All language subtitles for Yellowstone.Wildest.Winter.to.Blazing.Summer.E01.The.Wildest.Winter.720p.10bit.WEBRip.x265-budgetbits_track3_eng

I'll be following
some of the area's key wildlife.

We'll be getting to know families
through their highs and lows,

starting right now.

HUMBLE: And I'm looking
at the bigger picture,

understanding the science of the thaw
during each season,

across winter, spring and summer.

That's brilliant.

Living here is tough.

The changing climate
has brought freak storms,

flash floods

and raging fires,

making life for the animals
even more extreme.

With unprecedented access
to this remarkable place,

we're bringing you Yellowstone
as you've never seen it before.

Welcome to
Yellowstone: The Wildest Winter.

[WOLF HOWLING]

It's early March.

This is a world
blanketed in thick snow and ice.

And after four long,
hard months of winter,

the animals still have more weeks
of brutal cold to endure.

We're in the northwest of the USA,
2,000 metres up in the Rockies.

This is an area known
as the Greater Yellowstone Ecosystem.

It's the size of Scotland,
includes two national parks

and is bounded on three sides
by mountain ranges.

In this programme,

we'll be following the lives of animals
that have to adapt to extreme change

as winter turns into spring.

For many,
this is the ultimate challenge,

particularly for Yellowstone's biggest

and, at this time of year,
hungriest, carnivores.

Patrick's heading high up
into the mountains on their trail.

It's amazing to think that
somewhere out there are grizzly bears.

[BIRDS CHITTERING]

But it's right at the tail end of winter
and it's really cold,

so most of those bears
are still gonna be hibernating in dens

deep beneath the snow.

And for most,
that's a sensible strategy.

Right now, the weather is bitterly cold

and down to minus 21 degrees Celsius
up here.

It's usually later in March

that the majority of grizzlies
start coming out.

I'm in the Gallatin Mountains
in the northwest of Yellowstone.

[WIND HOWLING]

Our grizzly expert, Casey Anderson,
is out here monitoring bear activity.

-Hey, Casey. How're you doing, man?
-Good.

ARYEE: We're looking for any bears

that are emerging
from hibernation early.

And the most likely place to find them
is at the higher elevations

where grizzlies have their dens.

-Good view, huh?
-Absolutely stunning.

But it does look
completely devoid of life.

How're we even gonna start
looking for these bears?

You're right.
There's not much moving around out here.

Right now, the only bear that probably
will be out is those first big males.

ARYEE: Casey believes some grizzlies
are already leaving their dens

because of a recent spell
of unseasonably mild temperatures.

So, just a few days ago,
we had really warm weather,

and it felt like spring.

It's been so warm,

you've got to believe
the bears are thinking,

"It's getting close to spring."

And that can be really bad news,
'cause it's not spring.

And they come out here
and winter could hit again,

and that could really be devastating

to a lot of animals,
including the bears.

ARYEE: Last week, right here,
it was 15 degrees warmer than today.

Now it's back
to more typical March conditions.

-Oh.
-ANDERSON: Wow.

Casey, this weather's pretty... [COUGHS]

Whoo!

-This is pretty intense.
-That's intense.

How do the bears cope with this?

Bears are tough,
but this is difficult for them, too.

ARYEE: Suddenly, Casey sees an opening
that could be a bear den.

You see these natural rock formations.

-Yeah, it's like a little cave.
-Yeah.

ARYEE: It's perched
high on a steep slope.

ANDERSON: It's not easy-going.

ARYEE: The things I'll do for bears.

Would that be a good site
for a bear to hibernate in?

The statistics are this.

70% of bears
will dig in a north-faced slope.

At least 30% of this population
will do something else.

And "something else"
is something like this.

I mean, readymade, in the sun.

If they can get down in there
and trap the heat, it's perfect.

ARYEE: And it's not all one big sleep.

During hibernation,
the pregnant females also give birth.

ANDERSON: It's March now, and those
little guys were born two months ago.

[CHUCKLING] So, yeah, just imagine
these little guys, that big,

they're gonna grow to be
about that big in about another month.

And then, in another month from now,

they're gonna pop their heads out,
and this is going to be home.

And this is just amazing.
Think about that first view.

It's a pretty good one.

ARYEE: We head off
before we disturb any sleeping bears.

Emerging in these conditions
would mean the odds are against them.

And 50 miles further east,
that's exactly what's happened.

Scientists have tipped off
one of our camera teams

about a grizzly bear that
has taken the risk of emerging early.

It's clearly struggling.

The warmer weather of a week ago

has been followed
by plunging temperatures and more snow.

This could make finding food impossible.

