All language subtitles for Alaska A Year in the Wild Ch5 1080p EN SUB_Subtitles01.ENG

Alaska.

America's last frontier...

..and greatest wilderness.

Immense.

Unspoiled.

Awe-inspiring.

Home to half the world's glaciers...

..America's highest mountains...

..and ice sheets that stretch
to the North Pole.

Inhabited by the world's largest
land predators...

..herds of ancient beasts...

..and leviathans from the deep.

The land is hostile

but its richness and diversity
is unparalleled

in the northern hemisphere

All must be resilient and adaptable

if they're to survive a year
in the wild of Alaska.

Alaska is the largest
of America's 50 states.

It is seven times the size of the UK

but home to fewer than
a million people.

There are three million lakes...

..12,000 wild rivers

and 44,000 miles of coastline.

That's more than the rest
of the US combined.

It is the gateway to the Arctic.

Half a million square miles
of wilderness

that stretches from Canada
in the east

to Russia in the west.

Winter here is one of the harshest
anywhere.

Temperatures can plummet
to -60 degrees Celsius.

Snowfall measured in feet,
not inches.

And in the far north
the sun sets for two months,

casting a huge swathe
of the state into darkness.

The only light coming from
the Aurora Borealis.

Winter lasts seven months.

That's longer than spring,
summer and autumn combined.

Creatures must battle to avoid
starvation and predators.

To survive here is tough.

But Alaska has one of
the world's toughest.

Musk ox roam the Arctic tundra.

Vast treeless plains
where winters are long and brutal.

Out here they're exposed to the
worst that nature can throw at them.

But these conditions are nothing new
for musk ox...

..as they're relics
of the last great ice age.

They migrated here from Siberia
with giant bears and woolly mammoths

over 150,000 years ago.

The other giants went extinct.

Only musk ox survived.

Standing five feet at the shoulder

and weighing almost half a tonne,

they need a steady supply of food.

But there's a problem.

The Arctic blast has frozen
the snow solid,

trapping the vegetation below,

starving these giants
of vital nutrition.

MUSK OX GRUNTS

It's like digging through concrete.

Even their toughened hooves
are useless.

As hunger kicks in

they become irritable.

MUSK OX GRUNTS

Musk ox are naturally
jumpy and defensive.

MUSK OX GRUNTS

One is startled...

..and they bolt.

When musk ox sense danger,
they retreat to the high ground...

..where they close ranks.

..horns facing outwards,

prepared to fight off aggressors

such as Alaska's 11,000 wolves.

It's a defence strategy
that's helped them survive

two million years.

But this time it's a false alarm.

A waste of valuable energy

when food is in such short supply.

Many of the females are in
the early stages of pregnancy.

They must protect
their fat reserves...

..as it's only going to get colder

and birthing season is still
a massive six months away.

Musk ox are not the only ones
struggling to find food.

Harsh storms batter
the west coast...

..turning it into
a frozen wasteland.

Arctic foxes have evolved
to live out here.

They're one of Alaska's
most resilient creatures.

But even they're finding it hard
this year.

And they must compete
with the world's largest

and most formidable land predator.

Alaska in winter.

Temperatures drop low enough
to freeze the ocean...

..trapping many of the state's
2,500 islands in thick sea ice.

One of the most remote Alaskan
islands is St Lawrence,

which lies just 40 miles
off the Russian coast.

WIND HOWLS

Much of it is deserted.

Only scavengers are active.

BIRDS SQUAWK

Arctic foxes are well adapted
to live out here.

Each winter their coats
turn from brown to white

to help with camouflage

and double in length for warmth.

Their small squat bodies
and a thick layer of insulating fat

conserve heat.

Furry feet enable them walk on ice
and snow without sticking.

These adaptations help them
go longer between meals...

..which is vital if you live in
a place with so little to eat.

Throughout the winter
they're solitary

and travel great distances
to find food.

But in the right circumstances
they will gather.

The remains of a bowhead whale

that was killed by hunters
in the autumn

attracts foxes
from all over the island.

A feast like this will keep them fed
for months.

That's assuming they can get their
teeth into the frozen flesh.

And that it's not discovered by
the world's largest land carnivore.

Polar bears are most at home
on the Arctic sea ice.

They use it to travel huge distances
between islands and the mainland...

..and from where to hunt
their main prey...

..seals.

But they're also scavengers...

..and can smell food 20 miles away.

If one of Alaska's many polar bears
were to discover this carcass,

they would soon take possession.

Feeding quickly, the foxes
must remain constantly alert.

They'll need all the help
they can get

if they're to make it
through to spring.

Winter still has four months to run.

While freezing temperatures
grip the north...

..storms batter the south.

1,000 miles from St Lawrence Island,

in Alaska's south-east,

lies Glacier Bay.

This coastline is dominated
by an oceanic climate.

Winters here are warmer but no less
severe than in the north.

Wet, warm air blows in off the sea.

Rises...

..cools

and falls as snow.

More than seven feet every year.

BIRD SINGS

Over thousands of years,

much of this snow has thickened
to form glaciers.

Slow moving rivers of ice,

hundreds of feet thick...

..that carve steep sided valleys
out of solid rock...

..as they grind their way
down to sea level.

On the coastline,

higher temperatures stop
the streams freezing over...

..throwing a lifeline to one
of Alaska's most resilient

little birds.

The American dipper.

BIRD SINGS

Each winter, dippers leave
their frozen mountain streams

to feed on the coast.

Pushing her wings upwards
and outwards,

she quickly drops below the surface.

Dippers feed by diving down
to the riverbed...

..where they pick
amongst the debris...

..to disturb insects and fish.

She emerges with an insect larva,

splitting it open
by hitting it on the surface.

But it'll take more than scraps
like this

to keep her alive
through the winter.

She heads out to hunt
in open water.

And is rewarded with a fish.

Which she kills
by beating it against a rock.

She spends up to half the day
feeding

in water just a few degrees
above freezing.

So to keep well insulated
she preens her 4,000 feathers

and the thick layer of down
underneath...

..then fluffs up and squats down

to help keep her feet warm.

Before heading back to the sea
to do it all over again.

The mountains and valleys inland
from the dipper's stream

are cloaked in coniferous woodland.

Up here, heavy snow
continues to fall...

..carpeting the forest floor.

It makes it difficult
for Alaska's smaller animals

to forage on the ground.

To survive here you must be prepared
for the worst.

American red squirrels
are active all winter

and rely on food they cached
in the autumn.

Sitting on his favourite perch,

a male hungrily rips open
a spruce cone

to eat the energy-rich seeds inside.

He can get through 40 cones a day.

If he is to survive the winter, he
must have a cache of 10,000 cones.

