0:00:32 > 0:00:34The polar winter.
0:00:39 > 0:00:43This is the planet at its most hostile.
0:00:57 > 0:01:00Those that stay here at this time
0:01:00 > 0:01:04must face the harshest conditions on Earth.
0:01:26 > 0:01:28The High Arctic in late autumn.
0:01:28 > 0:01:33Empty and abandoned to ice and snow.
0:01:36 > 0:01:39Most animals migrated south weeks ago.
0:01:41 > 0:01:44The few that stay will face violent winds,
0:01:44 > 0:01:48plunging temperatures and months of darkness.
0:01:51 > 0:01:54A female polar bear searches for shelter.
0:01:59 > 0:02:02Other bears are out on the frozen ocean looking for food,
0:02:02 > 0:02:06but she won't feed again until next spring.
0:02:10 > 0:02:13Using as little energy as possible,
0:02:13 > 0:02:16she starts to dig a shallow nest.
0:02:23 > 0:02:25The snow here is easy to work.
0:02:25 > 0:02:27It's soft and light.
0:02:27 > 0:02:31A sure sign that soon, plenty more will accumulate on this slope
0:02:31 > 0:02:32as winter advances.
0:02:35 > 0:02:37And that is what she needs.
0:02:47 > 0:02:49If she has chosen well,
0:02:49 > 0:02:53the Arctic wind will do much of her work for her.
0:03:06 > 0:03:09Once the snow here is deep enough,
0:03:09 > 0:03:11she will dig down to make a den.
0:03:11 > 0:03:16She'll then lie, waiting for her cubs to be born as winter sets in.
0:03:33 > 0:03:37The sea ice already covers twice the area it did in summer.
0:03:37 > 0:03:39Those animals that, a few weeks ago,
0:03:39 > 0:03:43came down here to feed in the sea, are now locked out.
0:03:46 > 0:03:49But there are windows in this white desert.
0:03:49 > 0:03:52Gateways to the rich ocean below.
0:03:57 > 0:04:00Most birds have migrated south.
0:04:00 > 0:04:02But in the frozen Bering Sea,
0:04:02 > 0:04:04ducks of one particular species
0:04:04 > 0:04:07are gathering together in a single, immense flock.
0:04:13 > 0:04:15Spectacled eiders.
0:04:16 > 0:04:18Hundreds of thousands of them.
0:04:49 > 0:04:52With the seas that fed them throughout the summer
0:04:52 > 0:04:55all but frozen, this is the eiders' last refuge.
0:05:03 > 0:05:05Such patches of open water,
0:05:05 > 0:05:07kept free of ice by strong currents,
0:05:07 > 0:05:11are given a Russian name, polynyas.
0:05:18 > 0:05:21If this polynya stays open all winter,
0:05:21 > 0:05:24the ducks will have avoided an exhausting migration.
0:05:25 > 0:05:28It's a gamble and a tremendous risk,
0:05:28 > 0:05:30especially for the spectacled eider,
0:05:30 > 0:05:34for this polynya holds the world's entire population.
0:05:53 > 0:05:57Surrounded by ice, these spectacled eiders' survival
0:05:57 > 0:06:00depends on this single, vulnerable oasis.
0:06:01 > 0:06:05And conditions here can change very fast.
0:06:18 > 0:06:19A smaller pool.
0:06:21 > 0:06:25Here, common eider ducks are learning a bitter lesson.
0:06:25 > 0:06:28An early winter storm has caught them out
0:06:28 > 0:06:30and the ice is closing in.
0:06:33 > 0:06:38The pool is shrinking, and the ducks are freezing to death.
0:06:51 > 0:06:54These gamblers have lost.
0:07:09 > 0:07:13As the sun's influence continues to dwindle here in the north,
0:07:13 > 0:07:16the cold pushes south into Arctic lands.
0:07:34 > 0:07:39Winter brings a devastatingly-destructive force.
0:07:39 > 0:07:41Frost.
0:07:46 > 0:07:50Ice crystals form as moisture in the air freezes.
0:07:52 > 0:07:54Inside plants, the same thing is happening
0:07:54 > 0:07:57to the water in their cells and their sap.
0:08:01 > 0:08:05With these first frosts, most plants die.
0:08:05 > 0:08:08Their insides ripped apart by ice crystals.
0:08:15 > 0:08:18Coniferous trees, however, like fir and pine,
0:08:18 > 0:08:21can withstand very low temperatures.
0:08:24 > 0:08:28It's these trees that create the greatest forest on our planet.