The grizzly finally makes it down
from the mountains

to the valley floor.

There are plenty of bison here,

but even a starving bear
won't tackle these formidable beasts.

Bears rely heavily

on their extraordinary sense of smell
to find food.

Their nose bristles
with over a billion nerve cells.

It's their super sense.

And it's led this bear to a pond.

A dip in the sub-zero water
could zap his precious energy.

Grizzlies are superb at catching fish.

But it's not fish he's after.

It's a bison.

Long dead, frozen all winter,

and now released from its icy tomb.

This is probably the first meal
the bear's eaten in over four months.

It offers a huge protein hit.

But he'll need to hang on to it.

The carcass' smell attracts scavengers.

These coyotes won't fight the bear,

he's 15 times their weight,

but they will harass him for scraps.

[COYOTES YELPING]

He tries to mask its scent
by covering it with grass.

This will also
slow down the bison's decay.

Having lost up to a third
of his body weight during hibernation,

he's determined to keep
these precious nutrients for himself.

[CAWING]

Despite emerging from his den early,

this lone bear has hit the jackpot.

But the stakes are high,

and the majority of grizzlies
won't bother venturing out

until the consistent warm weather
of spring.

HUMBLE: But that still seems
a long way off.

The snow shows no sign of letting up.

All the animals here
face the same basic challenge,

finding enough food
to survive until spring.

Our crews are out across the region

to capture the stories
of how the wildlife is coping

in these last days of winter.

Yellowstone's elevated position
and horseshoe of mountains

channel and trap the cold air
driving in from the north

and moisture coming in
from the Pacific Ocean.

This leads to prolonged periods
of extreme weather.

When the snow melts in spring,

it feeds into a thousand rivers
and streams across Yellowstone.

These two-and-a-half thousand miles
of running water

are hugely important,
not just for Yellowstone,

but they provide an essential resource

for millions of people and animals
right across the western United States.

Scientists constantly monitor

how much snow is building up here
during the winter.

To understand what's going on this year,

I'm joining a team up in
the Beartooth Mountains in the northeast

on their cool commute to work.

This is possibly the best office
I've ever been to.

[LAUGHTER]

ZUKIEWICZ: This looks like
a pretty good spot.

HUMBLE: Wow.

It's right at about 205 centimetres.

HUMBLE: Okay.

HUMBLE: Lucas Zukiewicz
is one of the hydrologists

who spends the winter
carrying out health checks on the snow.

Our entire history of our snowpack,
starting mid-October,

is really in this snowpack here.

So we're gonna dig a hole
down to the ground

and it's pretty much the coolest
layer cake that you're ever gonna see.

HUMBLE: [LAUGHS] I love that.

I have a feeling
I might be here for months.

Right, okay, so...

HUMBLE: Yay! We've hit grass!

That is so cool.

I have to say, coming from a country
where, you know, if you get

four centimetres of snow,
it's newsworthy.

Look at that.

And to kind of understand
that that is a record of your winter.

-That's quite cool, isn't it?
-It's amazing.

And the best part of this job is,
it's never the same.

Every year is different.

It's like hitting the reset button
on it every year.

HUMBLE: So it's time for us to analyse
what the snowpack can tell us.

So, looking at it
from bottom to top here,

we're looking at a time series.

So we have our
early season October snowfall,

probably our Thanksgiving and
Christmas snowfall that we have here.

HUMBLE: You had a white Christmas?

We had a white Christmas this year.
It was great.

HUMBLE: Various measurements
enable Lucas and his team

to work out
how much snow is building up here,

and how dense it is.

The texture of it here
is completely different.

It feels much more compact.
Exactly as when we were digging it out.

The density reflects how much water is
contained in each layer of the snowpack,

and that varies depending
on the temperature when the snow fell.

Maybe we see some
pretty well-bonded snow in here,

which is generally
an indication of warm temperatures.

HUMBLE: Okay.

Warm temperatures actually
bond the snow pretty well together.

First of all,
we're gonna stick one right up here

on the surface of the snow.

HUMBLE: Measuring the temperature
is also key in helping to predict

when the bulk of the water
will flood down into the valleys.

And the next one at 170,

we're gonna stick that right below
that little crust layer that we saw.

HUMBLE: And these readings
also provide clues

as to why some mammals
hibernate deep in the snow.

ZUKIEWICZ: Stick it right in the ground.
HUMBLE: In the grass.

So we can see here
that our snow surface temperature...

ZUKIEWICZ: What does that one say?
HUMBLE: I would say, minus 8.

But as we move
further down in the snowpack?

-It's warmer.
-It's warmer. It's minus 3 degrees.

HUMBLE: That's mad.

Okay, and if we go
even closer to the ground...

