Original subtitles

This is a journey down the longest mountain chain on earth.

These are the Andes the spine of South America.

They span the length of the continent over five thousand miles

from the tropics almost to the Antarctic.

Surviving in the Andes is one of the greatest challenges in the natural world.

It's a truly hostile place to live bitter cold, thin air, relentless wind

...even the volcanic forces of the earth itself.

Faced with trials like these

how can anything survive here let alone flourish?

Our journey begins in the tropics at the northern end of the range.

The highest peaks in the Andes rise to nearly seven thousand metres.

And some are still growing.

Measured on the scale of geological time

the Andes are still young.

The mountains mark a line

where two great plates of the earth's crust collide.

The impact crumples the continent and huge volcanoes break through.

As the mountains rise into the clouds

their slopes are colonised by forest

cloud forest.

In the warmth of the tropics trees can grow high on the mountains

to well over three and a half thousand metres.

Animals were quick to exploit the new opportunities these forests provide.

Isolated in a maze of ridges and valleys all sorts of new species developed.

These Andean cloud forests rival the Amazon rainforest for diversity.

There are more kinds of hummingbird here than anywhere else in the world.

Almost every hillside has its own unique plants and animals.

The cloud forest also has its very own bear

the spectacled bear named after the markings on its face

This is the only bear in South America.

There are just a few thousand left.

Most kinds of bear are good tree climbers

but here that skill is essential.

Spectacled bears get much of their food from the treetops

so climbing trees is one of the first lessons this baby has to learn.

The cub is well grown

but it still has a long way to go to match its mother's skills.

The trees here can be twenty metres high

so it can't afford to make a mistake.

These high forests have few monkeys

so there's plenty of food for bears that are willing to climb.

But for an animal that can weigh well over a hundred kilos

that's quite a challenge.

Even when it's mastered the art of climbing

the cub still has to learn what to eat.

The bears' favourite food are bromeliads

plants that perch on branches high in the canopy.

They're especially fond of the fleshy base of the leaves.

Bears are adaptable animals and there's only one kind here.

Other animals are more specialised

so several species can coexist like the hummingbirds.

These damp cool forests have few flying insects

so many of the flowers rely on birds for pollination.

Plant and pollinator have a unique relationship.

Each hummingbird's beak is perfectly

adapted to reach the nectar in its chosen flower.

As the hummingbird moves from flower to flower

it transfers pollen and so fertilises them.

In exchange

it gets sugar-rich nectar to fuel its hovering flight.

At high altitude, the air is thinner and has less oxygen.

It's hard to hover.

Most bromeliads win their place in the sun by growing high in the trees.

But some kinds have gone a step further.

They've left the forest behind and climbed the mountain.

The puyas grow in the paramo

a zone of alpine grassland above the forest.

After several years

they throw up a stupendous five metre flower spike... and then die.

With just a once in a lifetime opportunity

it's vital that the flowers are pollinated.

Puyas have their very own hummingbirds

like the Andean Hillstar.

It lives higher than any other hummingbird.

Up here the air is even thinner and hovering is even harder.

So whenever it can it perches rather than flies.

As it moves from flower to flower it transfers more than pollen.

Tiny pollen-eating mites live in the flowers.

They crawl onto the hummingbird to hitch a lift to another plant.

At the next stop, some passengers get off and others get on.

Not every animal works in such harmony with the puyas.

The growing flower spikes are an irresistible honeypot

for spectacled bears.

They can destroy a lifetime's work in seconds.

For bear cubs, learning how to tackle puyas brings a sweet reward.

The spikes are rich in sugar

to make nectar for the hundreds of flowers.

They're packed with energy but how do you get at it?

A little parental guidance is called for.

Spectacled bears are versatile animals

but each new generation has to learn the tricks of the trade.

The mountains are an unpredictable place to call home.

Massive volcanoes rise above the cloud forest.

At any moment they can burst into violent life.

As you travel south down the chain of the Andes

you pass a line of brooding giants.

Among them are the highest active volcanoes in the world

rising to more than six thousand metres.