0:08:30 > 0:08:32This is the Taiga.
0:08:39 > 0:08:44It encircles the globe and contains one third of all the trees on Earth.
0:08:56 > 0:08:59As winter deepens, frigid air from the Arctic
0:08:59 > 0:09:02meets warm, moist air from the south,
0:09:02 > 0:09:05producing particularly heavy snows.
0:09:11 > 0:09:14For the big animals of the forest,
0:09:14 > 0:09:17there's no way of hiding from the winter.
0:09:21 > 0:09:24But size, for the bison of Northern Canada,
0:09:24 > 0:09:26is, in fact, their salvation.
0:09:26 > 0:09:29Big bodies lose less heat
0:09:29 > 0:09:31and can carry more insulation.
0:09:31 > 0:09:34That may be why these bison
0:09:34 > 0:09:37are the largest land animals in North America.
0:09:41 > 0:09:44And only a large predator can tackle them.
0:09:52 > 0:09:54Wolves hunt better in packs,
0:09:54 > 0:09:59but there are only two of them here and the prey they pursue are giants.
0:10:15 > 0:10:19A vast Arctic wilderness stretches all around.
0:10:20 > 0:10:22In it, somewhere, there are bison.
0:10:29 > 0:10:33These deep tracks in the snow are easy to follow,
0:10:33 > 0:10:36but which way were the bison going?
0:10:51 > 0:10:54They have detected a scent. The hunt is on.
0:11:00 > 0:11:02Running in the bison's tracks is easy.
0:11:02 > 0:11:04The snow here is compressed and firm.
0:11:06 > 0:11:10At this rate, the wolves will soon catch up.
0:11:14 > 0:11:17They attempt a shortcut.
0:11:17 > 0:11:22The giant bison can plough on through virgin snow,
0:11:22 > 0:11:24but for the wolves, deep snow is a hindrance,
0:11:24 > 0:11:26and now they're losing ground.
0:11:44 > 0:11:49The hunters rejoin the bison's tracks and the contest is on again.
0:12:07 > 0:12:10The bison are the only prey here in winter.
0:12:10 > 0:12:13The wolves have no option, they must tackle them.
0:12:15 > 0:12:18But bison are ten times their size.
0:12:36 > 0:12:40In winter, the line between life and death is so narrow
0:12:40 > 0:12:44that for a wolf, even a small injury could be fatal.
0:12:45 > 0:12:48It's crucial they select the right target.
0:12:49 > 0:12:52This one is very big.
0:12:52 > 0:12:54Good decision.
0:13:14 > 0:13:16This is smaller, a yearling.
0:13:17 > 0:13:21Even though it's young, it's none the less heavier
0:13:21 > 0:13:25than both wolves combined and it is extremely powerful.
0:13:52 > 0:13:54The male wolf backs off.
0:13:54 > 0:13:56Perhaps he's frightened of injury.
0:13:56 > 0:14:00But the female is more determined, or more desperate.
0:14:41 > 0:14:44Having given so much already, she must make the kill.
0:14:45 > 0:14:49This is a battle of life and death for them both.
0:15:00 > 0:15:03The bison has no strength left.
0:15:05 > 0:15:06The battle is over.
0:15:18 > 0:15:23Winter deepens. The snow continues to accumulate,
0:15:23 > 0:15:25smothering the forest.
0:15:36 > 0:15:40Some trees are loaded with three tonnes of snow.
0:15:42 > 0:15:45It shuts out what little light there is at these latitudes,
0:15:45 > 0:15:49and that shortens the growing season still further
0:15:49 > 0:15:52and limits how far north trees are able to grow.
0:16:01 > 0:16:06So, snow influences both the shapes of the trees
0:16:06 > 0:16:08and the extent of this forest.
0:16:14 > 0:16:16And it affects the animals, too.
0:16:16 > 0:16:19SQUAWKING
0:16:19 > 0:16:21It helps to have friends
0:16:21 > 0:16:24if you want to find food at this time of the year.
0:16:26 > 0:16:29Wolverines and ravens, a match made in the Taiga.
0:16:32 > 0:16:35It's the hardest time of the year to find food.
0:16:35 > 0:16:38But the wolverine knows that a raven's call
0:16:38 > 0:16:40is as good as a dinner bell.
0:16:45 > 0:16:49And the raven has just recruited the best can opener in the forest.
0:16:52 > 0:16:54The moose carcass is frozen solid,
0:16:54 > 0:16:58but the wolverine has immensely powerful jaws,
0:16:58 > 0:17:01well able to deal with frozen food.