It's almost on 0.

Yup. So the ground is generally close

to 0 degrees Celsius
through the winter.

So, the snowpack
is also insulating the soil.

But it also makes sense

when you look at something
like a grizzly bear

hibernating in the winter
beneath the snow.

I now understand why
it chooses to hibernate there.

Because it's warmer.

Snow caves are pretty warm.

That's brilliant.

This insulating effect not only
allows bears to hibernate in snow dens,

it keeps the grass alive,

vital food for herbivores.

And whilst it may look
just like a white wall,

we're actually looking
at an enormous reservoir.

When the weather warms up enough
to heat the snowpack right through,

billions of litres of water
run off the mountains

into the rivers and lakes
of Yellowstone.

Is the timing of the thaw
important for you?

It is. 'Cause it effects

when we see the bulk of the water

-move into our river systems.
-Right.

This is our reservoir
that we have in our mountains.

This is how we get our water.
This is how it flows through the park.

So do you think, when the thaw comes,

it's going to be a normal year
or an abnormal year?

ZUKIEWICZ: We're slightly below average

with the snowpack that we have here
in place at this elevation,

but really, it's gonna be
the next month or two

and the weather that we experience

that's gonna dictate what we see
this year in terms of our thaw

and how that impacts
the bigger ecosystem.

HUMBLE: It will be interesting to see
what happens in the coming weeks

as the weather has already
proved highly volatile this winter.

There was a jump in temperatures

and an unusually warm period
at the end of February.

March has now seen a return
to the colder,

more typical weather
for this time of year.

In recent years,

Yellowstone has experienced
milder winters more often,

and this one
appears to be following that trend.

Patrick has headed south

to see how
the temperature jumps this year

are affecting another iconic species.

[PANTING] Snow is a lot more complex
than it looks.

And for one animal, a bird of prey,

the precise depth and type of snow

can literally mean the difference
between life and death.

ARYEE: This is the great grey owl,

one of the largest owls in the world

with a wingspan
that stretches up to 1.5 metres.

It's a winter specialist.

It survives
in some of the coldest forests on Earth,

from Siberia to Scandinavia,

to here in northwest America.

Researchers believe

several hundred great grey owls
live in the Jackson Hole Valley,

all within 150 square miles of forest.

Our cameraman, Jeff Hogan,

has had a lifelong love affair
with this enigmatic bird.

I've been following and filming
the great grey owls

for just about 30 years now.

It's still just
as exciting and challenging

as it was the very first day.

So this is a fantastic place
for owls to be hanging out in.

I mean, it's mixed aspens
and conifer forest,

along with these meadows,
provide an incredible habitat

for the prey that the owl feeds upon.

ARYEE: Great greys feed on rodents,

mainly gophers and voles
that burrow under the snow.

Their huge facial discs
act like satellite dishes,

directing sound to their ears.

Their hearing is exceptional.

They can detect prey
from over 100 metres away

through snow almost half a metre deep.

But it's one thing
knowing where to pounce,

another to break through
to reach the meal.

Jeff is out looking for them.

He's concerned that
with the erratic weather conditions,

the owls face a big challenge.

HOGAN: Earlier this week,
we got a lot of snow.

And then the skies cleared.

So you can look around here

and see where the sun is beating down
on the surface of the snowpack,

and it really softens it up.

It doesn't melt it completely,
but it makes it really soft and wet.

And then at night,
when the temperatures plummet,

it'll freeze hard-like,
and turn it to ice.

And you can actually see
this layer of crust.

[CRUNCHING]

Boy, you can really feel that.

I mean, ouch.

This is hard.

And as the temperatures drop,
as night approaches,

this is gonna get harder and harder.

And these owls
have to bust through this crust

and then maybe another foot of snow
to get at their prey.

ARYEE: Jeff hasn't seen any great greys,

which could mean they've been
forced further afield to hunt.

So I guess I'm gonna
have to just keep on looking.

ARYEE: At this time of year,
eating enough food is critical.

If the great grey owls can't hunt,

they simply won't lay eggs
or even nest this season.

Their population
is already small and vulnerable.

Biologist Katherine Gura

is keen to see
how current snow conditions

might be impacting
the owl's ability to feed.

And that involves a simple experiment.

All right, Katherine,
you're stood out here with a ruler,

a metre-rule, and these flasks of water.

What do these have to do with owls?

So, this is about the same weight
as a great grey owl.

So what we're doing is dropping these

and we're seeing
how far they penetrate the snow,

because it in turn can show us
how easy or hard it is

for great grey owls to penetrate
the snow to get to their prey.

Right, Katherine, can I give you a hand?

