NARRATOR: In the middle of Botswana's barren salt pans, new life begins and must hit the ground running.

This foal joins the largest zebra population in southern Africa and one of the greatest migrations in the natural world -- a trek over thousands of miles to find food and water.

A gauntlet of obstacles lies ahead.

Strong family ties are vital for our foal's survival.

But there's a dark side to this order that can shatter lives.

For these zebras, it's all about life, death, and an endless exodus in this ancient land.

[ Theme music playing ] Thousands of years ago, a vast super lake spilled across the heart of Botswana.

Its waters covered an area larger than Switzerland... then vanished, leaving behind the great Makgadikgadi Thirstland.

Now hooves tread where waves once lapped.

Each year, far from human eyes, this remote expanse of salt pans hosts one of Africa's last great spectacles, when thousands of striped nomads wander the barren landscape.

There is no permanent water in this desert of salt.

It is only by the grace of fleeting seasonal rains that these plains zebras can survive here.

Thundershowers are meager and isolated, yet they leave a trail of grassy islands scattered throughout the pans, making home habitable... for the moment.

Families gather on these islands to feed on the green pastures.

A single stallion is at the helm of every family unit.

Like a devoted husband and father, he shares a protective and long-lasting bond with his harem of mares and their foals.

But not all his wives are equal.

Zebra mares observe a strict social order, with the most dominant, or lead mare, always walking in the front.

The others fall in line behind her, according to their rank.

The family stallion brings up the rear, keeping a watchful eye on his charges.

Right now, many of the families are growing in size.

After a year's gestation, foaling is timed to take advantage of the wet season's nutrient-rich grazing.

Sadly, only half of these foals will survive the year.

But for now, released from the confines of the womb, they celebrate their agility.

But one foal has no reason to celebrate.

Young zebras can typically canter within an hour of birth.

But this little one has been born lame.

His father walks more slowly, allowing him to keep up.

Stallions will take great risks for the well-being of their own offspring.

This young stallion has so far secured only one mare.

The frail little foal is their first.

Meanwhile, nearby, new families are being made.

Adolescent fillies seduce males with the perfume of estrus... while mature harem mares are more discreet, mating exclusively with their family stallions.

It's the peak of the breeding season.

And fillies that have just come of age are flirtatious.

They attract the attentions of rival stallions.

Many bachelors compete over the young mares.

Opponents wrestle from dawn to dusk.

With each passing day, the lame foal bravely battles on.

For a zebra, lameness can be a death sentence.

As the morning wears on, the other families drift away.

The zebras' diet of grass digests quickly, forcing them to keep moving to fresh pastures.

The small foal does his best to keep up... but he can't.

Nevertheless, his parents stay close by his side.

The small family has spectators.

Meerkats share the zebras' island pantry, although their meals are sometimes a little harder to find.

The family spends their days hopping between grass islands, in search of invertebrates in the sand.

All the while, the zebras continue their daily march across the pans, seeking out the rain's latest harvest.

These restless animals will walk more than 2,500 miles in the year ahead to feed themselves.

Some will not make it.

An old enemy also inhabits the islands.

Few lions survive in this difficult environment.

Out here, by day, they lack their weapon of choice -- camouflage.

They bide their time until nightfall, when they prey on the weak and unwary.

The day grows hotter, and the small family has not been able to move.

Zebra families are close-knit, and the parents will not readily abandon their weak foal.

He manages to stand long enough to suckle... then tries to find relief from the burning sun in his mother's shade.

Meanwhile, far away, the other families head to water.

Zebras drink daily when they can, and a morning of grazing in the hot sun has made them thirsty.

The seasonal rains fill depressions with fresh water.

As temperatures soar above a hundred degrees, even these hardy ostriches can't resist a cooling dip.

Across a distant pan, the lame foal and his parents also need to drink.

But the foal is too exhausted to stand, let alone walk to water.

The oppressive heat leaves the parents no choice.

They must go in search of water without him.

[Thunder rumbling] As the afternoon wears on, a storm begins to brew.

[Chirruping] The meerkats race home to the safety of their underground burrow.

But the lame foal has nowhere to hide... [Calling] And no one to hear his feeble calls.

[Calling] Far away, other families weather the storm together.

The rain transforms the face of the Makgadikgadi and adds a blush of pink to the landscape, as flamingos arrive to feed on brine shrimp that the showers resurrect.

The pans turn into shallow lakes.

But the water is ephemeral.

Wind and sun combine to suck it up.

And it quickly turns salty.

The day has a surprise in store...

The lame foal has eluded predators and survived the stormy night.

He is a bundle of courage, determined to master his unreliable legs.

And his devoted parents have returned to his side.

No one knows what the little foal's future holds, but he can count on their loyalty to help him on his way.