0:17:01 > 0:17:05The raven's bill is more suited to leftovers.
0:17:17 > 0:17:19The raven has to be patient.
0:17:26 > 0:17:29A wolverine's appetite is legendary.
0:17:29 > 0:17:33According to folklore, it can eat more at one sitting
0:17:33 > 0:17:35than any other creature in the forest,
0:17:35 > 0:17:39hence its other name, the glutton.
0:17:49 > 0:17:52What the wolverine can't eat now,
0:17:52 > 0:17:55it stores in the deep freeze.
0:17:55 > 0:17:58It will bury these food parcels across the forest,
0:17:58 > 0:18:01planning ahead for leaner times.
0:18:11 > 0:18:15For a few, the snow is an ally.
0:18:31 > 0:18:35Voles stay active throughout the winter beneath the snow,
0:18:35 > 0:18:38despite the freezing temperatures above.
0:18:44 > 0:18:46Travelling along tiny corridors,
0:18:46 > 0:18:51they move from pocket to pocket of perfectly refrigerated food.
0:18:54 > 0:18:57Snow is a great insulator,
0:18:57 > 0:19:00so down here, the temperature never falls
0:19:00 > 0:19:02more than a degree or so below zero.
0:19:02 > 0:19:05And that's warm enough for a vole to thrive,
0:19:05 > 0:19:08even if it lacks the stature of a bison.
0:19:16 > 0:19:18In some years, vole numbers boom,
0:19:18 > 0:19:23and then they are forced to break cover to search for more food.
0:19:51 > 0:19:55The great grey owl is a silent and very skilful hunter,
0:19:55 > 0:19:59but deep snow can be beyond its reach.
0:20:04 > 0:20:08But such snow is no barrier to one predator.
0:20:11 > 0:20:13The least weasel.
0:20:13 > 0:20:17A tiny hunter, and the vole's nemesis.
0:20:20 > 0:20:25Its body is exactly the same width as a vole's,
0:20:25 > 0:20:28so there's nowhere a vole can go that the weasel can't follow.
0:21:12 > 0:21:15The weasel's long, slender shape
0:21:15 > 0:21:17is perfect for hunting in tunnels,
0:21:17 > 0:21:20but the worst possible shape for staying warm.
0:21:20 > 0:21:23So they need a special way of doing that.
0:21:33 > 0:21:36She plucks the fur from its body tuft by tuft.
0:21:46 > 0:21:50And now she puts it all together to make a cosy blanket
0:21:50 > 0:21:54under which to sleep in her den below the snow.
0:22:08 > 0:22:12Midwinter in the northern forests.
0:22:12 > 0:22:16The sun is so low that it's twilight at midday.
0:22:22 > 0:22:24Further north in the high Arctic,
0:22:24 > 0:22:27the sun has been below the horizon for months
0:22:27 > 0:22:30and it'll be several more before it appears again.
0:23:20 > 0:23:24The male polar bear spends winter out on the frozen ocean.
0:23:27 > 0:23:30Few creatures can endure these conditions.
0:23:37 > 0:23:39If he's lucky, he will find a carcass
0:23:39 > 0:23:41that could provide a little food,
0:23:41 > 0:23:44possibly that of a fox or another polar bear.
0:23:47 > 0:23:51But otherwise, he must live on his reserves.
0:23:54 > 0:23:57This is the time to scrape by, to wait.
0:24:07 > 0:24:12But on lee-side slopes, beneath the snow,
0:24:12 > 0:24:14new lives are beginning.
0:24:33 > 0:24:37The cubs are born blind and tiny.
0:24:37 > 0:24:41An early birth is easier on the mother, who is barely awake.
0:24:56 > 0:24:58Despite her sleepiness,
0:24:58 > 0:25:01her instinct to nurse is overwhelming.
0:25:15 > 0:25:18The cub's clucking calls
0:25:18 > 0:25:21stimulate her to produce milk.
0:25:21 > 0:25:22And what milk!
0:25:22 > 0:25:25It's nine times richer than our own
0:25:25 > 0:25:28and enables her to double their weight every few weeks.
0:25:46 > 0:25:48It's over two months
0:25:48 > 0:25:51since the autumn snows first arrived.
0:25:51 > 0:25:55In two more months, polar bear families
0:25:55 > 0:25:57will emerge onto the snowy slopes
0:25:57 > 0:25:59all around the Arctic.
0:26:00 > 0:26:02But for now, they lie protected
0:26:02 > 0:26:04within their icy cocoons.
