0:00:13 > 0:00:18The Arctic - an icy ocean on the top of the world.
0:00:29 > 0:00:32Polar bears' lives are getting harder.
0:00:36 > 0:00:39The ice cap is shrinking.
0:00:41 > 0:00:42But that's not the whole story.
0:00:44 > 0:00:49Birds and animals are heading north to take advantage of this warming world.
0:00:52 > 0:00:56Another bear is there, too - the grizzly.
0:01:06 > 0:01:08On the same shores,
0:01:08 > 0:01:12there are families from the two different worlds.
0:01:16 > 0:01:22How will bears, brown and white, rear their cubs in a changing Arctic?
0:01:35 > 0:01:38The ice of the Arctic Ocean is skirted by tundra.
0:01:38 > 0:01:40There are a few towns,
0:01:40 > 0:01:44old hunting outposts or new oil installations.
0:01:44 > 0:01:47But man's main impact is on the climate.
0:01:54 > 0:01:58It's autumn. The cold has come late this year.
0:02:01 > 0:02:02After a good summer feeding,
0:02:02 > 0:02:05a pregnant grizzly heads for her den.
0:02:10 > 0:02:14There's a tunnel leading to a chamber dug in the frozen earth.
0:02:19 > 0:02:24She'll live on her fat reserves and won't re-emerge until spring.
0:02:24 > 0:02:29She'll have her cubs around Christmas - the solstice,
0:02:29 > 0:02:31winter's low point.
0:02:31 > 0:02:34BEAR SNORES
0:02:35 > 0:02:39Grizzlies and polar bears share this coast,
0:02:39 > 0:02:42but with opposite perspectives.
0:02:42 > 0:02:45One is at the start of the sea.
0:02:45 > 0:02:48The other is at the end of the land.
0:02:51 > 0:02:54Only pregnant polar bears stay on land.
0:02:54 > 0:02:57They find a place to settle and let the snow cover them.
0:03:01 > 0:03:05As soon as the sea freezes, the rest of the polar bears set off.
0:03:18 > 0:03:23Hibernation's out of the question. This is the hunting season.
0:03:37 > 0:03:40For the males and mothers with yearlings,
0:03:40 > 0:03:44darkness and blizzards are everyday life.
0:03:57 > 0:04:00The cubs of both bears are born in December.
0:04:06 > 0:04:09Polar bear cubs are tiny compared to their mother.
0:04:09 > 0:04:11She's the largest of all the bears.
0:04:11 > 0:04:14But her cubs are no bigger than a guinea pig.
0:04:17 > 0:04:22Both polar bears and grizzlies can have up to four cubs at a time.
0:04:22 > 0:04:24But twins are more normal.
0:04:37 > 0:04:40Polar bear mothers are thinner than they used to be,
0:04:40 > 0:04:43and cubs are less likely to survive.
0:04:43 > 0:04:47One of these cubs has a very short life.
0:04:58 > 0:05:01The surviving twin now has sole access
0:05:01 > 0:05:04to the richest milk in the whole bear family.
0:05:57 > 0:06:00Scattered in the ice are breathing holes.
0:06:00 > 0:06:04Polar bears stand motionless for days sometimes
0:06:04 > 0:06:07waiting for a seal to pop up.
0:06:13 > 0:06:16Underneath, in a cathedral of ice, seals are wary.
0:06:28 > 0:06:30ICE CREAKS
0:06:36 > 0:06:41Nothing else could muster the patience or tolerate the cold.
0:06:42 > 0:06:46It was the cold, in fact, that created polar bears.
0:06:46 > 0:06:47They were born
0:06:47 > 0:06:50out of climate change.
0:06:50 > 0:06:54A few hundred thousand years ago, this shore was a forest.
0:07:08 > 0:07:12It wasn't so long ago that there weren't any polar bears.
0:07:12 > 0:07:15Only brown bears, like grizzlies.
