The Blazing Summer Yellowstone: Wildest Winter to Blazing Summer

Stretching out before me is the magnificent Yellowstone.

This is one of the most dynamic...

..unpredictable and exciting environments on Earth.

Deep in the Rocky Mountains,

this vast wilderness is home to North America's

most iconic wildlife.

But every year, Yellowstone's animals are pushed

to their absolute limits.

Temperatures can swing from -40 in winter

to approaching plus 40 in summer.

And at the heart of this change is the thaw.

The melt can last from March to July...

..and it's one of the most dramatic, natural events on Earth.

How do the animals cope with such extremes of temperature?

We're here to find out.

I'm joined by biologist Patrick Aryee...

That's intense.

..and a team of wildlife cameramen and expert scientists.

Previously, we've witnessed how animals survive

Yellowstone's extremes.

Starting in winter, it was well below freezing

and some animals really struggled.

Then, in spring, temperatures jumped nearly 30 degrees in a fortnight

and wildlife had to cope with the thaw coming three weeks early.

Now, summer is here and there are new challenges.

The meltwater will dry up fast,

food becomes scarce...

..and if there's no rain,

wildfires will threaten to destroy the habitats animals rely on.

SQUEAKING

Welcome to Yellowstone's Blazing Summer.

So far in 2016,

every month has been hotter than average in Greater Yellowstone.

If the trend continues,

summer could reach record temperatures

and push animals to the brink of survival.

Yellowstone lies over 600 miles

from the Pacific and has a continental climate,

which means summers can be relentlessly hot.

Now, at the moment it's all still looking quite lush and green,

but in the coming weeks as the temperatures continue to rise,

the vegetation will start to wither,

valleys will become dust bowls and lakes and streams

will start to dry up.

Wildlife must travel further in search of food,

drinking water and shelter from the heat.

Young animals born back in spring are now entering their first summer.

They're a lot more mobile, but still need to avoid danger

whilst exploring on those unsteady legs.

For this latest generation,

the change in climate will make their lives even more challenging.

In spring, the beaver family was affected by the

unusually warm temperatures.

Huge volumes of meltwater flooded into the Snake River,

where the beavers have made their home in the south

of Greater Yellowstone.

Snow melting from all the way up there in the Teton Mountains

rushed down in a deluge and threatened to wash

our beaver dam away.

Beavers dam rivers to create a series of ponds,

where they live and feed, safe from predators.

After working flat out on emergency repairs to the dam,

the beavers just managed to save their home from the flood.

Now, in summer, the family could face the opposite challenge -

too little water in the river.

I've come to meet wildlife cameraman Jeff Hogan

who's been following the beavers.

Hey, Jeff.

-How's it going?

-There you are. How are you doing?

Jeff was filming great grey owls in spring.

Now, he'll use his specialist skills to study the beavers and has

installed an infrared camera inside their lodge.

SQUEAKING

I've got something to show you.

It was a bit of a surprise.

'This footage looks like the male and female I saw here in spring.'

-You see a couple of big, fat beavers?

-Yeah.

SQUEAKING

'But then, something unexpected.'

Oh, my gosh!

PATRICK LAUGHS

-They're so adorable.

-That's a great shot.

-Oh, my goodness.

-That's amazing.

No way.

Oh man, they're so adorable.

'Baby beavers are called kits and Mum has given birth to three.'

I would say they're probably about ten weeks of age, maybe.

'Kits are precocial,

'which means they're mobile and quite advanced from birth.

'Emerging with a full coat of thick fur, sharp chisel-like teeth...

'..and a characteristic flat tail.

'This, they use as a rudder to steer when swimming,

'which they can do within a day of being born.

'But these three still rely on their family to bring them food

'from outside the lodge.'

I've got another clip for you.

SQUEAKING

Look at all that willow.

This adult beaver just brought in three or four branches,

all bundled up.

And the little young ones will just jump on this.

They'll gobble that right down.

'At ten weeks old, these kits have stopped drinking

'their mother's milk.

'They now have an adult diet.'

In summer, the ponds the beavers create

become their vegetable gardens.