0:26:28 > 0:26:30A hundred miles above the Earth,
0:26:30 > 0:26:33the Aurora lights up the sky.
0:26:44 > 0:26:47After travelling millions of miles across space,
0:26:47 > 0:26:51solar winds, attracted by the magnetic pull of the poles,
0:26:51 > 0:26:53collide with the Earth's atmosphere.
0:26:55 > 0:26:58Trillions of charged particles
0:26:58 > 0:27:00dance across the sky.
0:27:07 > 0:27:11Above the Arctic, the Aurora Borealis -
0:27:11 > 0:27:14the Northern Lights.
0:27:14 > 0:27:17In the south, it's the Aurora Australis -
0:27:17 > 0:27:19the Southern Lights,
0:27:19 > 0:27:22that bring light to Antarctica's long winter.
0:27:30 > 0:27:34These spectacular lightshows are only a tease.
0:27:34 > 0:27:36Solar energy maybe,
0:27:36 > 0:27:40but no warmth that will help the emperor penguins.
0:27:52 > 0:27:55The Arctic winter is brutally cold,
0:27:55 > 0:27:57but in Antarctica,
0:27:57 > 0:28:00the darkest months are even more savage.
0:28:16 > 0:28:19The male penguins have not eaten for months,
0:28:19 > 0:28:23and have only each other for protection from the gales.
0:28:33 > 0:28:36Each has been entrusted with a single precious egg
0:28:36 > 0:28:39balanced on the top of its feet.
0:28:39 > 0:28:42If the egg were to drop onto the ice, even for a moment,
0:28:42 > 0:28:44the chick inside would die
0:28:44 > 0:28:46and all this would count for nothing.
0:28:55 > 0:28:58The emperors are not entirely alone.
0:29:03 > 0:29:05The Weddell seal.
0:29:05 > 0:29:08The only mammal to remain here throughout the winter.
0:29:14 > 0:29:16They must have breathing holes,
0:29:16 > 0:29:19and so have to constantly scrape away the ice
0:29:19 > 0:29:21that threatens to close them,
0:29:21 > 0:29:23rasping away fresh build-ups
0:29:23 > 0:29:25with special wide-gaped jaws.
0:29:30 > 0:29:35Beneath the ice, they are beyond the reach of the bitter winter winds.
0:29:39 > 0:29:42The sea is minus 2 degrees centigrade.
0:29:42 > 0:29:46A warm bath, compared to the conditions overhead.
0:29:58 > 0:30:03The roof of ice insulates this world from the wild fluctuations above.
0:30:05 > 0:30:07The temperature down here has barely changed
0:30:07 > 0:30:10for 25 million years.
0:30:19 > 0:30:22Of course, animals must still be hardy.
0:30:22 > 0:30:27These borchgrevinki fish have antifreeze in their blood,
0:30:27 > 0:30:30so they are untroubled swimming among the ice crystals.
0:30:36 > 0:30:39Many animals here are remarkably long-lived,
0:30:39 > 0:30:41perhaps because the conditions are so stable.
0:30:42 > 0:30:45Some sponges could be a thousand years old
0:30:45 > 0:30:48and large enough for a human to hide in.
0:30:50 > 0:30:52There could hardly be a greater contrast
0:30:52 > 0:30:56to the bleak, windswept world just above.
0:31:29 > 0:31:32But there is a constant danger here.
0:31:38 > 0:31:42Swirling patterns in the water reveal its presence.
0:31:44 > 0:31:46They are made by brine.
0:31:46 > 0:31:48Super-concentrated salt water.
0:31:48 > 0:31:50It's a warning.
0:31:54 > 0:31:57New sea ice forming above
0:31:57 > 0:32:00leaves behind brine that is so extremely salty,
0:32:00 > 0:32:02it sinks rapidly.
0:32:08 > 0:32:12As it descends, the sea water around it freezes instantly
0:32:12 > 0:32:15and forms a sheath of ice, a brinicle,
0:32:15 > 0:32:18that grows downwards towards the seafloor.
0:32:27 > 0:32:32Winter is reaching down from the cold world above.
0:32:46 > 0:32:47As it touches the seafloor,
0:32:47 > 0:32:50it kills whatever living thing it contacts
0:32:50 > 0:32:53by encasing it in a tomb of ice.
0:33:20 > 0:33:23Even in the relative warmth of the water,
0:33:23 > 0:33:25the lethal cold of winter
0:33:25 > 0:33:27threatens life on the seafloor.
0:33:37 > 0:33:42Another more constant attack rises from below.
