Original subtitles

David Attenborough: In the far north of our planet

lie vast frozen lands...

Of snow-covered forests...

And open tundra.

During the months to come,

they will be transformed

by the greatest seasonal changes on earth.

But now, in midwinter,

conditions are so hostile that life seems all but impossible.

But...

Not so.

In this world of extremes, animals must go

to extraordinary lengths to survive.

February, northern Canada.

The harsh winter

has brought together an extended family of wolves.

But this is no ordinary pack.

There are 25 of them.

A super-pack,

one of the largest ever recorded.

They're ravenously hungry.

They may have walked over 150 miles

since they last had a meal.

But now, at last, the lead male and female

have picked up a trail.

It's been left by the only substantial prey there is here

at this time of year...

Bison.

They're formidable animals,

not easy to attack.

The bulls are ten times the size of a wolf.

And they have horns

with which they could rip any attacker to pieces.

Gathered together and on guard,

they appear invulnerable.

The wolf pack's only chance...

Is to try and break up the group

and isolate one of them.

To do that,

they will have to work as a team

and try to start a stampede.

Even in thick snow, bison can run at up to 35mph.

The lead female wolf leads the chase.

A kick from a bison's hind leg could shatter her jaws.

But the pack must feed, and they take turns to attack.

The bison head for cover.

The deep snow slows down both attacked...

And attacker.

The herd splits into two.

But the wolves are far from giving up.

Hours pass.

The thicker vegetation has turned

a straightfonnard chase...

Into a deadly form...

Of hide...

And seek.

Discovered.

The lead female manages to chase the smaller group

into the open.

But here the bison are able to close ranks once again.

The leading wolves wait

for the rest of the pack to catch up.

The super-pack is once again at full strength.

Suddenly, two of the bison panic.

It's just what the wolves have been waiting for.

One of the bison is tiring.

The lead female gets a grip on its flanks.

The male joins her.

Together, they might be able to bring it down.

The rest of the wolves catch up and help.

After eight long, hard hours, the hunt is coming to an end.

Victory is sounded to summon the rest of the pack.

A single wolf wouldn't stand a chance

of making such a kill by itself.

The only way they have of surviving the winter

is as a super-pack.

These snow-covered forests encircle the arctic

from scandinavia, through Russia,

to Alaska and the rest of North America.

But close to the north pole,

the winters are too long and too cold

for even the hardiest of trees.

This is the tundra, and it stretches

all the way to the shores of the arctic ocean.

Here, conditions are even more extreme than in the forests.

During the two months of winter darkness,

temperatures may fall to minus 50 degrees celsius.

The ground deep beneath the snow

has been frozen solid since the last ice age.

There is no shelter of any kind.

Very few animals can survive here.

But this is one which does.

An arctic fox.

It has the warmest fur of any mammal.

And it can survive blizzards that may rage for days on end.

It must nonetheless eventually eat something.

But how is that something to be found

when you're all by yourself in this desolation?

Arctic foxes are wanderers.

And they can travel over 2,000 miles, from Norway to Canada,

in a constant search for food.

There might be something here.

A patch of grass, kept clear of the snow

by the near-constant wind.

The slightest hint of scent

might indicate the presence of prey.

Less than a metre below the surface

may lie a hidden network of tunnels,

shown here using a special filming burrow.

Tiny arctic lemmings.

With a carpet of edible moss beneath

and a thick blanket of snow above...

The lemmings spend their entire winter

hidden below the surface.

And here they breed.

For a hungry fox,

a group of lemmings could be a life-saving discovery...

If it can catch one.

Lemming Burrows may extend for up to 15 metres.

Pinpointing the position of one of the inhabitants...

Is not easy.

An acute sense of hearing is essential.

And the arctic fox

has a special trick.

It doesn't always work first time.

And it does require dedication.

With less than 25 lemmings per square mile of tundra...

You have to persevere.

And at last...

One plump lemming.

The foxes' tenacity and unique hunting skills

enable them to find prey which few others could catch.