Storing them is one thing,
keeping hold of them is another.

An intruder trespasses
on his territory.

He's got an eye on the cache.

He edges closer...

..but is spotted.

The territory owner warns him
by drumming.

DRUMMING NOISE

When that doesn't work,
he chases him off.

His hoard safe,
He quenches his thirst.

He has to be on constant alert if
he's to make it through to spring.

BIRDS SQUAWK

In a remote valley on the tundra,

1,000 miles north
of the squirrels...

..a group of Arctic specialists
has plenty to eat...

..regardless of the freezing
conditions.

Snowshoe hares rarely travel far
from their birthplace.

They feed on twigs, bark
and buds of stunted willow trees.

But despite their camouflage,

they're still vulnerable
to predators.

Lynx are Alaska's most skilful
and secretive hunters

and snowshoe hares
are their number one prey.

Late February and four months
into a brutal Alaskan winter.

But even out here
it's possible to thrive

if you've adapted to the conditions.

Snowshoe hares are perfectly
designed for life in the Arctic.

Their white coats
help them blend in.

Their huge back feet,
which give them their name,

let them move around easily
on top of the soft snow.

Essential, as hares are
the favourite prey

for one of Alaska's top predators.

Lynx.

They're stealth hunters
with incredible hearing,

excellent eyesight

and, like hares,

they have big furry paws
that act like snowshoes.

But hares have eyes
high on top of their heads,

giving them almost 360 degrees
of vision.

They also have acute hearing.

When one senses danger...

they bolt.

Four out of five lynx hunts
end in failure.

Hares are not the only Alaskan
animal to gain safety in numbers.

Back on St Lawrence Island,
100 miles off the Alaskan coast,

winter storms have buried the whale
carcass under six feet of snow...

..forcing the Arctic foxes
to dig deep.

But they can't stay down for long.

They take it in turns to keep
a look out for polar bears.

This group of ten foxes
may have travelled many miles

to join the feast.

FOX SNARLS

With the coast clear,
it's time for a clean up.

Scrubbing removes dried blood
and oil from their fur.

Fluffing-up traps air
and helps them keep warm.

Essential grooming
that could mean the difference

between life and death.

The sea ice surrounding St Lawrence
Island is now nearly six feet thick.

It stretches over 1,000 miles,

all the way to the North Pole.

This may look like a frozen desert

but there is life.

Ringed seals haul out on it
to warm up.

And polar bears roam across it
to hunt.

Each winter, polar bears fatten-up
by feeding on seals

ahead of the lean summer months.

The sea ice lets them
travel further,

giving them access to more prey.

Without the ice, polar bears
simply could not exist.

Thankfully for them
this winter is a cold one

and the sea ice will be here
for a few months yet.

Inland, the long winter
means ever-deepening snow.

Those animals not able to
dig through it

are forced to search further
and for longer.

WIND HOWLS

OX GRUNT

The musk ox herd has moved
to higher ground

where the wind-blown snow
lies thinner,

making access to food easier.

Up here, the wind chill
reduces the temperature

by a further ten degrees.

Musk ox have adapted to survive
such a battering.

Their massive bulk
helps them conserve heat.

Their fur is made up of two layers.

A long thick weather resistant
outer one

and a deep inner fleece.

Called qiviut, it's eight times
warmer than sheep's wool.

So little heat escapes

that their bodies can remain cloaked
in ice right through the winter.

OX GRUNTS

Access to food is essential...

..particularly for pregnant females.

The next three months will be
crucial both for them

and their unborn calves.

Especially as winter
tightens its grip.

Temperatures drop to
-30 degrees Celsius.

Ice crystals fill the air.

The longer winter drags on,

the more difficult it is for those
roaming the land in search of food.

Alaskan moose
are the world's largest.

At seven feet tall, they can
stretch up to ten feet high,

giving them access to nutritious
buds and young shoots.

MOOSE GRUNTS

During a long, harsh winter,

moose can't eat enough calories
to stay alive

so must rely on fat they put on
during summer and autumn.

If they use up these fat reserves,

they start consuming
their own muscle

and will quickly starve to death.

Young moose are particularly
vulnerable.

They allocate most of their food
to growth,

and come into winter
much leaner than the adults.

Many don't make it.

A scavenging magpie grabs
what it can of the frozen flesh.

The death of one animal
bringing life to another.

While it's still freezing
in the north,

in Alaska's south-east
temperatures are starting to rise.

Sediment-laden meltwater
pours from the land into the sea.

Strong winds and high tides
stir up the nutrients,

turning the Gulf of Alaska into one
of the most fertile bodies of water

on Earth.

It's incredibly rich in life.

Both above...

..and below the surface.

The shallow waters
along the edge of the bay

make this the perfect nursery
for young Pacific herring.

Called fingerlings,

they're only five inches long

and feed on microscopic plankton
that floats in the water.

For protection they form huge
schools of over a million fish.

And for good reason.

As the Gulf is home to Alaska's
biggest, most effective predator.

BIRDS SQUAWK

Late winter in the Gulf of Alaska.

BIRDS SQUAWK

Young Pacific herring
are under attack...

..from harbour seals...

..and steller sea lions.

In an attempt to avoid
the onslaught,

they head deep.

But are chased down.

In the confusion,
the herring are split up.

Some rushing back to the surface.

But even here, there's no respite.

BIRDS SQUAWK

As they're ambushed from above
by a raucous flock of sea birds.

But for the young herring,
the worst is yet to come

as they're now under attack from one
of the world's largest predators.

Humpback whales.

Every year, a small number
of humpbacks

overwinter in these waters.

They gorge on the shoals
of young herring.

Humpbacks hunt by diving deep,

then explode to the surface...

..their huge mouths gaping.

They devour thousands of herring
at a time.

WHALE SONG

Over the next few months,
their numbers will grow...

..as humpbacks from across
the Pacific Ocean

return to feed
in this quite unique bay.

EAGLE SCREECHES

An American bald eagle
is attracted by the commotion.

Bald eagles normally hunt
larger prey

but perhaps hungry
after the long, hard winter,

this one seizes the moment.

South-east Alaska
has around 20,000 bald eagles.

Roughly one-fifth
of the world population.

As winter draws to a close,
they return to their nest.

EAGLE SQUAWKS

Reunited with their
lifelong partners,

they quickly start re-building work.

This is the most challenging time
of the year for them.

Lower temperatures and bad weather
increase energy demands.

Shorter days reduce hunting time.

And with such a limited
breeding season,

it's going to be a battle
to raise a family.

Alaska in winter is one of the most
hostile places on Earth.

Food is scarce.

Conditions are brutal.

Only the fittest and best adapted
made it through.

With the northern hemisphere
swinging back round towards the sun,

life can once again flourish
in Alaska.

