Original subtitles

[WHIMPERING, SNARLING]

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 melt water will dry out fast, food becomes scarce,

and if there's no rain,

wildfires will threaten to destroy the habitats animals rely on.

[SQUEAKS]

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 quiet lash 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.

ARYEE: Young animals born back in spring,

are now entering their first summer.

They are lot more mobile, but still need to avoid danger

whilst exploring on those unsteady lakes.

HUMBLE: For this latest generation, the changing climate

will make their lives even more challenging.

In spring,

the beaver family was affected by the unusually warm temperatures.

Huge volumes of melt water flooded into the Snake river

where the beavers had made their home in the south of Greater Yellowstone.

Snow melting from the 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.

ARYEE: Hey, Jeff.

HOGAN: Hey. ARYEE: How's it going?

Hey, there you are. How you doing?

ARYEE: 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.

[SQUEAKS]

I got something to show you. There's a bit of a surprise.

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

See, it's a couple of big fat beavers...

Yeah.

ARYEE: But then, something unexpected.

Oh! Oh, my gosh! [LAUGHS]

ARYEE: That's so adorable. HOGAN: That's a great shot.

-Oh, my goodness. No way. -That's amazing.

ARYEE: Oh, man, they're so adorable.

ARYEE: Baby beavers are called kits, and mum has given birth to three.

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

ARYEE: 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 the 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.

HOGAN: I got another clip for you.

ARYEE: Oh, look at all that willow.

This adult beaver just brought in three or four branches, all bundled up.

And that little young ones will just jump on this.

They'll gobble out right down.

ARYEE: At ten weeks old,

these kits has stopped drinking their mother's milk.

They now have an adult diet.

In summer, the ponds that 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 moat to 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.

HUMBLE: Across Yellowstone, our teams have been documenting signs

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

As icy melt waters flowing of 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 cut-throat 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 this 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 snow melt have given these predators

a head start to flatten up.

ARYEE: 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 is now scorched, died away,

and has a very little nutrition.

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

in search of green shoots.

ARYEE: 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.

Scientist think this summer, the bison will look particularly impressive,

after an abundance of grazing during the warm spring.

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

[GRUNTING]

HUMBLE: 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 150 kilograms 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 ton.

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, the 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 found himself the perfect dust bath.

And, at various times, throughout the day,

he will roll in it. He will 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.

[GRUNTING]

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 eleven 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.

[WHISPERING]

-See it? -[ENGINE STOPS]

Uh... How's she gonna let me get out?

I'm gonna give it a go.

Bear with me on this.

[DOOR OPENS SLOWLY]

How beautiful is that?

She can smell me, my scent is going straight at her.

She knows I'm here.

She's not bothered at all.

HUMBLE: 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 being watered over the summer to improve grazing.

[SNARLING]

You see the sprinklers behind her, 'cause they're watering the grass.

This creates amazing habitat for ground squirrels.

It's just tons of them.

HUMBLE: A huge colony of grass-eating winter 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 the 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.

[SQUIRREL SQUEAKS]

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

They 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.

HUMBLE: 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.

[SQUEAKING]

A trill means it's a ground based predator.

[SQUEAKING]

The entire colony dive for the safety of their burrows.

She's on it. She's on one. Oh!

HUMBLE: This female is putting in a lot of work,

but without any reward.

Oh, there's another one there again, there's one running.

Ah, where is it, where is it? Long way off.

HUMBLE: Another pack member may help turn the tables.

Wolves real strength is when they hunt together.

JAMES: There's another one. [LAUGHS]

Look, there's another wolf.

I don't know which one to film then.

[SQUEAKING]

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

And these new comers are also trying a different hunting strategy,

to outwit their quarry.

[SQUEAKS]

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

and you'll think, "Well, why are they suddenly lying down?"

It's part of their hunting strategy.

You just lie down, and essentially just wait for the ground squirrels

to come up to them.

You know, that's so dozing... A ground squirrels comes up,

and they just leap out and grab it. [LAUGHS]

HUMBLE: It's working.