On the tundra's southern fringes,

winter is significantly less severe.

The slight increase in annual sunlight

has enabled a stunted forest to develop.

It's the northern edge of the world's largest woodland...

The boreal forest.

750 billion trees.

A quarter of all the trees on earth.

And it encircles the globe.

These forests store twice as much carbon

as a tropical forest,

and they play a crucial part

in regulating the climate of the entire planet.

One of the most remote tracts

stands in the far east of Siberia.

It's cut off from the rest of the world by towering peaks...

And precipitous valleys.

And it is the last stronghold

of the world's rarest big cat.

The amur leopard.

Hunting has brought it close to extinction.

Only 120 are left in the wild.

And this is one of the very few ever to be caught on film.

Each must patrol a territory of over 100 square miles

to find enough to eat.

In the cold of march,

prey is at its most scarce.

But leopards are clever opportunists

and watch for clues.

Crows.

They, too, are looking for food.

And their calls tell him that they've found something.

But he is not the only predator here.

On one of the trees, the marks of huge claws,

ten centimetres long.

They've been made by a hunter twice his size...

A siberian tiger.

Fewer than 500 remain in the wild.

These two rare big cats are sharing the same territory.

And fixed remote cameras

show that they even use exactly the same trails.

But leopards know they must be careful.

Siberian tigers are the biggest of all the big cats,

and could kill a leopard...

Should they ever meet.

In winter,

many forest animals rely on carrion for food.

And that includes leopards.

But he can't let down his guard.

The crows that led him here...

May also have alerted the tiger.

The crows are disturbed.

Another mouthful might be risky.

Survival sometimes depends on knowing

when to leave.

Only a few choose to take their chances here

in the depths of winter.

Elsewhere, vast swathes of the forest remain eerily empty.

Above, there is an othennorldly light show...

The Aurora borealis.

High in the sky,

electrically charged solar particles from space

collide with the earth's atmosphere

and create this ethereal display.

Meanwhile, in Canada, through the six long months of winter,

life below ground is biding its time.

The world's most northerly turtle...

The painted turtle...

Seen here in a special filming chamber.

They hatched last Autumn, but have remained

in a state of suspended animation ever since.

Their hearts have stopped beating...

And only their brains have remained active,

and even then, only very faintly.

Painted turtles wait underground

for this most important of moments...

The arrival of spring.

In April, the strengthening sunshine

triggers a miraculous transformation.

The turtles' body temperature rises just above freezing...

And their hearts start to beat once more.

Slowly, they return to life.

Thanks to this extraordinary adaptation, these young turtles

get a valuable head start in spring...

And are one of the first to emerge, ready to take

full advantage of the forest's renewed abundance.

In just a matter of weeks, the vast northern forests

flush green.

For Siberia's big cats, each spring could bring new hope.

Cubs.

Each of them increases the chance that,

even at this very late stage, both species might recover.

By June, the northern forests are full of life.

But several thousands of miles further north, in the tundra,

the spring thaw is only just beginning.

When it does, under 24-hour daylight,

its impact is even more extreme.

Five million square miles of snow

disappear in a matter of days.

Ten centimetres beneath the surface of the ground,

a snow queen is waiting to make her appearance.

A lapland Bumblebee.

She's barely alive.

All the other members of her colony were killed by the cold.

She survived, as Bumblebee queens do,

thanks to her larger size, her particularly thick fur,

and a natural antifreeze that she has in her body.

As temperatures continue to rise,

she begins to thaw.

She vibrates her flight muscles,

which raises her body temperature

to over 30 degrees celsius in just six minutes.

There is no time to lose.

She must now create an entire colony.

First, the queen must find a drink of nectar

to regain her strength...

Travelling as much as three miles a day

to find the flowers from which to collect it.

She works tirelessly.

As well as high-energy nectar...

There's pollen to be gathered.

Back underground, she uses the pollen to build a waxy cocoon.

And in it, she deposits tiny eggs.

