Original subtitles

Every year, winter transforms our world,

creating dazzling displays

of frost, snow and ice.

For us, it's a magical season, but for other animals,

it's the toughest time of the year.

I've been lucky enough to spend time

in the company of some of the extraordinary animals

that live through the wildest winters on Earth.

I'm fascinated by the strategies they've developed

to get them through those challenging months.

SQUAWKING

So now I'm finding out more about

how animals prepare for winter...

..how they stay warm in some of the coldest temperatures

on the planet...

..and manage to find food

even in the deepest snow.

I want to discover how their priorities

and survival tactics change

as winter comes to an end.

SQUEALING

I'm uncovering the fascinating stories behind

how animals living in some of the most demanding places on Earth

have evolved ingenious ways to survive,

no matter what winter may bring.

Winter,

the season of sparkling, icy beauty.

But this time of year poses a real challenge

for the animals living through it.

As winter arrives, temperatures start to drop.

Here in the Alps they can plummet

to a bone-chilling minus 33 degrees C.

All around the world

animals have to face these conditions day in, day out.

BIRD CHIRPS

And it's harder to find food.

The vegetation has, for the most part, died out,

and underneath all this ice and snow,

it makes it so much harder to hunt.

The days are also shorter.

Here in the Alps, we're getting about eight hours of sun,

But as you move closer to the North Pole,

there's virtually no daylight,

which ultimately means

there's even less time to feed.

Whether it's taking to the ice in the far north...

..or huddling up at the bottom of the world...

..every animal must find a way

to get through the toughest season of all.

The key to surviving winter for many animals is preparation,

and the work must begin months in advance.

On the island of Hokkaido in Japan,

forests are alight

with the blazing colours of autumn.

This change is a sign

that winter is fast approaching.

And for the Siberian chipmunk,

it's a critical moment.

This male must gather as much food as possible

to see him through what lies ahead.

And it's a race against time.

Chipmunks are one of the smallest members

of the squirrel family.

But to survive the winter,

they need to find and safeguard

up to four kilos of food

in their underground burrows.

And they have an ingenious technique

for gathering supplies,

using their very own built-in storage.

These expandable cheek pouches

can stretch to three times the size

of the chipmunk's head...

..allowing them to gather up to 165 acorns

every day.

He needs as many as he can get his paws on

before he goes into hibernation.

He's been working hard for weeks

to build up his winter larder.

But it can be a struggle to get the goods

before others do.

SQUEAKING

SQUEAKING

The competition is fierce...

..especially when an animal three times your size

appears in your territory.

But this chipmunk won't let the red squirrel

get the better of him,

defending his patch ferociously.

After all, his life depends upon it.

SQUEAKING

When the food gathering is complete,

he collects leaves and grasses

to create a cosy den to sleep in.

Once settled in,

he'll be waking up every few days,

feeding on his stockpile

to keep him going.

Chipmunks are not the only species

hard at work storing food.

As winter approaches,

animals all around the world

are frantically gathering nuts

and for very good reason.

Nuts are the perfect packaged foods

to see animals through winter.

Their hard shells preserve

all the goodness inside.

Acorns, for example, are packed full of

vitamins and calcium and fats.

They're a high-energy food.

In fact, this many acorns, about 100g,

is equivalent to 400 calories.

Now, that's the same as about

ten chocolate biscuits,

or...

..this many raspberries.

Now, the fact that nuts are so highly nutritious

and key to the survival of so many animals during winter

has led to some pretty remarkable adaptations.

The fox squirrel can hide anything between

3 to 10,000 nuts

in different places every season.

To remember where it's hidden those stashes,

it builds up a mental map of its surroundings.

This requires so much brainpower,

it's thought it actually causes

the squirrel's brain to grow in size

during prime, nut-hoarding season.

The ability to store food

has created a virtual lifeline

for so many animals,

but for others, that strategy

simply isn't an option.

They've got to approach it

in an entirely different way,

and that's resulted in some of the greatest

natural spectacles on Earth.

BIRDS SQUAWK

As winter closes in,

millions of animals are on the move...

..in the air...

..the sea...

..and on land.

They embark on these epic migrations

in search of new food sources,

or to escape the harsh weather.

Caribou, known in Europe as reindeer.