The slow, warm waters create optimal conditions

for edible plants to grow.

Mum, Dad and last year's young are working overtime collecting food

for the kits and keeping the lodge clean by washing grassy bedding.

In a matter of days,

the kits will leave the lodge and learn to forage for their own food,

whilst avoiding predators.

Around 50% of beaver kits don't survive their first six months.

It's a critical time for this family, and Jeff

will be following them every step of the way.

Across Yellowstone, our teams have been documenting signs

that an early spring thaw kick-started an early summer.

As icy meltwaters flowing off the mountains subsided,

streams warmed rapidly in the sun.

And the surface of the water started to dance.

Rising water temperatures trigger mayflies to hatch in their millions.

These conditions are the starting pistol for an important event...

The arrival of cutthroat trout.

Many have spent the winter in Yellowstone's deep rivers and lakes,

but migrate upstream to feed on mayflies and spawn

in these shallow waters.

Every year, the arrival of these protein-rich fish creates a

feeding bonanza for river otters, mink,

bears and birds of prey, like eagles and osprey.

Over 20 different species of birds and mammals.

This year, the early snowmelt has given these predators a head start

to fatten up.

While summer temperatures have created a frenzy of activity

on the rivers, Yellowstone's low altitude grasslands

are eerily quiet.

'In spring, herds of elk and bison were feeding here,

'but they've moved on as the green vegetation withers in the heat.

'What the locals call "the brown-up" has begun.'

Over the course of just a few months, this ground has gone

from being covered in feet of snow to lush grass,

which has now scorched, died away and has very little nutrition.

So grazing animals like bison and elk need to move further up

the mountains in search of green shoots.

As the summer continues, the brown-up will creep higher.

Bison and elk must keep moving.

By July, bison have arrived at summer grazing grounds

on Yellowstone's high plateau.

This is the only time mature males and females come together

and herds can reach a thousand strong.

Scientists think this summer the bison will look

particularly impressive after an abundance of grazing

during a warm spring.

So Kate's gone to check out what kind of condition they're in.

Oh, my goodness!

What a magnificent beast.

The male bison at this time of year are truly just...

They are in their prime.

'Bulls have piled on up to 150kg of fat and muscle

'and now is their chance to start throwing that weight around.

'July is rutting season, when males duel for the right to mate.

'And this year's favourable conditions mean it will be fierce.

'The largest contenders could be tipping the scales

'at nearly a tonne.'

You may think, "Isn't it a little bit early for sex?

"I mean, you know, it's the summer, they should be chilling out."

But remember that bison are the first to give birth.

Think back to the spring, the first calves we saw,

they were bison calves.

'Female bison have one of the longest pregnancies here,

'lasting over nine months.

'So to time the birth of calves with the start of next spring...

'..these males need to get on with it.'

This male bison has found himself the perfect dust bath.

And, at various times throughout the day, he will roll in it,

he'll cover himself in dust, he'll pee in the dust

and roll in that.

Just to make sure that he smells as virile and ready for it as possible.

LOW GRUMBLE

'Wallowing in dust baths is a show of strength.

'Each male competes to churn up the biggest dust cloud

'and intimidate its rivals.

'But when two heavyweights won't back down, they go head-to-head.

Heavily-muscled necks and thick skulls covered in a mat of

dense hair help absorb the colossal forces of each collision.

Only the winner earns the right to mate.

This ensures the strongest genes will be passed on.

Whilst I've been following herds of prey animals on the plateau...

..our camera crews are at lower altitudes on the trail of

Yellowstone's top predator, the wolf.

Over 500 wolves roam across Greater Yellowstone.

The mild winter and spring caused many packs to go hungry

as the prey was well fed and could outrun the wolves.

In summer, the stakes are even higher because there are young pups

to feed.

In the south of Greater Yellowstone,

biologists have been studying one wolf pack that seems to be defying

the odds and thriving this year -

the Pinnacle Peak pack.

This photo was taken during an aerial survey.

It reveals the pack has 11 pups.

Unusually, two females have given birth this year -

a sign this pack is doing well.