[Creature calling] The Makgadikgadi does not show mercy to all of its inhabitants.

An old stallion has not survived the night.

All his adult life he likely guarded and defended a most treasured possession -- his harem of mares and foals.

During the peak breeding season, he would have mated with his mares.

Now somewhere out there could be a harem that no longer has his protection and a mare carrying his unborn foal.

An unattended, ready-made family is a rare windfall for the next stallion that claims it.

Competition for available mares is intense.

Serious fighting is rare between stallions and typically ends before major bloodshed.

Family stallions vigilantly shepherd their harems, keeping rivals at bay.

[Calling] A stallion's family knows him by his unique voice.

It's the call of their protector and leader.

Only his defeat or death will break the harem's bond with him.

Stallions that win another's harem are spared the long-term effort of building up their own, one mare at a time.

Grooming helps establish and strengthen family ties.

But an acquired harem comes with secrets.

It's very likely that one of the mares is already pregnant with the former stallion's foal.

For the next year she will nurture his legacy in her womb.

Then she will have to raise her foal under her new family stallion.

Without its father's protection, her unborn foal could be in peril.

As the wet season draws to a close, rain becomes scarce.

Grasses turn brown, and their nutrient quality declines.

Without fresh drinking water, the zebras' carefree days are numbered.

From all corners, families begin to converge on deep, timeworn tracks.

The lead mares all know the way to trusted late-season waterholes.

Hundreds of groups are drawn to the same pool.

By now, the water is little more than hoof-deep slurry.

The ostriches can't get close.

The zebras rule the drinking hole through sheer numbers and attitude.

A stray wildebeest calf is shown no kindness.

In the heated congestion, tempers fray.

Family stallions anxiously search for stray harem members, relying on sound and scent as well as sight to find lost ones.

Amid the striped chaos, foals must stick to their mother's side, or risk getting lost.

Stripes are unique to each individual, and scientists continue to speculate how these patterns help zebras to survive.

Weeks pass without rain, and strong winds stir up dust storms that race off the pans.

Fine, salty sand fills the air, blocking out the sun and making life unbearable.

Grazing is still plentiful, but zebras must also drink to survive.

And the Makgadikgadi has turned dry.

Now every zebra is caught up in the same plight.

They cannot stay here.

The families gather together, turn their backs on home, and head west, trusting their memory to guide them to water.

Somewhere in the exodus, there's a harem with a new family stallion and a mare with her fallen stallion's foal in her womb -- safe for now.

Yet there's one family that must stay behind, tethered to their home beneath the Makgadikgadi sand.

An eerie stillness falls on the grasslands -- empty now of all the striped horses.

Only ghosts remain.

Far to the west lies the Boteti River, a shallow ribbon of water that pulses with life.

This miracle of water in the desert is a haven for birds of every description.

All along the shoreline, lapwing pairs are nesting.

In the cool morning air, chicks make the most of their parents' warm cloaks.

Lapwing chicks are precocious and forage for themselves soon after hatching.

On the shore, a bull elephant goes about his daily ritual.

But this is the last peaceful mud bath he will enjoy for some months.

Soon nearly 20,000 zebras will inundate these tranquil shores.

Yet for at least one Boteti resident, life is about to get better.

[Lion calling] The families have been trudging away from home for several days.

They have left the open spaces of the pans far behind them and entered a claustrophobic, wooded landscape.

Suddenly, they quicken their pace.

A familiar scent excites them.

The first families have arrived at the Boteti.

It's been weeks since they last tasted clean, clear water.

These pioneers of the migration are eager to drink, but they are also nervous in this new landscape and easily startled.

African rivers are fraught with danger.

The smallest fright triggers a tide of panic that ripples up the shores, alerting the lion to a hunting opportunity.

[Animal calling] The lion has killed a mare.

Never again will she see the pans of home.

A family stallion knows when one of his mares is missing.

Frantically, he searches for her.

He tries to find her scent and listens for her voice.

But there is no response.

As the weeks pass, zebras overwhelm the shoreline... threatening disaster for the lapwing family.

Now the parents must raise their fragile chick among thousands of clumsy hooves.

The immigrants enjoy a rare moment of contentment.

But their rest is short-lived.

[Elephant trumpets] It's a bewildering time for the zebra foals, who have never seen a river before, nor the angry gray giants that dwarf them.

[Elephant rumbling] Difficult months lie ahead for these families.

Their refuge will soon become a prison, a purgatory that many will never leave.

Over the weeks, the lapwing chick learns that zebra hooves are not the only hazard.

A deadly assault can come from the skies, too.

His parents warn him to hide from the eagle.

The threat passes over, and life settles down once more.

The dry season drags on, and the Boteti's shores become overgrazed and trampled bare.

The landscape turns to dust.

Now the exiled families face a new dilemma.

