The Arctic tundra:
Covering one tenth of the earth's surface,
this ice desert is one of the coldest
and driest places on earth.
The piercing sub-zero temperatures
and powerful winds of the tundra,
challenge even the planet's hardiest creatures.
This landscape is home to some extraordinary species,
that carve out their existence in this land of extreme cold.
Life here must adapt
or perish.
The Arctic tundra is a vast, treeless landscape,
that engulfs the earth between the North Pole,
and the coniferous forests of the Taiga.
In winter, all the water in the tundra freezes,
and it's defined as a desert
of over 12 1/2 million square kilometers,
reaching right around the planet.
Here the nights can last for months
and the vast plains are covered by snow,
in a winter that lasts three quarters of the year.
Beneath this snow lies a layer of frozen soil,
nearly one-mile-thick.
The animals that make the tundra their home,
have had to adapt to survive.
March, on the fringes of the Scandinavian tundra,
home to one of the hardiest mammals on the planet,
the reindeer.
Also known as caribou.
This herd of 3,000 reindeer
have spent the last six months here
on the northern edge of the Taiga forest.
Scratching out an existence
during near perpetual darkness
and temperatures as low as minus 30 degrees Celsius.
But they're about to begin an epic journey north
through the bleak and forbidding tundra.
No other animal's body is more suited to the journey ahead.
Their thick coat is perfectly evolved
to retain their body heat,
providing a natural heated blanket.
By distributing weight evenly over each hoof,
reindeer are the most energy-efficient animals on earth.
Their hooves adapt to the season,
turning hard and sharp in winter,
allowing them to dig down to the last remaining food;
lichen, buried under the snow.
Over 300 kilometers north, on the North Sea coast,
lie the reindeer's summer grazing grounds.
It will take the herd over two months to get there,
so they must start their journey across the tundra now
to arrive in time for the short summer
that lasts just a few weeks.
No cattle could survive here,
so for centuries reindeer have been domesticated
by Scandinavia's only indigenous people,
the Sami.
The Sami have adopted some modern technologies,
but reindeer remain at the heart of every aspect of life.
They've relied on the reindeer for the last 10,000 years.
They are Europe's last remaining nomads,
and building a life around the reindeer's migration,
has made living in the tundra viable.
The Sami use the reindeer for everything.
From food and clothing,
to the tents they live in.
Even domesticated reindeer migrate,
and food is not the only reason they're heading north.
It's their natural urge to give birth
in the land where they themselves were born,
that drives the herd northwards
into the harsh conditions of the tundra.
Following the reindeer's natural migration route,
is what allows the Sami to live this far north.
But the journey made by the wild reindeer
of the North American tundra,
is on a different scale.
Over 3 million wild reindeer migrate across the tundra.
This herd of over 100,000
makes the longest migration of any land animal.
Known as the Porcupine herd,
each year they travel up to 5,000 kilometers.
Once they leave the shelter of the trees,
the reindeer are more vulnerable to predators.
But they can run at speeds of up to 80 kilometers an hour.
The reindeer is also one of the only mammals on the planet
that can see ultraviolet light.
And in the tundra that means the fur of any predator
appears black against the landscape.
The abundance of reindeer attracts
one of the deadliest killers on the planet.
The grey wolf.
The grey wolf once had the largest distribution
of any mammal besides humans,
and they are highly intelligent predators.
Most grey wolves stay within the territory
where they were born.
But in some parts of the tundra,
grey wolves must travel great distances to survive.
This wolf pack is following the reindeer tracks
out of the Taiga forest,
onto the icy plains of the tundra.
And when they find the herd,
the hunt will be on.
The grey wolf is one of the deadliest killers on the planet.
They regularly take down bison six times their size.
But here on the Arctic tundra,
reindeer are their staple food.
With up to 10 wolves closing in,
the pack tries to split the herd.
If they can separate them,
they can identify the weak.
The reindeer try desperately to stay together,
but the wolves conserve energy,
waiting for their moment to strike.
Each wolf requires an average of up to
four and a half kilograms of meat a day.
And this pack must make a kill every few days.
Having finally split the herd, the wolves close in.
The hunt is on.
The reindeer must stay together.
This young female separates from the herd.
A reindeer could easily outrun one wolf,
but the wolf pack is working together.
This kill will feed the entire wolf pack.
But soon they will need to hunt again.
The Porcupine herd have only just started this journey
towards the summer grazing lands,
that lie 2,500 kilometers north.
And the wolf pack isn't the most deadly enemy
that they will face.
On their trek to northern Alaska,
the weather will be a constant threat to life.
In Greenland, conditions on the tundra are extreme.