-Absolutely.
-Okay, so what do I do?

So you want to drop that
from one metre above the snow.

-Okay.
-So that's right here.

-One metre? That's here?
-Yeah.

ARYEE: Okay,
so it hasn't really gone that far.

It's gone about, what, 17 centimetres.

With their prey often underneath
twice as much snow,

this is why
the owls are having trouble feeding.

Our concern is that it's changing
the timing of their behaviour.

So it there's not enough prey,

I mean, that's probably
going to spell disaster.

-Are you worried about that?
-I definitely am.

I've been working with these owls
for years,

I love watching them
throughout their nesting season

and it really concerns me if they're
not gonna be able to have enough prey

to even attempt to nest
or to eventually support their young.

ARYEE: This year,
with the tricky snow conditions,

the owls appear to be suffering.

To find out how
they're really getting on,

or indeed, if they're around at all,

Katherine needs
to conduct her survey at night.

The night-time call
of the great grey owl

is one of the early signs of spring,

and for scientists,
this is the first time

they'll be able to work out
exactly where they are,

what they're up to
and how they're doing.

If the great greys are going
to be successful in raising chicks,

they should be out there right now,

and we, hopefully,
should be able to hear them.

But the thing is,
this year, nothing is certain.

Jeff has also joined us.

He's hoping his luck finding owls
will change

under the cover of darkness.

The survey area
covers several square miles.

Now, my top speed in snow shoes
is half a mile per hour.

This could be a long night.

All right, this looks like a good spot
to stop and survey.

Okay, so what're we going to do?

So I'll do the male territorial call

and then we'll want to be
as quiet as possible

and we'll listen to see if one responds.

-All right, so, fingers crossed.
-Okay.

-Okay, now...
-I'll do my best.

[HOOTING]

-[OWL HOOTS]
-Yeah, that's it.

HOGAN: [WHISPERING]
I hear it. Yeah, this is great.

[HOOTING CONTINUES]

It's responding.

ARYEE: So is that probably a male?

GURA: So that's a male territorial call.
ARYEE: Right.

So they'll do that
either to attract a mate

and also to tell other males
that this is his zone, his territory.

Should I give it a go?

GURA: Mmm-hmm. You should try it.

[HOOTS]

No, that's too deep. [LAUGHS]

GURA: Let's see if he likes it.

[ARYEE HOOTING]

Mine's too manly.

GURA: You scared it off.
HOGAN: That's too big a racket.

You guys want to get beat up?

So really, given the conditions
that we're having this year,

this is a really good sign
that we can hear the great grey owls.

Mmm-hmm. I was definitely worried
with, kind of, the hard crust we've had,

that they might not be on territory yet,

but it's a good sign
that they're here and defending it.

[OWL HOOTING]

ARYEE: So there are males out there,
and they're defending their territory.

Given this year's unpredictable weather,
it's a promising sign.

Jeff and Katherine
will continue monitoring

and we'll be back to see
how the owls are getting on

later in the season.

HUMBLE: All across the region,
the challenge for much of the wildlife

is simply to hang on until spring.

It may appear that animals like bison

spend the winter
stoically struggling through the snow,

but there is a respite for some,

and it's thanks to a feature
that is synonymous with Yellowstone.

It's famed not just
for its landscapes and its wildlife,

but also for its geology.

Yellowstone has more geysers
than anywhere else.

In fact, 60% of all the geysers
in the world are here.

And the reason for that
is a giant magma chamber,

literally a pool,

a sort of lake of molten rock
sitting just below the Earth's crust,

literally right under my feet here.

Scientists believe
there's enough magma down below

to fill the Grand Canyon
more than 11 times.

And in west Yellowstone,

there's plenty of evidence
of all this geothermal activity.

Particularly with the dramatic geysers.

These hot springs intermittently
send fountains of water and steam

into the air.

It looks a fairly
inhospitable landscape,

but around 200 bison spend the winter
living and feeding here.

These bison are part of
what is known as "the central herd",

and they don't need
to work nearly so hard

to get at the vegetation
beneath the snow.

The earth here is warmed
by that magma chamber

bubbling away beneath the crust.

And that means there's far less snow

and the vegetation
is much easier to get at.

[LOWING]

But scientists have discovered

that these easy pickings
come at a high price.

The hot water pushing up
from deep underground

dissolves the chemical compound silica
from the volcanic rock

and deposits it on the grass.

Now, silica coats the vegetation
around geysers and hot springs,

and it's a little bit
like eating something

that has been covered
in a very fine dusting of ground glass.

It's enormously abrasive
and very, very tough on the teeth.

The other issue is the high levels
of fluoride in the water.