All the adults take it in turns to hunt and return to the den sites

with meat for the pups.

But the elk that make up the majority of wolves' prey have moved

to higher grazing grounds.

The biologists have been observing how the pack finds enough food

for all 11 pups. They've directed wildlife cameraman

Charlie Hamilton James to an area where they've seen

remarkable behaviour.

They think the key to the wolves' success here could be down

to human activity.

See it?

I wonder if

she's going to let me get out.

I'm going to give it a go.

Bear with me on this.

-WHISPERS:

-Well, well, well, well, well!

How beautiful is that?

She can smell me. My scent is going straight ahead.

She knows I'm here.

She's not bothered at all.

In all his 20 years of filming,

Charlie has never been this close to a wild wolf.

This female is from the Pinnacle Peak pack.

And something has drawn her here.

The grass is still green

because it's been watered over the summer to improve grazing.

You can see all these sprinklers behind her.

Cos they're watering the grass,

it's created some amazing habitat for ground squirrels.

There's just tonnes of them.

A huge colony of grass-eating

Uinta ground squirrels is exploiting this artificial oasis.

Usually, by mid-July, the grass would be turning brown and inedible.

The squirrels would have started entering their burrows to hibernate,

but not here.

This female wolf has spotted the chance of an easy meal.

And it's closer to the pups than the large elk herds 20 miles away.

They need these ground squirrels cos they're tied to their territory.

They've got pups here, they can't go anywhere else,

so they have to find food around here...

..just to survive and keep those pups alive.

But catching these burrowing rodents is tricky.

They spend much of their time looking for danger,

balancing on their hind legs to see over the tall grass.

The squirrels also have a range of alarm calls for different threats.

SQUIRREL TRILLS

A trill means it's a ground-based predator.

SQUIRREL TRILLS

The entire colony dive for the safety of their burrows.

Look at that! She's on it. She's on one. She's on one. Oh!

This female is putting in a lot of work but without any reward.

Oh, there's another one. There we go! There's one running.

Ah! Where is it? Where is it? Where is it?

A long way off.

Another pack member may help turn the tables.

Wolves' real strength is when they hunt together.

There's another one.

There's another wolf!

I don't know which one to film now.

SQUIRRELS TRILL

The ground squirrels can't watch all three wolves at once.

And these newcomers are also trying a different hunting strategy

to outwit their quarry.

SQUIRREL SQUEAKS

There's a lot of activity and then they'll lie down.

And you think, well, why are they suddenly lying down?

Part of their hunting strategy is to lie down

and essentially just wait for the ground squirrels to come up to them,

you know, and they're sort of dozing and they're half asleep, and

a ground squirrel comes up and they just leap up and grab it.

It's working.

Even the original female is having more luck.

With animals, you get these peak moments of activity and they last

for a few days or a few weeks and then they're gone again.

It's incredibly lucky that we've been able to be here for this

particular period of peak activity.

I've never seen it before, I don't know if it'll ever happen again,

but it's amazing to witness it.

These wolves have used all their intelligence to exploit this situation.

The food will increase the pups' chance of survival.

And more wolves means a stronger pack next year.

It's early July and no rain has fallen this month

at the Snake River, where the beavers have their home.

This, combined with the early snow melt,

means that the river is running 20% below its average.

If the level of the beavers' main pond drops too low, it could expose

the entrance to their lodge, which is usually underwater.

And this would make them easy pickings for predators.

Jeff is watching them closely to see how they react.

Oh, look! Wow!

That's Mum.

And it looks like Mum has made an executive decision.

She's got one of the kits in her mouth.

She's heading towards the dam.

She's moving one of her kits out of the pond,

maybe to search for a new home.

This is incredible!

And there they go.

I'm going to go chase them.

Scientists have observed beaver families relocating,

but Jeff has never witnessed it in 20 years of studying them.

Out in the open, kits are vulnerable to predators like bald eagles.

It's a tense moment for Mum and her young.

Here they come.

The beaver family's territory is large,

with five dams and pools along this river.

She's going to crawl over this next dam.