Only a few species can survive here all year round.
Around 10,000 muskoxen
tough out Greenland's winter where
the temperatures drop below minus 50 degrees Celsius,
and winds can reach almost 100 kilometers an hour.
Here each winter,
many of Greenland's reindeer freeze to death.
But in the tundra a carcass will not go to waste.
In the bleak winter of the tundra,
prey is so hard to come by
even Greenland's most cunning predator
resorts to scavenging.
A carcass provides a welcome meal.
The arctic fox is perfectly adapted
for living in the harsh arctic climate.
They have the best insulating fur in the animal world,
helping them withstand temperatures as low as
minus 50 degrees Celsius.
The arctic fox is a solitary animal,
but when scavenging in winter,
they congregate around any carcass they can find.
The arctic fox may resort to scavenging when times are tough
but they are one of the Arctic's most skilled predators.
And in the pure white snows of the Arctic tundra winter,
maintaining their camouflage is essential.
Even in Greenland's hostile conditions,
many animals have found a way to survive.
The animals that live in the tundra,
are in one of the best places on earth
to observe the Northern Lights.
The lights are formed by charged particles
from the solar wind colliding
with the earth's magnetic field,
which is strongest near the poles.
With spring approaching
and the sun's influence becoming stronger,
the display 80 kilometers above the tundra snow,
becomes more and more spectacular.
Beneath the snows of the tundra,
there is also a surprising amount of activity.
Lemmings, one of the most numerous mammals,
and prey, in the tundra.
Unlike most small mammals,
lemmings don't hibernate through the harsh northern winter,
which can last for nine months of the year.
Instead they remain active,
burrowing and tunneling under the snow,
eating grass, clipped and stored in advance.
Above ground, temperatures can drop as low as
minus 50 degrees Celsius.
But down here, the temperature rarely falls
more than two degrees below zero.
Lemmings are found across the tundra,
but they're solitary animals by nature,
meeting only to mate then going their separate ways.
Lemming populations can soar
and disappear in a matter of weeks
as entire communities migrate across the tundra
in search of food.
By May the sun is growing in strength.
In the North American tundra,
the reindeer that have survived the extreme winter weather,
are hundreds of kilometers into their epic migration.
The Porcupine herd are now approaching their calving grounds
near Alaska's northern coast.
But the tundra still has many obstacles
for the reindeer to overcome.
This urge to migrate thousands of kilometers,
defines the lives of the reindeer.
Much of the reindeer's food is still covered by snow,
but that's all about to change.
Spring has arrived.
Right across the Arctic,
the planet's most dramatic change of seasons has begun.
The sun is now high enough in the sky to raise
the temperature above zero for the first time in months.
And as ice turns to water,
the reindeer have finally reached their calving grounds.
It's time for the females to give birth
in the same place they themselves were born.
In an incredible synchronized birth,
almost half the young of the herd
can be born within 24 hours.
The calves can stand in minutes,
and within a day will have to keep up with their mothers,
as the herd continues north
towards the summer grazing lands.
Once it stands, the calf will hardly ever stop moving,
for the rest of its life.
Across the tundra, things are changing dramatically.
Even for the wolves, who now have pups of their own.
Their pups are just a week old
and are far too young to join the hunt for reindeer.
The mothers too must stay put to feed the young pups,
but the males are on the hunt.
This pair have traveled many kilometers
in search of the reindeer.
Ahead of them there are thousands of newborn calves,
and if the wolves don't make a kill soon,
their own pups will perish.
But at this time of the year it's not only the reindeer
whose calves are a target for the hungry wolves.
These Canadian muskox calves are just a few days old,
and small enough to be overpowered by a single wolf.
But with so many adults around,
each weighing nearly 500 kilos,
the odds are stacked against the wolves.
The moment the muskox spot the wolf,
they instinctively form a defensive ring
to shield their young.
It would take an entire wolf pack to take on this herd.
The reindeer and their calves are moving north,
where the melting snow is revealing more and more
of the tundra's lush vegetation.
As the sunlight grows stronger,
some of the planet's hardiest plants
can finally begin to grow again.
The snow may be melting,
but the soil below is frozen solid.
So there's only one place for the meltwater to go.
The lemmings are forced from their tunnels,
as their homes are turned into drain pipes.
As pools begin to form,
the tundra is transformed into a vast wetland.
The lemmings can swim, but to avoid predators,
they must find somewhere to hide.
But as it's no longer a land of pure white,
it's also harder for predators, like snowy owls,
to stalk their prey.
Snowy owls make their summer nests
north of the Arctic Circle, on high ground.