This chemical is a by-product
of historic volcanic eruptions.

In low doses, such as in toothpaste,
it's good for your teeth,

but here, it's so concentrated,

it actually softens,
rather than strengthens, the enamel.

Now, the combination of silica
and an excess of fluoride in their diet

means that the bison down here
lose their teeth significantly earlier

than the bison
up in the north of the park.

In fact, life expectancy
amongst this herd

is at least five years less.

So, although
these bison have an easier life

than their snowbound cousins,

it's definitely a much shorter one.

Finally, by mid-March,

other parts of Yellowstone
also get a reprieve from deep snow.

It's melting faster than it's falling.

Warmer air has come up from the south

and pushed out
the cold front in the north.

Daytime temperatures
rise above freezing,

unlocking the rivers.

And the animals make the most of it.

Underwater plants are more nutritious
than those beneath the snow

and are a vital food source
for this moose,

which needs to pile on the pounds fast.

This muskrat
is enjoying the vegetation too.

His double layer of waterproof fur
keeps him warm and dry,

even whilst eating on an icy platform.

And when he dives down,

his lips seal shut
behind his big rodent teeth,

so that he can gather food
without swallowing water.

Even a winter casualty is good news.

This elk carcass will sustain
many scavengers over the coming days.

And it may be here

thanks to Yellowstone's
most charismatic predator.

[WOLF HOWLING]

[GASPS] Oh, my God! Look at the wolf.

This is the most... [CHUCKLES]

This is the most incredible view.

And what becomes so evident
when you see a pack of wolves

running across snow like that

is just how perfectly adapted they are
as winter predators.

There are some things that,
in life, floor you,

and seeing a pack of wolves... [LAUGHS]

I'm completely,
completely overwhelmed by the sight.

To see what effect this year's thaw
is having on these animals,

I'm joining wolf biologist, Doug Smith.

We're on our way up a ridge on
Blacktail Butte in the Northern Range,

home to a pack of 11 individuals

that lay claim
to a territory of 250 square miles.

Doug and his team constantly
monitor the wolves in Yellowstone.

He's concerned that climate change
is having an impact on them.

They just ooze charisma, Doug.

HUMBLE: Even two kilometres away.

It's true.

SMITH: There's something enchanting
and mysterious about 'em

that has gone through the ages.

HUMBLE: Usually,
wolves thrive in the winter.

They're snow specialists.

Their feet fan out,

enabling them to run across deep snow
at over 25 miles an hour.

This gives them an advantage
over their prey, elk and bison,

which struggle with their cloven hooves.

Wolves generally have
even more of an edge in March,

when Yellowstone's herbivores
are weak and hungry.

[WOLVES GROWLING]

But this year is different.

By Yellowstone's extreme standards,

2016 has been one of
the mildest winters ever recorded.

Temperatures have fluctuated wildly,
but overall,

they've hovered three degrees
above the historic average.

A warmer winter is great for herbivores

as there's less snow
and they're less likely to die of cold.

But for their predators,
Yellowstone's wolves,

it can make life a lot more difficult.

Because this winter has been so mild,

do you think that that is going to
have a big impact on these wolves?

It certainly could.

I mean, hard winters
wear your prey down,

and that makes 'em
easier to kill for wolves.

A mild winter, the prey is
going to do a little bit better.

This winter was warmer
and below-average snowfall.

And it's early to tell
what the effect of that is.

But, um, we think that
wolf food consumption rates,

-kill-rates, are down because of that.
-Okay.

So these milder winters
favour the prey,

and so, does that mean fewer pups,
which leads to smaller packs?

This change in winter weather
could be a huge impact.

[WOLVES HOWLING]

HUMBLE: Wolf kill-rates
are down this year,

but our camera teams across the region
have caught some hunts on film.

Perhaps there will be clues

as to the problems
wolves are facing right now.

Talk me through what's going on here.

SMITH: I mean, that's classic
wolf-hunting behaviour.

What wolves are looking for
are behavioural cues

that indicate to them

-that there's a weak bison.
-Right.

But what's interesting is
the bison are staying in these areas

where there's either no snow
or little snow

because they've got firm footing
and they feel confident.

And so, what the wolves are doing
is trying to bump them into a place

that's more favourable to them,
i.e., deeper snow.

-This winter, there's less deep snow.
-Right.

SMITH: So, the wolves
are having a harder time.

Plus, these brown places
have fords for the bison to eat.

-So they're going to be healthier.
-Yeah.

SMITH: That's also bad for the wolves.

HUMBLE: The next hunt involves
the wolves' main winter prey, the elk.

Now, here's an elk encounter.
And this is even more dramatic.