In North America,

these incredibly resilient animals

travel to their wintering grounds

in huge numbers.

There can be close to 200,000 in one herd.

Majestic narwhals spend their summers

in the coastal waters of the Arctic,

but when winter approaches,

the whales head far out to sea.

Here, these almost-mythical creatures find food

deep beneath the surface,

coming up to breathe through holes in the ice.

And in Alaska,

hundreds of thousands of sandhill cranes head south

to Mexico, over 3,000 miles away.

Cranes are one of the oldest bird families on Earth

and it's thought that they've been making journeys like this

for millions of years.

It's an arduous flight, but they must persevere

in order to survive.

CRANE CALLS

Not all animals flee

the tightening grasp of winter, however.

In fact, one Arctic specialist

is eagerly awaiting its arrival...

..the polar bear...

..basking in the last rays of autumn sunshine.

Here in the Canadian Arctic,

the bears are gathering at the coast,

waiting for the sea to freeze

so that they can hunt on the ice.

Their main prey is ringed and bearded seals,

but they spend much of their time out at sea

and the bears need the ice as a platform to reach them.

The bears must bide their time on the land.

Over the summer, they live off their fat reserves,

but now these are dwindling.

Many bears turn to eating plants,

roots and berries,

but it's not enough to sustain them.

And as our climate changes,

winter sea ice forms later in the year

and is reducing,

leaving the bears to survive on these meagre rations

for even longer.

Polar bears are usually solitary animals,

so seeing them together like this is rare.

For them, it's a chance to size up future rivals,

but it also uses up valuable energy reserves.

At last, the wait is over...

..the ice is on its way.

With the arrival of deep winter,

much of the planet undergoes

a magical transformation.

As temperatures plummet...

..lakes and rivers freeze...

..and snowflakes dance in the air.

Landscapes become winter wonderlands.

But now, life is much tougher.

And one of the biggest challenges animals face is finding food.

Snow acts as an obvious barrier

to the food lying beneath it

and it's often much deeper than this, many metres in depth,

so any animals looking for vegetation

or any small rodents beneath it all

are going to have a very hard time reaching it.

Not only that,

but snow is excellent at absorbing sound waves...

..effectively acting as a layer of sound proofing

and stopping any animals that rely on their hearing

from detecting their prey.

Now, in the Rocky Mountains of North America

is an animal that is harnessing all of its skills

to overcome these challenges.

In this imposing mountain range,

the snow can lie in huge drifts.

This is home to a particularly elusive cat...

..the bobcat, a species of lynx.

To survive in these conditions,

it's always on the lookout

for its next meal.

Bobcats have evolved excellent hearing

with ears that can swivel back and forth

independently of one another

in order to pinpoint any noise coming from their prey.

And those characteristic ear tufts

are thought to amplify the sound.

But the deeper the snow,

the harder this task is.

Even the experts don't always get it quite right.

Perhaps the river can provide an opportunity.

It's fed by volcanic hot springs,

so it never freezes over.

It's a refuge of warmth, which draws in animals from miles around.

The bobcat's preferred diet is rabbit and hare,

but it's a resourceful cat

and will try its luck with almost anything.

Although this one doesn't seem to be very keen

on getting its paws wet.

It needs to find a suitable target.

DUCKS QUACK

No luck this time.

But these determined cats

are masters of perseverance.

With those finely-tuned ears,

perhaps this bobcat has caught the faintest of sounds

beneath the snow.

Its paws are soft and well-padded.

Using the boulders as stepping stones,

it can move without making a sound.

In this particular game of cat and mouse,

there's a clear winner.

To overcome the problem of finding food in deep snow,

one group of animals is using a different strategy -

changing its diet in winter.

As herbivores,

deer feed on grasses and other vegetation on the ground

and then browse the leaves of trees and shrubs, so when winter arrives,

their food is often hidden deep beneath the snow or has died back.

Now, in this wildlife park,

these deer are being given supplementary food,

but in the wild, deer have to become much more resourceful.

This is the Shiretoko Peninsula

in the far north of Japan,

where snow covers the mountain peaks for eight months of the year.

It's home to an incredibly tenacious animal -

the sika deer.

At this time of year,

there's little to eat in these snowbound forests.