0:07:16 > 0:07:20Bears were the most successful of the hunters,
0:07:20 > 0:07:23mainly because they weren't just hunters.
0:07:23 > 0:07:28Bears can run and hunt. But like us, they can eat what they find -
0:07:28 > 0:07:34delicate morsels of seafood, or roots and berries, or insects,
0:07:34 > 0:07:39or anything to be scavenged, like a washed-up whale.
0:07:41 > 0:07:45To help find hidden food, a nose.
0:07:45 > 0:07:49Bears have a better sense of smell even than a bloodhound.
0:07:49 > 0:07:51It's the most sensitive nose in the world.
0:07:53 > 0:07:56They became clever and powerful,
0:07:56 > 0:07:59probably the largest predators since the dinosaurs.
0:08:11 > 0:08:14They were adaptable. They could hunt anywhere.
0:08:14 > 0:08:16Even underwater.
0:08:19 > 0:08:21Then the climate changed.
0:08:21 > 0:08:25The Ice Ages began and the trees disappeared.
0:08:25 > 0:08:30The landscape went from green to brown to white.
0:08:32 > 0:08:38As the cold drove other life south, some bears stayed put.
0:08:38 > 0:08:40Another world had formed around them
0:08:40 > 0:08:43and they found they could adapt to it.
0:08:43 > 0:08:46These bears looked to the north,
0:08:46 > 0:08:50where the frozen sea stretched out like newly-created land.
0:08:57 > 0:09:03Out on the sea were big, blubbery prey fit for a bear.
0:09:05 > 0:09:08Seals hunted fish under the ice and emerged to breathe and rest.
0:09:19 > 0:09:21These ice grizzlies changed.
0:09:23 > 0:09:27They blended in. They got bigger. They ate only meat.
0:09:27 > 0:09:30They became polar bears.
0:09:31 > 0:09:35Polar bears took to the cold. They gave up hibernating.
0:09:35 > 0:09:40They turned the seasons upside down and hunted all winter.
0:10:07 > 0:10:11Problem was, the seals got better at escaping.
0:10:14 > 0:10:19Bears are great opportunists and they'll have a go at almost anything.
0:10:19 > 0:10:23This one has found some beluga whales.
0:10:30 > 0:10:33This one's trying to bring down a walrus,
0:10:33 > 0:10:36an animal four times his size.
0:10:36 > 0:10:42But bearded and ringed seals alone remained 95% of a polar bear's diet.
0:10:47 > 0:10:50This is an animal of seals and ice.
0:10:55 > 0:10:5810,000 years ago, the Ice Age ended,
0:10:58 > 0:11:01but enough of the ice caps stayed frozen
0:11:01 > 0:11:04for polar bears to keep their Ice Age lives.
0:11:08 > 0:11:13As the Arctic now lurches into an unnatural and untimely meltdown,
0:11:13 > 0:11:15what will the polar bear mother face
0:11:15 > 0:11:19as she emerges into the new March sun?
0:11:21 > 0:11:23The mother hasn't eaten properly for nine months
0:11:23 > 0:11:27and the cub has been draining the last of her reserves.
0:11:31 > 0:11:33She has to check for danger.
0:11:33 > 0:11:38He may be the father. But that means nothing to polar bears.
0:11:38 > 0:11:40Or their cubs.
0:11:47 > 0:11:51Bears occasionally eat each other if they're hungry enough.
0:11:57 > 0:11:59A cub's life is fragile.
0:11:59 > 0:12:03Each year, fewer than 5,000 polar bear cubs emerge
0:12:03 > 0:12:05and most die in their first year.
0:12:21 > 0:12:24It takes a few weeks of short practice walks
0:12:24 > 0:12:27and then the two of them are ready to head for the frozen ocean
0:12:27 > 0:12:29and the seals.
0:12:31 > 0:12:36Survival depends on the springtime ice, having good hunting there
0:12:36 > 0:12:38and avoiding other polar bears.
