Original subtitles

They are driven...to move.

To move...and to multiply.

Possessed by the insatiable need to breed...

they will journey to brutal African battlefields...

and brawl on South Atlantic shores.

For the sake of their young, they will blacken the skies...

and terrorize rainforest floors.

Right now, the world's wild parents

are on the march...

on the wing...

on the run.

And these are the tales of their sacrifice...

the most moving stories on Earth...

the stories of the great migrations.

Winter in the South Atlantic.

One of the worst places in the world...

to be left behind.

But that is Johnny rook's lot in life.

Here on a desolate archipelago off South America,

this bird of prey clings to life...

waiting for the migrants to return.

Now, the flare of a September dawn announces spring's feeble arrival.

And for Johnny rook, the wait is over...

because some of the world's greatest wanderers

are heading his way.

They've been traveling the globe for months, even years.

Only one thing can bring their wanderings to a halt--

none of them can give birth at sea.

From around the southern pole, nomads are now converging

on these shards of rock known as the Falklands.

They will give up the lives they know best--

on wind or waves-- for the sake of their young.

After months of migrating through frigid southern waters,

up to 25 miles a day,

rockhopper penguins torpedo in for a hard landing.

These sleek, hardy birds must abandon the sea to reproduce.

Then there are the true behemoths.

Back from 10 months of hunting off the Antarctic ice sheet,

the massive southern elephant seal humps ashore.

He has to make a stand here where the females are returning--

or lose his chance to breed.

He is four tons of raw sexual aggression.

For migratory credentials, little can beat the black-browed albatross.

From tip to tip, its wings span eight feet.

This superb glider can soar almost effortlessly 20 hours a day.

[albatrosses chattering]

Waiting in this bustling metropolis of hundreds of thousands of birds,

her mate shores up the nest from last year's breeding.

And after seven lonely months,

and tens of thousands of miles riding the southern sea winds,

they share an ecstatic restating of vows.

Their bond may last 30 years.

[squawking and chattering]

Up and down the shores, nests are being tended to,

bonds renewed...

and eggs laid.

For the next two months, the couple has only one goal:

to keep the egg alive.

But someone else has his eye on the eggs, too.

Johnny rook, otherwise known as the striated caracara,

has waited through a brutal winter for this bounty.

An egg tumbled from a nest is fair game for Johnny rook.

He'll soon have his own clamoring brood to look after.

[albatrosses squawking]

On another stretch of beach,

the shoreline quakes with desperate battles to dominate.

The stakes are unimaginably high.

Only a privileged few elephant seal bulls

will become beachmasters--

controlling harems of dozens of females--

and reproducing abundantly.

[low rumbling]

This is no place for a young male to stick his nose in.

[rumbling]

Usually trumpeted warnings make challengers back off...

but not all.

Blood runs freely from slashed noses and necks.

They even fight dirty, going for the eyes.

The loser's breeding chances, for now, are ground into the sand.

[rumbling]

But this beachmaster's triumph is just the beginning of his troubles.

Ahead lie dozens of fights-- and perhaps a hundred matings--

all for the sake of his bloodline.

The need to pass on one's genetic legacy

is a great motivator of migrations.

Nothing else could drive the nomads of the Falklands

to tolerate life on land.

Nothing else could make migrating mothers

stand up to great predators...

or to drive potential fathers

to travel great distances to deadly battlefields.

Parenting on the move is all about sacrifice.

And in the forests of northeastern Australia

another great journey spurred by parental dedication is about to begin.

On translucent tawny wings, a little red flying fox

flaps homeward after a night of intense foraging.

And she is one of millions.

[bats squeaking]

Somehow, she finds her pup in the din of the camp.

She wraps him in her nursing embrace.

He needs calcium from her milk to build his flimsy bones--

and he's leaching it away from her own fragile flying machinery

at an alarming rate.

The bats have eaten through the calcium and energy-rich eucalyptus blossoms

for miles around.

The situation is getting desperate-- the need to move intense.

But they can't migrate to greener pastures

until the last of the youngsters has been weaned.

So mother has become stingy and edgy.

Readying for the migration ahead,

she tongues oily secretions over every bit of her flight equipment.

A bat's wings are essentially enormous webbed hands,

elongated finger bones providing the struts

to unfold and manipulate the flight membranes.

As dusk settles, the migration begins.

The little reds, wings spreading three feet tip to tip,

blacken the skies with their departure.