Just getting around in these conditions

is difficult enough

and to add to the challenge,

many of the females are pregnant,

due to give birth in the spring.

To find food,

the deer dig down through the snow

using their hooves, looking for any vegetation that might be available.

But during harsh winters,

sika deer are able to adapt their diets

to add another food source

that can be found more easily...

..tree bark.

Perhaps surprisingly, tree bark does have some nutritional value.

But deer are only able to survive on bark

because of how their digestive system has evolved.

Deer stomachs are made up of four compartments

containing special enzymes

that allow them to digest plants and twigs and bark

and to break down cellulose,

a tough material that stands in the way

of all the nutritious stuff.

But not only is bark especially difficult to digest,

it also contains tannins,

which can be toxic.

Deer have overcome this by producing a special protein in their saliva

that neutralises the tannins,

rendering them harmless -

a remarkable adaptation that allows them

to make the most of the scant food available.

WOLF HOWLS

WOLVES HOWL

All around the world,

animals must be resourceful and creative

to secure the food they need in winter.

Wolves work together

to hunt large prey like bison

that could keep the whole pack going for weeks.

Voles burrow under the snow

to reach the vegetation they need.

And bald eagles will fiercely fight off any competition.

EAGLE SCREECHES

It's not easy staying well-fed in winter...

..and animals that can adapt to new circumstances

will be the ones to come out on top.

The Arctic fox can cope with sub-zero winter temperatures

in the extreme north

thanks to its thick white fur coat.

It's an accomplished hunter,

feeding mostly on lemmings and voles.

But it's a constant struggle to get enough food.

Here in Alaska, new opportunities are presenting themselves.

TRUCK HORN BLASTS

The town of Deadhorse

is one of the most remote settlements on Earth,

more than 200 miles north

of the Arctic Circle.

The Arctic fox knows there's food to be found here.

But it will need to be careful.

Not only does it have to avoid humans and machinery...

..but red foxes live here too.

They've also been lured into town

by the promise of sustenance.

The Arctic fox's sense of smell

is leading it towards much-needed food.

But the red fox is twice its size

and could easily kill it.

The Arctic fox has found what it was looking for.

This frozen meal of scraps

is enough to keep him going.

This intrepid little mammal

is successfully exploiting a new world to survive.

And it also has the uncanny ability

to vanish into the Arctic landscape

thanks to its white coat.

But he's not the only winter animal

to use this disappearing act.

The Yukon is the coldest place in North America.

Temperatures can fall to minus 63 degrees Celsius

and snow covers the ground

for five months a year.

This provides a distinct advantage for one of its residents,

if you can find it...

..the snowshoe hare.

It's fur perfectly matches this white world.

But the hare doesn't look like this all year round.

Throughout the spring and summer months,

its fur is reddish brown

to match its habitat at this time of year,

but as winter approaches and the snow starts to fall,

it transforms from brown

to purest white.

Snowshoe hares have many predators,

from coyotes to golden eagles...

..and lynx.

LYNX GROWLS

So the hare's winter white coat

makes for an excellent camouflage.

With its perfect disguise,

even out in the open,

it can still remain hidden from the sharpest eyes.

And if it thinks it's been spotted,

it has a getaway plan.

The aptly-named snowshoe hare

has especially large furry paws,

which stop it from sinking into the snow...

..and help it to be fast and nimble

and leap three metres in a single bound.

With all these impressive adaptations

and a little bit of luck,

the snowshoe hare will live to see another day.

Only a few species,

like this least weasel,

have this special ability to turn white in winter.

But how does this changing colour work?

Colour in the fur and feathers of animals

is all down to a pigment called melanin

that's produced by specialised cells in the skin

and a combination of different types of this pigment

creates a whole range of colours.

Now, white fur and feathers

don't contain this melanin pigment.

And the really clever bit is that animals that can change colour

switch off melanin production

as they grow their glorious white winter coats.

This remarkable change is triggered by day length.

As the days shorten before winter,

these animals shed their darker coats

and gradually grow their new winter ones.

It's also thought that white fur

might be more insulating than dark fur.

Because it doesn't have any melanin,

it's hollow and contains more trapped air in it.

Trapped air equals greater insulation and warmth...

..making this transformation a vital adaptation

for surviving winter.

Polar bears, on the other hand,

keep their magnificent white coats all year round.