0:33:42 > 0:33:45Pressure in the depths keeps water liquid,
0:33:45 > 0:33:48even though its temperature is far from freezing.
0:33:51 > 0:33:55Currents bring up this colder water, but it turns to ice,
0:33:55 > 0:33:58covering everything that can't move away from it.
0:34:20 > 0:34:24And then, the ice, being lighter than water,
0:34:24 > 0:34:28begins to float, lifting away anything attached.
0:34:49 > 0:34:52Even some of the faster-moving animals are caught.
0:35:08 > 0:35:11So the ice cleanses the seafloor
0:35:11 > 0:35:13and strews the ceiling above
0:35:13 > 0:35:16with remnants of life from below.
0:35:24 > 0:35:25CHIRRUPING
0:35:27 > 0:35:30A sign that winter is nearly over.
0:35:33 > 0:35:35The songs of male Weddell seals
0:35:35 > 0:35:38challenging their rivals to battle.
0:35:44 > 0:35:48The male seal's calls can be heard over 15 miles away.
0:36:00 > 0:36:03He aims to control the best breathing holes
0:36:03 > 0:36:06for they will determine his mating rights in spring.
0:36:14 > 0:36:17His calls create powerful shockwaves in the water.
0:36:19 > 0:36:20They are threats.
0:36:30 > 0:36:33This hole has already been claimed,
0:36:33 > 0:36:36and the owner will not surrender it willingly.
0:36:46 > 0:36:49No change this time.
0:36:49 > 0:36:53The challenger will need to find a hole with a weaker owner.
0:37:01 > 0:37:04The battles continue until the females arrive,
0:37:04 > 0:37:07and that time is now close.
0:37:34 > 0:37:37The sun returns to Antarctica.
0:37:40 > 0:37:42The longest night on Earth has ended
0:37:42 > 0:37:45and winter begins to give way to spring.
0:38:16 > 0:38:18Female emperor penguins.
0:38:18 > 0:38:20After four months feeding at sea,
0:38:20 > 0:38:23they are returning sleek and fat.
0:38:54 > 0:38:57Penguins, it seems, can fly after all.
0:39:00 > 0:39:03But a winter at sea has left them a little out of practice.
0:39:56 > 0:39:58There is no time to waste.
0:39:58 > 0:40:01Far away, the males are waiting.
0:40:11 > 0:40:15While the females were gone, the sea ice grew,
0:40:15 > 0:40:18and it's now twice the distance from its edge back to their colony.
0:40:26 > 0:40:3070 miles away, the males are in desperate need of help.
0:40:33 > 0:40:36Despite doing all they can to conserve their energy,
0:40:36 > 0:40:40many are close to dying from starvation.
0:40:53 > 0:40:55SQUAWK!
0:41:02 > 0:41:04SQUAWK!
0:41:09 > 0:41:11SQUAWKING
0:41:31 > 0:41:35Reunited after three months apart.
0:41:45 > 0:41:47The reward for her return?
0:41:47 > 0:41:50A first glimpse of her chick.
0:41:56 > 0:41:59The reunion made, it's time for the handover.
0:42:05 > 0:42:07The father finds it hard to let go.
0:42:10 > 0:42:14Some gentle persuasion is needed.
0:42:16 > 0:42:19He has endured the most appalling conditions on Earth
0:42:19 > 0:42:22to ensure the survival of his chick,
0:42:22 > 0:42:24and the bond is strong.
0:42:26 > 0:42:28The exchange must be quick,
0:42:28 > 0:42:32as the tiny chick, unprotected, could freeze to death in seconds.
0:42:44 > 0:42:47A task that began in autumn has been completed.
0:42:47 > 0:42:50Despite the huge odds against it,
0:42:50 > 0:42:52the precious chick has survived the winter
0:42:52 > 0:42:56and is now with its mother. And she has food.
0:43:06 > 0:43:09The chick's first fresh meal.
0:43:11 > 0:43:13Her mission is complete.
0:43:17 > 0:43:18But for other mothers,
0:43:18 > 0:43:22the journey ends in disappointment.
0:43:24 > 0:43:28Their chicks have not survived.
0:43:31 > 0:43:35The females' need to nurture remains strong.
0:43:35 > 0:43:37Any chick that strays from its parent
0:43:37 > 0:43:39is at grave risk of being kidnapped.
0:44:16 > 0:44:21The chaos may be a consequence of frustrated parental urge,
0:44:21 > 0:44:23but the outcome can be tragic.
0:44:40 > 0:44:43For those emperor penguins that survive,
0:44:43 > 0:44:46the worst is over for this year.