Next time, spring.

Migrants start to return.

Those animals that spent
the winter in hibernation

emerge hungry

having not eaten for eight months.

But spring in Alaska is short

and predators are many.

It's going to be tough
for both parents

and newborn.

Subtitles by Ericsson

Alaska.

America's last frontier...

MUSK OX GRUNTS

..and greatest wilderness.

BIRDS SQUAWK

Immense.

Unspoiled.

Awe-inspiring.

Home to half the world's glaciers...

..America's highest mountains...

..and ice sheets that stretch
to the North Pole.

ARCTIC FOX SQUEALS

Inhabited by the world's largest
land predators...

..herds of ancient beasts...

..and leviathans from the deep.

The land is hostile

but its richness and diversity
is unparalleled

in the northern hemisphere.

All must be resilient and adaptable

if they're to survive a year
in the wild of Alaska.

Alaska's been in winter's grip
for seven months.

Animals have scraped by...

..barely able to eke out a living.

Finally, there's a glimmer of hope.

Days are growing longer...

..and rising temperatures have
triggered one of the most dramatic

transformations on the continent.

The sea ice is melting.

The big break-up has begun.

By April, waves are back,

pounding the shore of Alaska's
largest northerly island.

St Lawrence lies 100 miles
from the Alaskan mainland

but shares a climate
with nearby Siberia.

It's bleak here...

..but not lifeless.

ARCTIC FOX SQUEALS

Five months ago, this female
Arctic fox was part of a group...

..kept alive by the frozen remains
of a whale carcass.

But now they've exhausted
every food cache

and this female needs a fresh
supply of meat more than ever.

ARCTIC FOX SQUEALS

Murres abandoned St Lawrence
in the autumn

when their feeding grounds
froze over.

Now they're returning in droves.

Around three million sea birds
nest here in the spring.

But this year there's a problem.

Access to the cliffs
is hindered by ice.

The murres will have to put
any plans for breeding on hold.

This delay is bad news
for the hungry fox.

It's mating season.

She's paired-up with a male and
due to give birth in seven weeks.

If she doesn't eat soon,

her body will reabsorb
her developing embryos.

A desperate act to preserve
every scrap of nutrition.

Salvation may be buried
under the snow.

Arctic foxes have such keen hearing,

they can find voles
even when they can't see them.

But voles are canny.

If they don't move,
the fox can't get a fix.

By paddling her hind feet,
she may panic them into moving.

But there's still a thick layer
of frozen snow to get through.

She needs a regular supply of voles
each day whilst she's pregnant.

It's a deadly game of hide-and-seek.

And right now...

..the voles are winning.

Whilst spring drags its heels
on St Lawrence...

..it's making headway
on the mainland.

It still drops below freezing
at night.

But there are only eight hours
of darkness.

Barely enough time
for the Aurora to shine.

Daybreak wipes the dazzling display
from the sky...

..and replaces it
with one on the ground.

GROUSE RATTLES ITS TAIL

Male sharp-tailed grouse
gather here each morning

for a ritual called a lek

so that females can choose
who to mate with.

And they're very fussy.

Only the fittest,
most attractive males will do.

GROUSE SQUAWKS

If he's to coax one down
from the aspen,

he needs to catch her eye.

Tricky when a younger male
wants to hog the limelight.

If he loses this spot, the hens
won't give him a second look.

He stands his ground

and it works.

Now he's got her attention.

Time to pull out all the stops.

He rattles his tail quills,

flashes his throat pouch

and throws in
some of his finest moves.

Proof that he's fit, healthy
and unencumbered by parasites.

But she's not convinced.

She always compares multiple males
before selecting a mate.

If he's to sire any chicks
this year,

he'll need to up his game
and try again tomorrow

Whilst grouse fight for the right
to produce this year's offspring,

500 miles away
in Katmai Wilderness Area,

some animals are already
raising theirs.

Female bears look after their young
for nearly three years.

This family is fresh
out of hibernation...

..and they're hungry.

When these twins were born
15 months ago,

they were blind, helpless and
weighed a little under a pound.

They're already eighty-times
their birth weight.

Big enough for a tussle.

But small enough to be vulnerable.

The beach is a good place
to find breakfast.

But it's also dangerous.

There are other hungry bears
out here.

And adult males will kill youngsters
they don't know.

They need to stick close to mum.

She's the only thing
keeping them alive.

It's May in Alaska.

The time when bears leave
their winter dens

in the Aleutian Mountains

and head to the coast to find food.

In spring, warm, wet air
blows over the sea,

cools

and casts a veil of fog
over Hallo Bay.

But it won't deter this brown bear
from teaching her twin

the art of clamming.

There's a lot to learn about
surviving in this wilderness.

Young bears must learn
where to find food

and how to harvest it.

Clams thrive here...

..but they're buried in the sand.

Bears have more scent receptors
than a bloodhound...

..so it's just a case
of sniffing them out.

Four-inch claws make light work
of digging...

..letting her guzzle hundreds
of clams at low tide.

Valuable extra protein for a bear
that hasn't eaten for months.

The cubs should be paying
attention

but seem more interested
in where the world's gone.

And with a milk bar so close,

it's hard to resist the easy option.

She's having none of it.

Maybe hunger will make them focus.

Almost 50% of bear cubs don't even
make it past their first birthday.

One of the reasons is wanderlust.

Cubs are keen to explore
every new sound and smell.

But it's easy to get lost
in the fog.

And bumping into the wrong bear
could be fatal.

Luckily, it's mum that looms
from the gloom first.

The twins must learn fast.

Or one day naivety will
get them killed.

Warm air from the Pacific
is opening up feeding-grounds

all along Alaska's
southern coastline.

350 miles east of Hallo Bay

lies the Copper River Delta.

The drainage basin for 24,000
square miles of Alaskan wilderness.

Meltwater bathes the mudflats
in minerals...

..feeding a habitat teeming
with marine invertebrates.

Food for hungry sandpipers.

The delta is a vital pit-stop for
almost five million shore birds...

..all racing to reach
their breeding grounds in the north.

BIRDS SQUAWK

Dunlins mingle with flocks
of western sandpipers.

Some have travelled from
as far away as Peru.

All have just two months
to find a mate,

lay eggs and raise a family.

They must refuel
as fast as possible.

There's still an 800-mile journey
ahead.

Slender bills with sensitive tips

help them find tiny worms
and molluscs.

Most feed for three days straight,

only stopping at high tide.

Only then will they have
enough energy

for the final leg of their trip.

It's not just migrant birds that
are in a rush to raise a family.

160 miles north of the delta...

..in a valley sheltered
by the Talkeetna Mountains...