After travelling more than 350 metres...

..and crossing three more dams...

..Jeff films the mum leading her kit up a small channel that comes off

the main river.

They're going to climb right up through this cascading stream...

..waddling up through the stones.

You can see that the beavers don't do quite so well on land,

especially with this river rock.

They do so much better in the water.

Unreal!

Never seen this, ever!

And there they go.

Later, at night, Jeff checks his camera in the lodge.

Let's see.

It reveals Mum has moved all the kits and the whole family has

abandoned their home.

Jeff is now on a mission to find out where the beavers have gone...

..if the kits survive and whether this huge gamble will pay off.

Whilst the low-lying rivers and grasslands are sweltering

in temperatures of nearly 30 degrees...

..2,000 metres up, Yellowstone peaks have a recent dusting of fresh snow.

And the mountain meadows are a riot of colour.

It is amazing, the contrast up here to down in the valley.

Down in the valley, summer has really taken grip -

the temperatures are quite high and the grass is starting to go brown.

But up here, 800 metres higher, it's a totally different story.

It's breezy, it's cool, and look at all these magnificent wild flowers!

Susan Marsh is a naturalist and she pays very close attention to these

high-altitude wild flowers.

Where most people see pretty petals,

Susan sees a living record of how this ecosystem is being affected

by this year's weather and the changing climate.

We've looked a lot at how animals can indicate

the state of how a year is progressing,

as far as the weather is concerned.

Are the plants just as valuable as indicators?

Yes. I think they are

and the one advantage

that they have, in my opinion,

is that they don't run off!

And they don't fly away.

-Very true.

-I can tell by how tall they are, first of all.

-Right.

-This one is fireweed.

And it, typically, in a really lush year, will grow head high.

-Wow!

-Even at this elevation.

These particular ones, you can see, are only a couple of feet tall.

-Yeah, yeah.

-To me that's an indication of heat and dryness.

The plant needs to set seed and it has a very short growing season,

so it's not going to waste its energy making a big, tall stalk,

or making great big leaves.

-Right.

-These leaves are small this year, smaller than usual.

Through these plants, Susan can chart this year's erratic weather

but can plants also indicate larger changes?

Everyone is talking about the fact that the climate is changing.

Is that something that is becoming evident in the plants?

It's typically on the mountain tops.

So that's above the tree line.

Above the trees, where there's rocks and wind and cold.

It's the coldest part of Yellowstone, above 3,000 metres,

where Susan is seeing the effects of climate change hit hard.

This is the alpine zone, a realm of high-altitude specialists.

But as temperatures keep getting warmer,

non-specialist plants are able to survive higher up the mountains

and they're invading this fragile zone.

Does it concern you that you are seeing

a march towards a very different climate

and, therefore, a very different ecosystem?

I think there will be some good and some bad,

depending on what species you are, as climate change continues.

But, yes, I don't want to lose the wildflower parts that I love.

I don't want to lose the alpine zone.

I don't want to see those go,

but I don't think I can stop it.

Climatologists studying Greater Yellowstone

have charted temperatures increasing

by nearly a fifth of a degree every decade.

This seemingly small change is having far-reaching consequences.

Across Yellowstone,

scientists are seeing how animals are being forced to adapt.

Even the most iconic species like the grizzly bear are being affected.

To find out what's going on,

Patrick has gone to the Gallatin mountain range

in the north-west of Greater Yellowstone.

I've come to meet our bear expert, Casey Anderson,

to see how one group of grizzly bears is coping,

as the changing climate threatens an important food source.

If you look up at this knob up here,

take a look at the trees just around the bottom of that.

Those are white bark pines.

Let's have a look.

That entire forest of white bark pine, ancient trees,

some of them are 300 years old,

they've all died in the last couple of years.

They're gone.

What's caused it to die off?

There's a pine beetle that's always existed up there,

but we've had these cold winters

that usually just killed most of the beetles,

but now, with climate change, those winters are not as harsh,

we're not having that beetle kill

that we're used to in the middle of the winter,

so the beetles are really starting to infest the forest.