0:44:51 > 0:44:54There will soon be abundant food for everyone.
0:45:04 > 0:45:08The emperors have taken on the polar winter and won.
0:45:08 > 0:45:10The gamble has paid off.
0:45:11 > 0:45:14All other animals escaped,
0:45:14 > 0:45:17only they remained to raise their young.
0:45:17 > 0:45:20And now, it is they who will now benefit most
0:45:20 > 0:45:23from the rich southern spring.
0:45:31 > 0:45:36Another arrival is the certain confirmation that spring is here.
0:45:36 > 0:45:40The Adelies, having spent winter at sea, have come back,
0:45:40 > 0:45:45but they have not even mated yet, let alone laid their eggs.
0:45:53 > 0:45:56Now, at last, the male emperors can return
0:45:56 > 0:45:59to where they are most at home.
0:46:14 > 0:46:17One season ends and another begins.
0:46:19 > 0:46:22The penguins will soon be joined by migrants
0:46:22 > 0:46:27and the far south will bustle with life for a few frantic months.
0:46:37 > 0:46:41But there are only a special few, north and south,
0:46:41 > 0:46:43who can survive winter
0:46:43 > 0:46:46at the farthest ends of our planet.
0:47:19 > 0:47:25Next time, Frozen Planet is with the people of the polar regions.
0:47:26 > 0:47:29From traditional ways of survival...
0:47:30 > 0:47:33..to the very frontiers of science.
0:47:55 > 0:47:58More than any other season in the poles, winter
0:47:58 > 0:48:01was to pose the greatest challenge to the Frozen Planet crew.
0:48:01 > 0:48:05The team endured winds of over 100 miles an hour
0:48:05 > 0:48:09and temperatures as low as -50 degrees centigrade.
0:48:10 > 0:48:12Their boats were trapped in sea ice for days,
0:48:12 > 0:48:15while bears trapped others indoors.
0:48:20 > 0:48:22Some of the coldest conditions experienced
0:48:22 > 0:48:25were near the Arctic circle in Northern Canada.
0:48:25 > 0:48:30In winter, temperatures drop to -40 degrees, and stayed there.
0:48:32 > 0:48:35On the edge of the vast Taiga forest,
0:48:35 > 0:48:37the team hoped to film one of the most remarkable
0:48:37 > 0:48:40predator-prey relationships on the planet.
0:48:42 > 0:48:45What they experienced was the struggle against the elements.
0:48:45 > 0:48:48What they witnessed was a more profound struggle
0:48:48 > 0:48:51for life and death.
0:49:01 > 0:49:02Wood Buffalo National Park
0:49:02 > 0:49:05covers 28,000 square miles.
0:49:05 > 0:49:07The size of Denmark.
0:49:07 > 0:49:10One of the few cameramen to have filmed wolves
0:49:10 > 0:49:13and bison here is Jeff Turner.
0:49:13 > 0:49:15I first tried to film bison and wolves
0:49:15 > 0:49:17in this national park 15 years ago.
0:49:17 > 0:49:19And getting around on the ground
0:49:19 > 0:49:22is incredibly difficult at any time of the year,
0:49:22 > 0:49:24but in the winter, it's tough.
0:49:24 > 0:49:27We quickly realised the only way we'd get anything here
0:49:27 > 0:49:29was we had to get up in the air.
0:49:29 > 0:49:31The Frozen Planet team had never attempted
0:49:31 > 0:49:34aerial filming in such low temperatures.
0:49:36 > 0:49:39The first challenge for director Chadden Hunter
0:49:39 > 0:49:42was protecting the sensitive aerial camera.
0:49:42 > 0:49:46At -40, electrical cables short-circuit like fireworks.
0:49:46 > 0:49:49- Oh!- Ooo!
0:49:49 > 0:49:53- How cold can you fly this chopper? - Minus 40.
0:49:53 > 0:49:55Aerial cameraman Michael Kelem
0:49:55 > 0:49:57comes from sunny California
0:49:57 > 0:49:59and has never experienced temperatures so low.
0:49:59 > 0:50:02What kind of temperatures can you operate down to?
0:50:02 > 0:50:06Me? Usually about 70 degrees Fahrenheit in LA-kind of weather.
0:50:06 > 0:50:09- Yeah? - I'm only rated for Santa Monica.
0:50:10 > 0:50:14Operating delicate controls while wearing gloves is not easy.
0:50:14 > 0:50:18A computer and joystick are needed to control the aerial camera
0:50:18 > 0:50:20attached to the outside of the helicopter.