..one of Alaska's permanent
residents must also act fast.

Arctic ground squirrels
sleep through the winter

in cosy burrows
lined with fur and lichen.

But now, according to
their body clocks,

it's time to rise and shine.

It's this male's first glimpse
of daylight for eight months

but he can't hang about.

SQUIRRELS SQUEALS

Noisy neighbours are popping up
everywhere.

Male squirrels emerge before females
to establish territories.

Firstly, rivals must be driven out.

Sometimes shouting's enough.

SQUIRREL SQUEALS

But when verbal warnings
aren't heeded,

things get physical.

By keeping rivals at bay,

he increases his chances
of meeting females.

And he'd rather be a lover
than a fighter.

At last, a female.

She'll only be receptive to mating
for four hours in any given year.

Get his timing wrong,

and he'll be painfully rejected.

Success.

He's at first base.

Now all he has to do
is keep an eye on her

and be patient.

He won't help raise his offspring.

But waiting for the right moment
to conceive them

is a chance to get to know
each other.

Every day, the sun has a little
longer to warm the ground.

Snow melts and rivers begin to flow.

Ice jostles and jerks its way
downstream.

Even in Alaska,
ice doesn't sit still forever.

As mountain streams thaw out,

American dippers move in.

There's plenty of food here
to feed their growing family.

But the creek's become flooded
with meltwater.

A gentle cascade
is now a raging torrent.

Their nest and the chicks inside

are in serious danger.

This American dipper spent winter
on the coast...

..where open water allowed her
to ride out the cold snap

on a diet of fish.

But every spring she returns
upstream to her favourite creek...

..to raise a family.

They've hatched four chicks.

But this year there's a problem.

The sudden thaw has flooded
the creek with meltwater.

She had nested on the edge of a
waterfall to keep predators at bay.

But now a tonne of water
crashes down every second.

A thick outer shell of moss
protects her chicks from the spray.

But access into the nest
is treacherous.

Only strong toes and a powerful grip

stop her sliding to oblivion.

Chicks need feeding
every four minutes,

keeping both parents very busy.

They scan the shallows
from their favourite boulder.

Highly oxygenated water
supports an abundance of bugs...

..which the dippers hunt,

either by snorkelling
in the gravel bed...

..or by diving for richer pickings
further down.

They hunt for an hour at a time,

making up to 35 feeding trips
between them.

To help them stay waterproof, they
spread oil from their preen gland

through their feathers...

..before taking the plunge again.

Dipper chicks stay in the nest

for longer than most other birds
their size.

They won't fledge until they're
almost fully developed.

That's over two weeks away.

And with the thaw still in progress,

the river will keep creeping
towards their nest.

1,000 miles north-west
of the dippers,

just outside the Arctic Circle,

rising temperatures
are both a blessing and a curse.

Musk ox still haven't shed
their thick winter coats

and they're feeling the heat.

MUSK OX GRUNTS

Resting on a windy ridge
helps a little.

Back in the depths of winter,

females were pregnant...

..food was scarce

and woolly coats were the only thing
that kept them alive.

Surviving until spring
has its own rewards.

After an eight-month pregnancy,

musk ox cows have given birth.

Calves are up on their feet
within hours of being born.

And for good reason.

They need to suckle
at least 20 times a day.

Mums use all their energy
for making milk

so there's none left
for growing a summer coat.

And until there is,
they can't shed their winter ones.

Any physical effort
gets them hot and bothered.

And calves caught dawdling
are given short shrift.

It may not feel like it now,

but this calf will find safety
in the herd.

Come winter,
they'll rely on the adults

not just for food and warmth

but for protection from
ravenous wolves as well.

If they're to survive,
best stick close to mum.

Whilst musk Ox calves
fatten-up in the north,

600 miles south,
on the Seward Peninsula,

there are new arrivals
of different kind.

Sandhill cranes,

fresh in from California.

Cruising at an average altitude
of 5,000 feet,

they've been riding the thermals
for over 2,000 miles.

Now, with their breeding ground
in sight,

they spiral back down to earth.

The breeding season starts as soon
as their feet touch the ground.

Cranes form lifelong partnerships

and nothing puts them in the mood
for mating more than a dance.

Youngsters head off
to do their own thing.

No-one wants to see dad dancing.

It starts with a wing stretch.

And once he's got her attention...

..it's time to dance.

It's not about how elegant you are.

It's about relaxing
and letting go of inhibitions.

CRANE SQUAWKS

Dancing strengthens the pair-bond.

If you can bust a good move,

you're also likely to have
the skills required

to drive predators away
from your nest.

MUSIC

CRANE SQUAWKS

MUSIC

They renew their commitment
to each other by singing.

Which may also stimulate ovulation.

CRANE SINGS

And after all that song and dance...

..mating is over
in under four seconds.

Sandhill cranes build their nest
on the ground,

which makes them vulnerable
to predators.

If they're to hatch any chicks,

these big birds will need to keep
a low profile

for the next 30 days.

Alaska is home to 30,000
brown bears.

2,000 of them live
in Katmai Wilderness Area.

Adults are normally solitary.

But in spring,

meadows brimming with sedge grass
draw them together.

Sedge contains a lot less protein
than meat or fish

so bears need to eat a lot of it
just to maintain their weight.

Regular naps aid digestion.

With the gathering comes an
opportunity to woo a mate.

Competing males try to give
each other space.

Submissive body language keeps
low-ranking bears out of trouble.

Any that don't read the signs

end up in a brawl.

BEARS GROWL

Young bears avoid trouble
by staying on the side lines.

These two are almost
three years old.

They've been nurtured by their
mother since they were born.

She's gone grazing with the other
bears on the meadow.

They don't know it yet

but she won't be coming back.

Two young bears have been abandoned
by their mother...

..and are now facing
life on their own.

She's been their teacher
and their comfort blanket

for the past three years.

But the time has come
to break up the family.

She has a new admirer.

He'll trail after her
until she's ready to mate...

..fighting any other bears
that get in the way.

There's no way her cubs will
get past 900 pounds of muscle

and escape with their lives.

They may have parted ways with mum,

but they've still got each other.

Which will help smooth the way

as they set-off on the road
to independence.

Their mother will be fertile
for up to 30 days.

Footloose and cub-free,

she may mate with several males
in that time.

If she has twins again,

it could be that each cub
has a different father.

But she won't know till spring...

..as her fertilised eggs
don't start to develop

until she's back in hibernation.

In that way, she can save raising
new cubs until next spring,

when there'll be plenty
of food about.

Other animals already have
hungry youngsters to feed.

And Eagle Beach,
700 miles east of the bears,

is the perfect place
to find baby food.

This male bald eagle
returns here every spring.

And not just for the hunting.