Had she laid them directly on the frozen ground,

the cold would have killed them.

And now she warms them

by pulsating her body.

She has also constructed a little pot

in which she stores nectar

to provide her with a drink when she needs it.

For the next three weeks...

This single mother

works around the clock, gathering nectar

to top up her pot...

And vibrating her body

to prevent her developing young from freezing to death.

Eventually, a new generation of bees

starts to emerge.

She leads each young worker to her honey pot

and encourages it to drink.

By the end of the following week,

the number in her little colony has increased to eight.

Her timing has been perfect.

The tundra is now in full bloom.

And the Bumblebee families help to pollinate

the largest wild-flower Meadow on earth.

But the summer here is one of the shortest on the planet,

and all of the tundra's residents

are now racing to breed.

Alaskan snowy owls have a brood of six fluffy chicks

and only eight weeks in which to raise them.

The parents provide them with 30 lemmings a day...

For the chicks will need to triple their weight

before they reach independence.

Unusually for an owl, snowies hunt by day.

And over the next two weeks,

they take full advantage of the arctic's continuous light.

But this morning, the female returns to an empty nest.

Her chicks are nowhere to be seen.

They're hiding.

They're so big, the whole group might be spotted by predators,

so they have scattered across the tundra.

But that makes feeding them all much harder work.

Over 600 meals later,

the parents' labours are starting to pay off...

As the chicks stretch their newly developed wings.

Just a month is left before winter returns.

Two weeks more,

and their transformation is almost complete.

The chicks' wings might at last be able

to do more than just lift them from the ground.

Getting there!

Keep going!

Airborne!

The youngsters are ready for independence.

And the exhausted parents can take a well-earned rest.

The tundra has come to life once again.

But in the longer term, its very foundations

are now at risk.

The ground itself is giving way.

In some places, it's dropped by more than 60 metres.

Grasslands that once supported thousands of different species

have become wastelands.

Arctic temperatures are rising

as a consequence of climate change.

The deep soil, which has been frozen solid

for thousands of years, the permafrost,

is now thawing at a rate never witnessed before.

Without the ice to bind it together,

the ground becomes unstable.

In Canada, thousands of tonnes of the tundra

have collapsed in a matter of weeks.

And in Siberia, huge scars are appearing.

By the end of the century, an area of arctic permafrost

one third of the size of Europe

could have thawed.

The warming of the tundra

is having a profound impact on its wildlife.

For millennia, caribou have made annual migrations.

Every summer,

driven by the seasonal changes of the far north,

and following long-established pathways,

they have trekked almost 400 miles north.

This herd alone in north-east Alaska numbers over 200,000.

Their destination

is a vast wilderness

known as the arctic national wildlife refuge.

These summer pastures provide rich grazing,

just what's needed to raise newborn calves.

This one, fattening up on its mother's milk,

would normally double its weight in just a few weeks.

But now grazing time is being disrupted.

In summer, the tundra becomes waterlogged.

These are excellent breeding conditions

for mosquitoes and other biting insects.

But as the climate warms,

there are concerns that insects will breed earlier

and eventually reach plague proportions

just as the caribou need to feed.

Individual animals could lose

a quarter of a pint of blood a day to biting insects.

So the caribou may end their grazing early

and head for cooler, mosquito-free pastures.

But to get to such places,

they will have to cross rivers swollen by seasonal runoff.

For a young calf, a deep river crossing is very dangerous.

He does what he can to stay close to his mother.

But he doesn't have the strength

to resist the fast-moving current.

He is one of the lucky ones.

Reunited with his mother,

he can continue on his journey with the herd.

But other calves are less fortunate...

And must now fend for themselves.

Some are too exhausted to take another step.

But this is not a safe place to take a rest.

Grizzly bears.

For the past few weeks,

there has been little food for them on the tundra.

And this one is extremely hungry.

He's looking for the weak and weary.

And he's found one...

Too tired to flee...

And too weak to resist.

The herd's finally reached

the northern limits of its range.

