- 10 hours ago
Almost all mammals are warm-blooded (endothermic), relying on internal metabolic processes to generate heat. To survive freezing cold, they rely on three main adaptations: thick insulating layers of fur or fat (blubber), high-calorie diets to fuel body heat, and behavioral tactics like hibernation or migration....
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AnimalsTranscript
00:30The Arctic. It is intensely cold, yet nonetheless mammals live here.
00:44This icy territory is ruled by polar bears. And for this young inquisitive bear, these
00:56frozen seas are both its home and its playground.
01:11This might appear to be a game with a walrus, but if so, it's the walrus who's winning.
01:48The young bear still has much to learn as it starts to find its way around in this freezing
01:56world.
02:01From frozen seas to snow-capped mountains, specialized and hardy mammals have found many ways of flourishing
02:10in the coldest places on Earth.
02:35Many polar bears spend most of their time on the coast hunting seals.
02:43But this young female is heading inland.
03:03Guided by her keen sense of smell, she's making for the mountains.
03:25It's twenty degrees below zero.
03:30But she's well adapted to these temperatures.
03:35She has two layers of fur, and beneath them, insulating fat.
03:42So she loses little body heat.
03:56After walking for hours, she at last finds what she has come for.
04:09Svalbard reindeer.
04:12The smallest reindeer in the world.
04:23Inland, they rarely encounter polar bears.
04:35But now, they are about to do so.
05:00Polar bears are not built for high-speed pursuits.
05:20Andoy tail bears are not put in place.
05:57She has been outrun.
06:08It's unusual for a polar bear to chase prey for so long.
06:16But even so, she doesn't give up.
06:24Her progress is hardly graceful.
06:43Soon, she's back on their trail.
06:50And she catches them up.
07:03This time, she chases the reindeer towards deeper snow.
07:09Perhaps this will slow them down.
07:14The group splits.
07:17For a moment, she is unsure which way to go.
07:44Both prey and predator are now exhausted.
07:51But she's not giving up.
07:57The two reindeer separate.
08:04She follows one downhill.
08:10Back into the deep snow.
08:22Here, her great strength and longer legs help her to plough through it.
08:27Oh, shit.
08:42Oh, shit.
08:57This astonishing behavior is rarely seen.
09:16However, in this part of the Arctic, several bears have been seen hunting in this way.
09:23But it's too early to know whether, as the world warms, a diet of reindeer alone could be enough to
09:32sustain them.
09:40Mammals like the polar bear have had millennia to find ways to survive in the cold.
09:48Since the extinction of the dinosaur, there have been over 50 glacial periods.
09:55During the coldest, ice sheets over half a mile thick lay where Edinburgh and New York now stand.
10:09Today, Alaska's northern wildernesses are still much as they were during those colder times.
10:31One particularly hardy and resourceful mammal has survived here for tens of thousands of years.
10:44A wolverine.
10:59Like all mammals, he's warm-blooded.
11:03And to maintain his body temperature, he must eat a lot.
11:10But it's not easy to find food in this vast, empty wilderness.
11:19Wolverines have to travel up to 50 miles a day in search of it.
11:35But his feet, like snowshoes, are broad and help him cross snowfields without sinking in.
11:49And he has an extremely sensitive nose.
11:58It's so sensitive, he can locate a carcass, even though it's frozen solid.
12:13A caribou that has been killed by the cold.
12:25The wolverine's powerful jaws enable him to strip off the frozen flesh.
12:39He can even crunch through solid bone.
12:49But he doesn't finish his meal.
12:59Some of it he carries away.
13:10Surprisingly, perhaps, this male drops his food in the middle of nowhere and then leaves.
13:26And this is why a female wolverine.
13:33The food is a gift for his mate.
13:44It will stave off her hunger for several days.
13:49Wolverines are very secretive animals and very few people have ever seen this caring behaviour.
13:59Several days later, it becomes clear how important these deliveries of food have been.
14:10The female emerges from her den beneath the snow.
14:20And another head appears.
14:25Their three-month-old kit.