Their plumage changes little with the seasons,
and their nests are easy to spot
against the exposed tundra soil.
This female has 10 eggs to protect.
Her plumage is darker and more muddled than the males.
Some tundra animals do change with the seasons.
This arctic hare's upper body will darken
for the few short weeks of summer.
In places, the growing season lasts just six weeks,
so the plants here have had to adapt.
This explosion of life attracts
a massive gathering of migratory birds.
In spring, hundreds of millions of birds,
make the annual trip to the Arctic tundra,
but one species has flown further than the rest.
The arctic tern flies to northern Europe
all the way from the Antarctic.
No animal on earth migrates as far.
Its annual trip of 70,000 kilometers means
it will fly nearly 2 million kilometers in its lifetime.
And the reason the terns fly so far to these wetlands
lies just below the surface.
As the pools warm from the extra sunlight,
insects are hatching.
Right across the tundra,
billions of mosquitoes are hatching.
It's what the birds have been waiting for.
But even a billion birds can't cope
with this many mosquitoes.
The insects form vast swarms,
and head off in search of a meal.
In Alaska, the emergence of the mosquitoes
coincides with the arrival of the Porcupine herd.
They've finally completed their epic migration,
to take advantage of the lush vegetation.
But the presence of the mosquitoes,
makes the tundra at this time of the year,
one of the most inhospitable places on the planet,
and the herd must keep moving in search of respite.
Once this massive reindeer herd is in motion,
not even the hundreds of fast-flowing,
meltwater rivers can stand in their way.
The reindeer can swim amazingly fast,
up to 10 kilometers an hour.
For many of the calves this will be the first time
they've crossed a river so big.
The herd may have shaken off the mosquitoes,
but crossing the river comes at a price,
and some get separated.
The hungry wolves are not far behind.
For the mother it's too late,
and the herd must keep moving.
Of the tens of thousands of calves
born in the tundra each year,
only half will survive.
Even in summer, the fight for survival goes on.
For the North American muskoxen,
this is rutting season.
These giant remnants of the last ice age,
have hardly changed in over 14,000 years.
Males weighing almost 500 kilos,
engage in bone-crunching battles
for their right to breed with the best females.
Their brains are protected by
17 centimeters of skull and bone.
But if neither animal backs down,
these epic duels can escalate
into a fight to the death.
The muskoxen are one of the tundra's hardiest animals.
But one mammal has mastered the tundra like no other.
Lemmings, they breed at an astonishing rate.
This female gave birth to two litters during the winter.
But she's heavily pregnant once again,
and is now preparing a nest to give birth once more.
They have a gestation period of just three weeks,
and these newborns will be pregnant
when they're just one-month old.
There are five or six in each litter,
and they're born deaf and blind,
but they grow remarkably quickly on a diet of milk
and constant attention from the mother.
The young are covered in fur within days.
And with such a startling reproductive rate,
lemming populations can explode within weeks.
Thanks to their sheer numbers and high visibility,
lemmings are hunted by virtually
every predator in the tundra.
Their underground tunnels are no longer hidden by snow,
and they're now at their most vulnerable.
The number of predators on the tundra
is also on the increase.
The arctic fox's fur is changing from white to brown,
making it incredibly well camouflaged,
against the tundra's summer terrain.
The fox's diet is not limited to lemmings.
This male is searching for eggs.
Right now he needs to find food and lots of it,
he has many mouths to feed.
In fact the arctic fox has more pups
than any other carnivore on the planet.
It's thought they may have up to 25 in a single litter.
Soon these pups will have to fend for themselves,
in one of the most unforgiving wildernesses on the planet.
The pups need to gain weight,
and learn the skills they'll need to survive,
when the harsh tundra winter returns,
in just a few weeks time.
To feed this many pups,
the males have their work cut out.
But fortunately, in the arctic summer,
the sun never sets,
and they can hunt around the clock.
After just five weeks,
these pups will be weened,
and they will most eat lemmings.
With so many arctic foxes on the tundra,
it's easy to see what is happening to all the lemmings.
But it isn't just the arctic foxes
that prey on the lemmings.
The snowy owls are also enjoying
the abundance of lemmings on the Scandinavian tundra,
and the more lemmings there are to eat,
the more snowy owl eggs are produced.
These eggs laid over a month ago,
are now beginning to hatch.
Within days of hatching, these young snowy owls
are ready to begin their lifelong diet of lemmings.
The chicks will be fed strips of meat
until they're big enough to swallow whole animals.
By the time the chicks are just a few weeks old,
they're able to swallow whole lemmings.
Strong stomach acid digests the flesh,
but the bones and fur of the lemmings are regurgitated.
