The Islands of Svalbard in Arctic Norway.
They might be remote, but they're under surveillance.
WHIRRING
Spy cameras are capturing
the most intimate images ever taken of polar bears.
They're revealing some remarkable behaviour, and discovering an animal
of surprising curiosity and intelligence.
Snowcam doesn't operate alone.
Blizzardcam can travel at 40 mph,
powered by propellers and gliding on skis.
Snowballcam can operate at temperatures of 40 below.
Its spherical design makes it almost indestructible.
Together they explore the islands, looking for bears.
Their first mission is to film a mother with cubs
emerging from maternity dens hidden in these hills.
The only clue to the den's presence is a snowy mound.
Driftcam and other spycams can lay in wait for days.
They're left unattended, primed to film the moment they sense movement.
A whiteout soon makes their task seem like mission impossible.
But help is a paw swipe away.
The cub's first steps outside the den...
filmed by his mother.
She pushes the camera down the slope.
A tracking shot!
As she films, there is no human presence of any kind.
She even adjusts the camera to record her own exit.
She must get her cub to the sea-ice before it breaks up and thaws,
otherwise they'll be trapped on the island for the summer,
with little to eat.
She needs to be careful.
Males roam the ice-fields below,
and they kill cubs.
They will try to mate with the mother so she has their cubs instead.
But the larger males find deep snow and steep slopes heavy-going.
She wisely keeps her cub to the higher ground.
Back at the den-sites, other cubs are yet to emerge.
They appear over a five-week period from March to April.
After ten days of waiting, something stirs.
The mother has waited six whole months for this moment.
She blinks in the sunlight.
She spent her confinement in semi-darkness.
She checks that the coast is clear, and then reveals her secrets.
Time for a stretch.
She's been cooped up with her cubs since she gave birth three months ago.
They learn by example,
but their first lesson seems to be about snowballs.
When she leaves, she expects them to follow.
But the first steps are always the most difficult to take.
A frozen sea now surrounds the islands.
It stretches all the way to the North Pole.
It is out on this ice that most polar bears spend their lives.
But in spring males return to land to search for females.
Males may be a risk to cubs, but this one is otherwise engaged.
He's found a lone female.
But polar bear courtship is never straightforward.
She likes to play hard to get.
It's also a challenge for blizzardcam.
She's testing his fitness, making sure he's a good catch.
His skills on the slopes show room for improvement.
And now the female invents a new challenge - a climbing contest.
Her huge claws act like crampons.
Being lighter and nimbler, she has the advantage.
Males can be twice as heavy, reaching three quarters of a ton.
HE GROANS
She's after a mate that's playful and energetic,
one with strong genes.
But his chances are slipping away.
She tested his performance and pushed him too far.
Meanwhile, the mother with one cub is still sticking to higher ground.
But deep snow is a real struggle for her little cub.
SHE CALLS
She encourages him with reassuring calls.
She's aware of his difficulties and uses her body as a shield.
She must stay attentive
if her cub is to survive in this harsh Arctic world.
Realising he's exhausted, she digs a hollow to rest in.
In day-dens like this she suckles him six times a day.
Meanwhile, the courting male is yet to prove he's up for the job.
But the female doesn't like being ignored.
She tries to reignite his passion.
Time to turn up the heat.
He's certainly interested now.
She's falling head over heels for him.
He's now totally captivated.
But still she gives him the runaround.
But in courtship there are always casualties.
Blizzardcam is at the bear's mercy.
But again a bear helps with the filming.
Sealed with a kiss,
the couple's whirlwind romance will last three weeks.
Out on the frozen sea, a young male has killed a seal.
He caught it when it surfaced through a breathing hole in the ice.
To film from a different angle, blizzardcam deploys snowballcam.
This technical miracle rolls with no visible moving parts.
Its lens even boasts a self-righting mechanism.
A close-up reveals that he's eating the blubber.
This provides the most nutrition and is always eaten first.
Seals make up 95% of a polar bear's diet
and are only found near the sea-ice.
The two-cub family are attracted to the frozen sea to hunt seals as well.
She hunts the pups of ringed seals that hide in snowy dens on the ice.
She finds them by smell, even a metre down.
She pile-drives the snow with a force of two tons,
but the roof of the den holds.
