Original subtitles

Ati'en borough: Antarctica.

The earth '5 coldest continent,

the one that is most hostile to life.

Here, 7, 300 kilometres from the south pole,

it's 40 degrees below zero.

Of all the millions of species of animals on earth,

only one can live here permanently.

A weddell seal.

She can survive because she can dive below the ice.

Here, she is protected from the storms above

and here, too, she can find food.

But she is a mammal and she has to breathe air.

So she has to keep a lifeline open to the world above the ice.

Not only for her, but now for her newborn pup.

He's less than a week old and still very vulnerable.

A blizzard blows in and with it storm-force winds.

It could last for a week.

Being mammals, seals can generate heat within their bodies.

And their fur, with a thick layer of fat beneath it,

prevents most of that heat from escaping,

even in cold conditions like this.

What is more, she is able to feed her youngster

with that mammalian speciality, milk.

And while she does so, she shields him from the worst of the blizzard.

She has worked hard throughout the winter

to prevent her breathing hole in the ice from freezing over.

That requires constant attention,

filing back the edges of the hole with her teeth.

Her pup needs to join her under the ice as soon as he can swim properly.

She encourages him to take his first plunge

but hardly surprisingly, he's not keen.

Now, guided by his mother, he has to learn how to hunt underwater

and to find his way back through the maze

to his hole in the ice.

A warm body, fur, milk and maternal care

are essential for the weddell seals' survival

in this freezing environment.

And those qualities have helped the mammals

to colonise the entire globe.

Equatorial east a frica.

It's hard to imagine a place more different from Antarctica.

To survive here, mammals need additional talents.

This tree shelters the territory of a tiny mammal

that spends its whole life in frenzied activity.

It used to be called an elephant shrew,

but now it's called by its African name of sengi.

This is a female rufous sengi.

And like all sengis, she's so active, she's permanently hungry.

To get all the food she needs,

she has to be both industrious and ingenious.

She has made an intricate network of trails

that enable her to hunt her insect prey very efficiently.

But these pathways have another important function

when she meets her enemies.

Having a map of these trails in her head can mean the difference between life

and death.

Like most mammals, and unlike reptiles, her legs are directly beneath her body.

That makes her less stable, but much faster and more agile.

Not only has she outrun this reptile, she's outwitted him.

And just as well,

for she is a mother and has a youngster to care for.

The sengi relies on speed and cunning for its success.

Other mammals have very different techniques.

Here in Madagascar,

one of the most bizarre of all mammals is on the prowl.

The a ye-a ye, like the sengi, lives on insects.

But the ones that she seeks she can't see,

for the y're buried deep inside branches.

They're beetle grubs.

To find them, she has a special talent.

She taps her fingers on the wood, up to eight times a second,

and listens for the tiny change in resonance

that indicates a hollow spot within.

Her hearing is so acute she can identify the precise position

in which to gnawa hole in order to reach the grub.

And she has a grotesquely long middle finger with which to skewer it.

It takes a young a ye-a ye four years to perfect this technique.

But once it has done so, it can collect prey

that no other mammal can reach.

The arctic tundra.

Food is hard to find here, too.

Indeed, this land is so barren that few large animals can live here.

Yet one mammal has found a way to do so.

It's late spring,

and as the mounting strength of the sun warms the land,

eight million reindeer move north.

But the vegetation is so meagre

that the only way the herds can get enough

is to keep constantly on the move.

Newborn calves soon discover that they will have to spend every day

walking in search of food.

They ha ve extraordinary endurance.

Some of these animals, before they die, will have trekked for a distance

equivalent to three times around the earth.

Grazing is now at its best.

But this is also the time when the reindeer's worst enemy appears.

Biting flies.

The flies not only drive them to distraction,

but they can drain a pint of blood each day.

But the reindeer have a defensive strategy.

Each individual tries to push its way into the centre of a group

where there are fewer flies.

With all this pushing and jostling, mothers need to keep their calves close.

Sometimes, the flies become so bad

that the reindeer can stand them no longer

and they bolt to higher ground where the flies can't follow.

But the price of escape can be high.

In the rush, one mother has lost her calf.

Others have already found it.

The herd has long since moved on.

But her maternal instinct is so strong,

she'll stay to search for her missing calf for days.

The reindeer are free from flies for now.

But with no food on these high slopes,

they will eventually be forced to descend

to find new pastures and face the biting swarms once more.