Out on the ice,

conditions are some of the harshest on Earth.

The bears face high winds

and temperatures of minus 50 degrees Celsius.

Their insulating white fur

provides their main protection.

But in this frozen world,

even these coats aren't enough to keep them warm...

..so polar bears have a dense layer of blubber

beneath their fur that can be up to ten centimetres thick.

This also protects them as they hunt for seals...

..often having to swim between the ice floes...

..their huge paws acting as paddles.

The combination of this layer of fat and thick white fur

means that polar bears lose very little heat to the environment.

Now, we have a thermal imaging camera trained on me at the moment

to show you what I mean.

Now, these cameras show up hot objects

as white or yellow or orange,

and then cold objects

as purples and dark blues and even blacks.

Now you can see, even though I've got loads of layers on,

I'm mostly orange

and then my face is really yellow,

as are my hands, because I've got hand warmers in my gloves,

but it goes to show how much heat I am losing to the air around me.

Now, if we look at a thermal image of a polar bear,

it's a very different picture altogether.

The polar bear is mostly dark blues

with just a little bit of light at its extremities

like its nose, where it's losing a tiny bit of heat,

but that just goes to show polar bears lose hardly any heat at all,

making it one of the most resilient animals on the planet.

This is Valdez Harbour in Alaska,

a winter refuge for a charismatic little creature.

Sea otters spend nearly their whole lives on the water.

But unlike polar bears and other marine mammals,

they don't have a layer of blubber for insulation...

..so they have evolved the thickest fur coat of any animal.

The outer layer is made up of long waterproof hairs...

..while underneath, there's a short, dense underfur layer.

This keeps cold water completely away from the skin.

This female has an extra challenge on her hands.

PUP MEWLS

Sea otters can give birth all year round

and this is not ideal timing.

To keep her pup warm,

she has to groom it constantly.

She also blows air into its fur -

the fluffier it is, the warmer it will be.

When it's a little older,

she takes it out to sea to hunt.

To find food, she has to leave it at the surface.

PUP MEWLS

But thanks to its fluffy coat

and especially large lung capacity,

it's so buoyant, it just won't sink.

PUP MEWLS

When she surfaces,

its cries lead her back so she can feed it too.

The evolution of thick winter coats

is yet another exquisite adaptation

that allows animals to withstand the coldest temperatures,

but even then, that may not be quite enough.

But nature always finds a way,

and some species have developed a very different,

but equally effective, survival strategy.

In the frozen mountain forests of southern China,

2,500 metres above sea level,

lives an astonishing animal.

Rarely seen,

this is the highest-living monkey in the world -

the Yunnan snub-nosed monkey.

These monkeys have developed some remarkable adaptations to cope with

the freezing temperatures of their Himalayan home.

Their noses are almost completely flat

to avoid getting frostbite...

..and they're covered in dense fur

that can be up to 15 centimetres long.

But in this heavy snowfall,

even this isn't enough...

..so they do something very clever.

Snub-nosed monkeys are social animals

who live in large family groups.

As night approaches,

they gather together amongst the branches of trees.

Mothers and babies are usually at the centre

with all the other members of the family surrounding them.

They'll stay huddled like this until morning.

In this bitter cold,

they simply wouldn't survive the night on their own.

So what's the science behind huddling?

Exactly how does it work?

Well, we have a thermal imaging camera trained on me

to help explain exactly what's going on.

Now, heat is a thermal energy

that's constantly flowing around us

and as it flows, it naturally moves from hotter objects

to colder objects.

To show you what I mean,

I'm going to fill this solitary mug

in the snow

with some hot chocolate.

Now, you can see it's hot -

white or yellow in the centre - but very quickly,

it's losing that heat

to the colder air around it,

but if I fill...

..all of these mugs of chocolate

huddled together like our monkeys...

..we should be able to see something

very different is happening.

All of the mugs are losing their heat much less quickly,

particularly the one in the centre

and that's because it's protected by the hot mugs around it,

but also, it's gaining some heat from the collective huddle

that's hotter than it is.

Therefore, the heat is transferring

to that mug in the centre.

In just a few minutes,

you can clearly see the difference, can't you?

This cup is now completely cold,

having lost all its heat to the elements,

while this one is nice and cosy and warm

in the centre.