Back at the carcass,
the spycams stay on to film bears attracted to the leftovers.
The mother and single cub.
She could smell the remains from 20 miles away.
In the den, she spent six months without eating
while the males fattened up on seals.
She leaves little behind.
Males are still on the lookout for females.
For her cub's safety, she heads back to the hills.
But, as spring continues,
lengthening days bring sudden and dramatic change.
The highest tides of the year combine with rising temperatures
to trigger a vast breakup of the ice that surrounds the islands.
In just one night it can crack apart and drift 20 miles or more.
Svalbard is a series of islands once more.
The mother and single cub are still on the snowy hills,
but signs of change are all around.
At the shoreline, things are not as expected.
The sea-ice has drifted northwards
and, with it, the bears' food supply.
It's a huge swim for an adult bear.
For the cub, it's out of the question.
Their ship has sailed and left them behind.
They are marooned on the island for the summer.
The two-cub family managed to board the sea ice
before it drifted too far.
This new and ever-changing world requires a different spy camera.
Icebergcam.
It effortlessly steers between ice sheets
and its turret rotates to follows the bears.
The bears' lives are now governed by the state of the drifting ice
and the movement of the seals.
The cubs are expected to keep up but their mother knows their limits,
avoiding long, hazardous swims.
But all the while she keeps them on the move,
tracking the seals that gather around the leading edge of ice.
Back on land, icebergcam follows the one-cub family.
With the seals gone, beachcombing is her best option to find food.
He practises his climbing skills...
..but it's early days.
She has found something just below the surface.
She checks how deep she has to dive,
then takes the plunge.
It's seaweed.
Kelp is not wildly exciting,
but it does contain carbohydrates and some protein too.
The cub must find her acrobatics rather strange.
Hungry bears eat virtually anything.
It's a question of making the most of what's around.
And it's never too soon to start hunting.
Polar bears investigate every unfamiliar sight and smell.
They are the most curious subjects ever filmed by spycams.
This fascination suggests a surprising intelligence,
one that evolved for the extraordinary challenges
of hunting on ice.
Ice floes present real difficulties for a predator,
continually changing their shape and form.
Seals are also tricky prey.
In open water they are just too agile to catch.
It becomes a little easier when they haul out on ice.
But they hug the water's edge for a quick escape.
The bear immediately has a problem.
There is no cover between him and his prey.
He wrong-foots the seal by seemingly walking away.
Every hunt presents a different challenge,
so he plans a new strategy each time.
He slinks into the water,
using a channel between the ice floes to act as cover.
He swims, hardly making a sound,
reaching six miles per hour at times.
His front legs provide propulsion, while his back legs steer.
His low profile makes him seem like a floating sliver of ice.
He checks the seal's position and takes wind direction into account to work out his final approach.
As he closes in he makes a clever move,
diving deep beneath the ice floe.
He emerges on the blind side of the seal.
So far, so good.
He can hold his breath for minutes,
and calculate the seal's exact position.
Slo-mo reveals just how close he got.
His skills show a remarkable intelligence at work.
He hunted in all three dimensions,
making full use of the opportunities offered by water and ice.
Back on Svalbard, it's high summer.
Barnacle geese that had overwintered in Scotland have started to breed.
Their calls bring hope to hungry bears.
The cub stays back as his mother explores the possibilities.
Bears have only recently discovered this new source of food,
seeking out colonies that nest on the ground rather than on cliffs.
The eggs are a rich source of protein.
Just 250 are as nutritious as one ringed seal.
She carefully picks up an egg in her jaws before swallowing its contents.
The geese launch an attack.
Some have goslings, a bite-size snack for a bear.
In just one day, one bear can devour over 1,000 eggs and hatchlings,
destroying a whole colony.
But, as the threat escalates, so does the defence.
Arctic skuas join the attack.
A skua lands a direct hit.
She's had enough.
In future, the birds will have to start nesting on cliffs
to avoid polar bear attacks.
Skuas may have saved the colony this time
but they've made the bears' lives a lot more difficult.
Further north on Svalbard,
other landlocked bears have found a more reliable meal,
a carcass of a stranded fin whale.
Icebergcam investigates the happy gathering.
The whale is 24 metres long and weighs 60 tons,
a once-in-a-lifetime feeding opportunity.
An adolescent eats confidently alongside four adult bears.