They can count on the Boteti for water, but there's no grass nearby.

Each day the families plod farther away from the river in search of adequate grazing.

Eventually, hunger and thirst force them into exhausting 40-mile round trips between food and water -- a distance too far to cover in one day.

But they cannot return home.

Months of no rain have made the pans parched and sunbaked.

Only desert specialists can survive here now.

Still, for the meerkats' dominant female, it's a harsh time to be pregnant.

Food is harder to come by, and dry-season temperatures soar.

There is no escape from the sun.

Back at the Boteti River, life goes on.

The lapwing chick continues to thrive under his parents' watch and grows bigger with each passing month.

For the zebras, the season's dry stranglehold is as deadly as the lions.

They have found grazing miles away from the river.

To maximize their feeding time, they have stretched their thirst to the limit of their endurance.

It's been a week since they last tasted water.

They set off once more for the river, slaves to the same punishing routine they've obeyed for months.

Families gulp long drafts.

But there is no time to rest.

Sated, they must leave at once to go again in search of grazing.

All along the shoreline, parched families arrive, drink, and depart.

For the old and the weak, the tug of war between thirst and hunger takes its toll.

The grueling trek weighs heavily on the pregnant mares, many near the end of their 12-month term.

They must deliver soon, but the Boteti shores are no place for a newborn foal.

For a mare carrying a foal that does not belong to her family stallion, the time of reckoning draws near.

As the day wears on, wave upon wave of families trudge to the river.

[Elephant trumpets] The zebras' constant skittishness shatters the fragile truce.

By evening the elephants have reclaimed the waterfront.

[Elephant rumbling] And the last zebra leaves the Boteti shores.

But finally, throughout Botswana, storm clouds are massing.

[Thunder rumbling] After many torturous months, the dry season has mercifully ended.

This is the moment the zebras have been waiting for.

They no longer have to drink from the river.

Instead, they turn east and begin the journey back to the pans and grass islands of home.

Their exile is finally over.

Back in the pans, the meerkat family has a few new faces.

The pups are struggling to master the signature meerkat posture.

A babysitter has been left in charge while the adults forage far away from the burrow.

It's been a long shift, but his duty is nearing an end.

The others should be home soon.

The oncoming rains are a welcome sight.

They will bring beetles for the growing family.

Out on the pans, the epic spectacle of thousands of striped horses has returned.

The rains have released them from their punishing exile.

At last, the pregnant mares can deliver their precious burdens.

The season of green grass and of birth has begun.

With each passing day, newborn foals appear on the plains.

This one, just minutes old, learns to find its feet.

Others grow stronger every day.

But one small newborn has attracted attention.

A stallion rushes in and attacks it.

The foal's mother does her best to drive the stallion off, but he is relentless.

An attack like this has rarely been witnessed in wild zebras.

The attacker is a new family stallion, and somehow he knows the foal is not his.

His predecessor sired it.

In desperation the mare does all she can to rescue her foal.

The ordeal is finally over.

The mare returns to guard her newborn.

But he's fatally injured.

The stallion, his forelegs bloodied from the attack, chases intruders away, clearing a perimeter around his mare.

While the stallion's brutality seems senseless and cruel, he has acted purely on instinct.

In this difficult environment, he is hardwired to ensure that he and his mares devote their energy to caring only for his offspring.

Out on these wide, open plains, nothing escapes the attention of vultures.

Their appearance disturbs the grieving mother.

Her calls and high-stepping are a desperate attempt to persuade the foal to follow her.

But he cannot.

The mare will not readily abandon her foal.

She has carried him safely in her womb so far and for so long.

But it's over.

The foal is dead.

The family stallion comes for her.

She gives up her vigil to follow the others.

Perhaps the sacrifice of her foal was inevitable.

More vultures arrive and begin wiping away the sorrow from the land.

For every foal that does not survive in this sometimes cruel land, another lives on, enjoying the protection and loyalty of both mother and father.

Soon the summer wet season is back in full swing.

The meerkat pups are now old enough to join the family outings.

But the days are long, and it can be hard work keeping up.

It doesn't help that the grass is so spiky and tall.

The adults are vigilant and know when one of their brood is lagging.

A beetle is just the thing to encourage a tired pup.

But a whole beetle can appear daunting to a little meerkat.

He's in the market for something a little more bite-size.

All around, the Makgadikgadi animals settle into a brief spell of contentment.

The zebra families have walked thousands of miles over the past year to satisfy their needs for water and grazing.

But for the moment, they have everything they want close at hand.

For many families, new life is about to begin.

Soon mares will mate with their family stallion.

As long as there is rain, grass, and room to roam, these nomads of Africa will continue to leave their tracks across this ancient land.

A year from now, they will return to these green pastures to bear the next generation of remarkable survivors.

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