0:12:42 > 0:12:46Some polar seals give birth straight under the ice.
0:13:02 > 0:13:06Bearded and ringed seal pups need the solid ice to breathe,
0:13:06 > 0:13:07suckle and sleep.
0:13:07 > 0:13:10They can swim, but they would soon die
0:13:10 > 0:13:12if they had to stay in the water.
0:13:30 > 0:13:34One of the tricks seals use to outsmart polar bears
0:13:34 > 0:13:38is to fashion dens for the pups that can be reached only from underwater.
0:13:41 > 0:13:46Polar bears, in turn, have learned to recognise a very faint pup smell
0:13:46 > 0:13:48seeping up through the ice.
0:13:54 > 0:13:57The mother's nose leads her to the den,
0:13:57 > 0:14:00and all she needs to do is break through.
0:14:04 > 0:14:07All the pup or mother seal needs to do
0:14:07 > 0:14:10is dive and swim to one of its other dens.
0:14:12 > 0:14:14Not all is lost.
0:14:14 > 0:14:17The cub is learning something about hunting.
0:14:21 > 0:14:26But the mother is racing the spring, the growing seal pups and the melting ice.
0:14:34 > 0:14:38April, and the pole tilts a little towards the sun.
0:14:40 > 0:14:42Ice reflects sunlight away.
0:14:42 > 0:14:46Land, though, absorbs the warmth.
0:14:51 > 0:14:54Along the coast are grizzlies.
0:14:56 > 0:15:02The grizzly mother and her two cubs are a month behind their white cousins.
0:15:06 > 0:15:10These grizzlies are called barren-ground brown bears.
0:15:10 > 0:15:14They're descended from the ancient brown bears that stayed on land.
0:15:17 > 0:15:19They're not winter animals.
0:15:19 > 0:15:24There's no point in leaving the den until the spring thaw is under way.
0:15:33 > 0:15:34Spring starts earlier.
0:15:34 > 0:15:39The world's changing, and the cubs should feel the benefit.
0:15:47 > 0:15:49These snow geese are better off.
0:15:49 > 0:15:53Millions of them fly up from California to feed on the tundra.
0:15:53 > 0:15:56Most years, they're flying earlier and in greater numbers.
0:16:03 > 0:16:10Other birds, bald eagles, fight over fish taken from rivers further north.
0:16:23 > 0:16:27She's produced milk for them for three months inside the den
0:16:27 > 0:16:29and kept out the cold.
0:16:31 > 0:16:33Now it's warmer outside than inside.
0:16:35 > 0:16:39Anyway, the grizzly cubs need the freedom to move,
0:16:39 > 0:16:41to run around and explore.
0:16:42 > 0:16:45It's the first few weeks of learning about their world.
0:17:26 > 0:17:30When they're strong enough, she takes them a little further afield.
0:17:33 > 0:17:36The snow and ice melt,
0:17:36 > 0:17:40and little streams become raging rapids to a cub.
0:18:14 > 0:18:16Grizzlies have claws like pitchforks
0:18:16 > 0:18:20and the same subtle sense of smell that helps polar bears find seals.
0:18:22 > 0:18:24Through earth and ice,
0:18:24 > 0:18:28a grizzly can sniff out insects, plant bulbs, pine cones -
0:18:28 > 0:18:32anything a grizzly can eat, which is almost anything.
0:18:45 > 0:18:49The grizzly's digging creates insect and rodent refugees,
0:18:49 > 0:18:52which a coyote is happy to hang around for.
0:18:58 > 0:19:01COYOTE HOWLS
0:19:01 > 0:19:04For days at a time, he'll follow the bear family,
0:19:04 > 0:19:06profiting from the grizzly's nose and claws.
0:19:08 > 0:19:10It's as though the family has acquired a friend.
0:19:32 > 0:19:36The coyote's certainly no threat to the cubs, but tree-climbing practice
0:19:36 > 0:19:41is a good idea anyway, in case of wolves or other grizzlies.
