There can be few places on earth as bleak, cold, hostile to life...
as these Arctic snowfields.
But for one animal, the polar bear, this is heaven.
We tend to think as polar bears as wandering across these snowfields...
hunting for seals...
but in fact some bears spend their winter actually under the snow...
and when the summer comes and the ice melts...
they are as likely to be swimming in the water as on the ice.
So here, for the first time...
is a full picture of that most impressive, formidable of hunters:
the polar bear.
After four months of winter darkness...
light returns to the High Arctic once more...
and reveals a world frozen and still.
The Arctic is an ocean...
sealed by ice and bordered by land.
But this is not a world of permanent winter...
and each season brings great changes...
to which polar bears must adapt.
High on the slopes of the Arctic mountains...
life begins to stir.
It's April...
and this bear has been under the snow in her den...
all winter. But she's not alone.
Born in December, and now about four months old...
her cubs are ready to face the outside world.
Their woolly fur helps to insulate them from the bitter cold.
The temperature here regularly drops...
to a nippy minus thirty five.
Throughout the winter, other bears have remained out...
on the frozen sea ice, hunting.
But winter is a long, lean time for them...
as seals can be hard to find.
In peak condition, a male bear can weigh as much as ten men.
But this bear has just endured a winter and its weight is very low.
Ringed seals, the smallest of the Arctic seals...
are they favoured prey.
But adult seals are experienced and very wary...
at the slightest sign of danger, they disappear into another world.
More at home in the water than on the ice...
they have access to a number of well spaced breathing holes...
and so can easily outmanoeuvre a hunting bear.
But what bears are really after in spring...
are this year's seal pups.
Never having encountered a polar bear before...
they seem unaware of the danger.
This bear hasn't got it quite right yet.
Yet more hungry bears will soon appear in the surrounding hills...
as emerging families prepare for life on the sea ice.
Having been confined to their den since birth...
it's important for cubs to exercise and gain strength.
For once they leave the safety of their den...
they will find little relief from the trials of life ahead of them.
This female has had nothing to eat for five months...
and her body weight has dropped by half.
But she still has a difficult time ahead...
because she can't go down to the sea ice to hunt...
until her cubs are stronger and more co-ordinated.
It takes time for the cubs to acclimatise to the temperatures...
outside their den.
And although they have thick fur...
they have little insulation from fat at this age...
and so depend on the richness and energy of their mother's milk...
to keep them warm.
Females without cubs have spent the winter out on the sea ice.
Free from the responsibilities of maternal care...
they have meet other demands: males.
Competition for females is high.
This large, scarred male...
will try to keep the small female away from his rivals...
by herding her into remote areas.
That way he gets exclusive access to her.
The scars on his head and neck are evidence of fights with former rivals.
When the cubs are strong enough, and driven by her need for food...
this mother leads her cubs away from the den for the last time.
They are about to enter a much more dangerous world...
down on the sea ice.
Because ice conditions vary from year to year...
seal distribution is unpredictable...
so bears may have to range over thousands of kilometres...
in search of the best hunting grounds.
They hunt along pressure ridges...
which form as ice sheets collide with each other.
It is under the snow drifts in the lee of these ridges...
that ringed seals give birth to their pups.
There may be a number of chambers to the lair...
but there is usually only one access to the sea beneath.
Under the snow, the pup is protected from bad weather...
and is out of sight.
But bears have an astonishingly acute sense of smell...
and can detect the presence of a seal, deep within the snow...
at a distance of a kilometre or more.
Even so, the bear must pinpoint the exact position...
of the seal beneath him.
And the slightest crunch of snow could give him away.
This time the seal got away...
only about one in twenty hunts are successful...
so the odds seem to be in the seal's favour.
But with so many hungry bears prowling the ice...
a pup's future is far from secure.
Hunting requires skill and patience.
It's hard enough for a lone bear...
but a female encumbered by cubs, will be even less successful.
If she doesn't manage to catch enough seals...
she stops producing milk and her cubs soon starve.
So far this family is doing well.
The mother has found enough food to keep both cubs alive.
But getting enough food is not the only problem...
facing a female with dependent cubs.
Given the chance, a large male might kill the cubs.
Their mother would then become sexually receptive again...
so he could mate with her and ensure...
the next generation carries his genes.
She's very protective and the cubs aren't allowed to stray far from her.
At three times her weight, a 600 kilogram...
male is a fearsome opponent, and she avoids any chance of an encounter.