Pine beetles are no bigger than grains of rice

but these small creatures cause big problems.

Not only do their young eat the trees' living tissue,

but they also introduce a destructive fungus.

Eventually, this combination kills the entire tree.

This is bad news for the animals

that rely upon the food and shelter this tree provides.

Towards the end of summer, as other food sources dry up,

these pine nuts usually provide vital protein for grizzlies.

One aerial survey revealed around 80% of mature white barked trees in

Greater Yellowstone show signs

of moderate-to-severe beetle infestation.

To survive, the bears must adapt

and Casey has witnessed some intriguing behaviour.

Grizzlies are leaving the wilderness

to congregate on this cattle ranch to feed.

What they are eating is this caraway root

that actually came in with livestock.

It's actually an introduced species not native to the area

and they're coming down here and taking advantage of it.

And all the bears in the area are starting to migrate towards this meadow

because there's not a lot of food out there in the summer but,

right here, this is like a bear buffet!

It's a race against time.

The bears must pile on enough fat

to see them through five months of hibernation.

While the root is at its most abundant in summer and autumn,

the grizzlies gorge throughout the night,

eating up to 20,000 calories in a single sitting.

As the day heats up,

the hot sun forces them back into the shady forest to rest.

But Casey and our mobile camera team

have seen two bears that are still out in the midday sun.

Hey, Casey, do you copy?

They're, like, totally tumbling around out there.

Well, they're little playful guys!

These two yearlings are orphans.

Unfortunately, their mum died last autumn but,

against the odds, they have turned up in this meadow.

I've joined Casey to see how they're doing.

Right here, there's two yearling grizzly cubs,

right out here, digging around.

Oh, yeah, right there.

They're still young and inexperienced.

Cubs usually stay with their mums for up to three and a half years

but, even with this protection,

almost a third won't survive in Yellowstone.

It's a miracle that these two

made it through an entire winter on their own.

Do you think that having one another

is one of the reasons why they've made it this far?

I think it's got to be one of the biggest reasons.

If they didn't have each other, I don't think there's any chance

that one of them would have survived.

They've got each other's back.

Whilst feeding on this working ranch,

there are lots of unusual sights and sounds.

But without a mum to teach them,

it's hard for the cubs to know what is and isn't dangerous.

You find yourself really worrying about them

because they don't have

that notorious Mama Grizzly looking out for them.

Yeah, they're looking a little bit nervous.

So they're looking at something over in the distance.

They've obviously sensed something in that direction.

I think that these two have probably been chased,

probably once a day, by something, whether it's another grizzly,

a pack of wolves, or even cattle.

Surprisingly, the dangers may not come from the ranchers

or their cattle.

Most have learned to live alongside their grizzly neighbours.

One of the biggest threats comes in the form of other bears

close by in the shade of the forests.

A big male grizzly, known as a boar, could kill and eat the cubs

but it looks like these two have found a way to avoid this danger.

The big boars and other bears are out at night

because when it's hot, like this,

most bears will not come out and dig,

because it just wears them out.

And as the sun comes up, they go back to the forest.

With these little guys, they're kind of on the opposite schedule.

When the danger goes away, it's time to eat.

Let's do it in the heat of the day when there's nobody else out here.

Where you don't have to worry about anything.

That's what they're doing and it's working for them.

It's an amazing strategy.

The two cubs are a fantastic indicator

of just how intelligent bears can be.

Even as climate change kills off the white bark pine,

the bears are adapting to exploit the opportunities.

With over 700 grizzlies in Greater Yellowstone,

the latest data suggests their population, for now, at least,

has remained stable.

Yellowstone hasn't reached its record temperature of 36 degrees

but climate data has revealed that July, this year,

was the seventh month in a row with above average temperatures.

The relentless heat

and the early thaw are a dangerous combination.

They may create perfect conditions...

..for wildfires.

In normal years, the snowmelt would come down off the mountains,

and it would hang around places, like this,

soaking into all this dead wood, but not this year.

What it did was come rushing off in a great torrent

into the rivers, into the streams, into the lakes

and it didn't have time to soak into all of this dead, dry wood.