0:19:46 > 0:19:49What a mother can't show, they learn by trial...
0:19:49 > 0:19:51and error.
0:19:55 > 0:19:57There's a lot to learn.
0:20:00 > 0:20:03A mother bear teaches by example,
0:20:03 > 0:20:07and one of the hardest lessons is catching ground squirrels.
0:20:08 > 0:20:10The rodents are maddeningly quick
0:20:10 > 0:20:14and have the ability to vanish from one place and pop up in another.
0:20:17 > 0:20:20If you ever see a grizzly dancing on a hillside,
0:20:20 > 0:20:22they're probably chasing ground squirrels.
0:20:43 > 0:20:47Finally the mother does what her mother probably taught her to do,
0:20:47 > 0:20:50corner the squirrel in its burrow and quickly dig it out.
0:20:50 > 0:20:54It's a lot of effort for a mouthful of fur and bones,
0:20:54 > 0:20:56but at least the cubs are copying her,
0:20:56 > 0:20:59chasing their own imaginary ground squirrels.
0:21:03 > 0:21:06The pole tilts further towards the sun.
0:21:07 > 0:21:12The days are longer, and it should be peak hunting for polar bears.
0:21:13 > 0:21:18Seal numbers may be down this year, or they may have moved,
0:21:18 > 0:21:20but pups have been hard to find.
0:21:23 > 0:21:26Other bears can lead the family to seals.
0:21:27 > 0:21:31The mother has no instinct toward sociability.
0:21:31 > 0:21:34Those bears would kill the cub before they'd share.
0:21:34 > 0:21:38Big brothers don't even share with each other if they can help it.
0:21:46 > 0:21:51In the cold, clear air of the Arctic spring, the mother bear can smell
0:21:51 > 0:21:54everything that's happening, even over the horizon.
0:22:08 > 0:22:11The mother is focused on one smell.
0:22:16 > 0:22:19A few seal pups are hiding around here.
0:22:32 > 0:22:33Gone.
0:22:33 > 0:22:37It's important to find seals and the cub is keen to help.
0:22:54 > 0:22:59She breaks into another den and watches another seal swim away.
0:23:03 > 0:23:07Her mother taught her where to find seals a generation ago,
0:23:07 > 0:23:08but they are not there any more.
0:23:08 > 0:23:10It can be frustrating.
0:23:22 > 0:23:24At least the cub won't go hungry.
0:23:24 > 0:23:28The mother will provide milk for another year if she can.
0:23:32 > 0:23:35She should average catching a seal about once every five days.
0:23:35 > 0:23:38A seal is a big meal,
0:23:38 > 0:23:39much more than a grizzly can get,
0:23:39 > 0:23:43grubbing for roots and dancing around with ground squirrels.
0:23:46 > 0:23:47It's time to move on,
0:23:47 > 0:23:51and find another colony less wary of polar bears.
0:24:23 > 0:24:27They walk past Arctic islands and icy coasts
0:24:27 > 0:24:30in the constant search for seals.
0:24:30 > 0:24:32He struggles to keep up.
0:24:34 > 0:24:37A mother has to wait if a cub gets a little footsore.
0:24:58 > 0:25:01Throughout May, the days get longer,
0:25:01 > 0:25:04and by June, the sun never completely sets.
0:25:09 > 0:25:13The ice breaks up around the Arctic Ocean and Hudson Bay.
0:25:20 > 0:25:22The seals have finished pupping.
0:25:36 > 0:25:41It's late June, and the cub would dwarf a grizzly of the same age.
0:25:42 > 0:25:46They've had three months of hunting and now it's over.
0:25:46 > 0:25:51There's never been so much ice-free water at this time of year.
0:25:51 > 0:25:53In the endless summer days
0:25:53 > 0:25:57birds such as guillemots fly in to feed and court.
0:25:58 > 0:26:02Polar bears aren't the only ones affected by the rising temperatures.