No animal makes a longer migration across the lands of the earth

than these mammals.

Other mammals have found a more economic way

of travelling huge distances, and at greater speed.

They go by air.

Giant stra w-coloured fruit bats inhabit the great forest of the Congo.

Their wings are nearly a metre across.

In late October every year,

they set off on a long journey across the forest canopy.

Flocks of hundreds become thousands.

And tens of thousands become hundreds of thousands.

T he y're fast and powerful fliers

and can travel more than a thousand kilometres in just a few nights.

How they know where and when to travel is a mystery.

But they all end up in one place,

I(asanka, a remote swamp in Zambia.

There are ten million of them here.

They crowd together in just one small patch of forest

no bigger than two or three football pitches.

And here they take up residence for a few weeks.

It's the largest fruit bat roost on earth.

After their long journey, they need to rest and relax.

The roost is so crowded

that complete strangers rub shoulders and even snuggle up together.

As evening approaches,

they prepare to reap the reward for their long journey.

They've come from all over central Africa

to this one place because here, at this time of year,

there is an extraordinary glut of mangoes and other fruit.

Streaming out from the roost, they set off to collect it.

Each bat guzzles at least two kilos' worth of fruit every night.

In just a few weeks, this megaroost

will devour more than a billion separate fruits.

It's only the power of flight that allows these mammals

to travel so far and so fast that they can reap such a brief harvest.

After six weeks, the trees have been stripped of their fruit.

Then, once again, the immense aerial armada takes to the air,

each bat returning to its own particular patch

of the vast Congo forests.

The land mammals of a frica

also travel together in stupendous numbers.

The herds that graze the east African plains

are not nearly the size they were a century ago,

but they are still immense.

Grazing together is a good defence. There's safety in numbers.

But hunting together also brings advantages.

This h yena, however, is searching for food on her own.

She needs to be careful.

But she smells food and she takes risks.

Bruised and bloodied, she is lucky to have survived her mistake.

But she's not totally defeated.

She belongs to a clan.

A call to arms rings out through the night.

Reinforcements assemble.

Every adult in the clan responds.

If a clan attack together,

they have a chance of challenging the lions.

It's a clan against a pride, each at full strength.

And the clan outnumbers the pride.

The combined power of the h yenas eventually forces the lions to retreat.

A ttacking as a coherent team requires a high degree of social cooperation

and that is another of the mammal's specialities.

Social bonds between mammals begin when mothers feed their young on milk.

And few look after their young with greater care

than the mammal which dominates this landscape.

A female polar bear is trying to find food for her cubs.

But this is a particularly difficult time of the year.

The sea ice on which she hunts is melting beneath her feet.

She must look for food on land.

They're all safely ashore.

But they could still face months of hunger.

Finding food is not so easy on this cold and barren coast.

The search may be a long one.

Polar bears have an extraordinarily sensitive sense of smell,

and she has caught a faint whiff of something promising.

It's the immense carcass of a bowhead whale.

A whale carcass could provide more than any one family could eat.

But they're not the first here to find it,

by any means.

The smell has brought in bears from miles away.

Bear families seldom get on with one another.

She's taking a risk bringing her cubs here.

Male bears can and do kill and eat small cubs.

Another family challenges her.

She must decide whether to compete for food

or run away and go hungry.

She keeps her cubs close to her and stands her ground.

Their mother's courage has won the cubs a meal.

Living as a family may bring rewards, but it can also create problems,

for siblings can also become rivals.

A coat/, a south American relative of the raccoon.

These babies were born in a nest high in a tree

and are about to come down to the ground for the first time.

Some more reluctantly than others.

Once on the ground, the mother coati rounds her babies up

and takes them away to join a single large group.

Together, these families form a gang up to 40 strong.

Once again, numbers bring safety.

The first to spot danger will warn everyone.

But keeping order isn't easy.

And when they find food it's a free-for-all.

Meerkats in the kalahari desert also live in large groups

but the y're rather more organised.

Each family band is controlled by a queen,

who is nearly always the only female to breed.

She has been kept very busy suckling her five pups.

And it's high time they became more independent.

Today is the new brood's first trip to get breakfast for themselves.

It takes weeks for youngsters to learn how to find food.

This one is trying to catch ants,

but hasn't quite grasped the necessary technique.

But this youngster has persuaded an adult

to show him what to do.