So this is, basically, fuel for fires

and having so much dead, dry wood around

means that there is a danger this year

of bigger and more intense fires.

A single spark could set this landscape alight.

Every summer, an average of 26 wildfires

are started by lightning across Yellowstone National Park.

Our crews are out, following up on reports of wildfire.

Flames can reach heights of 50 metres, exceed 1,200 Celsius,

and rip through the landscape at up to 40mph.

By mid-August, the tinder-dry conditions

mean five major fires have taken hold,

and are raging across the region.

In the Beartooth Mountains is wildlife cameraman Jeff Hogan.

Oh, no, this is nuts!

He's filming a wildfire that's consuming a huge area of forest.

And it's headed straight towards the family of great grey owls

he's been following since spring.

This fire is huge, and it's raging.

It's right in the backyard of our great grey owl family.

This is really a threat.

So far, the chicks have done much better than expected.

There was only a 20% chance all three would make it out of the nest.

Oh, he's going to go, he's going to go.

Jump, jump!

Oh, wow!

Jeff thought their biggest challenges were over.

But now, he'll have to wait until the fire's died down

to see if these young owls survive.

Oh, my goodness.

The aftermath of a fire might seem devastating,

but it's actually part of the forest's natural cycle.

It brings growth and new life.

All this ash is actually really fertile

and as soon as it rains,

new green shoots are going to start popping up,

and that's going to encourage grazers like elk and deer

to come into this area and, eventually, grizzly bears.

But not only that, some plants have actually evolved

to benefit from fires. These here are lodgepole pine cones

and they only open up once they reach a specific temperature

that can only be produced by a fire

and then these seeds will eventually fall off,

down into the ground

and be fertilised by the ash.

Fires are a natural part of life here.

But by the time they die down,

they will have burnt nearly 100 square miles of land.

This year's fires will have been the most destructive

inside Yellowstone National Park since 1988.

Large-scale fires used to sweep through the park

around every 300 years.

But scientists now believe that the warming climate could result

in them happening every 3-5 years by the end of this century.

This could result in the destruction of the forest

that's home to the fragile population of great grey owls.

Jeff is searching the area at the edge of the burn

for any sign of the owl family.

There's a lot of ground to cover

so Jeff calls in expert animal tracker Dan Hartman.

After four days' searching,

Dan finally hears an adult great grey.

OWL CALLS

And close by, one of the young owls.

OWL CALLS CONTINUE

After another few minutes watching and listening,

he spots the other two siblings.

All of them have survived.

And they're even making their first attempt at hunting.

The owl chicks have all made it through their first summer,

but we still don't know the fate of the beaver mum and her three kits.

I've joined Jeff on a tributary of the Snake River,

where he's seen signs that the beavers are making a new home.

He thinks it's a safer location,

as the water level is higher than at their old pond.

Oh, look.

There's your beaver sitting there.

Oh, my... Is it that beaver there?

That's the beaver, right there.

This is just gold dust.

This looks like Mum.

And in the few weeks since moving, the family has been busy building.

That is a new lodge being built right now.

They just make a big pile of sticks,

then they go into it and start digging it up

and they'll pile mud and stuff up on top of it.

This is a lodge at its early stages.

This is rare.

Rarely do you see the very early stages of a whole new beaver pond

with a lodge like this.

They're concentrating on their dam,

strengthening it with rocks and plugging any leaks

with weeds and mud to create a deep, wide pond.

The water table here is rising so that they can reach out

and get more of this food, the trees that grow around here,

cotton woods, alders, willows.

The beavers can now access all this untapped food...

..without having to venture far onto dry land, where they are vulnerable.

'Finally, Jeff spots what we've both been hoping to see.'

-Oh, yeah.

-There's a young one.

-There's the young one.

-Yes, yes.

We've got our three young beavers right here, the three kits.

-They're getting big.

-They are.

They're getting big fast.

Mum's risky gamble appears to have paid off.

This deep pond with a new lodge and plenty of food

is everything the kits will need to thrive.

They are so inquisitive, aren't they?

And they're just...