0:26:05 > 0:26:09The winners in the Arctic now, generally, are the land animals.
0:26:11 > 0:26:13Where there was white, there's green.
0:26:15 > 0:26:20Grass, bushes, even trees are spreading north.
0:26:21 > 0:26:26With summer grass come grazers - caribou, also known as reindeer.
0:26:44 > 0:26:46They should be benefiting.
0:26:46 > 0:26:50But caribou are creatures of routine and confused by change.
0:26:52 > 0:26:54With time, they'll adapt.
0:26:55 > 0:27:00Where their numbers increase, wolves and bears should profit, too.
0:27:10 > 0:27:13Caribou know how to keep their distance.
0:27:13 > 0:27:17It's easier to go back to digging out ground squirrels.
0:27:21 > 0:27:24The grazers everywhere are feeding on new growth.
0:27:24 > 0:27:27And if you can't eat them, join them!
0:27:27 > 0:27:29Bears can eat grass.
0:27:39 > 0:27:41It's not very digestible.
0:27:41 > 0:27:44The cubs try it, but they need protein.
0:27:46 > 0:27:49Down by the water are limpets and barnacles.
0:27:49 > 0:27:54This bear's mother showed her and now she's showing her cubs.
0:27:54 > 0:27:57They're like little family secrets.
0:28:04 > 0:28:08There are opportunities when the caribou are at a disadvantage,
0:28:08 > 0:28:10wading through a freezing river, for example.
0:28:26 > 0:28:30The cubs aren't quite ready for this lesson.
0:28:50 > 0:28:52She'll save the river crossing for next year.
0:28:52 > 0:28:56The cubs, and the caribou, are safe.
0:28:58 > 0:29:00It's back to the barnacles.
0:29:06 > 0:29:08Beyond the shore,
0:29:08 > 0:29:12many polar bears are far north, deeper into the Arctic Ocean.
0:29:20 > 0:29:24The ice cap has retreated away from the land.
0:29:24 > 0:29:31In midsummer, the distance between the ice and the shore of northern Canada used be about 50 miles.
0:29:31 > 0:29:34Now it's over 200 miles.
0:29:34 > 0:29:37Climate change has been happening for 20 years,
0:29:37 > 0:29:39and it's now a different world.
0:29:43 > 0:29:45Some animals don't seem to be bothered.
0:29:49 > 0:29:51Narwhals prefer the broken ice.
0:29:58 > 0:30:03And guillemots can only live in open water.
0:30:05 > 0:30:09It's hard for polar bears to catch anything from a swimming start.
0:30:15 > 0:30:18Seals in the water are much too fast,
0:30:18 > 0:30:20yet frustratingly close.
0:30:26 > 0:30:30Guillemots can fly after fish, but there's a new problem.
0:30:30 > 0:30:35Fishing boats can get in now too, and have stolen the birds' food.
0:30:39 > 0:30:44Commercial trawlers affect whales, such as belugas, who also eat fish.
0:30:45 > 0:30:47On the other hand,
0:30:47 > 0:30:50there's less danger from polar bears at their breathing holes.
0:30:52 > 0:30:57Midsummer has passed, and polar bears have to make a choice.
0:30:57 > 0:31:01The cub needs a solid surface for sleeping and suckling.
0:31:01 > 0:31:06Should they head north to the permanent ice or swim south to land?
0:31:07 > 0:31:13Many biologists believe they should be classed as marine mammals, like seals.
0:31:28 > 0:31:33Polar bears can close their nostrils and have webbed paws.
0:31:39 > 0:31:42Even cubs are at home in the water.
0:31:42 > 0:31:47But how could they know how far it is this year to solid ice, or land?
0:32:05 > 0:32:08Most head south to land.
0:32:11 > 0:32:15The marathon swims are testing polar bears to the limit.
0:32:20 > 0:32:22They face strong currents.
0:32:22 > 0:32:25A bad storm, and they'll both drown.