But because this is where
he's always raised his family.

He returned here three months ago
with his partner of 13 years.

Their nest survived
the winter gales

but was in need of some repair.

They quickly get it up to scratch

and today is a big day.

The female hatched her solitary egg
this morning...

..and by the sound of it
the chick's doing well.

EAGLE CHICK CHIRPS

For the next two weeks, the male
will do most of the hunting.

There are fish here,
if you know how to get them.

Sand lances hide in the sand
to escape predators at low tide.

Finding them is simple if you're as
clever and well-equipped as a raven.

Each fish is a high-fat,
high-energy snack.

Perfect food for eagle chicks too.

But this dad hasn't got the hang
of digging them up.

There is another way.

He looks to cash in
on the raven's success...

..and launches a raid.

In a split second...

..the raven loses half his catch.

One for him.

The rest he'll take back
to the nest.

The female spends most of the day
brooding her new hatchling,

but the return of her mate gives her
an opportunity to stretch her wings.

And a chance for him to feed
his progeny for the first time.

Last year's chick was weak
and died after only two days.

This one seems stronger.

But it will need feeding
at least eight times a day.

If this family are to avoid
another tragedy,

the next few weeks are critical.

Spring in Alaska arrived
with the melt...

..and triggered a season
of rapid transformation.

THUNDER

The race was on to start a family.

Sandhill cranes saw eggs
become chicks.

Dippers saw chicks
become fledglings.

Musk Ox calves survived
the school of hard knocks.

And two young bears
learned to cope without mum.

Spring saw many flourish

but did it all come too late
for the Arctic foxes

to raise a family of their own?

Next time, summer is coming...

..and new challenges begin.

Youngsters must grow up,

fatten up...

..and stay out of danger.

Summer is when the clock
starts ticking

and the countdown to winter begins.

Animals must make the most
of the good times

or it'll all be for nothing.

BIRDS CHIRP

Subtitles by Ericsson

Alaska. America's last frontier...

..and greatest wilderness.

Immense.

Unspoiled.

Awe-inspiring.

Home to half the world's glaciers...

..America's highest mountains...

..and ice sheets that stretch to
the North Pole.

Inhabited by the world's largest
land predators...

..herds of ancient
beasts..

and leviathans from the deep.

The land is hostile, but its
richness and diversity

is unparalleled in the northern
hemisphere.

All must be resilient
and adaptable if they're to survive

a year in the wild of Alaska.

Summer has arrived.

With the northern hemisphere tilted
towards the sun...

..days are long, the air is
warm...

..and snow has been banished
from all but the highest peaks.

The far north is bathed in gold,
even at midnight.

BIRD SQUAWKS

But things are about to
change.

Animals are in a race
against time.

What they do now,

could mean the difference between
life and death

when snow and ice return.

The ebb and flow of the
seasons is mirrored on the coast of

Katmai every day.

Where three million acres of
wilderness meets

the Pacific Ocean in a deep
crescent known as Hallo Bay.

Here, tides rise and fall for
seven sandy miles.

Leaving opportunity for
brown bears in their wake.

It's rare for a mother bear, to
bring cubs so small to the bay.

But she's hungry... and combs the
beach for food.

Her cubs are just six months old
and more used to the safety of their

den than wide open spaces.

Everything out here is new...

EAGLE SQUAWKS

..and very scary.

Bald eagles aren't a threat but
there are good reasons to be jumpy.

Many brown bear cubs die in
their first year.

And many are
killed by other bears.

Right now the coast is clear.

It's a chance for

this female to tackle the other big
cub killer... malnutrition.

So far mum's milk has provided her
cubs with all of their nutrients.

But a recent growth spurt has
fuelled an urge to try solid food.

Crabs, clams, almost anything will
do.

But the search is futile.

The cubs do their best to help.

They're learning fast,
but they're hungry.

What this family
need is a feast of epic

proportions.

And there's one heading
their way.

Over 300 million salmon
are coming home...

..to spawn in the same rivers that
they were hatched in.

Once they hit
shore and head upstream many will

become food for bears.

But there's
no telling when they'll arrive.

Until then food is scarce. And this
family will grow weaker by the day.

700 miles north-west of
here and just 40 miles off the

Russian coast summer visitors to
St Lawrence Island have

already arrived.

Every year, over three million
auklets nest in colonies

along the coast.

They look for a
suitable spot to lay a single egg.

Unaware that there are predators
waiting.

It's midsummer in Alaska.

And on St Lawrence Island, an
arctic fox is on the prowl.

The coast is alive with
the clack and clamour of over

three million auklets.

It's just what he's
been waiting for.

St Lawrence is smothered in snow for
almost eight months a year.

With auklets absent, food is hard to
come by.

If there's nothing to scavenge

foxes are forced to hunt for voles
under the snow.

It's a great deal of
effort, for very little reward.

But now auk is back on the menu.

And he has a new camouflaged coat to
hunt them in.

Eggs are good. But an adult
bird is even better.

His mate is
pregnant and she needs a regular

supply of protein.

They can't rely
on speed in this terrain.

Only stealth will net them a meal.

But there are eyes everywhere.

And when a few birds panic, it
sets-off a chain reaction.

Once their chicks hatch, the auklets
won't be going anywhere.

FOX CALLS

The foxes need to bide
their time...

..keep their distance...

..and wait for the auklets to
settle in.

Alaska has over half a million
square miles of wilderness.

It's big enough to fit two
Great Britain's in, end to end.

One thousand miles south-east of St
Lawrence Island

on the pacific coast of
south-east Alaska...

..summer is in full swing.

Warm air frees billions
of gallons of water from glaciers.

Feeding a multitude of rivers and
lakes.

There's more wood here than
in any other forest on Earth.

Good news for a family of beavers.

Yearlings help their parents with
chores.

This family has enjoyed a
surplus of food all summer.

But now, they must prepare for lean
times ahead.

They harvest as many green
sprigs as they can...

..ferry them across the pond...

..dive, and store
them underwater.

Down here, they'll
stay fresh. Providing food, even

when the pond is frozen over.

Bigger branches are used to
reinforce the lodge.

This is their fortress. And
it needs to be strong enough to keep

predators out.

Beavers rely on deep
water for safety.

So, to ensure there's always plenty
of it they build dams.

The rush of water is
like an alarm bell to a beaver.

Holes must be plugged up.

Timber is gathered from the
surrounding forest.

And by clearing forest, they
create new habitat.

Grass grows in patches of light
where trees once stood.

Providing Sitka deer with
tender stems to nibble on.

Pollarded willow put out new shoots
within easy reach of a porcupine.

She can devour up to a pound of
leaves every day.

But not all beneficiaries of

the beavers' building work are so
benign.