Svalbard. A group of islands...
700 miles north of Norway.
In April bears converge in prime seal habitat...
where they can be sure of finding unwary seal pups.
These cubs are a year and a half old...
and now rely largely on meat.
Their increasing size puts more and more pressure on their mother...
to provide enough food for the three of them.
Bears tend to wolf down a fresh kill...
because it's very likely to be stolen from them by larger bears...
even their own mother.
Cubs have a great deal to learn...
before they can survive alone in the Arctic.
If there's food, a mother will stay with them for 2 and a half years.
Like most animals, adult polar bears...
do not waste hard-earned energy...
but for the cubs play continues to be...
a vital part of their training.
It's only by continuing to be inquisitive...
that they learn how to adapt to new situations.
But they still don't have the skills to hunt successfully for themselves.
And this keeps them totally dependent on their mother.
They start to imitate her hunting techniques at an early age...
but they are simply not heavy enough to break through...
into the lair of a seal pup.
The only other mammal to be found on the sea ice...
is the Arctic fox.
In some places its life is intricately bound to that of the polar bear.
Arctic foxes are the jackals of the north.
Although they will hunt seal pups for themselves...
they can only kill pups less than a week old.
So scavenging is important. Foxes will follow bears far onto the ice...
to feed on the remains of their kills.
Away from land, foxes are totally dependent on bears...
for their survival.
Gulls also home in on the feast.
Nothing from a polar bear kill is wasted.
Keeping fur in good condition...
is as crucial for foxes as it is for bears.
Fox fur is very fine and very dense.
And like bear fur each hair is hollow which maximises insulation.
Such bounty is too good to waste.
This canny fox will hide its prize...
as an insurance against harder times.
No bear is above scavenging from another's kill.
This family has travelled for many miles...
drawn by the smell of a dead seal.
Abandoned carcasses will have been stripped of their energy-rich fat...
as all bears eat this first...
in case an intruder arrives early and steals the kill.
But there is still a lot of meat on the bones...
invaluable food for younger bears...
who are not yet proficient hunters...
or for a family whose cubs are still growing...
and in need of protein.
This seal was killed by a large male bear...
who once threatened these cubs.
Now he has unwittingly provided them with food...
and increased their chances of survival.
It's June. As summer progresses...
the Arctic ice begins to loosen its grip...
and the polar bear's world is transformed.
Seals begin to have an easier time of it.
There is more open water for them to retreat to.
The pups themselves have also become more wary.
The bearded seal is a huge animal.
It prefers to lie on drifting ice floes.
So when the solid ice sheets begin to break up...
these seals can be found closer to land.
Weighing as much as a bear...
and five times as much as a ringed seal...
a bearded seal is a valuable prize: if caught.
Bears have very individual characters.
They learn the essentials of hunting from their mother...
but then each develops its own solution...
to the problems of survival...
based on its own, unique experiences.
This young bear, now hunting on its own...
uses melt channels and the cover offered by ice...
to sneak up on its intended victim.
Small ice floes conceal its approach as it gets closer.
Once again the bear goes hungry.
Its first year alone will be the hardest.
With 24 hours of sunlight, the temperature rises...
and the bears' hunting platform fast disappears.
But for others the release of water offers new opportunities...
a developing bloom of planktonic life attracts millions of birds.
Here, over the short summer, they feed and raise their chicks.
For most animals and birds...
summer is a time of plenty...
but bears now enter the most difficult period of the year.
There is little left of the ice...
and so stalking seals is virtually impossible.
They are still, for the most part, solitary creatures...
and they continue to give each other a wide berth.
Open water is no obstacle to them.
Their fur is ideal, not only to keep them warm in winter...
but now in summer, to shed water.
As ice floes melt away...
bears are forced to head for land.
They can spend many hours in this freezing ocean...
and have been known to swim a 100 miles or more to reach shore.
The polar bear, as these unique pictures reveal...
might just as appropriately be called the 'sea-bear'.
It is a superbly competent swimmer and has partially webbed feet...
for efficient paddling.
In more southern areas, the ice disappears altogether...
and bears spend the next five months on land.
Here food is scarce.
But they have one adaptation that is the most astounding of all...
they can reduce their metabolism to extremely low levels...
and save energy, whilst still able to remain active and hunt.
This is how they could cope with their intermittent success at hunting seals.
And how they will cope with little food in the months to come.
Akpatok, a remote Canadian island...
whose towering cliffs offer ideal nesting ledges...
for hundreds of thousands of guillemots.