This female elk is very healthy
and she's actually attacking the wolf,

-but she won't leave the dry ground.
-Yeah.

Classic example of the importance
of snow depth and footing.

Look at the elk.

A healthy elk will
always outrun a healthy wolf.

So, talking to the old-timers
who lived here in Yellowstone

during the 1960s and 1970s,

every winter was a deep-snow winter.

It was the rare winter
that was not much snow.

Now, it's the rare winter
where you have deep snow.

It's more common to have shallow snow,

and that's switching this balance
between predators and prey.

HUMBLE: With so few successful hunts,

scientists have noticed
that some of the wolves

are turning
to a summer feeding strategy.

Instead of working as a pack,
they're hunting alone,

digging into burrows
to catch small mammals.

It's much less rewarding,
much harder work,

and for this time of year,
definitely unusual.

The repercussions could be huge.

The female wolves
are pregnant right now,

and poor feeding
may lead to weaker pups.

We won't know until early summer.

It's the end of March.

The signs of spring
are getting stronger every day.

ANDERSON: Guess I weigh
more than a coyote.

HUMBLE: With temperatures warming,

many more grizzlies
are coming out of their dens.

Our bear expert, Casey Anderson,

is out searching for them
up in the Gallatin Mountains.

Sometimes, it's not that hard to
work out where they've passed through.

ANDERSON: Hey, look.

You can see right here,
it's just all, kind of, wore out.

You can see these little claw marks.

Well, sometimes,
when the bears come out of the den,

they can be a little mischievous.

And if you look right here,

one of the first stops the bear had made
was this snowmobile seat. [CHUCKLES]

Just rippin' and clawin' and bitin'.
Just playin', really.

It's part of living in grizzly country.

HUMBLE: It's never certain
when bears will emerge in Yellowstone,

but this year has been
more unpredictable than ever.

Well, it's been
really a strange year so far.

And the spring temperature's definitely
has gotten a few bears out early.

We know that one bear has gone down,

pulled that bison carcass
out of the pond.

That was a risk worth taking.

HUMBLE: But it was a risk.

Other early grizzlies
may not have been so lucky.

The adaptations
animals make in Yellowstone

to chime with
its extreme seasonal changes

are finely balanced

and in tune, not just with temperature
and degree of snow cover,

but also with length of day.

Right up here.

There's a long-tailed weasel.

He's running around right up here.

So, these long-tailed weasels,
as soon as spring actually is here,

they will turn brown,

and they'll be camouflaged
for the spring, summer and fall.

And winter comes again,
and they turn white just like this.

The fact that
he's still completely white

shows that it's very much winter.

HUMBLE: The change in colour
is triggered by hours of daylight,

not by temperature.

He won't turn brown until next month.

And just like the fox and the coyotes,

he's looking for all the rodents
that live underneath the snow cover.

He's just tunnelling down,

going and grabbing these things
and popping up and eatin' 'em.

HUMBLE: But whilst he's still white,

if the snow melts too quickly,
he'll lose his camouflage advantage

and could be at risk
from predators himself.

And one mammal
who would happily eat him is a fox.

You can see this
like a little story unfolding here.

This is a fox doing

what they're so good at
in the wintertime.

A bear's greatest sense
is their sense of smell

whereas a fox's greatest sense
is their sense of hearing.

And they literally hear a little rodent
way down in the snow.

They'll stop,

and you'll see they'll do this thing

where they pitch their head
side to side.

And what they're doing is
really triangulating and zoning in

at the exact location of that rodent.

And then they just do
this giant leap up in the air

and get this momentum with gravity
and just... Poof!

Right down through the snow
and grab that little guy.

He doesn't even know it's coming.

He thinks he's down there all protected,

and little does he know,
up there is a fox missile

coming straight down and getting him.

And look at that.
That's quite a ways down.

A little vole
is a pretty good snack for a fox,

whereas, for a bear, it's nothing.

And there's no way it could just survive
on voles alone through the winter,

so that's why they choose to hibernate.

There's just nothin' out here to eat

if you're a big, old,
bumbling-around bear.

ARYEE: Down in the south,

there's also still plenty of snow

in the forest habitat
of the great grey owl.

Cameraman Jeff Hogan

has been out night and day tracking them

to find out
whether they're breeding successfully.

[WHISPERING] Come on.

We have an owl.

ARYEE: Jeff's been hearing
and seeing the male owls consistently,

which is a reassuring sign.

He'd feared
they might have left the area

due to a lack of food.

Look at this setup here.

ARYEE: This year,
the issue has been icy snow.

It's prevented the great grey owls

snow-plunging deep enough
to catch their prey.

The owls each need
at least one rodent a day,

and if they don't eat enough now,
they just won't breed.