Now, in the Antarctic,

one particular species is using this huddling strategy

in such a beautifully complex way

that scientists are only just beginning to fully understand it.

Emperor penguins are one of nature's great survivors.

They can endure the extreme cold of an Antarctic winter

where temperatures can plummet

to minus 40 degrees Celsius.

And the key to their survival

is how they huddle together.

One by one, the male emperor penguins lock themselves together

in a tightly-packed group

to keep warm and shelter from the intense winds.

These huddles can contain

as many as 4,000 penguins.

And they are constantly moving -

those on the outside push forward

to get closer to the warmth in the centre of the group

and away from the full force of the Antarctic storms.

But the penguins on the inside of the huddle

also move around

to stop themselves from getting too warm.

Recent studies have shown that temperatures at the centre

can reach an incredible 37 degrees Celsius...

..so the penguins move away to avoid overheating,

with others replacing them.

It's one of the most phenomenal examples

of cooperation in nature

and a vital strategy for the emperor penguins' survival.

Bracing yourself against everything that winter throws at you

in such a sophisticated way

is testament to just how resilient

and awe-inspiring nature is,

but nature is also incredibly versatile

and other animals are avoiding the onslaught of winter altogether.

To save energy when food is in short supply,

some animals go into hibernation.

After feeding up in the autumn,

hedgehogs find a cosy den.

Here, they fall into a state of inactivity,

which can last all winter.

Their body temperature drops,

their heart rate slows

and they live off their fat reserves

for about four months.

When winter arrives in North America,

the Arctic ground squirrel retreats beneath the frozen ground...

..where it will sleep for an astounding eight months.

A thermal camera inside a filming burrow

shows how the squirrel's body temperature cools.

It can drop to a staggering

three degrees below freezing.

Its major organs shut down almost entirely,

but every few weeks,

it shivers and its muscles send a flow of warm blood

around its body, rebooting its brain.

It will do this about a dozen times during the winter

until finally, it's time to wake up again.

Bats are another group of animals that are known to hibernate

and new research has revealed that one particular species -

the Ussurian tube-nosed bat from Japan,

no bigger than the size of my palm -

may hibernate in the snow.

For many years, their whereabouts during the harsh winters

remained a mystery, but now it's thought that when temperatures drop

and the first snows fall,

they leave their roosts in the cavities of trees

and the crevices of rocks

and settle onto that snow.

As more snow falls,

they become covered and surrounded,

their tiny movements creating a cavity

with much more stable temperatures than their tree roosts,

exposed to the elements,

and there they'll remain in what's called a super-cooled torpor

or deep sleep.

It's believed they'll stay there until the snow melts,

potentially hibernating in their cavities

all the way through to the spring.

The shortest day of the year occurs at the end of December

in the Northern Hemisphere.

It's known as the winter solstice.

Gradually, days begin to lengthen

and some animals start planning for the future.

The Himalayas,

home to one of the planet's most majestic

and elusive creatures...

..the snow leopard.

Living in the world's highest mountains,

this big cat's home range can be as large

as 400 square miles.

These cats are endangered.

Scientists estimate there may be as few

as 4,000 left in the wild.

So the odds are well and truly stacked against them

when it comes to finding a potential mate

in this winter landscape.

But this snow leopard doesn't seem to be too fazed

by the challenge.

He has a tried-and-tested strategy.

First, he patrols the well-worn tracks of his territory

over and over again.

This is his patch,

but it might overlap with the territory of a female

and, with any luck, their paths will cross.

Next, he uses scent marking

to advertise his presence.

Snow leopards scent mark their territory by spraying urine

and scent chemicals and rubbing scent glands against rocks

or patches of earth.

He also checks for the scent of any potential mates

who may have passed by.

He's very diligent,

sometimes spraying as many as 20 times an hour.

He wouldn't want to miss his chance.

Scent marking and detecting is a crucial part

of the lives of snow leopards.

It's how they communicate as solitary animals

and it's incredibly important when it's time to breed.

Snow leopards may have tens of millions of scent receptors.

We humans only have a paltry five million.

Their ability to detect different chemicals in a scent mark

is nothing short of extraordinary.

It can take a snow leopard over a week

to cover his entire territory,

walking hundreds of miles in search of a mate.