This young owl's eyes are clearly too big for its beak.
There are many more birds around the tundra
this time of year.
Most are unable to fly and their mothers
must protect them at all costs.
Having to feed such a large number of chicks,
means that this female snowy owl,
is on the lookout for any opportunity.
As these goslings prepare to take their first swim,
the female snowy owl spots her chance.
The owls know the adult geese
won't give up their young without a fight,
and must work together to lure the larger birds away.
The two owls attack
sending the large geese fleeing for their lives.
Although the geese match the owls for size and weight,
both the male and female could easily
take down a goose single-handed.
But the owls aren't hunting the adults,
they just need them out of the way.
The female owl now turns her attention to the goslings.
Realizing the danger, the geese now give chase to the owls.
This young gosling is far too big to be swallowed whole,
and will have to be shared among the entire brood.
The summertime abundance of food is almost over,
and within weeks the threat of starvation
will once again become reality,
for all the animals of the tundra.
The Arctic tundra occurs at latitudes
between 60 and 80 degrees north.
Here summer can last just six weeks,
before the return of winter.
The sun shines for almost 24 hours a day,
but its low angle means the air temperature
seldom rises above 10 degrees centigrade,
and the frozen soils never thaw.
So plant life has had to adapt.
Found as far north as Greenland's Kaffeklubben Island,
the world's most northerly landmass,
the arctic poppy,
is one of the planet's northernmost flowers.
It can only survive here by being heliotropic,
meaning it turns its face to follow the sun.
Only by concentrating the solar heat
can the arctic poppy warm its petals sufficiently,
to reproduce in the short tundra summer.
By early September,
like all reindeer across the Arctic tundra,
Alaska's Porcupine herd are entering the mating season.
Known as the rut, the actual mating will take place
over just a few days to ensure all the calves
are born at the same time next spring.
But first, the herd must establish the hierarchy.
Reindeer grow fresh antlers each year,
under a layer of fur called velvet.
When fully grown, the blood supply cuts off,
and the males shed their velvet
in preparation for battle.
They have the largest antlers relative to their
body size of any deer species.
And size matters.
These battles may turn into a fight to the death.
This males antler size and body weight,
give him a clear advantage.
The prize?
Control of up to 20 of the best breeding females.
And status of the dominant male of the entire herd.
In the domesticated herds of Scandinavia,
the Sami reindeer herders
have just six bulls for every 100 females.
By September, the Sami herders prepare to leave
the summer calving grounds in search of
fresh grazing further south,
and will now begin the journey
back to the winter pastures.
But there's a large river to cross,
and that means rounding up over 3,000 reindeer.
The survival of each and every one of them,
is vital to the Sami's livelihood.
The ancestors of these very animals
have been making this migration for thousands of years.
But to avoid any unnecessary casualties,
they're moved across the fjords in smaller groups.
By September, the snowy owl chicks
are beginning to fledge,
and they're now left unattended for long periods of time.
Although armed with talons of over two-centimeters long;
until they can fly, they're still vulnerable.
Any predators that may unwittingly
wander into the nesting territory,
will have to deal with the adult owls,
who are watching from on high.
During nesting season,
the snowy owls must defend their nest against predators,
and are fast and powerful enough,
to scare off a large grey wolf.
The arctic fox is no match for the owl,
and the young are safe for now.
But in just a few days the owlets
will be left entirely alone.
Before they can fly, the adult owls,
will abandon the nest completely.
If they're to survive, the young owls
will need to learn to fly before winter comes.
After less than six weeks the short summer is over.
For the birds, the lush wetlands that attracted them here,
are freezing over, and they must leave or face starvation.
Early snow catches out the fox and her cubs,
who are still too young to fend for themselves.
Across the tundra, the reindeer are heading south.
The Porcupine herd, over 100,000 strong,
now breaks up as they return towards
the shelter of the forests for winter.
The calves, born just a few weeks ago, are now strong,
but for the mothers, tired from the mating season,
there are many dangers ahead,
as they set out on the 2,500-kilometer journey,
together for the first time.
With the pressure on to keep moving,
the herd is forced to take risks.
Crossing a river so recently frozen,
can be a deadly mistake.
Struggling to escape from waters this cold
can exhaust a reindeer in just seconds,
and is exactly what the wolves are waiting for.
But the reindeer are incredibly tough,
and there will be no easy pickings for the wolf pack today.
The reindeer's annual migration
is one of the most epic battles for survival on the planet.
By October, this vast landscape,
that covers 10% of all land on earth,
is once again returned to a frozen desert.
As the tundra sun falls below the horizon
for the last time this year,
it will not rise again for another three months.