The tutor is not his parent, just an enthusiastic instructor,

and one who will adapt his lessons to the ability of his student.

This new one is a beginner, so he starts with something easy,

how to dig for insect larvae.

Other meals, like this one, are much trickier.

So, the tutor disables the scorpion's sting

before he lets the youngster tackle it.

The family also cooperates in defence.

Every member does a tour of guard duty, keeping an eye out for danger.

So, while one watches, everyone else can rest.

And on warm days, one can easily nod off.

The secret of meerkats' success

is that everyone takes a turn in communal duties.

But many mammals do more than just share their workload.

Some can share their knowledge, and do so across several generations.

Elephant survival depends on profiting from the experience of many lifetimes.

This baby elephant was born last night

and the whole herd seems to welcome this new addition.

But the mother is young and inexperienced.

This is her first baby.

If she is to produce milk, a mother must drink.

And the newborn calf must keep up with her

as the herd continues on their long journey to find water.

After eight kilometres, the calf is flagging.

Enough is enough.

The young mother encourages her calf to continue

but there is still a long way to go

and the calf is already getting dehydrated.

The elephants are now so close to water that they can smell it.

Water at last!

This is the calf's first encounter with a waterhole.

She's not sure what to make of it, or indeed, how to get out of it.

Her mother tries to help her

but she has no experience of dealing with babies.

As the herd moves deeper into the swamp, the calf follows.

But now, she is in real trouble.

Elephant babies can and do get permanently stuck in deep mud.

Her mother's attempts to help her baby are only making matters worse.

It's stuck beneath her and she's pushing it deeper still.

But now, the baby's grandmother spots the problem and steps in.

Drastic action.

She pushes mother out of the way with an unceremonious poke in the rump

and enables her granddaughter to scramble free.

Mother and calf ha ve learned a valuable lesson from grandma.

Such passing of wisdom across generations

has been an important element in the survival of elephants.

The largest animal on land, the elephant, is a mammal.

And so are the largest animals in the sea.

A female humpback whale and her calf.

Every few years, she will travel nearly 5, 000 kilometres,

from the rich waters of the antarctic

to these warm but comparatively sterile waters of the pacific,

to give birth to a single calf.

The seas around Tonga are not only a nursery for humpbacks,

but also their mating ground.

This 50-year-old female has come here to seek the best partner.

And she starts by announcing her arrival to potential suitors.

One by one, the males arrive.

But as they do, she swims away,

compelling her half-a -dozen or so suitors to follow her.

She leads, while the males jockey for position behind her.

The males bellow threats to one another, creating huge plumes of bubbles.

So far, it has been a relatively gentle affair.

Now the competition becomes serious.

Hour after hour, the males battle for position right behind her.

And now, the 40-ton males begin to smash into one another.

This is the most massive battle in all nature.

Rival males can kill one another.

As the conflict reaches its climax, they try to force each other downwards.

A t last, a Victor takes his place alongside the female

and remains unchallenged.

By inciting the males to fight,

the female has secured the best mate for herself

the one who is most likely to father the strongest offspring.

Together, the couple dive to the depths.

But still, no one knows where they will mate.

All mammals, including ourselves, share a set of winning characteristics.

Warm bodies, extraordinary senses and highly developed intelligence.

And those qualities have contributed to their and our success.

But perhaps the most important characteristic of all

lies in the strength of our family ties.

It is the mammal family that has conquered the earth.

Tonga is famous for humpback whales

but even here, finding and filming whales in the open ocean

would prove challenging.

For the life team,

capturing the humpback whales' unique mating contest,

known as a heat run, would need local knowledge,

hours on the water and a big slice of luck.

We've heard that one of the boats, further in land by submarine rock,

has seen a female with a calf and an escort,

which is something which might build to hopefully a heat run.

So we're gonna head over there and take a look.

Ati'en borough: Any adult female with a calf could be coming into season

and so might be a target for amorous males.

Mun ns: When we got there I was pretty excited,

a little bit nervous, I didn't know what to expect.

Once I got in the water and dived down,

it was surprisingly quiet and mellow.

I certainly didn't expect what happened next.

The calf just came straight up towards me.

She seemed really relaxed and definitely interested in me.

It's literallyjust swimming around

within metres of them, flicking its tail,

just being inquisitive, I think, and having a bit of fun.

It's obviously quite young,

so it's staying on the surface quite a long time.