Tonight, they have to travel many miles

with their newly weaned young--

and inexperience on the wing will prove deadly.

Parenting is risky business.

Migrants around the world will risk everything

for the next generation.

But before you can breed, you must earn the right.

And in Africa, one species readies for battle.

ln the war-wracked country of Sudan lies Boma National Park,

the largest intact savannah in East Africa.

Mile upon mile of what looks like pristine wilderness unfolds--

but much of this is an empty paradise.

During the Sudan's decades of ruinous civil war,

the park supported rebel armies and untold refugees.

The wildlife was decimated...

and it was long feared

that one of the most spectacular migrations on Earth--

not seen by outsiders in 20 years--

had been wiped out.

Then in 2007, aerial surveys began spotting them...

handfuls...

then hundreds of them.

Eventually, estimates reached in the hundreds of thousands.

Miraculously, the white-eared kob had survived.

A magnificent antelope that lives nowhere else on Earth.

The kob have been migrating

in numbers perhaps equal to those in the Serengeti--

covering hundreds of miles

from their wet season feeding grounds in the south

to their breeding battlegrounds in the north.

And it saved them.

Life on the move kept them a step ahead of the guns

and human hunger.

By November, the blinding equatorial sun

has turned their southern water holes into sucking mud--

a trap for unwary youngsters.

And so they must move north toward permanent water.

Their pace quickens with the males' need

to reach their ancient battlegrounds.

After months on the move,

they arrive at the northern edge of their migration--

a network of swamps and rivers--

where they can unleash their unique breeding spectacle.

This is where the antelopes' leks will form--

vast fighting arenas, where gladiators duel,

sometimes to the death, for the right to mate.

Their breeding season brief, their hormonal rage intense,

they are about to dispense with ritual--

and get straight to the bloodletting.

Head-butting males are conspicuous icons

of the need to breed.

But in the hidden world of the Costa Rican rainforest,

it is a seething sisterhood of hunger

that assures the success of the next generation.

And unleashes one of the most feared migrations on Earth.

The army ants are on the move.

The engine of this merciless hunger--

a brood of 200,000 larvae and their caretakers,

demanding 30,000 corpses a day.

The nursery lies at the heart of a twitching, throbbing structure

built almost entirely of the ants themselves.

Long legs stuck together with tarsal claws,

they are the scaffolding, bricks and mortar of the nest.

But they've been in one place for three weeks,

ravaging the forest floor for miles in all directions.

lt's time to migrate.

ln the darkness, they pour out of the nest,

porters carrying the precious larvae.

They are virtually all sisters, daughters of one queen.

They will migrate about 330 feet each night--

the equivalent in human terms of a marathon.

Deaf and virtually blind--

they nonetheless communicate brilliantly

through touch and complicated chemical signals.

And now the message goes out to bivouac.

Almost magically, they form a temporary nest of their own bodies.

The larvae and food are taken into the nursery at its center.

Tomorrow they will do the whole thing again--

marching for two to three weeks to reach fresh hunting grounds,

where they can set up another raiding base--

and reach new heights of slaughter.

[birds calling]

On migration central-- the Falkland lslands--

the multitudes are busy multiplying.

Female elephant seals barely escape the males' attentions

long enough to give birth to pups conceived here last year.

ln the brief three weeks the pup has with his mother,

his body weight will triple...

as hers shrinks by a third.

The bull moves in soon after the birth

to impregnate her again.

Each beachmaster on these shores

may have dozens of females in his harem--

and 100 matings to complete-- in less than a month.

All the while having to fight off more and more challengers.

Unable to leave his harem to feed at sea,

he's losing 50 pounds of blubber a day.

[rumbling]

[albatrosses chattering]

Already the albatross chicks are hatching in staggering numbers,

downy and demanding.

With unending patience, the new mother waits

for her mate to return from his foraging--

until near starvation, if she must.

He, meanwhile, may be covering thousands of miles on the wing,

simply to find food for his brood.

He returns, heavy with seafood.

After a brief greeting, they transfer parental responsibilities.

He fills the chick's belly...

and the family is content.

But Johnny rook is hungry too.

[chick chirping]

Sometimes a parent never returns from the sea.

And the raptor executes his cruel mercy.

ln the roiling surf, rockhoppers porpoise home with their gullets full.

They take turns shuttling to the sea daily,

nabbing tidbits of krill to feed their growing chicks.

Once ashore, the rockhoppers trade their long, graceful sea migrations

for a daunting and dangerous vertical one.

