,

the clutter in the rooms makes things more difficult.

He's lost her...

...but her scent is everywhere.

He's not giving up.

Eventually, she leads him to a quiet corner.

Her choice is made.

Equipped with an array of sharp super-senses,

nocturnal mammals have little difficulty

in finding not only food,

but mates.

But some of the most successful of all

don't only use their own senses...

...they also rely on each other.

The Ngorongoro Crater in northern Tanzania.

One of the greatest mammal hot spots in the world.

With such an abundance of prey,

the crater attracts great numbers of predators.

Amongst them, spotted hyenas.

And this female is a member

of one of the most exceptional and caring families.

She will nurture her cubs for 18 months.

And she is not a single parent.

Far from it.

She has the support of a sisterhood.

A clan ruled by females,

60 adults strong.

With so many mouths to feed,

hyenas must hunt almost every night.

As dusk falls, they head out,

splitting up into small groups...

...to widen their search for prey.

They are well equipped to hunt in darkness,

with excellent low-light vision,

a superb sense of smell

and highly acute hearing.

But they aren't the only ones out hunting.

A pride of lions has already made a kill.

The hyenas try their luck at scavenging.

There is no easy meal to be had here.

But not far away,

they find one of the most impressive mammals

in the crater.

One with the reputation

of being particularly dangerous.

Cape buffalo.

A single one of them would be enough food

for the whole hyena clan.

But a full-grown buffalo weighs three quarters of a tonne

and is very formidable.

The small group of hyenas look for a weakness

in the buffalo's defence.

It's just too risky.

But when the odds are stacked against them,

hyenas play their trump card.

They summon reinforcements.

Their calls echo across the crater.

Clan members up to three miles away...

...hear their cry for assistance.

BUFFALO GRUNTS

HYENAS YELP

The buffalo is still standing strong.

More reinforcements are needed.

Now, with the combined strength of the whole clan...

BUFFALO SNORTS

...they have a chance.

But a wounded buffalo is particularly dangerous.

One stab from those horns could kill.

They must force the buffalo off its feet.

There's no escape from so many hyena.

Their ability to work as a team

makes the spotted hyena

one of Africa's most successful predators.

But there is one mammal that has brought working together

to a whole new level.

Nearly a metre beneath the surface

of the Kalahari Desert,

there are tunnels...

...where normally, animals live in permanent darkness.

Only our lights make them visible.

Damaraland mole-rats.

The heart of their colony is their nesting chamber.

And here,

amongst the mass of bodies,

lies the queen.

She is the only female who breeds.

All the rest, whether male or female,

are workers.

Their main task is to dig for food.

But the dry season brings a challenge.

The soil becomes so hard and dry

that mole-rats are unable to dig out the tubers

on which they feed.

And their larder is nearly empty.

Digging is now so difficult,

they have to save their energies

until conditions improve.

It's late November.

The rains, at last, have returned.

Each downpour helps to soften the soil.

And the workers can start digging again.

Now, using their huge incisors,

they are able to cut through the rain-soaked soil.

The first tubers they find, they eat on the spot.

Once they've had their fill,

they carry away the tubers they find

to a chamber that serves as a larder.

The colony works without pause.

After the rains, they may dig half a mile of new tunnels,

shifting nearly three tonnes of soil.

All in order to restock their larder.

Finally, they have accumulated enough food

to see them through the next dry season.

Thanks to their dedicated teams of workers,

mole-rats have succeeded

in an underground world in permanent darkness.

But there is one group of mammals,

that has colonised the dark with such success

that they've spread to almost every land on Earth

outside the polar regions.

Dusk on the north-west coast of Trinidad.

Deep inside a sea cave,

a colony of greater bulldog bats

are waking up.

Whether their English name is a libel or a compliment

is, perhaps, debatable.

Bats are the only mammals that have true powered flight.

Getting airborne requires a thorough preflight check.

Their wings are membranes of skin

stretched between greatly elongated fingers.

Licking helps keep them supple.

These particular bats are also equipped

with an unusual feature.

Their feet have enormously elongated hook-like claws.

They're certainly useful for back scratching.

And ear picking.

But most importantly of all,

they are for hunting.

Inside their cave, it's pitch-black.

But these bats have a sixth sense

that enables them, in effect, to see in the dark.

Echolocation.

They make a series of very loud, short calls...

...and by listening to the echoes,

are able to create a mental map

of their surroundings.

It's so detailed

that they can navigate in total darkness.

And bulldog bats use this talent to catch fish,

which is not easy.

Their calls bounce off the surface of water

so they can't reveal anything beneath.

But they can, nonetheless, give clues.

A bat will scan the surface of the water

with broad echolocation calls.

When something is detected,

they're able to focus on it.

A fin cutting the surface

is enough to make them start fishing.

But catching one requires precision flying.

Using its feet like grappling hooks,

it rakes the surface of the sea.

But this is, literally, a shot in the dark.

The bat's timing has to be exactly right

to coincide with the fish breaking the surface.

Eventually, repetition brings a reward.

Thanks to this super-sense,

these remarkable bats have become

astonishingly successful fishermen.

Bats were almost certainly flying in the night skies

when the dinosaurs became extinct.

And now, nearly one quarter of all mammal species are bats.

And that is not all.

They also form

the most numerous gatherings made by any mammal.

Austin, in Texas.

Every evening in early August,

crowds gather around Congress Avenue Bridge...

...waiting for one of the city's great spectacles.

As the sun sets...

...the stars appear.

Mexican free-tailed bats.

The gaps on the underside of the bridge

provide excellent roosts for the bats.

And now, 1.5 million of them live there.

These free-tailed bats live very successfully

right alongside us.

There are now more bats than people in Austin...

...and their numbers are still increasing.