By nesting on cliffs...
these birds gain some protection from likely predators...
foxes and bears, who also use the island as a summer retreat.
The only food accessible to bears...
are the rotting carcasses at the bottom of the cliff.
The sight and smell of food so close is a strong lure.
Unable to reach the birds, this bear opts for vegetation...
which flourishes here because of the rich guano.
Polar bears are closely related to brown bears...
and, like them, are able to digest plants.
Such meagre meals are probably not about energy intake...
it's more likely that vegetation provides vitamins and minerals...
absent from their seal diet.
It's September, and all around the Arctic the ice has retreated.
Here on Wrangel Island, north of Siberia...
walruses can be found hauled out on the beach in late summer.
One year in ten, the ice melts so far north...
that walruses become stranded on this sandy spit.
Bears also get left behind by the retreating ice.
A bounty such as this offers relief from hunger.
A mature walrus is so big and has such thick skin...
that a bear is seldom able to take one.
But a young animal is easier prey...
once it has been separated from the group.
Wrangel Island bears are lucky to have...
such rich pickings in this otherwise lean period.
Though solitary for most of the year...
at this time these bears tolerate company.
It's extremely rare to see so many bears of all ages...
and both sexes together.
But, on a full stomach and with so much more food close to hand...
there is little to be gained by being aggressive.
Churchill, on the shores of Hudson Bay, in Canada...
it's on the same latitude as Scotland...
and it's home to the most southerly population of polar bears.
Here bears undergo one of the most extreme fasts...
known for any mammal.
It's now October, and apart from seaweed and a few berries...
they've hardly eaten at all, since the ice melted away in July.
It's probably not even worth wasting their energy...
Iooking for such insignificant meals.
Bears risk overheating at this time...
as they are better adapted to keeping warm on the ice.
The best way to conserve their dwindling energy reserves...
and to keep cool...
is simply to remain inactive, or to take a dip.
Year after year the same bears appear in Churchill.
So it seems that though bears may wander over vast areas...
when out on the sea ice...
their navigation is good...
and they stay within a familiar home range.
Respite from the gruelling heat...
comes with the first storms of winter.
But relief from hunger is still a long way off.
For although the fresh water lakes freeze over quickly...
the sea takes a great deal longer.
And that is where the seals are.
Males stay close to shore during the summer and autumn.
And even though they are hungry, in Churchill they tolerate each other.
Indeed these bears go beyond tolerance and actually socialise.
And why not, at this time there is nothing to compete over...
no food and no females.
When it's cooler and overheating is no longer a risk...
male bears sometimes engage in play fighting.
Females and cubs have spent the summer further inland...
avoiding the danger of hungry males.
Now, with the approach of winter...
they move back to the coast in anticipation of the sea freezing over.
But they still remain cautious, and are wary of other bears.
Play fighting between males is harmless.
It's one way to establish who is who in the pecking order...
and to assess your future opponents.
For come spring...
when competition for females is high...
the fights are for real and are extremely aggressive.
It's better to find out in rehearsal...
that you don't have a hope of beating a particular rival...
than to suffer serious injury later on.
It's now early November...
and the long awaited freeze up is slowly happening.
But until the ice can support the bears...
they continue to bide their time on land.
By mid November day length is short...
and the sea ice is now strong enough to support the bears.
High among the mountains...
pregnant females dig shallow dens...
and wait for the snow to cover them.
Up here they are safe from other bears...
who would kill them to satisfy their hunger.
All other bears walk out onto the newly frozen sea.
Having lost up to a third of their body weight...
and weakened by their long fast...
they begin their search for ringed seals once more.
The Northern Lights play in the winter sky...
whilst below in the mountains...
and by now well covered by a deep layer of snow...
this pregnant female settles down for the next four months.
Her cub is born, helpless and blind...
after only sixty days in the womb.
Deep under the protective covering of snow...
and tucked into its mother's thick fur...
the cub stays warm, despite the appalling conditions outside...
where temperatures drop to below minus 50 degrees.
It's only by having such tiny and immature cubs...
that a female's body can cope with the continuing lack of food.
So, unlike most mammals...
much of the infant's growth goes on outside...
rather than inside, the mother's body.
In a few months, this cub will emerge...
to face an unfamiliar world outside.
In time it will learn the skills...
necessary to hunt and survive in a place...
which is forever changing with the seasons.
Only by adapting to the challenges ahead...
will it survive to continue its own line.