[SQUEAKS]

Even the original female is having more luck.

JAMES: With animals, you get these peak moments of activity,

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

And 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.

HUMBLE: These wolves have used all their intelligence

to exploit this situation.

The food will increase the pups chance of survival.

[SQUEAKS]

And more wolves means a stronger pack next year.

ARYEE: It's early July,

and no rain has fallen this month at the Snake river,

but 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 under water.

And this would make them easy pickings for predators.

Jeff is watching them closely to see how they react.

HOGAN: Oh, look. Wow! That's mum.

ARYEE: 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.

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

maybe to search for a new home.

HOGAN: This is incredible.

And there they go.

I'm gonna go chase 'em.

ARYEE: 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.

ARYEE: The beaver family's territory is large,

with fives dams and pools along this river.

HOGAN: She's gonna crawl over this next dam.

[GRUNTS]

ARYEE: After travelling more than 350 metres,

and crossing three more dams,

Jeff films her mum leading her kit, up a small channel,

that comes off the main river.

They're gonna climb right up through this cascading stream,

waddling up through the stones...

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

especially this river rock.

They do so much better in the water.

Unreal, never seen this... Ever.

And there they go.

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

Let's see.

ARYEE: 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.

HUMBLE: 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, um, I think they are,

and the one advantage that they have, in my opinion,

is that they don't run off.

-HUMBLE: [LAUGHING] Yes, very true! -And they don't fly away.

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

-Right. -Uh, this one is fireweed.

-Okay. -And it typically,

in a really lush year, will grow head-high.

-Wow. -Even at this elevation.

And these particular ones, you can see, are only a couple feet tall.

-Yeah, yeah. -And, 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 gonna waste its energy making a big, tall stalk

-or making great, big leaves. -Right.

These leaves are small this year, smaller than usual.

HUMBLE: 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?

MARSH: It's typically on the mountaintops.

-So that's above the treeline? -Above the trees,

where there's rocks, and wind, and cold.

HUMBLE: 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'll 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 wild flower parks that I love.

I don't want to lose the alpine zone.

[BUZZING]

I don't want to see those go, but I don't think I can stop it.

HUMBLE: 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.

[GROWLING]

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.

ARYEE: 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...

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

-Those are white bark pine. -ARYEE: Let's have a look.

ANDERSON: 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.

ARYEE: What's caused it to die off?

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

but we've had these cold winters

that have 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.

ARYEE: Pine beetles are no bigger that 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 on 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 whitebark 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.

ANDERSON: What they're eating is this caraway root

that actually came in with the livestock.

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

and they're coming down 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.

ARYEE: 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.

MAN: [OVER RADIO] Hey, Casey, do you copy?

[BEARS GROWLING PLAYFULLY]

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

[LAUGHS] Well, little playful guys.

[BEARS GROWLING PLAYFULLY]

ARYEE: These two yearlings are orphans.

Unfortunately, their mum died last autumn.

But against the odds, they've turned up in this meadow.

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

Well, they're right here.

There's two yearling grizzly cubs right out here, digging around.

ARYEE: [WHISPERING] 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.

I mean, do you think that having one another

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

I think it's gotta 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've survived.

Yeah, they've got each other's back.

ARYEE: Whilst feeding on this working ranch,

there are lots of unusual sights and sounds.

[COWS MOOING]

[WHIPPING]

But without a mum to teach them,

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

ANDERSON: You find yourself really worrying about them

because they don't have that notorious mama grizzly

-looking out for 'em. -Mmm.

Yeah, they're looking a little bit nervous.

It's like they're looking at something

over in the distance.

ANDERSON: They obviously sense 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.

ARYEE: Surprisingly, the dangers may not come from the ranchers or their cattle.

Most have learnt 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

'cause when it's hot like this, most bears will not come out and dig

'cause it just wears 'em out.

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

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

The danger goes away, it's time to eat.

"Let's do it in the heat of the day when there's nothing else out here.

"We don't have to worry about anything."

And that's what they're doing, and it's working for 'em.

It's an amazing strategy.