Black bears also forage here.

Plants make up the bulk of
their diet. But the scent of beaver

could prove too good to ignore.

Forays onto land are unavoidable.

The further they go, the bigger the
risk.

But beaver security is always
on high alert.

The alpha female
sounds the alarm...

..and sends every beaver within
earshot bolting back to the water.

Soon, it's like they
were never there at all.

Black bears
prefer to eat meat, but they have

plenty of other options.

Unlike the bigger brown bear, they
evolved in these forests.

Their ancestors were
consummate climbers.

And it's a skill that's been handed
down.

Cubs can climb as soon as they can
walk.

It gives them access to forage that
other animals can't reach.

Come autumn, there'll be a glut of
nuts and berries to choose from.

Until then, aspen pods will curb
their hunger pangs.

If they can keep hold of them.

It's only a snack. But mum
knows where more

emergency rations are.

She'll need to make full use of
this forest if her cubs are going

to make it through until autumn.

About 17 million acres of forest
cloaks Alaska's southern coast.

Where over 60 inches of
rain fall annually.

Many plants are
green here, all year round.

But summer adds a splash of colour
to the undergrowth.

Plants take advantage of the long
days...

..and burst into bloom.

Drawing in pollinators, from both
near... and far.

At just three inches long and
weighing little more than a penny

this female rufous hummingbird has

flown over 3,000 miles from
Mexico to nest in south-east Alaska.

No other hummingbird breeds this far
north.

Males play no part in raising
their young.

She's raised this
chick all on her own.

Hatched from an egg the size of a
jelly bean

in just three weeks she's already
outgrown the nest.

They require more than their own
body weight in nectar each day.

And if this chick is to
fledge successfully, the next

24 hours are critical.

It's July in Alaska...

..and the forest resonates with the
drone of tiny wings.

Rufous hummingbirds must soon
depart for their wintering grounds

in Mexico.

But the trip of almost
3,000 miles can't begin...

..until this year's youngsters have
fledged.

By beating her wings at up

to 60 times a second, a chick
warms up for her maiden flight...

..whilst her mother hunts for more
fuel.

Nectar is a precious
resource...

..that other hummingbirds aren't
always willing to share.

But this mum has a cunning plan.

There are sapsuckers nearby.

They're also busy
raising chicks.

Adults drill into
trees, to release sap which they

lap-up... along with any insects
stuck in it.

It's rocket fuel for
growing chicks.

So when no-one's looking...

..the hummingbird launches a raid.

She must drain as many wells as she
can, before the sapsucker returns.

Hovering takes the youngsters
a little while to master.

But in order to fledge she just has
to manage a straight line.

The chick has a few more weeks to
strengthen her flight muscles...

..before she flies all the

way to Mexico on her own.

At the end of July,
summer turns a corner.

South-west Alaska loses half an hour
of sunlight every week.

Temperatures plateau...

..and start to drop off.

Animals sense the change.

Bear cubs are born with
very little fat.

But they need a thick layer of it
in order to survive hibernation.

Their mum's milk is rich but it's
not enough on its own.

The whole family
needs solid food.

Their fate, and

the fate of all brown bears in
Katmai, depends on the salmon.

Pacific salmon make one of the most
incredible journeys on Earth.

Every year, over 300 million
of them

head towards Alaska's shores.

Often travelling thousands of miles
to spawn in one of 12,000

wild rivers.

The salmon must find the one that
will lead them to their birthplace.

With a coastline that
stretches for 40,000 miles

their journey demands stamina
and remarkable navigation skills.

Predicting where they'll turn up
first is impossible.

All the bears can do is wait.

Mum checks for signs
but there's barely a ripple.

Her cubs are eager to play.

But their mum has put all her spare
energy into making milk.

For her, the
salmon run can't come soon enough.

But instead, her worst nightmare
arrives.

A big, hungry male.

He won't catch anything here.

And he's a real danger to the cubs.

It's rare but when males are
under pressure they can resort

to cannibalism.

She'll protect her cubs furiously.

But there's no fish worth
fighting for here.

Better to be of
sight and out of mind.

In summer bears leave their
favourite stomping grounds

and move towards shallow creeks,
where salmon will be easy to catch.

Leaving much of Katmai
deserted.

Solitude is what this mum needs.

The cubs learn by copying her.

She checks for danger.
And so do they.

There are no bears here...

..but she catches wind of something.

All she has to do is track it down.

The cubs sense her excitement.

Finally, it's a salmon.

The first the cubs have ever seen.

Self-preservation kicks in.

Fish like this provide essential

energy that bear cubs can convert
into fat.

One fish won't feed a family of
four.

But nearby, there's a sign
that it could be the first of many.

Just 100 miles from here,

but on the other side of the
Alaska Peninsula lies Bristol Bay...

..where a deadly combination of high
winds and high tide has left

an early run of salmon stranded.

Whimbrels are first
to discover the bounty.

Tender fish

is an easy treat for birds more used
to probing the sand for crustaceans.

Further up the bluff is a colony of
Arctic ground squirrels.

Most females have pups.

They're over six weeks old, fully
weaned and can't

rely on mum for food any more.

But they must double their weight
or they won't survive hibernation.

Males gather grass to stockpile in
their burrows...

..whilst youngsters munch through as
much seed as they can.

Nothing is wasted.

Even the skin of a dead relative is
valuable extra protein.

They don't like to wander too far
from their boltholes...

..but they can smell fish in the
air.

It's an opportunity too good
to miss.

They need to build-up their
fat reserves...

..and oily fish has a
lot more calories than grass seed.

Come autumn, young females will

settle down to sleep with their
mothers.

But young males must first
find a territory of their own.

They're going to need all the energy
they can muster.

And only the
fittest squirrels will survive.

Whilst a twist of fate has landed
the squirrels with welcome feast...

..it's nothing compared to what's
just arrived over 800 miles

away on the other side of the gulf.

After four years out in the open
ocean

thousands of Chum salmon have
finally

arrived in south-east Alaska.

Nothing will stop them now.

Their spawning ground
is in the mouth of a river,

just beyond the high-tide line.

They don't waste any time.

Each female makes a small
pit in the gravel...

..where she'll lay up to
4,000 eggs.

Once they've been fertilised...

..she covers them over...

..and stands guard
until she's too weak to continue.

A voyage that's all about life, ends
in the death of the salmon.

As soon as they enter
freshwater, salmon stop eating.

Their stomachs slowly disintegrate.

GULL SQUAWKS

And they finally succumb to the
inevitable.

All the gulls have to do is wait.

Whilst the journey is over
for some travellers

for others, the
advance continues upstream.

Pink salmon spawn further inland...

..where predators lurk, ready to
pounce.

It's the end of July...

..and a big wave
of salmon has just hit Alaska.

Thousands of fish fight their way

upstream, driven by an irresistible

urge to reach their spawning
grounds.

This is what brown bears
have been waiting for.

It may be this adolescent's first
season away from his mum.

The perfect opportunity to
hone his hunting skills...

..and take
advantage of the glut of food.

But his lack of experience quickly
shows.

Many young bears copy their
mother's fishing methods.

In his case it's the dash, splash
and grab technique.

It's one he's yet to master.

Perhaps gaining some height
will help?

Apparently not.

The snorkelling method is another
way to catch a salmon.

Especially when
they're in such large numbers.

But seeing them is one thing.

Catching them is another.

The deep water isn't helping. It
gives the salmon an easy getaway.

Eventually he spots
a carcass floating downstream...

..only to discover that the best
bits have already been eaten.

He craves fat...

..and the fattiest bits on a salmon
are the skin, brain and eggs.

With so much food about, anything
substandard is quickly rejected.

Eventually perseverance pays off...

..and he nets himself a large female
pink salmon.

Flush with success he
goes for another...

..and almost loses the first.

Perhaps he should learn
to finish what's on his plate,

before going in for seconds.

Summer arrived with the auks...

..and filled Alaska with light...

..warmth and improving prospects.

It was a season
rife with possibilities.

Where hard work and persistence paid
dividends.

And where the death of one
generation brought hope to another.

But now, change is in the air.

Autumn is coming.

Next time...

The salmon season goes into
overdrive.

And animals battle it out
for a share of the spoils.

Young must come of age before
winter puts Alaska in lockdown.

With freezing temperatures
imminent it's do or die for many

predators... including the biggest
killer of all.

Subtitles by Ericsson

Alaska.

America's last frontier...

..and greatest wilderness.

Immense.

Unspoiled.

Awe-inspiring.

Home to half the world's glaciers,

America's highest mountains

and ice sheets that stretch
to the North Pole.

Inhabited by the world's largest
land predators,

herds of ancient beasts

and leviathans from the deep.

The land is hostile,

but its richness and diversity

is unparalleled
in the northern hemisphere.

All must be resilient and adaptable

if they're to survive a year
in the wild of Alaska.

Autumn is the season
when Alaska's wildlife

must make the final preparations
before winter.

Summer saw the groundwork done
by the adults.

Time is now running out
for the youngsters.

Days are growing short.

Snow and freezing temperatures
are imminent.

Many young must soon
start their lives alone.

Those not prepared will perish.

Nowhere is the struggle for survival
more apparent

than in the
Katmai Wilderness Area.

Three million acres of wildness.

Home to the highest density
of brown bears in the world.

They're here to gorge
on the millions of salmon

that are coming to the end
of their epic migration.

A journey that takes them back
to the very same

rivers where they were born.

Having travelled thousands of miles
to spawn,

the final leg is by far
the most dangerous.

Brown bears need to build up a thick
layer of fat for hibernation.

The salmon are their salvation.

Competition is fierce.

But the salmon don't only
attract bears.

Katmai is also home
to American Wolves.

This adult female finds a good spot.

And starts to hunt.

But the salmon
are too quick for her.

Then she gets company.

A mother bear is also actively
hunting the same stretch of river.

Never stand in the way
of a mother bear...

..especially one with two hungry
cubs to feed.

The wolf may also have young.

She can't risk getting injured
in a fight...

..so reluctantly gives up her spot.

Back in the spring,

these two cubs emerged from
hibernation.

They scraped by on a diet of clams
and milk.

If they're going to survive winter,
they must start

packing on the pounds.

Their mother replaces the wolf
on the bank.

One lunge and she does
what the wolf couldn't.

The lump on the salmon's back
identifies it

as a male Humpy, or pink.

She quickly devours it
without sharing

and moves on,

the cubs dragging along behind...

..leaving the wolf to pick up
the scraps.

She now wants to fish the prime spot
at the river mouth.

But it's taken

by a 1.000 lb male,

over 200 lbs heavier than her.

Upstream, the river is deeper,
making fishing near impossible.

She must feed the cubs...

so puts herself in danger.

A growl

and a charge...

..but he's not budging.

Undeterred, she grabs a fish...

..which draws in the big male.

Fortunately, there's plenty of fatty
salmon in the river to go round.

But this won't be the case for long.

She must reap the harvest
while she can.

Brown bears are not the only ones
fishing in the Gulf of Alaska.

Humpback whales have returned.

They've adapted their hunting
technique especially for here,

and they're hungry.

It's autumn

and one of Alaska's most iconic
migrants has returned.

These humpback whales
spent the winter

in their calving and mating grounds
off Hawaii and the Gulf of Mexico.

Following their 3,000 mile
migration,

they've arrived at their feeding
grounds in the Gulf of Alaska.

They've not eaten for six months,

so waste little time.

They have a unique way of fishing,

one not seen anywhere else
in the world.

Herring shoal here
in their millions,

for protection from seals and
Steller sea lions.

But this shoaling actually works
against them

now the humpbacks are here.

Once the whales have their sights
on a shoal,

they dive.

And start to sing...

..as loud as a jet aircraft.

The sound panics the herring

and drives them up
towards the surface.

One whale starts blowing bubbles

surrounding the herring...

..a vertical barrier as high
as a four-storey house,

which the herring
won't swim through.

The trap is set,

the whales move in
for the kill.

Together, they devour thousands
of fish at a time.

At over 45 feet long
and nearly 30 tonnes,

they have quite an appetite,

so quickly regroup
to do it all over again.

This North America coast
is the only place in the world

where humpbacks combine
bubble netting with singing.

They've learned that by engaging
their feeding siren,

they can turn these waters
into the perfect place to hunt.

500 miles north-west of the whales,

on the northern edge
of the Gulf of Alaska

lies Prince William Sound.

3,500 miles of rugged coastline...

..home to one of the highest
concentrations

of sea otters in the world.

Here because these nutrient rich
waters provide them with an endless

supply of food, which is vital
for their survival...

..as unlike most marine mammals,

sea otters don't have
an insulating blubber layer.

Instead, they burn calories
to keep warm.

To do this, they must eat a quarter
of their body weight every day,

so regular feeding is essential.

They can dive for four minutes
at a time...

..feeding on clams, snails, starfish
and sea urchins.

But body heat alone is not enough
to survive out here,

so sea otters
have the added protection

of the thickest coat of any mammal.

Up to one million hairs crammed into
every square inch

compared to the average human,

that only has 100,000 hairs
on their entire head.

But looking after this coat takes
time and effort,

so when not foraging,
they spend hours grooming...

..drying their fur...

..removing salt and excess oil.

Fluffing it up traps air,

providing four times
as much insulation

as the same thickness of fat.

Essential, as it's the only thing
that lies between them

and the freezing cold
Alaskan water.

The next six months
are the most difficult,

especially for mothers with pups.

Calm days will soon be replaced
by storms,

disrupting feeding,

increasing the chance
of separation and drowning.

One in five sea otter pups
won't see their first birthday.

Starvation is the biggest killer.

They must stick close to Mum
if they're to survive.

As autumn advances,
parental guidance is crucial.

But for some it lasts much longer
than just one season.

Over the past three months,

this mum has kept her two cubs
secreted away in the forest.

Unlike brown bears,
black bear cubs don't rely

on a diet of salmon
for their survival.

Mother's milk and vegetation
is more than adequate.

But Mum can't resist the lure
of a salmon lunch

and it's the best way for her to
get nutrition to produce milk.

She leads them to the river
for the first time.

They're understandably cautious.

Brown bears also fish here

and pose a serious threat
to the cubs.

She expertly catches a fish...

..then slinks back into the safety
of the forest to feed.

They'll spend the next three years
by her side

before heading out on their own.

That break-up can be traumatic...

..with youngsters sometimes
reluctant to leave.

This three-year-old cub
nestled in the rocks

waits expectantly to be fed.

His mother rebuffs him.

A clear sign it's time
he started hunting for himself,

as she can no longer
catch enough fish to feed them both.

He's not going to give up
without a fight.

His begging becomes more aggressive.

But she stands her ground.

Eventually he gets the message...

..and the family breaks up.

Just 60 miles north of the bears
in the Tongass National Forest,

another youngster is about
to take a leap into the unknown.

It's mid-Autumn in the
Tongass National Forest.

And a very big day
for a young bald eagle.

He hatched in early June.

Since then, his parents
have worked tirelessly.

And he's grown quickly.

His fluffy white down turned grey.

He grew flight feathers.

And learned to feed himself.

He was fully feathered in 56 days...

..and almost as big as his parents.

With age came a change in attitude.

He no longer waits to be fed.

And drives them off to fetch more.

His parents continued to make food
deliveries.

But didn't hang about.

Now, he's starting
to explore his environment.

Stretching his wings
to strengthen his flight muscles.

He's about to make
his maiden flight.

A huge leap of faith.

The ground being 150 feet below.

After a brief hesitation...

..he's off.

He doesn't go far...

..returning to snatch food
from his parents.

Survival is instinctive.

Good manners are not.

Parental duties over, they leave...

..forcing the youngster to start
looking after himself.

Just as the first autumnal storm
approaches from the Arctic.

On the island of St Lawrence,

40 miles off the Russian coast...

..three Arctic Fox cubs play.

They're only 12 weeks old.

This den site has been their
refuge since they were born.

But not for much longer.

They've already grown
their thick adult coats.

And now resemble Mum...

.and Dad.

They're perfectly camouflaged
amongst the rocks.

At this age, life is simple.

They pass the days play fighting...

..which helps improve
hunting techniques.

Strength and speed.

The braver they become,
the further they venture.

The more adventurous of them,
even attacking and killing fungi.

All of which is vital.

Their lives have reached
a critical point.

The nesting sea birds
are starting to migrate.

Their parents are no longer
returning with food.

A clear sign that it's time
for them to start life alone.

One by one, they drift away.

And the den lies quiet

until next year.

It's not just on St Lawrence
that food is drying up.

In Katmai Wilderness area, the
salmon run is starting to dwindle...

..heaping pressure on this mum
and her three yearling cubs.

She watches as bears downstream
catch the last of the salmon.

But it's too dangerous for her
to take her cubs into the melee.

Nor can she leave them alone
on the beach.

She's trapped upstream...

..while the others
hold the best fishing spots.

Her cubs are hungry.

She must revert to plan B.

Low tide gives her access
to mussel beds and razor clams.

Slim pickings, compared to the
salmon the other bears are catching.

But every morsel is vital...

..if they're going to survive
their first Alaskan winter.

The sun tracks low
across the autumn sky.

Winter is fast approaching.

North facing mountain slopes

won't feel the warmth of the
sun's rays until spring.

Shaded rivers are already
coated in frost.

In the Chugach National Forest,

in Alaska's south,

Coho salmon have at last
reached their spawning grounds.

They haven't eaten
since returning to the river,

and are now close to death.

But they still have one final act
before they die.

And that is to breed.

The females dig deep depressions
in the gravel.

Called a redd, this will be
the nest for her eggs.

The males line up, waiting
for the moment she lays.

Then they will rush in
to fertilize them.

They may only get once chance...

..so fights are frequent
and violent.

Even the largest males
carry severe injuries.

Half starved, their bodies
are in a state of collapse.

Wounds fester.

But still, they battle
to keep control of a female.

Their attention elsewhere
leaves them vulnerable to attack.

At around 10lbs,

this Chum salmon weighs
roughly the same as the eagle.

It's far too heavy to carry away...

..so he drags it into the shallows.

But he's not alone.

And stealing a meal
is easier than catching one.

As winter draws ever closer...

..and food becomes scarce...

..tensions rise.

But Alaska still has one
last offering.

A spectacle that throws a lifeline
to eagles

from across much of north America.

Late October.

Clear skies reveal
the Aurora Borealis.

Temperatures drop...

..chilling both land and water.

Soon, most of Alaska's rivers
will freeze completely...

..locking away vital food
under a thick layer of ice.

But not here.

The Chilkat River in southeastern
Alaska is different.

Upstream, water trapped
underground is warmed.

It slowly percolates up...

..and seeps into the river.

Keeping a five-mile stretch
of the Chilkat free of ice.

Even during the coldest winter.

The warmer water means salmon
can spawn here later.

This attracts eagles
from thousands of miles away...

..for one final feast
before winter hits.

At 3,000 strong, this is the
world's largest gathering

of bald eagles.

Such a glut of food means there
is little reason to squabble.

And a chilling calm descends.

The salmon pay the ultimate price.

They've done what they came
all this way to do.

Their cycle of life is now complete.

Every year,
300 million returning salmon

bring life to much of Alaska.

Even in death, they fertilize
the land along river banks...

..nourishing the vegetation...

..providing food for grazers...

..that in-turn feed predators.

Nutrients from far out
in the Pacific Ocean...

..creating life
hundreds of miles inland.

With winter closing in...

..Alaska's wildlife
must steel itself...

..ahead of seven months
of ice and snow.

But it's these extreme conditions
that have helped transform them

into some of the most
resolute creatures on the planet.

So that when spring
finally returns...

..they'll be ready to face
another year in the wilds of Alaska.

Subtitles by Ericsson