14:29It was born and has been nurtured two metres below the surface.
14:39This may well be the first time it has seen the world above the snow.
14:49The kit is strong enough to accompany its mother.
14:53And they look for a meal together.
15:1190% of mammal males take little or no part in raising their young.
15:22But fatherly devotion helps wolverines to raise a family during this, the coldest time of the year.
15:42Not all mammals have to travel huge distances to find their food if they know where to look.
15:51Winter in Canada's northerly forests.
16:08It's minus 25 degrees.
16:22Most rivers are frozen over.
16:27But this one is kept ice-free by constant springs bubbling up from its bed.
16:34And that allows chum salmon to spawn late in the season.
16:45And they attract hungry brown bears.
17:02While most other bears are already hibernating,
17:07these few that know about this special place
17:11continue to fatten up deep into winter.
17:19And these fish, each containing over 4,000 calories,
17:24are well worth staying awake for.
17:29But not all of the bears are equally skilled at fishing.
17:46Some do little more than put their head under the water and hope for the best.
18:00But their underwater vision is much like our own.
18:05And it's clearly a struggle.
18:11An elevated view might help.
18:32But it didn't.
18:38Upstream, in a secluded part of the river,
18:41a mother is fishing with her two young cubs.
18:54They both will rely on her milk during hibernation.
18:59So she puts on as much weight as she can,
19:02up to 2 kilograms a day.
19:09In the months to come, the fat she gains now
19:13will keep her alive during her long winter sleep.
19:29By passing on her knowledge of this special place,
19:35and teaching her young cubs the skills they need to survive,
19:41their mother has given them a good start in this icy world.
19:51Full of fish, the family is now ready to hibernate.
19:58And so avoid the hardships of winter.
20:10Old, disused mines are excellent winter shelters for mammals.
20:19By sleeping down here, they can avoid the worst of the winter.
20:34And some use their time here in unexpected ways.
20:41A colony of both little and big brown bats.
20:48The smallest weighs just six grams.
20:52And what little body fat they have will last them six months.
20:59To do so, they change their bodily functions in a remarkable way.
21:05Their heart rate drops to just 10 beats a minute.
21:10And at times, they take only two breaths an hour.
21:18Thermal images reveal that their body temperatures in midwinter
21:23are only just above freezing.
21:29They are now using only 2% of the energy they would do were they awake.
21:36The whole colony has put life on hold.
21:46Except for some solitary males.
21:54This one is shivering.
22:01Not from the cold.
22:04But to wake up.
22:13Vibrating his muscles re-warms his blood.
22:19And his heart is now beating 10 times faster than it was.
22:25This awakening consumes as much fat as he would need for the next two months were he to continue to
22:32hibernate.
22:36So this is a risky thing to do.
22:42But there's a reason.
22:48Before hibernation, some males failed to mate.
22:53Now they have a chance to try again.
22:58Every step costs precious body heat.
23:06He's searching for a small cluster of females.
23:12He must be careful not to wake them.
23:14Or they too would expend the precious calories they will need if they are to survive the winter.
23:26He mates with one.
23:31And then quietly leaves.
23:34And goes back to sleep.
23:44Five months later, the females wake.
23:52When they mated in the autumn, the sperm they acquired was not used, but stored.
24:00Only now will it fertilize an egg.
24:06So a male who mates during hibernation still has the chance of being a father.
24:18But bringing babies into a cold world of snow and ice is not easy.
24:44Each February in the Arctic, thousands of female harp seals haul out onto unstable pack ice
24:52and give birth.
24:55A newborn pup doesn't have enough fat to survive in the cold water.
25:04So mothers have to feed them as quickly and intensively as they can.
25:14And harp seals have a special way of doing that.
25:20The females produce supercharged milk.
25:26It contains ten times more fat than human milk.
25:33This enables each mother to rear her young faster than almost any other mammal.
25:39Just twelve days.
25:48For the young that appeared early in the season, the value of doing so is already visible.
25:59This one is fattening up nicely.
26:07But it's still very demanding.