0:32:54 > 0:32:58Aerial surveys find floating white corpses.
0:32:58 > 0:33:01Cubs wash up on the Arctic shore, dead.
0:33:20 > 0:33:25Those that make it are now safe, at least from drowning.
0:33:25 > 0:33:29They're exhausted, and they won't find much food here.
0:33:29 > 0:33:31In the past, they wouldn't have needed food.
0:33:31 > 0:33:34It's summer, the polar bears' off-season,
0:33:34 > 0:33:37and they'd do a summer version of hibernation,
0:33:37 > 0:33:40sleeping, and living off their fat.
0:33:42 > 0:33:45Sleeping hidden away was safer, too.
0:33:46 > 0:33:50Most of the Arctic coast is grizzly country.
0:33:52 > 0:33:57Parts of Hudson Bay and Greenland are the same latitude as Scotland,
0:33:57 > 0:33:59but bleaker.
0:34:00 > 0:34:02Here, hunger will drive them inland,
0:34:02 > 0:34:07and be more like grizzlies in summer, awake and trying to find food.
0:34:09 > 0:34:14Trouble is, they appear to have forgotten how to be like grizzlies.
0:34:14 > 0:34:19She may know kelp is edible, but she overlooks the shellfish.
0:34:25 > 0:34:29It may help that food on the tundra is increasing as the climate warms,
0:34:29 > 0:34:31but will she find it?
0:34:35 > 0:34:38The Arctic in summer has always been rich,
0:34:38 > 0:34:40thanks largely to continuous daylight.
0:34:40 > 0:34:45Now, though, the permafrost is melting and the land is even richer.
0:34:47 > 0:34:51But the melting releases millions of tons of carbon dioxide,
0:34:51 > 0:34:53so the planet gets even warmer,
0:34:53 > 0:34:55and the ice shrinks.
0:34:56 > 0:34:59While polar bears need to branch out,
0:34:59 > 0:35:01grizzlies do what they've always done,
0:35:01 > 0:35:05following traditions passed down the generations.
0:35:05 > 0:35:07At the end of a long hike
0:35:07 > 0:35:09is a salmon river.
0:35:09 > 0:35:12It's July and the fishing season.
0:35:13 > 0:35:17Many bears have arrived early to stake a claim.
0:35:20 > 0:35:23Heading upstream to breed are the salmon.
0:35:43 > 0:35:46It's a dangerous place for a mother to bring her cubs.
0:35:46 > 0:35:49It's packed with hungry and frustrated bears.
0:35:53 > 0:35:55She needs to find a fishing spot,
0:35:55 > 0:35:59but even the poorer places are taken by the younger bears.
0:35:59 > 0:36:04The cubs are bigger by now and need a lot of milk.
0:36:04 > 0:36:07If she has to fight for a fishing spot, she'll fight.
0:36:31 > 0:36:34The cubs are confused and can't keep up.
0:36:50 > 0:36:53Bigger grizzlies arrive.
0:37:10 > 0:37:16Claws rip flesh. A mother couldn't risk injuries like these.
0:37:16 > 0:37:19So when life along the river gets too violent,
0:37:19 > 0:37:21she leads her cubs down the beach,
0:37:21 > 0:37:27and gives them a lesson in the peaceful and delicate art of digging clams.
0:37:27 > 0:37:29Clams are still good food,
0:37:29 > 0:37:33and finding and opening them takes just as much skill and education.
0:37:33 > 0:37:38The intelligence of bears has been a revelation to scientists.
0:37:38 > 0:37:41Their memory, knowing when, where and how to find food,
0:37:41 > 0:37:44is very impressive.
0:37:50 > 0:37:54By August, the fish have reached the high lakes at the top of the rivers.
0:37:54 > 0:37:59They've spawned and are slowly dying and sinking.
0:37:59 > 0:38:01Bears can swim well, of course,
0:38:01 > 0:38:06but the bonanza of food lying on the bottom rotting seems out of reach.