It's not diving down for very long, maybe a couple of minutes.

And the mother will be about five or ten metres below,

just keeping an eye on it.

Ati'en borough: But even a calf has great power in its fins and tail.

Roger will need to be careful.

Got it?

That was the most silly thing I've ever seen in my life.

He's just gambolling around like a little newborn lamb,

but it weighs two tons.

A couple of bumps,

it would just come round, flash its fluke at me or whatever.

I got a great shot of it chasing Jase around.

Jason is back-pedalling like this, back to the boat.

Jason: It's just a baby, like a little puppy,

you're playing with a little puppy, but it's four metres long.

- It's just ludicrous. - Was his mum all right?

She is just totally chilling out underneath, pecs back,

just hanging like this at about 15 metres.

Guy: Just watching? Mu n ns: Yeah. Just hanging out,

probably didn't even see it, I don't think.

Ati'en borough: It's one thing to be close to a playful baby,

it will be another to be in the path

of a testosterone-charged group of males,

each 70 times her size.

There's one back there.

Ati'en borough: There are enough males here for a heat run.

But are they in the mood?

Guy: Yes!

Looks pretty good.

- When you guys are ready. - Let's go.

Quick as you can.

Okay, guys.

Simon blakeney: These whales can weigh up to 40 tons

and things are moving surprisingly quickly,

so as well as getting the camera in position to get the shots,

which they have to be fairly close,

we have to be really careful that they don't get bumped or hit.

If they get a knock from one of these guys,

it can do them some serious damage.

Coming right towards you.

Ati'en borough: To avoid disturbing the whales' behaviour,

the team need to free dive without scuba tanks,

holding their breath as long as they can.

Munns: On a good dive, I can hold my breath for maybe two minutes.

These guys, they can go for 20 minutes or more

before they have to come up for a breath.

There's no contest.

Ati'en borough: More and more whales are gathering.

But it's not turning into a heat run yet.

Hard to say what was going on then.

- Were there five that time? - Five, yeah.

Munns: They're kind of moving around, coming up and under and over,

and hopefully something's starting to happen.

Maybe love's in the air?

Ati'en borough: Love may be in the air, but it isn't in the water.

Despite keeping tabs on the whales over the next 70 days,

there was still no sign of a heat run starting.

You'd think it'd be quite easy to keep track of a 40-ton animal

and we've got six of them out here and we keep losing them.

One minute they're there, we get up reasonably close,

within 30 seconds they've dived and they're gone again.

And then it takes another maybe five minutes, 10 minutes,

and then they'll come up again and they'll be 300 yards away,

and it takes ages just to get close to them.

So, we just play a continuous game of cat and mouse.

"Cat and mouse?" It's whales.

Ati'en borough: The mating season is coming to an end

and the crew haven 't completed their mission.

But then, at last, the whales' behaviour seems to have changed.

Well, this is it.

We've just spotted about six or seven humpbacks on the horizon

and we think it's a heat run.

The last 16-17 days on the water

are probably going to come down to the next two hours

as to whether we get our shots or not.

Ati'en borough: The chase is on.

There was at least three or four whales going past then

and they're all competing, knocking into each other and crossing

as they try to get in the pole position behind the female.

That's right at you. It's right at you.

A'i'i'en borough: The whales are moving so fast

that to stand any chance of filming them,

the crew needs to be dropped right in front of the charging group.

Just as Roger gets alongside the males,

the tempo of the chase suddenly shifts to a full-bore with the flick of a tail.

Facing the charging males deep underwater,

Roger keeps shooting, holding his breath until the group pass over.

A quick gasp of air and Roger's back down again.

The whales continue to rush by.

In the end, Roger just can't keep up any longer.

Exhausted, it's time to return to the boat for the last time.

Amazing!

That was the most amazing experience I've ever had.

There were about seven or eight,

we both dived down about 20 metres in front.

And then the female came through fast, quite close,

and then they all just started diving towards me, so it was just sort of

like standing in a stream of traffic.

They were just sort of one one side, one the next side, one the next side.

And then after about 40-45 seconds, I was getting a little bit out of breath

and then, sort of, looked up

and there's one sitting right on top of me.

- Did you get it? - I think so. I hope so.

If not, we're both fired.

A'i'i'en borough: It's taken 78 days and hundreds of dives

but at last the team have been able to re veal

a secret of these whales' lives that few people have ever seen.