0:50:20 > 0:50:24- 'It's actually warmed up to -38.' - Michael would have to choose
0:50:24 > 0:50:27between dexterity or warmth.
0:50:27 > 0:50:28INDISTINCT RADIO
0:50:28 > 0:50:30With their camera mounted on the nose,
0:50:30 > 0:50:33the aerial team could now fly hundreds of miles
0:50:33 > 0:50:35in search of the animals.
0:50:36 > 0:50:38Jeff, meanwhile, is still on foot,
0:50:38 > 0:50:41scouting the other side of the national park.
0:50:41 > 0:50:43'I wonder what Jeff's getting on the ground?'
0:50:43 > 0:50:45Oh, man, it's cold!
0:50:45 > 0:50:47With the wind today, it's about -37,
0:50:47 > 0:50:50so...we've got to keep these heaters in here.
0:50:50 > 0:50:53Keep the camera running at these temperatures.
0:50:53 > 0:50:56From 3,000 feet up,
0:50:56 > 0:50:59- Chadden catches a glimpse of the elusive wolf pack.- Yeah. Come in.
0:50:59 > 0:51:03'I can see wolves. I can see wolves near buffalo.'
0:51:03 > 0:51:05- 10, 15. There's a big pack.- 'Wow!'
0:51:05 > 0:51:07We've got a big pack of wolves here.
0:51:07 > 0:51:09The wolf pack turns out to number
0:51:09 > 0:51:12an extraordinary 25 individuals.
0:51:12 > 0:51:14One of the largest ever filmed.
0:51:14 > 0:51:17'There's two more walking in from the left.'
0:51:17 > 0:51:19It looks like they're already on the hunt.
0:51:19 > 0:51:21The helicopter allows the team
0:51:21 > 0:51:24to shadow the wolf pack without disturbing them.
0:51:24 > 0:51:28So, let's go back into that nice slow circle, move around them.
0:51:29 > 0:51:31'They look pretty determined.'
0:51:31 > 0:51:33The pack are moving in on their prey,
0:51:33 > 0:51:35and the aerial team are perfectly placed.
0:51:39 > 0:51:41'They're making their, definitely making their move.
0:51:41 > 0:51:43'There's buffalo on the move.'
0:51:44 > 0:51:46The chase is on.
0:51:46 > 0:51:48Extreme concentration is now needed,
0:51:48 > 0:51:51both from the pilot and the cameraman to keep the shots smooth.
0:51:53 > 0:51:55'Yeah, there's more coming in now.
0:51:55 > 0:51:57'There's a nice tight little pack challenging them.
0:51:57 > 0:52:01'We've got a nice shot on the pack, the wolves coming up at the back.
0:52:01 > 0:52:03- 'You have the still? - Yeah. I got them.
0:52:03 > 0:52:07- 'I'm going to bring it up a bit. - OK, OK, tighten up just a hair.
0:52:07 > 0:52:10'I want to get two shots of the wolves at the back of the pack.'
0:52:10 > 0:52:13The wolf pack have picked out a young bison.
0:52:14 > 0:52:16- 'Holy- BLEEP!'
0:52:16 > 0:52:19As Michael struggles to hold the shot steady,
0:52:19 > 0:52:21no-one is prepared for what came next.
0:52:21 > 0:52:25'Oh! Hey, look, I just knocked him down, pretty much.'
0:52:27 > 0:52:29A one-ton bull charges through,
0:52:29 > 0:52:32taking out both the wolves and the young bison.
0:52:33 > 0:52:36I've never seen anything like that in the wild.
0:52:36 > 0:52:38That is unbelievable.
0:52:38 > 0:52:42The team have filmed extraordinary new behaviour from the air,
0:52:42 > 0:52:44but Jeff was nowhere nearby.
0:52:44 > 0:52:47To complete the sequence, they will need to work together.
0:52:48 > 0:52:51Only by using the helicopter to position Jeff
0:52:51 > 0:52:55will they be able to get both air and ground coverage.
0:53:03 > 0:53:08This pack will now feast for days, so the crew must move on.
0:53:09 > 0:53:12Jeff takes the team deeper into the wilderness
0:53:12 > 0:53:15in search of a new wolf pack.
0:53:15 > 0:53:18With everyone onboard, there are more eyes for spotting.
0:53:20 > 0:53:23Bison on the run can only mean one thing - wolves.
0:53:23 > 0:53:26But this time, only a pair.
0:53:26 > 0:53:28- 'I got...- No, there's a big...'
