Mammals

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,