ARYEE: The two cubs are a fantastic indicator

of just how intelligent bears can be.

Even as climate change kills off the whitebark pine,

the bears are adapting to exploit new opportunities.

With over 700 grizzlies in Greater Yellowstone,

the latest data suggests their population,

for now at least, has remained stable.

HUMBLE: 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 snow melt 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 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.

[THUNDER RUMBLING]

A single spark could set this landscape alight.

Every summer, an average of 26 wildfires are started by lightning

across Yellowstone National Park.

Our crew are out following up on reports of wildfire.

Flames can reach heights of 50 metres,

exceed 1,200 degrees Celsius,

and rip through the landscape at up to 14 miles per hour.

By mid-August, the tinder-dry conditions means five major fires have taken hold

and are raging across the region.

ARYEE: In the Beartooth Mountains

is wildlife cameraman Jeff Hogan.

Oh, no, this is nuts!

ARYEE: 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,

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

This is really a threat.

[SCREECHING]

ARYEE: 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.

[WHISPERING] Oh, he's gonna go, he's gonna go! Jump, jump!

Oh, wow!

ARYEE: Jeff thought their biggest challenges were over...

[FIRE CRACKLING]

...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 three to five 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 SCREECHING]

And close by, one of the young owls.

[SCREECHING]

After another few minutes watching and listening,

he spots the other two siblings.

[SCREECHING]

[SCREECHING]

All of them have survived.

[OWL SCREECHING]

And they're even making their first attempts 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.

[QUACKING]

HOGAN: Oh, look!

There's your beaver. It's sitting there by the stack.

ARYEE: Oh, my... It's that beaver there!

That's the beaver right there.

ARYEE: This is just gold dust.

This looks like mum,

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

HOGAN: 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 out,

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

This is a lodge at its early stages.

HOGAN: This is rare.

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

with a lodge like this.

ARYEE: 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, cottonwoods, alders, willows.

ARYEE: The beavers can now access all this untapped food

without having to venture far onto dry land where they're vulnerable.

HOGAN: [WHISPERING] There's a beaver right there!

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

-[WHISPERING] Running up there. -Oh, yes.

There's a new one!

-There's a young one. -Yes, yes, yes!

ARYEE: Whoa!

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

They're getting big.

-They are. -They're getting big, fast.

ARYEE: 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're 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.

HUMBLE: 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.

[CAMERA SHUTTER CLICKING]

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're called the "rock rabbits."

-[PIKA CALLING] -Oh, there was one.

-That was a call? -[LAUGHS] Yeah, that was a pika.

Come on, come on, Kaitlyn. I want you to scout...

There he is. He's right there!

HUMBLE: Oh, my goodness! There he is!

Pikas are thought to evolved from ancestors in Siberia,

one of the coldest places on Earth.

Their odd appearance is all about keeping warm.

[PIKA CALLING]

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's 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.

HUMBLE: So that's what they're doing now?

HANLEY: Yes, they're haying, yeah.

They'll get these huge hay piles under their rocks

and they'll that in the winter and eat.

-HUMBLE: Really? -Yeah, they're the only mammal

that doesn't hibernate up this high.

HUMBLE: And they can survive? HANLEY: Yes, they survive.

I mean, the snow must come here, what, in October?

Yes, it would be October most of the time.

-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?

HANLEY: Yes.

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

HUMBLE: 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.

[CALLING]

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 gonna move up-slope.

They're already up-slope at this point! You can't go any farther.

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

They're running into the sky.

HUMBLE: 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.

HANLEY: I have hope.

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

-[BOTH GIGGLING] -'Cause they're too cute to go extinct.

[BOTH LAUGHING]

That's one very good reason we should all be there to save the pika,

is that it's just too cute to go extinct!

[CALLING]

ARYEE: 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.

[HOWLING]

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.

[SCREECHING]

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.

HUMBLE: 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 gonna change,

and it's changing pretty rapidly,

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

There'll be some good and some bad depending on what species you are,

as climate change continues.

HUMBLE: There are still many challenges ahead,

but if there is 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.