They're just fabulous to watch.

The kits will stay with their parents for the next two years.

In that time, they'll learn the engineering skills needed

to build a dam and a lodge.

The secret to the beavers' success

is adapting the landscape to suit their needs.

It's engineering on a scale that has only been surpassed by humans.

Every year, the challenges in Yellowstone are getting greater,

as climate change results in more extreme weather.

Yellowstone's residents have developed

clever strategies to survive.

But the last animal I want to see

is quickly running out of options as temperatures rise.

I've come up to 3,000 metres and the fragile alpine zone.

Only one specialist mammal is active up here all year round -

the pika.

And Kaitlyn Hanley is the hardy researcher who studies them.

I've got glimpses of pika.

Are they a member of the rabbit family?

They call them rock rabbits.

-SQUEAKING

-Oh, there was one.

-A little call?

Yeah, that was a pika.

Come on, Kaitlyn.

-I want you to...

-He's right there.

Oh, my goodness, there he is!

Pikas are thought to have evolved from ancestors in Siberia -

one of the coldest places on Earth.

Their odd appearance is all about keeping warm.

A plump, round shape minimises surface heat loss

and thick fur covers their entire bodies,

even their toes.

For pikas, summer is all about collecting food.

I imagine that up here,

the season where there is any food at all is pretty short.

Yes, and they don't hibernate in the winter

so they actually collect hay through the entire summer.

And they'll use that as their food source during the winter.

-So that's what they're doing now?

-Yes, they are haying, yes.

They'll get these huge hay piles under the rocks

and they'll use that in the winter.

And, yeah, they're the only mammal that doesn't hibernate up this high.

And they can survive?

Cos the snow must come here, what, in October?

Yeah, so it would be October...

Through to?

March, May.

So, they've got a matter of months to collect enough hay

to get them through the whole of the winter.

Yes. They're busy little bees, that's for sure.

Pikas love a cool climate.

Just a few hours' exposure

to temperatures of 21 degrees can prove fatal.

So they can only exist in Yellowstone above 2,000 metres.

Soon, even here, they may have nowhere left to go.

Because these animals are such high alpine specialists,

they can't survive at the lower elevations.

Does that make them particularly vulnerable

-to things like climatic changes?

-Absolutely.

They are very sensitive to heat.

And so as climate change and the habitat changes for them,

they're going to move upslope.

You're already upslope at this point, you can't go any further.

And so, for the pika, you know, they don't have anywhere to move.

They're running into the sky.

Scientists have already seen pikas disappear

from one-third of their former strongholds

in warmer states to the south.

But Yellowstone's high country still provides sanctuary.

At least for now.

I have hope. I don't think we should lose hope.

Because they're too cute to go extinct!

That's one very good reason

we should all be there to save the pika

is they're just too cute to go extinct!

PIKA CALLS

The arrival of autumn marks the end of the great thaw.

We've seen how the dramatic seasonal changes

affected Yellowstone's wildlife.

The mild winter meant the wolves struggled

to hunt strong, well-fed prey.

And many went hungry.

WOLF HOWLS

But in the summer, they used their cunning

to find food and keep their pups alive.

The beavers survived the spring run-off

and were able to build an entirely new home to raise their three kits.

Our great grey owl runt beat all the odds

and fledged with its two siblings...

..giving this vulnerable population a much-needed boost.

The grizzly bears' race to fatten up started early

with the mild winter conditions.

The wet spring and early green-up revealed a bounty of food.

But by summer, they had to use all their resourcefulness to survive.

This has been a magical window into the lives of wildlife

in a truly spectacular landscape.

We've also seen a bigger picture unfold,

as scientists try to predict

what the future for Yellowstone will look like as the climate shifts.

I think what we do know is all of it's going to change

and it's changing pretty rapidly

and we don't really know how it's going to change.

There will be some good and some bad,

depending on what species you are, as climate change continues.

There are still many challenges ahead.

But if there's one thing that all of Yellowstone's animals share,

it's their incredible ability to adapt to extreme change.

And this will give them the best possible chance to survive,

whatever the future brings.