They're so high that even in the tropics

their summits are crowned with ice and snow.

In the heart of the Andes

volcanic activity has built more than mountain peaks.

It's thrust a high desert plateau

three miles up into the sky the Altiplano.

Sulphurous steam from the world's highest geyser field rises into cold

thin air... a vision of earth before life began.

Much of the water here evaporates in huge caustic lakes.

This must be one of the most extreme environments on earth.

How could anything possibly live here?

Incredibly

the Altiplano salt lakes actually attract animals.

Flamingos come here to breed.

Their season starts with a massed courtship dance.

Three kinds of flamingo nest on these caustic lakes.

These ones are Andean flamingos.

These lakes are prime flamingo habitat.

With no outlet dissolved salts washed down

from the surrounding mountains are concentrated by evaporation

ideal conditions for the flamingos favourite food - brine shrimps.

They thrive in water ten times as salty as the sea.

The birds catch them by filtering water through bony combs in their beaks.

The three kinds of flamingo have different sized 'filters'

so they can live together by exploiting different parts of this briny soup.

Only a handful of other waterbirds can live here.

Andean avocets subsist on fly larvae.

The key to success up here is being a specialist.

Brine flies live in a world that's wafer-thin

sandwiched between the salt and the piercing wind.

But their swarms are large enough to support a lizard.

Brine flies are its staple diet.

Being cold blooded

it hunts only when the temperature has risen enough for it to move.

For a lizard living on the edge of what's possible

even a patch of fly-blown salt pan is worth fighting for.

Even the steaming outflow from a geyser attracts life.

This frog also survives on flies

but this really is living on the edge.

A few hops one way and it would be boiled alive

a few the other and it would freeze to death.

This desert on the roof of the world even has mammals

Vicuna South American relatives of the camel.

But what can they eat up here?

There's more to the Altiplano than caustic lakes

and not all the springs are hot and salty.

Fed by meltwater from the snow-clad peaks some run cold and fresh.

They water small patches of marsh called bofedales.

In the drier parts of the Altiplano

these green oases are the key to the vicunas' survival.

They provide grazing and fresh water to drink.

All sorts of animals depend on them.

Like viscachas rabbit-sized rodents.

Early in the morning the marsh is frozen hard

so the viscachas bask in the sun until the ground warms up

along with the leaf-eared mice that share their jumble of boulders.

Only when the grass has thawed can they start to graze.

In the drier parts of the Altiplano little grows away from the bofedales.

The few flowers give a sip of nectar for the Andean Hillstar.

Up here perching is vital to save energy in the thin air.

There may be no woods here

but there is a woodpecker the Andean flicker.

It nests underground and hunts for insect grubs in the marsh.

At this extreme altitude

the main problems any animal has to face are cold and lack of oxygen.

Viscachas overcome the cold by having incredibly thick fur

but they have to keep it in good shape if it's to save them from freezing.

To make better use of the thin air

some animals have a high concentration of red blood cells

and specialised lungs.

It also helps if you don't exert yourself.

Viscachas hardly ever move more

than a stone's throw from their protective rocks.

Nothing moves fast without a good reason

but up here, even a small patch of grass is worth fighting for.

Deciding whether to use hard-won energy reserves

can be a matter of life and death.

The arrival of a red fox means it's decision time.

Up here the air is so starved of oxygen that a sustained chase is impossible.

The fox has to try and take its prey by surprise

Not easy in this open country.

The viscachas are rarely more than a short dash from safety.

Viscachas have thin muscle walls to their lungs

so they can breathe more freely at high altitude.

But a rapid escape is exhausting even for them.

The panic's over for now.

It's time for everyone to catch their breath.

On the Altiplano the air is in such short supply

that neither hunter nor hunted can afford to waste it.

It's at night that the effects of the high altitude bite hardest.

When the sun goes down

the air's too thin to retain its heat

and the temperature plummets.

For the Andean Hillstar every night is like a winter.

Even at lower altitudes

hummingbirds save energy at night by slowing down their metabolism

almost as if they were hibernating.

Up here, that ability can make the difference between life and death.