They continually chatter away to each other.
It's all about keeping aggression under control.
ROARING
Their massive claws rake the skin like knives, cutting it into strips.
At two years old, this bear is testing his status,
standing up to other bears.
Sharing food helps everyone survive
in an environment where prey is usually hard to come by.
As summer progresses, the temperature creeps above freezing
and the larger ice sheets fragment into ever smaller plates.
To avoid being trapped on shrinking ice floes,
the cubs must get used to an endless polar assault course.
Rolling is clearly fun, but it also has a purpose.
It squeezes out water trapped in the fur.
Her cubs are growing fast and are full of energy.
But to keep them fit she must keep them fed.
A male has killed a bearded seal.
For the sake of her cubs, she needs to be cautious.
Burying the carcass will help reduce its odour,
concealing it from other bears.
If it hasn't already been seen, that is.
The bears at the whale carcass are in food heaven,
but their peace is about to be shattered.
This male heavyweight prefers to eat alone.
He is bigger than the other bears
and likes to throw his weight around.
This is no time for heroics.
The mother tries to guide her offspring away.
But the young bear is an easy target.
The male could kill with just one bite.
The youngster daren't turn his back.
But, despite the male's persistence,
he seems to be just teaching the young upstart a lesson.
Reunited with his mother, she appears to scold him.
SHE BARKS
Authority established, the male is now king of the carcass.
Back at the kill site, the family finally steal a meal.
This is a high-risk strategy.
Like the male at the whale carcass, some bears don't do sharing.
She stands up to make herself look bigger.
The cub copies.
Luckily this bear has no appetite for a fight.
There is a feeding etiquette around a seal carcass.
Bears that approach correctly are often allowed to share,
particularly if they are known.
They greet.
Away from the carcass,
young males often become friends, hanging out together.
As ever, our spycams prove a huge hit with the curious bears.
With the driftcams out of action,
blizzardcam returns to frontline duties.
And deploys back-up.
Snowballcam's arrival fascinates the curious bears,
particularly as the steep slope gives it momentum.
He tries some fancy footwork.
More bears join the team.
Time for kick-off.
It's polar bear football.
Their ball control needs practice
but they are experts at dribbling.
The game descends into argument.
The spycams return to the benches.
The bears might be play-fighting, but things still get out of hand.
Meanwhile, on Svalbard, a kittiwake colony brings hope
to the hungry mother and cub.
They can't reach the nests but there is still food to be had.
Grass is the bears' emergency rations
and it flourishes wherever bird droppings provide fertiliser.
It provides little real nourishment but it helps stop hunger pangs.
But, to survive, the bears will need protein.
In comparison, the ice bears have it easy,
but the rising summer temperatures can cramp a hunter's style.
He's tracking bearded seals,
an ambitious quarry.
She has battle scars from a previous bear encounter.
It won't be easy.
The bear has two to choose from. The odds are good.
But he's treading on thin ice.
He spreads his legs to distribute his weight and progresses carefully.
But it's not enough.
For a hunting bear it doesn't get much worse than this.
The seal could hardly fail to notice.
But this battle-hardened seal is in no rush.
Finally he gains some purchase. He's back in the game.
He still believes he's in with a chance.
He can charge at 25 miles per hour.
But bears usually wait until they're 30 metres away.
This one started at 300.
She has all the time in the world to escape.
Only the bears unexpected dunking in the ice
could explain such an amateur performance.
The ice is now so thin, it only supports the weight of the lighter cubs,
leaving the mother struggling.
This is a sign that the mother must head north
to the more permanent icecap as quickly as possible.
But a combination of wind and current destroys her best-laid plan.
A sudden swell turns ice into open ocean.
The cubs are too young to swim long distances safely.
But going back is not an option.
The cubs' only hope is to keep up.
They paddle for their lives, staying as close to Mum as possible.
She can swim 50 miles or more, but the cubs will soon be struggling.
On the island, months of having to make do are taking their toll.
The cub is half the size of those on the ice.
A colony of walrus blocks their path.
Just one would make a substantial meal.
But walrus can weigh a ton and a half
and their tusks can reach a metre in length,
hardly a pushover.
Her only hope is to find one that is weak or injured.
She assesses the colony.
With a cub to provide for, she can't take risks.
She provokes the walrus to test their reactions.