26:14And it's mother sometimes slips away.
26:43As the pups accumulate fat,
26:48they need to be fed less often.
26:57And this allows a mother to spend longer under the ice in a more tranquil world.
27:14As the ice melts, it drifts, sometimes over six miles in a day.
27:22So after a lengthy swim, it's not always easy for a female to locate her pup.
27:49She flares her nostrils in an attempt to pick up its scent.
27:59No, not that one.
28:07Definitely not.
28:24A sniff and a kiss confirms this pup is hers.
28:42But sadly, not all mothers get it right.
28:48Some never find their pups again.
28:55Alone and hungry, an abandoned pup understandably seeks comfort.
29:18But this nearby mother won't share her milk.
29:26Her priority is our own pup.
29:53The nursery continues to drift.
29:58But most mothers do eventually find their own pups again.
30:08During their 12 short days together, each mother tries to provide her pup with nearly 15 kilograms of fat.
30:18which is enough to keep it warm no matter how cold the water.
30:26So the mammalian ability to produce rich milk enables harp seals to breed on the sea ice.
30:44High above the sea, there are other icy worlds.
30:56These are the Kluwane Mountains of North America.
31:03And they carry the world's largest ice field other than those around the poles.
31:11Summer here is shorter than almost anywhere else on earth.
31:18But it has been colonized by diminutive relatives of rabbits, pikers.
31:27This young male has been awake all winter, living on the food reserves he built up last year.
31:37For him, summer can't come soon enough.
31:44As the sun's warmth returns for just a few weeks, this harsh world is transformed into a rich, high-altitude
31:54meadow.
31:58It's what all the pikers here have been waiting for, for almost 10 months.
32:07There's no time to waste.
32:12Ready.
32:14Steady.
32:18Now they must collect as much food as quickly as they possibly can.
32:30But some of them seem in less of a hurry.
32:41Clearly biting their time.
32:46The others are gathering leaves non-stop.
33:05Except this one.
33:12They build haystacks, and that takes a lot of work.
33:17Each mouthful has to be carefully placed to allow the sunlight to dry it.
33:25They also add a few leaves from other plants that contain chemicals which will help preserve the hay during the
33:31winter.
33:39As many as 11,000 return journeys may be needed.
33:47To build a reasonably large haystack.
33:55And then it has to be guarded against opportunistic neighbours.
34:08The weather is showing signs of changing.
34:13It's time to make a move.
34:26This piker specializes in stealing from its neighbours.
34:52Got away with it.
34:55Again.
34:58Piker are one of the few mammals that prepare for winter in this way.
35:05With their food successfully stored, they're ready for the winter lockdown.
35:25The Tsinghai-Tibet Plateau is around 4,000 metres above sea level.
35:35It's the largest and highest plateau in the world.
35:43The air here is so thin that it hardly retains any heat.
35:55Here, it's almost always very cold.
36:04A snow leopard.
36:06A female.
36:08Her dappled coat making her hardly noticeable against the broken rocks.
36:16The plateau's top predator.
36:30Her ancestors have lived and hunted here for over 2 million years.
36:46But recently, people have also come to live up here.
36:59A Tibetan homestead.
37:07The settlers have brought domesticated yak.
37:16And protect them with fences and dogs.
37:25Tibetan mastiffs.
37:29They were bred originally to protect the livestock kept by Buddhist monks.
37:34And now, they are guarding the herders' yak.
37:45A yak is tempting prey for a hungry snow leopard in winter.
37:57But this female has been seen.
38:13The mastiffs outweigh even the biggest snow leopard.
38:34She's also outnumbered.
38:37She's also outnumbered.
38:38So, she retreats.
38:43She'll have to change her pan.
38:53She'll have to change her pan.
38:56This herd is unguarded.
39:04But they would not be easy prey.
39:12An adult yak weighs over half a tonne.
39:16And has horns up to a metre long.
39:21Even a calf is about twice the weight of a snow leopard.
39:36The leopard edges closer.
39:40If you choose from the summer elephant.
39:43You are better than the advertisers.