Mammals have evolved many ways

to deal with the problems of living in the dark.

But none have done so more successfully than bats.

In recent years, however,

other mammals have started to alter their habits...

...and are changing from being active in the day

to coming out at night.

And they're doing so in order to avoid us.

A coyote.

A species of dog as wild and untamed

as any wolf or jackal.

And this animal that was once mostly active in the day

has started to take the night shift.

Under the cover of darkness,

they're now living right in the heart

of America's biggest cities.

This is Chicago, home to over nine million people.

For an animal to be successful here,

it helps to be active when we are not.

Just as early mammals became nocturnal

in order to avoid daytime dinosaurs,

these coyotes are now doing so

in order to avoid us.

And, as a consequence, they're thriving.

Greater Chicago is now home to over 4,000 coyotes.

They keep a low profile where they can.

Though Chicago, like any city, is full of dangers.

But these clever coyotes are now streetwise.

Some have even learnt

when it's safe to cross the road.

The reason for these urban journeys?

Chicago's downtown parks.

Little oases of wilderness

that attract a surprising variety

of other wildlife

in considerable numbers.

The coyotes don't live on trash.

They are skilful hunters.

Before dawn arrives...

...these wily coyotes retreat into the shadows.

It's the adaptability and ingenuity of these mammals,

indeed of all nocturnal mammals,

that has enabled them to become active

in conditions that we avoid.

They have mastered the dark

and found the richest rewards.

And it should really be no surprise.

After all,

they've been doing just that for millions of years.

One of the greatest challenges facing the Dark team

was filming fennec foxes.

They travelled to Tunisia and into the Sahara.

Helping them was Italian wildlife photographer

Bruno D'Amicis.

Having worked here before,

he knew just how difficult this would be.

We don't know much about fennec foxes.

The studies done on this species in the wild

can be counted on one single hand.

You have this animal living in the largest desert of all,

moving mostly at night,

so, yeah, it is...

...it is super challenging, it is very difficult.

Bechir Belhadj, a local fennec expert,

was key to helping them track down the best place to film.

Bruno, Bruno.

Oh, there's the fennec.

Yeah, that's great.

Thank goodness they're here.

Oh, here. You see, you see?

You're looking at fennec scats.

Looks like a... beetle casings.

Yeah, many beetle casings.

The signs were encouraging.

But producer Stuart Armstrong knew

that the challenge was still immense.

Great that we've found tracks and signs of fennecs

but it's rolling dunes, you know,

something will disappear so quickly behind a dune,

and then you add in the challenge of doing it in the dark.

Early next morning, Bruno and Stuart got to work

setting up numerous camera traps.

Using super-sensitive low-light cameras

would give them the best chance.

With new technologies, we can get a beautiful glimpse

of what goes on at night,

with... directly with the moonlight.

So it is super exciting.

And wildlife cameramen Pete Cayless

and Marco Andreini started their night shifts.

At least we know that there are foxes around.

Our wish is to see one, um, in front of us.

With clear skies and a full moon,

filming conditions are excellent.

But being nocturnal,

extremely shy and living in such remote locations,

fennec foxes have been filmed only rarely.

But after only a few nights,

this ghost of the desert revealed itself.

Oh, wow.

HE CHUCKLES QUIETLY

I actually can't believe it.

And when they checked the camera traps,

the news got even better.

Yay!

Look at that! No way.

Look at the size of those ears.

Yeah. They're huge. Yeah.

Sweet little thing.

That's so encouraging.

That's super encouraging.

Yay!

All was going well.

But their good luck soon vanished.

The foxes had disappeared.

Night after night brought no rewards

for camera operators or camera traps.

Keep trying, that's the only thing I can do.

I really hope they will... they will come.

Nothing.

Nothing, nothing, nothing.

Frustrating to say the least.

The crew eventually discovered the reason

for the fox's sudden disappearance.

A few miles away, they found a recently abandoned camp,

and amongst the litter was the most shocking find.

We're all a bit stunned.

We discovered one of the foxes on the floor

and we thought that was shocking enough,

and then just... just up here...

...is a second fox.

It's just heartbreaking.

There's... no end to this horror.

Here, it is illegal to kill a fennec fox.

But it's difficult to police such a remote place

and, sadly, they are still heavily persecuted -

trapped for pets, but also for food, fur

and, in this case, more shockingly,

it seemed, for fun.

I'm heartbroken, I'm heartbroken.

Saharan wildlife is some of the most threatened on Earth,

and only with local champions can the situation here change.

As a young man, Bechir used to trap foxes,

but he hunts no more.

He's become an advocate,

helping to spread the message throughout the local communities

that fennecs need protecting,

and he hopes a film about these foxes could help with that,

which made him and the crew

even more determined to not give up.

Bechir knew of another potential location.

A remote oasis,

and the signs are encouraging for everyone.

Wow. There are loads of tracks.

There must be more than one animal. This cannot be one animal.

This is very exciting, isn't it? Yeah.

New location, a new day, new hope.

But would the tracks and signs turn into success

for Marco and Pete?

How are you doing? How was your night?

Ah, it was a long, long, long, long night.

I must have been crazy when I chose this hide.

It's too small.

But it worked.

There was one fluffy...

...then two fennec foxes there.

To see two foxes, possibly a courting pair,

brought the team a lot of hope.

These animals are so incredible.

It's like the spirit of this desert.

It was so beautiful.

I'm so happy...

...now.

In remote corners and against many odds,

these endearing foxes still survive.

And, hopefully, the support of local communities

will help to conserve not just fennecs

but other threatened wildlife across the Sahara.

Next time...

...mammals continue their journey into our world...

THEY SQUEAK AND CHIRP

...a world changing faster than ever before...

...and full of new challenges.