They've made their nests high on the sheer cliffs

far from the freezing sea spray.

And each day, pudgy with baby food,

they must scale these unforgiving rock walls.

Centuries of penguin passage have left their mark--

everywhere the cliffs are scarred by penguin claws.

They are irrepressible--

and undaunted by missteps and stumbles.

At the top, red-eyed, yellow-browed and full of spunk,

they celebrate their ascent and reunion...

[braying]

and are quickly assaulted by their ravenous chicks,

now nearly as big as the adults.

[chick shrieking]

"More food" is the chorus ringing out

up and down the shores and cliffs of the Falklands.

Migrants who spend their lives

gracefully plying hundreds of miles of sea and air,

feeding at their leisure,

are now bound to these frozen shards of rock and sand--

battered by the calls of their young:

More food.

[pup barking]

lt's nightfall in Australia.

Rush hour is in full swing.

The little red flying foxes are migrating--

and parched with thirst.

But a drink on the wing is a dangerous undertaking...

especially for the inexperienced young.

Some freshwater crocs try to snap them out of the air.

Others wait for fatal mistakes.

But many more make it through...

and after many hours on the wing, they find their new paradise.

Fresh, succulent eucalyptus at the height of its bloom.

At dawn, they select a camp nearby--

their new base for feeding excursions.

lt's time to get down to the business

of creating the next generation of flying nomads.

Males spar for territory.

They may have harems of up to five females,

although the little reds are so little studied,

no one knows for sure.

Courtship involves a great deal of nuzzling and stroking.

The act itself is brief.

But the couple sometimes clings to each other for hours.

After a long day,

they wrap themselves in their elegant capes,

trying to catch a nap.

Tonight, the newly weaned young will join the feeding frenzy.

They are now fully fledged members of the colony,

ready to investigate the bounty of this land--

and darken the dusk with breathtaking numbers once again.

Morning in Costa Rica, and the army is on the move again.

Each day, about a third of the nest spills out in a deluge of ants.

And for most of their prey, resistance is futile.

Even fearsome wasps high in treetops

are no match for the implacable ants.

They watch helplessly as their own larvae

are stripped from their honeycomb cribs.

Now the porters take up their burdens

and carry the moveable feast back to the unquenchable young.

Generations of ants will come and go.

But the restless hunger of their sisterhood will be immortal.

On the savannahs of the Sudan,

the clash of males is reaching a fever pitch.

A male kob's life boils down to this:

here and now, kob on kob, pound for pound.

The bodies of the fallen litter the battlefield.

The females approach the victorious males warily...

and with a discerning eye.

They gravitate to the eye of the storm,

knowing that only the fittest gladiators

can make a stand at the middle of the deadly arena.

And a chemically choreographed dance of mutual seduction begins.

The kob's love letters-- hormone-laden urine.

He soaks the soil with his brew.

The smell may be packed with complex information

about his genetic and physical fitness.

Suitably pleased, she answers with her own stream of urine.

His clownish expression is known as flehmen:

he's filtering the scent

through a complex set of receptors in the roof of his mouth.

There's no mistaking it: she's ready to mate.

Finally, the lovers unite... albeit, briefly.

After two months, the breeding season is over.

lt's time for the long trek back to their southern feeding grounds,

with the females carrying the next generation of nomads--

and fighters.

ln the Falklands, too, the mammoth gladiators

are turning away from their battlefields...

and a spectacular exodus must now begin.

For the young on these bleak southern shores,

it is the season of abandonment.

With barely a backwards glance, the starving elephant seal females

desert their giant three-week-old babies on the shore.

The males, utterly spent, have nothing to do with their young.

With this abrupt weaning,

the pups make their first forays into the shallows.

They, too, will return to these shores after thousand-mile journeys.

The rockhopper parents also take leave of their young--

heading back into the water

with the joy of a creature returning to its element.

After months on awkward shores, they're going home.

The young albatross fledglings, left behind days ago,

rev their engines on their nests,

testing the four-foot wings and howling winds

that will power them around the world.

lt's time--

to fly...or die.

For Johnny rook, the casualties are merely a last chance to feast.

[Johnny rook squawking]

Soon there will be little left but scraps

to sustain him through a brutal winter.

The last fledglings now make a leap of faith.

Once on the wing, they may not come to shore for a decade...

and then, only to breed.

From now on, they are migrants,

circling the southern world...

wedded to brilliant skies...

and slipping the surly bonds of Earth.