Not even the deepest snow will stop him.

At last, his determination pays off,

he picks up the scent of a female.

Eagerly, he rubs his own scent

over the scent she has left to declare his presence and interest.

He may be able to smell the marks of the female,

but now he needs to find her.

Then, across the mountains,

comes the cry of a female snow leopard.

SNOW LEOPARD CALLS IN DISTANCE

He returns the call.

If they do finally meet,

these rare leopards will have a chance

to add to the next generation...

..and with such low population numbers,

every new litter of cubs is precious.

SNOW LEOPARD CALLS

As the snow begins to melt...

..and the sun's rays become stronger,

spring will soon be on its way.

But what causes these dramatic changes between the seasons?

It's all down to the fact that planet Earth is tilted

23.5 degrees off its axis.

So when it's winter in the northern hemisphere,

where we are in the UK and where I am here in Austria,

the planet is in this position

and it's tilted away from the sun,

which means in the northern hemisphere,

days are shorter and it's colder,

but as the Earth moves around the sun...

..over 365 days,

spinning on its own axis every 24 hours, obviously,

as it hits spring around here

and then summer here,

you can see the northern hemisphere is tilted towards the sun,

which means days are longer and warmer.

Now, if our planet wasn't tilted at all,

we simply wouldn't have any seasons

and the Earth would be a very different place indeed.

High in the northern hemisphere,

with the arrival of spring,

Arctic ground squirrels are beginning to stir

from their very deep sleep.

It takes three hours for them to heat up

and a full day for their entire bodies

to be fully functional again.

As soon as they're up and about,

males spring straight into action.

SQUIRREL CHIRPS

First, this male needs to reclaim his territory.

SQUIRREL CHIRPS

He sees off any rivals.

He's ready for the most important day of his year.

Female Arctic ground squirrels

emerge a few days after the males.

He needs to look his best...

..but he mustn't miss his chance.

Females are only fertile

for 12 hours each year.

SQUIRREL CHIRPS

He approaches her cautiously.

He doesn't want to scare her off.

But what will she make of him?

He politely taps a greeting...

..and she returns the gesture.

THEY CHIRP

He can't afford to be complacent.

She could go in search of another partner at any time,

so he won't leave her side for 24 hours.

And with any luck, the circle of life will start all over again.

While some animals are beginning to pair up,

others are already a few steps ahead.

CALF BLEATS

CUB GRUNTS

CHICK CALLS

Arctic fox cubs emerge from their den

at just over three weeks old.

Their mother has her work cut out with six...

..but they can have up to 14 cubs in a single litter,

the most of any of the fox family.

Weddell seal pups are born straight onto the ice.

They'll double in weight in just the first week

and soon after, they'll take their first swim.

Young wild goats make the journey to their spring pastures

when they're only a few weeks old...

..following their mothers,

who'll protect them for the first year of their life.

Young animals everywhere

are out exploring their new world

and the rising temperatures are enough to put a spring

in everyone's step.

The last places to feel the full effects of spring are the poles

and beneath the snow in the Arctic, new life is emerging.

CUB GRIZZLES

These polar bear cubs are just two months old.

They were born beneath the snow

while their mother lay in her deep winter sleep.

They're seeing the world for the first time.

CUB GRUNTS

They need to find their feet...

..and mum is on hand to help.

CUB GRIZZLES

After five months in hibernation,

this is a chance to stretch her legs.

Following the long winter,

a mother bear's first task is to find food.

She's headed for the sea ice to hunt,

before it melts fully in a few months' time.

Polar bears are dedicated and protective mothers.

CUB CALLS

They keep their cubs close

and call to them when they wander too far.

POLAR BEAR ROARS

CUBS CALL

Over the next two years,

she will teach her cubs to swim and to hunt

and how to survive the challenging Arctic winters by themselves.

Until then, as they step out into a new year,

she will always be at their side.

POLAR BEAR GROWLS

CUB GRIZZLES

MOTHER BEAR GROWLS

From the first frosts to the first thaws,

our animals have developed remarkable adaptations...

..from making sure they have enough food...

..to staying as warm as possible in the coldest months.

The strategies they've evolved to survive and thrive

in our winter wonderlands make for some of the most inspirational

stories from the natural world.