SHE GROWLS
GRUMBLING
All are healthy. She won't take the gamble.
But all is not lost.
She has caught a new scent.
The cubs are in trouble.
They are exhausted.
The male cub rests his head on his sister.
They crowd into the mother's slipstream, trying to gain any advantage.
At last there is hope.
They have finally reached the pack ice that forms the polar icecap.
It's the ultimate hunting habitat for polar bears.
The icecap stretches all the way to the North Pole.
Seals are found wherever it meets the sea.
It's been a long journey.
They are 100 miles from Svalbard
and 150 miles from the den-sites where they were born.
For now she can relax, having fulfilled her mission.
It's the perfect spot to spend the few months left of summer.
It is four months since Svalbard was surrounded by sea-ice.
It could be another two before it freezes again.
Guided by her sense of smell,
the mother discovers what's left of the stranded whale.
But it looks like the remains have been stripped clean by bears.
The massive backbone says it all.
There's not a scrap to be found.
This was their last hope.
With the carcass gone, the bears search the shore for scraps.
All that remains are sun-bleached bones.
There is little nutrition here,
but at least the cub has found something to chew on.
Calcium from the bones will help the mother's milk supply
but the cub needs meat to survive.
Now they have another problem.
Other bears can't be trusted with small cubs.
But fortunately they seem more interested in what lies beneath the surface.
It looks like there is still meat to be found here,
partially preserved by the cold water.
Despite her hunger, the mother can't risk joining in.
But the other bears don't stay long.
The mother grasps her opportunity.
Her cub's survival depends on her success.
The remains lie four metres down.
And, at the deepest point, flesh still clings to the backbone.
She emerges triumphant.
The meat must be rancid, but it's still a lifesaver.
She brings some back to the shore.
This is the moment the cub has been waiting for, but still he has to wait.
However unfair it seems,
she must regain her strength or her cub won't survive anyway.
Finally, she leaves him some scraps to chew on.
A young male arrives, a dangerous situation for the cub.
She growls a warning, but it's not enough.
The cub slips.
The mother must get her cub away from danger as quickly as possible.
They head north.
She knows that this is where the ice, and with it the seals, will first return.
It's now September, but the sea might not freeze again for another two months.
Her cub is unlikely to survive that long.
But there is hope on the horizon.
An ice-rainbow heralds change.
In the far north, temperatures drop at last
and ice sheets start to grow rather than disappear.
Then a miracle happens.
Building pressure combines with powerful southerly currents
to push the drift-ice southwards.
The mother and cub are thrown a lifeline
by a change in the weather and ocean currents.
It's a huge swim out to the ice floes for the little cub.
He finally makes it to the ice,
nine months after he was born.
His mother has triumphed against the odds to reach this land of plenty.
On the way, she taught her cub the survival skills
for what could be an increasingly ice-free future.
More than anything,
the cub learnt that curiosity is the key to survival.
But there is one more challenge ahead.
A young male has caught a seal.
They can't walk away from the chance of fresh meat.
He charges, but she refuses to be intimidated.
She needs a meal far more than he does.
She drives home her determination.
Well-fed bears eat only the blubber, leaving the rest for others.
They waited the whole summer for this moment.
Their first taste of fresh meat for four months.
They are safe from starvation.
Of all the subjects ever filmed by spycams,
the polar bear has shown the greatest curiosity and intelligence.
And none more so than this mother.
Against the odds, she brought her cub up
in one of the longest periods without ice in Svalbard's history.
The cub faced many challenges over the summer, but to reveal his story
the spy cameras faced challenges of their own.
Snowcam met its demise under the paws of a bored young male.
Blizzardcam nearly met its match
with the most playful bear it ever encountered.
The bear wanted to know how it worked.
Blizzardcam deployed snowballcam as a decoy.
This was the polar bears' favourite spy camera
and this young male was no exception.
Never before had it come under so much pressure.
Valiantly, snowballcam kept filming until the very end.
Fortunately, for most of the time,
the spycams were ignored, capturing intimate moments like this.
But icebergcam finally found itself trapped between ice floes.
As ever, the mother's curiosity is piqued.
The curiosity that helped the mother and cub survive
is now testing icebergcam to destruction.
This same curiosity is this cub's, and all polar bears', best hope for the future.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk