Original subtitles

Where the coastal mountains meet the Pacific

lies the Alexander Archipelago,

a remote island chain,

running for almost 500 kilometres along the Alaskan panhandle.

Defended by ramparts of rock and ice to the east

with 5,000 kilometres of ocean to the west

this frozen frontier is one of the last great wildernesses of North America.

This is part of the largest temperate rainforest on Earth,

and a stronghold for the country's highest diversity of megafauna.

Feasting on the abundance of fleeting summers

to make it through relentless winters,

both big and small

live here in perfect balance,

their worlds connected in surprising

and intricate ways that allow each of them to thrive.

There are still places on Earth that remain pristine,

where wildlife flourishes.

These are the last regions that could be called Eden.

For six months of the year,

North America's icy mountain realm is gripped by winter.

With the arrival of spring, life stirs once more,

as the world's largest population of grizzly bears

emerge from hibernation.

A mother with hungry cubs must hurry

to make the most of brief times of plenty

in this unspoiled, untamed land.

In spring, the best feeding opportunities

can be found where it's milder,

along the coast.

Tell-tale footprints signal the arrival

of newly emerged grizzly bear families.

After six months of hibernation,

this female and her cubs are in need of a protein hit.

Twice a day, low tide exposes a seafood smorgasbord.

A fresh fish looks tasty

but defensive spines mean it's probably best avoided.

Betrayed by their squirts, the real prize is the butter clam.

Surprisingly delicate paw work prevents the clam digging deeper.

Now, add brute force,

et voila, a clam canape.

But when you smell a clam,

and can't find it,

it can be frustrating.

But if you copy mum's technique,

it should work.

Or you could just use your teeth,

but there may be some shell in that.

But bears patrol the coast in search of something other than food.

His cowboy swagger denotes a dominant male.

All 300 kilograms of him.

And he's keen to kick off the breeding season.

But a mother with yearling cubs is in no mood to mate.

A grizzly can hit a top speed of more than 50 kilometres per hour.

Males may kill cubs to bring a female into season.

But all that muscle mass

makes it hard to keep up the pace.

With this overeager male safely out of reach

the young family can make the most

of this Eden's other spring feeding ground,

sedge grass meadows.

While the succulent shoots provide few calories,

they'll tide a hungry bear over.

Even the cubs are happy to eat their greens.

But they still prefer mum's milk.

She'll nurse them for nearly two years.

All the while teaching them the dangers and rewards

that come with this bountiful Eden.

Triggered by spring sunshine,

the first boom and productivity

takes place offshore

as a vast injection of protein turns the waters a milky white

with herring spawn.

Hundreds of millions of fish gather in the shallows to breed,

each hen fish releasing 20,000 eggs.

For resident Steller sea lions,

it's the first great feeding opportunity of the year.

Flying nearly 1,500 kilometres, one of the longest bird migrations,

tens of thousands of red knots arrive from South America,

to take advantage of a feast.

That's also the cue for marine megafauna.

It's one of the greatest gatherings of whales on the planet.

14 metre-long grey whales.

Mothers with new-born calves have navigated

the 10,000 kilometres from Baja, Mexico,

the longest seasonal journey of any mammal.

But it's worth it.

In vast mouthfuls of fatty roe and krill,

each consumes more than a ton a day.

And so the smallest creatures here

sustain the biggest,

enabling grey whale calves to put on a third of their adult body weight

before their autumn return to the south.

In spring, life also stirs in this pristine forest

that crowds the shoreline.

Covering over 68,000 square kilometres,

roughly twice the size of Belgium,

it's part of the largest tract of temperate rainforest on Earth.

Bathed in nearly 300 centimetres of rain a year,

each 700-year-old spruce may carry over 200 kilograms

of moisture-loving lichens, mosses and ferns on its branches.

It's one of the last places in North America

where prey and predators exist in equilibrium.

Early migrants like Rufous hummingbirds arrive.

The climate here is perfect for sap-rich trees to grow,

so it's worth a 6,000 kilometre journey.

They refuel on the sugary resin before pairing up to breed

in this most northerly of all hummingbird habitats.

Yet life here is built on superficial foundations.

In some places, ice fields only retreated in the last 200 years,

so the soil is still shallow and nutrient poor.

But this Eden has an answer.

It's intricate connections between species

as revealed under the magical display of the Aurora Borealis.

Flying squirrels emerge from their tree hollows in search of a mate.

With spring in the air, this young male sniffs the breeze.

From a neighbouring tree drifts the heady aroma of a receptive female.

He eagerly sets off to track her down.

For a flying squirrel,

gliding is the perfect way to get around this 30-metre high canopy.

In a matter of seconds, the scent source has been located.

She's just come into season.

But she's playing hard to get.

He'll have to prove he's a worthy partner.

If he can't keep up, he's not worth the effort.

But just when it looks like a match made in heaven,

she decides that he's failed to make the grade.

Yet, the intoxicating scent of female is still in the air.

He must find this femme fatale.

The lower he gets, the more enticing it becomes.

Desperately digging, this confused Lothario

thinks he's found the mother of all mates.

But his consolation prize is...

A white truffle?

The furtive fungus omits an odour that mimics female pheromones.

The truffle tricks him into solving

the biggest problem for this mineral starved forest.

When a squirrel carries a prize truffle to the treetops,

it's spores are dispersed far and wide.

As they germinate, they help form a vast underground web

of fungal filaments.

Effectively extending the range of tree roots,

enabling them to extract enough nutrients

to allow these great forests to flourish.

By early summer,

long hours of daylight promote a flush of growth

across the archipelago's coastal meadows.

But for grizzly bear families,

high calorie food is scarce.

And aggressive males must be avoided.

So some head inland

to secluded rivers in the heart of the forest.

This young mother has just the one cub.

His siblings may have been taken by a male.

But she has led him to a place where he will be safe

and females gather to feed in peace.

Most are related and all have young to feed.

But for now, they must wait.

Downstream, along Alaska's 11,000 kilometre seaboard,

half a billion Pacific salmon.

Among the largest concentrations in the world.

After four years of fattening up at sea,

some may swim 3,000 kilometres upstream

before spawning in the very upriver pool in which they were born.

A rich reward for the eager bears.

Unfortunately for this young mother and cub,

all the prime fishing spots are taken

by the older, more experienced females.

So she leads her cub upstream, away from the competition.

But there's a reason they have this place to themselves.

Rapids.

For the cub it's a brutal baptism.

But the inexperienced mother coaxes him straight back in.

Her desperation to feed overrides her urge to protect her cub.

But fortune favours the brave.

Finally, the ravenous cub gets a first taste of salmon.

Over the next five months, that the salmon will run,

grizzly bears will eat up to 45 kilograms of food a day.

That's over 50,000 calories.

And this cub will have the rest of the summer

to master the art of fishing.

Got it.

It's not just the bears that benefit from this mass migration.

To avoid a catch from being stolen, the woods offer private dining.

With the fatty head preferred to everything else,

leftovers litter the forest floor,

but they won't go to waste.

From nearly a kilometre away,

fishy fumes are picked up

by the sensitive antennae

of a two centimetre-long indispensable insect.

The burying beetle.

This male has two things in mind.

Fresh meat and a mate.

But he arrives to find he's too late to the party.

The good news is that he's spotted a female.

The bad news is he'll have to fight other males to win her.

Battles are brief but brutal.

He hurries to claim his beetle bride, they have an urgent task to accomplish.

Living up to their name, the new couple

proceed to dig the salmon a grave.

In the safety of their cosy crypt,

the pair secrete an antibacterial saliva to preserve the flesh.

The fresh corpse provides a feast

for a newly-hatched brood of larvae.

And there will be plenty of surplus fish to fertilise the surrounding soil.

In a football field-sized area,

there can be as much as three tons rotting underground.

Known as fish trees,

spruces grow three times faster along these rivers.

It's possibly the largest transfer of nutrients

between water and land anywhere on Earth.

Because of the sun, the entire forest prospers.

It's autumn.

The long days and short months of summer

brought with them great riches.

But now animals that can depart will soon be journeying south.

Yet for some, this is the time to secure your bloodline.

Crowned by antlers spanning two metres or more

and weighing around 18 kilograms

a 700 kilogram moose proclaims dominion over his realm.

This antler free female

and the five or so others in his harem

will stick around as long as he's the best bull on offer.

Younger males go head-to-head, honing their combat skills.

Though without the impressive headgear and imposing physique,

they only have a 10% chance of mating.

But one male is willing to try his luck.

At five years old, he's almost fully grown,

but he'll never be a mighty moose.

To win over a female,

he needs a different game plan.

From a discreet distance,

he closely observes what it takes to be main moose.

The females are in season for less than two days.

But the dominant male has a mood-enhancing move

that guarantees romance.

He scrapes a shallow pit

and urinates into It.

It contains potent pheromones that bring females into season.

They find the aroma so intoxicating,

they can't resist a roll.

"Ah, so that's how it's done."

Anointing himself in the musky pee,

this young pretender seizes his chance.

With the help of the alpha's aroma,

he gets the come on he's been dreaming of.

Under the nose of the moose monarch,

she leads the cheeky youngster off to mate.

Proving that the smartest moose

isn't always the one with the biggest antlers.

As autumn gives way to winter,

temperatures plummet to minus 20 degrees Celsius.

For its remaining megafauna, like the moose,

it's the beginning of a long, hard six months

of meagre resources.

Those who don't make it

provide a lifeline for others.

While most rivers are now locked in ice,

the Chilkat continues to flow throughout November.

Heated to seven degrees by thermal springs.

It supports one of Alaska's last salmon runs,

offering one final feeding bonan: za,

for America's national bird,

the bald eagle.

Over 4,000 stop off here, in the largest gathering on Earth,

to fuel up on salmon ahead of their migration south.

For a young eagle,

this is the first true test of survival.

Every catch is ferociously contested by adults much bigger than him.

But to make the journey ahead, he needs to bulk up.

To avoid serious injury,

disputes are settled by locking needle sharp,

five centimetre-long talons.

He moves in on the unguarded carcass,

only for it to be snatched away.

At dusk, eagles retreat to the safety of the treetops.

They may have one of the most acute

daytime eyesight's in the animal kingdom,

but in the dark, they're virtually blind.

On the ground,

they could easily be ambushed by nocturnal predators,

like a coyote.

But night may also offer an opportunity to feed.

Under the safety of darkness, a mother grizzly

leads her two cubs to the river's edge.

Brown bears have a membrane in the back of their eyes

that reflects light within the lens,

giving them excellent night vision.

While the cubs amuse themselves,

mum gets on with the serious business of fishing.

With the coast clear,

the daring youngster makes his move.

Profiting on the leftovers.

While almost three quarters of fledglings die in their first year...

this wily eagle has found a way to gain the strength he needs

to escape the Alaskan winter.

These late salmon runs are vital

to grizzly bears right across Northern America.

As temperatures drop to minus 28 degrees Celsius,

icicles adorn their fur.

So they're known here by the First Nations as Ice Bears.

They've endured the freezing conditions

for a month or more, waiting for the salmon to arrive

and many are pregnant.

But if their fat reserves are too low, they won't give birth.

Every salmon increases the chance

of surviving the long winter hibernation.

But across southeast Alaska, the predictability of the salmon run

has been thrown into doubt.

The damming of rivers,

logging, pollution and climate change

could mean this entire habitat is at risk.

On this fragile planet,

home to nearly eight billion people,

the threat to remaining wilderness grows ever greater.

But if we take steps to keep our world safe,

enriched by natural wonders,

it's exquisite symmetry,

kept in balance by intricate relationships,

these last frontiers...

will remain...

forever Eden.