Just three hours after sunset it's already twenty below.

Even running water freezes hard.

This is the moment of truth for the Hillstar.

Now all it can do is wait.

With the rising sun the Hillstar comes alive again.

It picked its roosting place so the very first rays

reach in to warm its chilled body.

This time, it's won through

Every night is a battle to survive a twelve hour winter.

But the Altiplano also has a true winter.

For a few weeks each year

its savage climate becomes even more severe.

For those who can this is time to leave.

They must search for food in lakes lower down the mountains.

When the flamingos have gone

the high Altiplano is left to the elements

and those animals that have no choice but to sit it out.

The cold can be so severe that even the salt lakes freeze over.

Any birds that breed late in the season can be trapped here.

Their young can't yet fly

and their food is now out of reach locked beneath the ice.

Many of these stragglers will die frozen into the ice.

Their fate is already sealed.

But some places never freeze.

The Andes' inner fires keep the geysers and hot springs free of ice.

Here at least, winter will never come.

In this tiny island of warmth in the most marginal

and extreme of worlds, life hangs on.

The Altiplano may be extreme

but there's somewhere even more severe.

As you travel south down the chain of the Andes

winter becomes even harder.

The mountains here may not be as high as the giants further north

but they're much closer to the Antarctic.

The snowline creeps lower and lower

and in the deep south the ice never melts.

This is Patagonia.

Three huge ice-sheets dominate the Patagonian Andes.

Covering over seven thousand square miles

they're the largest expanse of ice outside the poles

so vast that they generate their own weather.

Towers of rock rise from the edge of the ice

the remnants of ancient volcanoes stripped bare by the glaciers.

Only the condor soars among these icy peaks.

This is one of the windiest places on earth.

Chilled air spills from the edge of the ice-sheet.

Funnelled down the glaciers and between the peaks

these freezing blasts can reach a hundred miles an hour.

Almost nothing lives on the ice-sheet itself.

Surviving even on its edge requires unimaginable stamina.

The guanaco a southern cousin of the vicuna.

It's larger and has a thick woolly coat

and it needs it to survive the Patagonian winter.

Snow is not the only peril the guanacos face.

The puma, the lion of the Andes.

This most adaptable of big cats lives throughout the mountain chain

from the cloud forest to the high desert

and the snows of Patagonia but it's secretive and hardly ever seen.

For all the hunters here winter is a lean season.

They're poorly camouflaged against the snow.

The grey fox follows the puma to scavenge any scraps from its kills.

She has hidden stores of food during the summer.

If she can sniff them out she'll survive the winter.

The really hard times last four months.

But slowly the days get longer and the land comes back to life.

The snowline creeps back up the mountains.

This is what the condors have been waiting for.

As the snow retreats the casualties of winter are revealed

animals killed by cold or starvation and the remnants of puma kills.

Condors are the vultures of the Andes.

They have superb eyesight.

They can spot food from miles away

and can locate even more distant carcasses

by watching for other condors gathering.

The grey fox is a scavenger too.

The winter's survivors are lean and hungry

and there's stiff competition for any chance of a meal.

There's a well defined pecking order at carcasses.

One fox may defer to another

but neither of them can argue with a condor.

With a three metre wingspan and weighing up to fifteen kilos

it's the world's largest flying bird.

The fox simply can't compete.

At this feast the condor is king.

Caracaras have to wait their turn too

or make do with scraps that fall from the condors' table.

Spring brings a flood of migrants to take advantage

of the brief Patagonian summer like buff-necked ibis.

They waste no time in starting to breed.

Great grebes over-winter on the coast

but as soon as the lakes are free of ice

they move inland and start fighting for territory.

Only the winners will have a good chance of raising a family

The losers are forced onto lakes higher in the mountains

where the summer is that much shorter.

Territory is also the key to breeding for male guanacos.

They gather a group of females on their patch of ground

and guard them closely against rival males.

He must always be on watch.

Younger males will seize any opportunity to raid the harem.

Soon the reedbeds are alive with nesting birds.

And where there are nests there are nest thieves.