39:55And, if they want to go hose them down.
39:55And put whatever number you want,
39:56By some directional.
39:56By some gesture.
39:56So aç your która went away.
39:59My child because of a size woman is�� where they can move away from the other porta.
40:28As the calf disappears behind the slope, she follows.
40:34Her impact takes them both careering downwards.
40:44But she holds on.
40:46She holds on.
41:15It was a risk worth taking.
41:31The people here may lose ten yaks a year to predators like snow leopards.
41:38But the local community aims to live alongside snow leopards and compensate herders who lose
41:46yak.
41:50So they're not hunted here.
41:57Thanks to these decisions, this once persecuted mammal is now thriving here.
42:30Today, for many mammals...
42:33The cold is not their biggest challenge.
42:37A far greater threat comes from changes in the climate.
42:47Here, along the coast of Canada's Hudson Bay, there is open water where there should be ice.
43:00An Arctic force.
43:04At the beginning of each winter, foxes here form unlikely alliances with polar bears.
43:14It's late in the year and both species are waiting for the sea to freeze.
43:20Once it does, polar bears will once again be able to hunt seals out on the ice.
43:31And Arctic foxes will scavenge from their leftovers.
43:36But right now, both are hungry. And both must wait.
43:50She needs to be careful not to push her luck.
43:55Polar bears are not sociable creatures.
44:11Ten days pass, but there is still no sea ice in sight.
44:20For the foxes, the situation is becoming desperate.
44:31A few edible mawsons in the seaweed are all that she can find.
44:46The wait for one Arctic fox has been too long.
44:54The starving survivors cannot ignore this opportunity.
45:07Desperation has led to cannibalism.
45:15Something being seen more and more in the Arctic.
45:25Others begin to gather.
45:38As each tries to see off the competition,
45:42the sound of the quarrel attracts even more starving foxes.
45:51None are willing to surrender this meal.
46:10But each is unable to keep the others at bay.
46:17The commotion hasn't gone unnoticed.
46:23A cross fox.
46:26This stronger, more aggressive cousin from the south
46:29has been moving north as the winters have become steadily milder.
46:39It is now the top dog here.
46:59With the arrival of this newcomer,
47:02life for the long-time residents will only get harder.
47:24At last, the sea ice has formed.
47:31And for one Arctic fox, with luck, a meal is not far away.
47:41Mammals living in the coldest parts of the world
47:44have found remarkable ways to succeed where others could not do so.
47:57But as global temperatures continue to rise,
48:03only time will tell if they will be able to survive in this warming world.
48:25To capture one of the cold's most elusive mammals,
48:29the crew travel to the tundra of northern Alaska.
48:33Home to the legendary Wolverine.
48:40The ambition was not just to film Wolverines in this vast landscape,
48:45but to record the emergence of their kits for the first time.
48:51The crew joined forces with a crack team of Wolverine scientists and experts.
48:57The crew joined forces with a wolf.
49:03Everything's working, and, um, yeah, we just need some Wolverines now.
49:09Wolverine biologist Tom Glass has an early report of activity.
49:13There are some pretty old tracks, and then there are some fresher ones.
49:16It looks like a promising one.
49:19With a Wolverine in the area, producer Will Lawson leads the team to investigate.
49:25As a Wolverine can cover up to 600 square miles,
49:29they will need to roam far and wide.
49:37To build a picture of the Wolverine's movements,
49:40they set cameras along travel corridors and potential hotspots.
49:48But, as the days pass, it becomes clear it's going to be a challenge.
49:54It's, like, corrupted or something.
49:58The lens is really frosted up.
50:01Disappointing.
50:03After weeks of frustrations, finally the team gets a reassuring sign.
50:09What we got?
50:10Wolverine came and checked our camera here.
50:13Yes! This is encouraging.
50:18I'm not sure what's happened here, but I don't think it's worked.
50:22This is the heartbreak of camera traps.
50:28How annoying.
50:30At least we know a Wolverine has definitely been here.
50:34Though the camera traps haven't recorded the behaviour,
50:37they have confirmed it's a Wolverine hotspot.