0:53:28 > 0:53:31Jeff must anticipate the animals' every move
0:53:31 > 0:53:34and direct their helicopter to where he needs to be dropped off.
0:53:34 > 0:53:36They're going this way.
0:53:38 > 0:53:40I had to figure out where the buffalo were going to run
0:53:40 > 0:53:43and try to get there ahead of them.
0:53:43 > 0:53:46If I got dropped off in the wrong position, we would blow it.
0:53:47 > 0:53:49There wasn't going to be a second chance.
0:53:58 > 0:54:01That moment, when you get out of the helicopter,
0:54:01 > 0:54:03and it leaves you behind,
0:54:03 > 0:54:06you feel an incredible sense of isolation.
0:54:08 > 0:54:10On the lake. I'll guide you in.
0:54:10 > 0:54:12Just down to the right.
0:54:12 > 0:54:13Down. Zoom in.
0:54:15 > 0:54:18- Watch it. You're on the back guy. - We're on the back guy.
0:54:18 > 0:54:20'On the back. Which one is he going for?'
0:54:20 > 0:54:23- I don't know. - Oh, there's one broken off.- Oh!
0:54:23 > 0:54:27- Oh, my gosh! - They're coming in now.
0:54:27 > 0:54:29When I saw the herd coming around the corner,
0:54:29 > 0:54:31I knew we'd picked the right spot.
0:54:31 > 0:54:33I was right in front of them.
0:54:33 > 0:54:36And the buffalo running right towards you,
0:54:36 > 0:54:38it definitely does get your heart pounding.
0:54:40 > 0:54:44The bison have poor eyesight and can't see Jeff.
0:54:44 > 0:54:46It's now a test of nerves.
0:54:46 > 0:54:49Weighing one ton and running at 40 miles an hour,
0:54:49 > 0:54:52one wrong step and the bison could kill Jeff.
0:54:52 > 0:54:54At the last second, they spot him
0:54:54 > 0:54:57and three peel away to the other side.
0:55:00 > 0:55:03At the back of the herd, the wolves have closed in.
0:55:05 > 0:55:08They're trying to separate that little one.
0:55:11 > 0:55:14- Oh, they've got it! - Both wolves are on him.
0:55:14 > 0:55:17- Both clamping down on him. - He got stomped there.
0:55:17 > 0:55:21What followed was one of the most emotional and powerful scenes
0:55:21 > 0:55:24the Frozen Planet team were ever to film.
0:55:25 > 0:55:27Jeff has picked his position perfectly.
0:55:27 > 0:55:30He is now only 50 metres from the animals
0:55:30 > 0:55:34and able to film a truly epic battle.
0:55:35 > 0:55:39I had never been so close to a wolf and bison battle.
0:55:39 > 0:55:40I could hear them breathing.
0:55:42 > 0:55:44And the power of the buffalo,
0:55:44 > 0:55:47the way he just threw this wolf around like it was a rag doll.
0:55:48 > 0:55:51I couldn't believe the beating this wolf was taking.
0:55:55 > 0:55:57The struggles we'd had with the winter
0:55:57 > 0:55:58and the cold and the snow,
0:55:58 > 0:56:01just felt so insignificant
0:56:01 > 0:56:03compared to these two animals
0:56:03 > 0:56:05that were struggling for their very lives.
0:56:07 > 0:56:10For over an hour,
0:56:10 > 0:56:14I watched this wolf and bison battle each other to a standstill.
0:56:15 > 0:56:18They were both unbelievably exhausted.
0:56:26 > 0:56:27Watching these two animals
0:56:27 > 0:56:30engaged in this massive life-and-death struggle
0:56:30 > 0:56:33was one of the most powerful things I'd ever witnessed in the wild.
0:56:35 > 0:56:39As a film-maker, you're definitely torn watching something like this.
0:56:39 > 0:56:41You know you need to keep filming,
0:56:41 > 0:56:43and you know this is a natural event,
0:56:43 > 0:56:45but it's also incredibly sad
0:56:45 > 0:56:48to know that one of these two magnificent animals
0:56:48 > 0:56:50isn't going to make it.
0:56:53 > 0:56:56The bison is fatally wounded.
0:56:57 > 0:56:58The battle is over.
0:57:01 > 0:57:04The team have managed to capture a remarkable hunt
0:57:04 > 0:57:07from both ground and air.
0:57:07 > 0:57:09All of them have been humbled
0:57:09 > 0:57:13by witnessing an extraordinary winter struggle for survival.
0:57:25 > 0:57:27Subtitles by Red Bee Media Ltd