As soon as eggs are laid the fox is quick to take advantage.

She's found the nest of an upland goose.

Now the birds will have to start all over again.

There's little a bird can do to drive a fox away from its nest.

But a male guanaco packs more of a punch.

Soon there will be baby guanacos to defend

and he's not taking any chances.

Male guanacos are exceedingly territorial at this time of year

and they won't tolerate intruders of any kind.

The fox already has a family to feed.

Her cubs will be safer away from the aggressive guanacos' territory

so she moves them to another den.

There can be as many as five cubs in a litter.

Their mother has to carry each individually to the new den

so moving house takes a lot of energy.

Even so, foxes often move their cubs several times.

The longer a den is occupied

the greater the chance a puma will find it.

The cubs are still dependent on their mother's milk

but soon she'll be weaning them onto solid food.

By the time winter returns they'll have to look after themselves.

Few of these cubs will live as long as a year.

If they're to survive they have a lot to learn

and only a brief summer to learn it.

High summer in Patagonia.

At the edge of the great ice-sheet

the mountains are almost clear of snow.

This far south midsummer days are long

and occasionally it can even be warm.

Patagonia seems almost benign.

The puma hunts mostly at night but summer nights are short.

There may be more food at this time of year

but there's less time for the puma to catch it.

At dusk, a deadly game of cat and mouse begins.

The guanacos move to the ridge tops.

From there they have a better chance of spotting a prowling puma.

But under cover of darkness

the odds are stacked in the big cat's favour.

This time the puma killed a full grown guanaco

but the most vulnerable are the young.

The cat won't have long to wait for the new season's baby guanacos.

All the births are concentrated over just a few days.

That way the puma is spoilt for choice

and it can't take all the young.

The sooner a new-born infant can stand

and run, the better its chances of surviving the summer.

Within days of giving birth the female guanacos come on heat.

For the males, this will be the payoff for all the hard work

they've put into defending their harem.

But they can't afford to relax their guard.

This is when other males are most tempted to intrude.

First, there's a stand off.

Fighting's dangerous so males

try to intimidate their opponents by posturing.

But this time threat has to be backed by physical force.

Guanacos are heavy, powerful animals

and they can inflict a vicious bite.

This 'neck wrestling' is a way of avoiding being bitten.

The battle over the winner takes his reward.

So long as he can fend off intruders

the resident male will mate with all the females in his group

and sire a whole new generation.

This may be midsummer but at any time

the mountain can spring a cruel surprise.

On a sunny summer's day

ferocious storms can strike out of the blue.

From behind its fringing peaks

the ice-cap hurls a frozen blast down the mountains.

These sudden winds can reach a hundred miles an hour.

For everything that lives here

these sudden storms are part of the Patagonian summer.

They can strike almost daily.

Even in the strongest winds the grebes keep fishing.

All kinds of grebe carry their young on their back

but here in Patagonia it's a life saver.

From their earliest days

the chicks feel the brutal force of the Andes.

But these birds are great survivors

and if they can make it through the storms

this is an ideal home.

Sometimes grebes feed feathers to their chicks.

This may help bind the fish bones together

so they can be regurgitated safely as a pellet.

Young of all kinds have to grow fast

if they're to survive the coming winter.

The young guanacos build up their stamina

by playing in the last of the summer sun.

The mother fox has only a few more weeks

to teach her cubs how to fend for themselves.

Carrion from a puma kill gives them their first taste of red meat.

But meat is a luxury.

To survive they will have to eat insects fruit, leaves, even grass.

They may be playing now

but in a few weeks they'll be hunting for real

on their own.

Only the most resourceful can live through an Andean winter.

All along the chain of the Andes

survival depends on adapting to some of the harshest conditions on the planet

thin air, bitter cold, relentless wind.

But for those that can live here

the mountains provide all their needs.

Our journey of over five thousand miles ends here

almost in the Antarctic

where the glaciers of Patagonia plunge towards the Southern Ocean.

The mighty force of the mountains can give life

but at any moment

it can take it away.

Living in the Andes

is one of the greatest challenges in the natural world.