These coastal pastures bordering the arctic ocean

remain cool enough to provide relief

from the swarms of insects.

Mothers and calves can finally feed in peace.

For now, this immense herd is stable.

But in the long term, its survival is now uncertain.

The seasonal extremes of the far north

have always tested its inhabitants to the limits.

But climate change could present them

with one challenge too many.

Only if we can mitigate its effects

will the remarkable wildlife here

stand a chance of survival.

Filming in the extremes of the far north...

The team's greatest challenge was to capture

the epic showdown between super-packs of wolves

and bison in midwinter,

The crew travelled to

wood buffalo national park in northern Canada,

a remote wilderness the size of Switzerland.

To stand a chance of filming this drama,

they must take to the skies.

Drawing on local knowledge,

pilot Matt erhardt helps to pinpoint

one of the last free-roaming herds of bison

and the wolves that specialise in hunting them.

Some of the wolves have run fonnards.

Just have all your kit ready to go.

With a positive sighting,

it's time to mobilise the film crew.

Cameraman Jamie mcpherson has rigged the helicopter

with a gyrostabilised camera system,

enabling him to capture rock-steady images

from a safe distance.

You'd think filming from a helicopter's easy,

because you can just fly around and film stuff.

But you've got to be incredibly careful,

not influence the behaviour,

not scare the wolves or the bison.

There we go. Yeah, that is them.

- It's a big pack. - Yeah.

They're really chilled out with the helicopter.

Really encouraging.

But before Jamie can start filming,

the chopper must first drop the accompanying ground crew.

- Good luck. - Ok.

We got put down

in this vast open space,

and now we're going to try and hike in and see

if we can get close to them,

or hopefully they'll get close to us.

To intercept the pack, the team must scramble into position.

But trudging through knee-deep snow

is hard going.

Every time I catch up with Justin, he just keeps on going.

He's a machine!

Yeah, go ahead, Matt.

Over radio: They're starting to head

a little bit towards the north-west,

so they're starting to move away from you.

Oh, goddamn it!

David: The ground crew will have to dig deep

if they're to film the fleet-footed wolves.

Over the following week,

Jamie manages to track the wolf pack

from the comfort of the helicopter...

While down on the ground,

Justin and will are having a tougher time of it.

- Ohhh! - It's really

incredibly awkward getting around.

Even lunch offers little consolation.

It's frozen bread,

frozen brie and frozen pickle.

And with no wolf activity visible from the air,

Jamie is soon grounded.

Yeah, I'm just looking for an update.

The winter weather takes a turn for the worse.

It's snowing, and it's at a temperature where it could

potentially stick to the blades and become really dangerous.

For the next few days, the crew are forced to sit it out.

Finally, the skies clear.

But after nearly three weeks on location,

there's precious little filming time left.

We've got one last shot

to get what we're looking for.

And just hoping that it comes together at the last minute.

There, there's the trail there,

so they're on the West Side of that trail there.

Soon enough, they find the bison,

along with wolves

who appear to be in hunting mode.

The spotter plane just found the wolves with the bison,

so we're scrambling to get there as quick as we can.

There's something about

being in the presence of prey and predator on the ground

like this which is very special.

Justin is in prime position to capture the showdown.

As a chase begins,

Jamie picks up the action from the air.

It'd be amazing if we could get round that.

In a stop-start pursuit lasting an entire day,

Jamie manages to record the full jaw-dropping drama.

They've definitely got that female.

I think they're going to bring it down.

Perfect, Jim. We got it.

With the hunt nearly over,

the crew reposition Justin once more.

We got on the ground just in time to capture

from a really far distance

the last moments of the bison's life.

There's a moment of confliction

between your loyalty for each animal.

One is filled with a mixture of both celebration for the wolves

but a sadness. Both exist somehow simultaneously.

Bearing witness to this rarely seen age-old battle

between predator and prey leaves the crew

with an appreciation of just how challenging life is

in the frozen extremes of the far north.