He didn't catch it either.

There's something
right here underneath him,

'cause he's back.

He's gonna make another attempt.

Oh, he jumped!

Oh, he's in the ground now.

I don't think he caught anything.

He just flew up with nothing.

I've been here since dawn
and he hasn't caught anything yet today.

ARYEE: It appears
the owls are still struggling.

Then, at last, a sign of hope.

A female arrives.

[OWL SHRIEKING]

This could get exciting.
We got two great greys right here.

Following one bird is pretty exciting,

but to have two birds...

It's amazing. It really is amazing.

Let's see what goes on.

Oh, here, he's flying in.

Oh...

Mating. Mating!

Oh, my.

I've never seen this before.

This is great news.

It's incredible. Absolutely incredible.

The end of March.

Courtship, mating.

Next step is nesting.

ARYEE: Eventually,
the pair choose to nest

on an old, broken spruce trunk.

How many eggs are laid

will depend on
how much food the owls consumed

earlier in the season.

On average, they lay four,

but this year, it could be less.

We'll be following them
to see what happens.

It's now April,
and the temperatures are warming up.

This is Jackson Lake in the Tetons,

and normally,
it would be frozen well into May,

but already the ice is breaking up.

The arrival of the melt

is a tipping point
for the wildlife of Yellowstone,

and this year,
after an extremely mild winter,

it's three weeks early.

At long last though, it's official.

Spring is here.

As the days get longer,
the sun is higher in the sky,

and its increased energy melts the snow
and raises daily temperatures.

Although there's still
snow on the ground,

the warming temperatures

are actually changing
the shape of the crystals

within the snowpack.

Now, they've turned
into tight, little balls

and there's a lot of water
in between them.

So the pack's become a lot slushier.

It's literally at melting point.

All this snow is just water in waiting.

Millions of tons will gradually melt,

flooding into the lakes and rivers
of northwest America.

It's a process
that will continue until July.

It's the valleys
that lose their snow first,

and then, finally, the mountain peaks
release their huge reservoir.

Soon, these warmer temperatures

will lure the last male grizzlies
out of hibernation.

And with the snow retreating,

plants, too, are bursting into life.

A nutritious feast for hungry bears.

Patrick's back in the Gallatin Mountains
with Casey Anderson

to find out why a top predator
sometimes chooses the vegetarian option.

ANDERSON: Look right here.

This is a biscuitroot.

ARYEE: This is a grizzly favourite.

Bears are omnivores.

They don't just survive on meat,

their diet also includes insects,
fungi and lots of vegetation.

Many bears time their emergence

to coincide with biscuitroot
coming into flower.

So that is what
they're looking for right there.

This bit of root at the bottom.

There're tons of calories in them.

So, how much biscuitroot
do they have to get through?

I've watched them eat hundreds,
if not thousands of these roots.

And what does it taste like?

You tell me.

[LAUGHS]

I was afraid you were gonna say that,
but I'm up to the challenge.

Bottoms up.

It's like carrots.

-Yeah?
-Yeah.

-Like, kind of, starchy carrot.
-Yeah.

To be honest with you,
whenever I'm hikin' around out here,

sometimes, I'll look in my backpack
and see what I have for lunch,

and I look on the ground, and I'm like,
"I'm gonna go grizzly style here,"

and start diggin' away.

ARYEE: As they put on weight
after the winter

and more grizzlies come out,

they begin
to communicate with each other.

Each male can have a home range
of over several hundred square miles,

and they need to work out
who else is out there on their patch.

So this...
This is an old backcountry camp in here.

People come up and camp from time
to time with a little tent over here.

And this old outhouse...

That tree right next to it,
it's the rub-tree

where these big males
will rub their back

and urinate all over the place
right by the outhouse.

-[LAUGHS] So, it's a bear toilet?
-It really is.

ANDERSON: You can look here.

There's these big claws right here.

And then look right here, Patrick,

where the sap stuck all the hair.

-Oh, yeah.
-Stuck to the tree all down to here.

ARYEE: So, all this here,

this is...

-ARYEE: Bear hair.
-Yeah.

So, what they do,
they come over and just...

Usually, come over
and put their back on the tree

and they,
they'll rub their scent all over,

and it gets really good,

and they reach up and grab like this
and they sometimes bite the tree,

and they drop down,
particularly the males,

and then they do this thing,
what I call "the cowboy walk".

So, they just stick it in
and twist their feet like this.

[ARYEE CHUCKLING]

Like, real rigid legs
and they just really twist...

So, each bear that comes to that tree
will step in that exact same spot.

And they do it over and over again

and it leaves
these big divots in the ground.