0:38:06 > 0:38:11That is, if you assume grizzly bears don't dive.
0:38:11 > 0:38:14From the surface, it's an impressive lesson for the cubs.
0:38:31 > 0:38:35Diving for salmon continues for a week or two,
0:38:35 > 0:38:37until the fish get too rotten.
0:38:37 > 0:38:40By now, it's early September,
0:38:40 > 0:38:42the last days of summer.
0:38:47 > 0:38:51Polar bears are wandering miles inland in their search for food.
0:38:51 > 0:38:53They haven't found much.
0:38:53 > 0:38:56They missed the salmon season because they didn't know about it.
0:38:56 > 0:38:57It's a pity.
0:38:57 > 0:39:01The mother would have been a match for any of the grizzlies.
0:39:06 > 0:39:11Polar bears in the summer are spread out over impossibly vast distances.
0:39:11 > 0:39:15It's hard for us to keep track of what they're doing,
0:39:15 > 0:39:19but it's certain many are travelling further and looking for food.
0:39:20 > 0:39:22It's much easier for grizzlies
0:39:22 > 0:39:25with their well-worn paths and their seasonal food.
0:39:26 > 0:39:30August was salmon, September is berries.
0:39:30 > 0:39:33Right down to the Arctic Ocean is a carpet of bushes,
0:39:33 > 0:39:34bilberries, bog cranberries,
0:39:34 > 0:39:38bunchberries, crowberries, loganberries, cloudberries.
0:39:38 > 0:39:41A grizzly can eat 14,000 a day.
0:39:45 > 0:39:47Polar bears eat berries, too,
0:39:47 > 0:39:51and it's at berrying time that they're most likely to meet.
0:39:56 > 0:40:00It was thought that the two bears hardly ever saw each other,
0:40:00 > 0:40:03much less had any closer contact.
0:40:05 > 0:40:09It's certainly true that mother bears would avoid each other.
0:40:13 > 0:40:16As for the possibility of a male of one species
0:40:16 > 0:40:20and a female of the other mating in the wild -
0:40:20 > 0:40:22no, scientists thought it unlikely.
0:40:22 > 0:40:24Bears are wary of each other.
0:40:24 > 0:40:27There's no room for a mistake like that in the wild.
0:40:28 > 0:40:31There are some very pale grizzlies,
0:40:31 > 0:40:36but that's always been considered a normal colour variation.
0:40:36 > 0:40:41Then, in 2006, a hunter named James Martell
0:40:41 > 0:40:44shot a white bear with brown markings.
0:40:44 > 0:40:47It seemed worth checking its DNA.
0:40:47 > 0:40:50Its mother was a polar bear, its dad a grizzly.
0:40:51 > 0:40:54It has a name now, a Pizzly.
0:40:54 > 0:40:57Or if you prefer, a Growler.
0:40:57 > 0:41:01They can breed successfully with either grizzlies or polar bears.
0:41:01 > 0:41:05But cubs learn only from their mothers.
0:41:05 > 0:41:07There's little scope for a halfway bear.
0:41:11 > 0:41:15The polar bear nose leads them both into trouble.
0:41:15 > 0:41:17As far as she's concerned
0:41:17 > 0:41:21she's found one of the best feeding spots since coming ashore.
0:41:26 > 0:41:29At night, people burn their rubbish,
0:41:29 > 0:41:32partly in an effort to keep the bears away.
0:41:32 > 0:41:34The bears come anyway.
0:41:39 > 0:41:42From hunting in a clean, frozen world,
0:41:42 > 0:41:46they now scavenge in a hellish inferno of our own making.
0:41:52 > 0:41:55Polar bears don't stop at night raids on rubbish dumps.
0:41:55 > 0:41:59People in Arctic towns and oil installations
0:41:59 > 0:42:03worry that bears are targeting houses and even people.
0:42:12 > 0:42:14The bigger towns put out bear traps.