50:41So, specialist pilot Mark Keech takes Will up for an aerial view.
50:52With the hope of locating a potential den.
50:58With thousands of hours and many years spent surveying wildlife from the air,
51:03Mark knows exactly what to look for.
51:07It's probably a Wolverine track there. Our shadow is just about to go across right now.
51:14I'm sure you can see that. It's definitely a Wolverine track there.
51:18This could be, actually, the den here.
51:21That would be great.
51:22Yeah, I think there's a very good chance that that's the den.
51:25There's multiple tracks.
51:28So, would you say that this sign looks like a promising option?
51:31That would be great.
51:37With this exciting discovery, the crew decides to set up a remote camp near the den,
51:4430 miles from the nearest road.
51:46Here's where the den is.
51:47This is the route we took in, so we can connect to that route really easily.
51:51Alright, I think we've got a plan.
51:55The film crew heads out over the vast tundra, deep into the Wolverine's territory.
52:01hauling everything they need to be self-sufficient in the field.
52:12We are exactly one and a half miles from this den.
52:17It looks like it's in that drainage we can see ahead, but on this side of it.
52:23It's pretty cool to actually be here, standing so close.
52:38The camp established, the crew devises a strategy to watch the potential den around the clock.
52:47With Will and Matt working the perimeter, Neil sets up his filming hide, his home for the foreseeable future.
52:58It's hard to tell from the ground, one, exactly where the den is, and two, how active it's been.
53:08All Neil can do now is wait.
53:33All Neil can do now is wait.
53:36Is there a Wolverine in the hole?
53:38We've done 200 hours in the hide without seeing one yet.
53:41That's more of the question.
53:52Oh.
53:53Oh.
53:56I'm joking, it's actually coming in, coming in, coming in, coming in.
54:14Beautiful to see, finally get to see it, thank goodness.
54:19With the female at the den finally confirmed, Matt and Will head in to resupply Neil.
54:27On the way, they make an exciting discovery.
54:30So we've got these Wolverine tracks coming this way down the valley.
54:34And there's more than one set of tracks.
54:37So they come together right there and follow the same path.
54:41They look to be about the same age, which is pretty, pretty cool.
54:46With signs of two adult Wolverines in the area, they meet Neil and find he's already filmed them both.
54:52So this is what we have, the blonde one, and then that's the other one.
54:58Oh wow, there's quite a marked difference.
55:00Oh wow.
55:01Yeah.
55:01That's the male.
55:03Really?
55:03Yeah.
55:06There's that Wolverine.
55:08I mean I could try and get Mark in the way, shall I?
55:10I'll finish it.
55:11Okay boys.
55:19Neil's managed to make it back to his filming hide, just hoping that the Wolverine didn't see him.
55:26Not only did he make it back, but Neil manages to film the larger, darker male delivering an edible gift.
55:38The male brought some food in.
55:40He's a bit bigger because he actually got his bum stuck.
55:43His wee legs were sticking out the top of the hole for a minute.
55:53With the mating pair using the den, the team has high hopes that the female has kids.
56:01All the signs are pointing towards it having young.
56:08But as days pass, there's no sign of kids, and the team's time with the Wolverines has run out.
56:14I'm feeling quite, yeah, quite disappointed.
56:18I don't want to be going because it feels so close.
56:22On their final day, under the cover of freezing fog, Will and Neil take the opportunity to leave camera traps
56:30behind.
56:31It will be their last roll of the dice to get the vital shots and finish the Wolverine's story.
56:38Okay.
56:40That's done.
56:47That's done.
56:48Days after the crew's departure, the cameras finally start recording.
56:58And against the odds, record the Wolverine's kit emerging for the very first time.
57:09Mammals like the Wolverine have colonized the coldest parts of the planet.
57:16We can only marvel at their ability to survive in these unforgiving landscapes.
57:31Next time, we journey to the hottest places on Earth.
57:36To discover how mammals overcome challenges and adversity.
57:42And use heat in the most surprising and unexpected ways.
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