So if you're a smaller bear

and you're gonna have to
really reach for the next foot divot,

you know there's a bigger bear in town.

ARYEE: This is a well-known rub-tree.

We're setting up a camera to see
how many of the big males are out there.

-See this right here?
-Right.

It's gonna take a recording
and it's gonna text me to my cell phone.

-No way.
-Yeah, real-time.

So, as soon as a bear's there,
I'm getting a text.

So, hang on...
You're gonna get a text from a bear?

Exactly. That's exactly
what's gonna happen.

ARYEE: A few days later,

Casey's called me in
to look at the results.

ARYEE: All right, what have we got?

Let's take a look
and see what it's caught.

ANDERSON: Uh-oh.

[LAUGHTER]

ARYEE: That's just brilliant!

ANDERSON: That is an elk, a cow elk.

So this is something
that always happens.

You set up your camera trap,
and you think you got the right angle,

and then one of the animals comes along
and wants to change the angle.

[LAUGHS] Oh, man.

ARYEE: Hey, he's giving it a good go.

ANDERSON: I think it shows
their playfulness.

They come over,
it's something new, curious,

and then they come over and it's like...

"Yeah, I think I'm gonna
play a little soccer with it."

ARYEE: That's just great.

Let's just have a look
at a couple of the other clips.

ARYEE: Whoa! [LAUGHS]

ARYEE: First clip.
ANDERSON: Exactly what we wanted.

ARYEE: Wow!

ANDERSON: That's a big male. So...

I guess it's what
we would expect this time of year,

is that these big guys are gonna be
the first ones coming out of the den.

Females and the cubs are still up high.

Casey, Casey, this is a huge bear.

ANDERSON: Well, remember,
when we set this camera trap,

we were anticipating
we'd get the whole bear,

but he's bigger than that.

ARYEE: He stands at two and a half
metres tall.

ARYEE: He's giving it a real bear hug.

ANDERSON: That's a bear hug for sure.

Wow! And there he goes, doing that

kind of "cowboy walk"
you were talking about, right?

ANDERSON: He's really trying to
grind in a scent, leave those marks.

-That cowboy walk...
-[ARYEE LAUGHS]

That means one thing.
"I'm in town and I'm the boss."

But what are they picking up

and how do you think
that affects their behaviour?

ANDERSON: Well, as they emerge,
it's the beginning of the mating season.

So, it's important for males to know
if there's a bigger male around.

And he's like... [SNIFFING]

"Oh, this big dude's here.
Maybe I don't want to be here."

And they go the other way.

And equally, for the females,

they want to know who's going to be
the father of their next offspring,

and if there's any big,
tough guys around.

ARYEE: Although the unusual weather
a few weeks ago

had brought some of them
out of hibernation early,

these males appear fighting fit.

Spring is in the air,
and the bears are getting frisky.

But they're not the only males
getting boisterous.

These elk are shedding their antlers.

New ones will regrow
over the next few months,

ready for the autumn rutting season.

But perhaps the biggest male show-offs
are down in the south.

And Kate has a front-row seat
for their fabulous performance.

It's mating season for the sage-grouse,

and they really like to
make a proper song and dance about it.

[POPPING]

That sound...

It's really difficult to describe it.

It's like they're sort of,
popping and they're drumming.

[POPPING]

It's that combined with these wonderful,
very showy, puffed-up, white chests,

and those fanned-out black tail feathers

that will attract the females.

Oh, there's one. [GASPS]

And they will literally do a fly-pass.

They'll sort of fly over
and look down and go,

"Oh, yeah, no, I don't mind
the look of that one.

"Oh, I'll give that one a go."

Greater Yellowstone
is a stronghold for the sage-grouse,

a species under threat.

Once numbering tens of millions,

there are now just a few
hundred thousand of these birds left.

And many of them rely on Yellowstone,

where there's still
plenty of their habitat.

Sagebrush.

It's now under 11 degrees,
perfect for breeding.

But success will depend
on how the thaw progresses.

Chicks won't do well
if the temperatures soar too quickly.

So far, during the thaw,
some of our animals have done well,

and some haven't.

The jumping around in temperature
at the end of winter confused some bears

and made life difficult for the owls.

One of the mildest winters on record
and a lack of snow

prevented the wolves
hunting successfully.

Yet, the elk and bison
emerged from the season

in high numbers
and with plenty of fighting spirit.

Soon, this landscape will be transformed
from brown and barren

to lush and green.

But the arrival of spring
doesn't necessarily mean

that life will get easier
for our animal families.

All those new-born youngsters

will mean that there's
lots of competition for food,

and the predators will be ever-present

on the lookout
for the young and the vulnerable.