0:42:14 > 0:42:17A bear goes for the meat, and ends up...
0:42:17 > 0:42:19in bear jail.
0:42:21 > 0:42:26It's kept in custody until the sea freezes again.
0:42:29 > 0:42:32For a mother and cub in this alien and changing world,
0:42:32 > 0:42:36staying out of trouble is the hard part of finding food.
0:42:42 > 0:42:45The grizzly family is coming to the end of a good summer.
0:42:47 > 0:42:49They're full and sleepy.
0:42:49 > 0:42:52The cubs have done well on their Arctic education
0:42:52 > 0:42:55and try different foods on their own now.
0:42:55 > 0:42:58She'll slowly cut down their milk supply.
0:43:03 > 0:43:07These northerly grizzlies could benefit from climate change,
0:43:07 > 0:43:10with vast new territories opening up.
0:43:10 > 0:43:13But what opens up for bears also opens up for us,
0:43:13 > 0:43:17with our hunger for oil and increasing need for farmland.
0:43:19 > 0:43:20The land is being fenced
0:43:20 > 0:43:26and these "dangerous" bears are being driven out and killed.
0:43:27 > 0:43:29If we want the land,
0:43:29 > 0:43:33they are as helpless and vulnerable as polar bears.
0:43:42 > 0:43:46By mid-September, the polar bears have made their way to the shore.
0:43:49 > 0:43:52They're waiting for the sea to freeze.
0:43:57 > 0:44:03Soon the first autumn snows make the landscape at least look right for polar bears.
0:44:03 > 0:44:06They gather at the places where the sea freezes first.
0:44:14 > 0:44:17The young males pass the time play-fighting.
0:44:17 > 0:44:21They're working out who's the best fighter.
0:44:21 > 0:44:25Later, on the ice, defending food or females,
0:44:25 > 0:44:27it helps to know when to pick your fights.
0:44:50 > 0:44:53The freshwater lakes freeze first.
0:44:53 > 0:44:56The bears carefully test the ice.
0:45:13 > 0:45:17Long before the sea freezes, the grizzly family head home.
0:45:19 > 0:45:24In the past five months, the cubs have learnt grizzly traditions from their mother.
0:45:24 > 0:45:27It now guides them back to their den.
0:45:37 > 0:45:41Only pregnant polar bears don't wait on the shore.
0:45:41 > 0:45:44They lie down in the hills and let the snow cover them.
0:45:44 > 0:45:51In the past, when she emerged with cubs in spring, there would have been ice and seals,
0:45:51 > 0:45:53but nothing seems certain any more.
0:46:01 > 0:46:04The hills are soon covered by a blanket of snow
0:46:04 > 0:46:06with the bears lying snugly under it.
0:46:10 > 0:46:17Sleep is eking out calories collected from seals and salmon and berries and rubbish.
0:46:22 > 0:46:25The polar bears on the shore wait.
0:46:25 > 0:46:28It may be January before the sea freezes.
0:46:28 > 0:46:32For a cub that has made it through so much,
0:46:32 > 0:46:34it may be too late.
0:46:43 > 0:46:48A mother who's lost her cub has no choice but to start again.
0:46:51 > 0:46:56Since the winter and the ice have both been shrinking, fewer cubs are surviving.
0:46:58 > 0:47:00But some are.
0:47:02 > 0:47:05He has survived,
0:47:05 > 0:47:08perhaps in part because he is a lone cub.
0:47:14 > 0:47:17Eventually, the sea freezes.
0:47:31 > 0:47:35The polar bears' world reappears in midwinter...
0:47:37 > 0:47:41..and the family head out to hunt seals.
0:47:54 > 0:47:57His story has really only just begun.
0:47:59 > 0:48:01And what happens next?
0:48:01 > 0:48:03Who knows?
0:48:18 > 0:48:20Subtitles by Red Bee Media Ltd
0:48:20 > 0:48:22E-mail subtitling@bbc.co.uk