[theme tune playing]
[David Attenborough] Sixty thousand years ago,
humans left Africa for the first time.
Since then, we haven't stopped,
traveling to every corner of the Earth.
But our journey is just one of many.
At any given moment,
billions of animals are on the move.
[music becomes stirring]
And the health of our planet depends on it.
[music abates]
[music fades, intensifies]
Migration is the most vital survival strategy.
[music intensifies]
Whether to feed...
to breed...
[elephants roar]
...or to find a new home.
And it's not without risk.
[music intensifies]
- [growls] - [screeches]
[trills]
This series traces extraordinary journeys
in a world that is changing faster than ever.
[rousing music playing]
And only now are we beginning to understand
that all life on Earth
depends on the freedom to move.
[music intensifies]
[music ends]
[somber music fades in]
[wind howling]
Every year, this land in Botswana is transformed.
These scars are the only sign that it was covered by water
just three months ago.
[poignant music playing]
Then, rich and green.
Now, baked and barren.
This change drives animals to move en masse.
[bellowing]
[dramatic tribal music playing]
Cape buffalo are marching across the Kalahari Desert
towards the last remaining water.
Groups have come together and formed a mega herd.
[grunting]
The largest in Africa.
[music continues]
[music abates]
All are making the same annual pilgrimage
to one remote marsh.
[chirping]
And others are relying on them to do so.
These lions are buffalo specialists.
And the mega herd's arrival
is the most important event of their year.
For weeks, they've been waiting for the buffalo army.
Eyes fixed on every shape crossing the horizon.
[menacing music playing]
[buffalo calls]
[growls softly]
[birds shrieking]
[insects buzzing]
[growls softly]
Finally.
[dramatic music playing]
[music abates]
[rasping, snorting]
The approaching horde is a wall of horns and muscle.
But the lions must find a weakness.
And this could be it.
A lone bull.
He may be separate from the herd,
but he is four times heavier than a lion
and one of Africa's most dangerous animals.
The pride must approach with care.
[buffalo snorting]
One by one, they casually walk towards him
as if uninterested in a hunt.
In fact, they're falling into position.
[menacing music playing]
- [lion growls] - [buffalo snorts]
[buffalo snorting]
[music intensifies]
[lion roars]
The females take it in turns to attack...
tiring the bull.
[dramatic tribal music playing]
Now, the heavier males join the fight.
[music intensifies]
[buffalo bellows]
[lions snarl]
[buffalo groans]
[music abates]
[buffalo bellowing]
[bellowing fades]
The pride has honed their technique so well
that in just three minutes,
they have defeated their most formidable opponent.
[stillness]
[music fades away]
The migration on which the lions depend
is one of millions driven by the seasons.
And they, in turn,
are a consequence of another journey.
[music reprises]
Our planet's year-long loop around the sun.
As it travels,
it does so on a tilt of 23 and a half degrees.
And it is this that creates our seasons.
[music intensifies]
To understand how, keep your eye on the North Pole.
For half the year, it's angled away from the sun,
bringing darkness and winter.
[music soars]
For the other half, it swings towards the sun,
bringing longer days.
It's this annual cycle
that drives the greatest movements of life on Earth.
And in the Northern Hemisphere, this brings the year's biggest change.
Spring.
[music fades out, ends]
In late March, the days lengthen faster than at any other time.
[poignant string music playing]
Sunlight increases, quickly heating the land.
[thunder rumbles]
Triggering rainstorms.
The Northern Hemisphere suddenly becomes warmer
and wetter.
Perfect for plants.
[music intensifies]
The land turns green.
[music fades away]
And one animal exploits the boom in plant growth like no other.
- [chirping] - [tiny footsteps]
A week ago,
this desert locust in Ethiopia
was a shy, solitary creature that moved very little.
[dark playful music playing]
Not anymore.
When available food skyrockets,
locusts switch to swarm mode.
[music intensifies]
[chorus of chirping]
They start marching
and multiply ten times faster.
[strident string music playing]
As their numbers explode,
they strip the land bare.
So to find more and more food,
they must keep moving.
[music intensifies]
The swarm grows.
And grows.
[music intensifies]
Devouring every plant in its path.
But this is just the start.
On foot, they can only move so far.
[music ends abruptly]
To go further,
they must change form.
[soft squelching]
They grow wings.
[suspenseful music playing]
[music becomes uplifting]
Now, with an even larger appetite,
the entire army takes to the sky.
[music becomes dramatic]
They eat...
and fly.
Eat...
and fly.
[cacophonous buzzing]
They come together to form a super swarm,
200 billion strong.
The biggest seen in 70 years.
It consumes 400,000 tons of food
every single day.
So if the whole swarm is to feed,
it must move further and faster.
[music intensifies]
It travels 100 kilometers a day
across farmland and towns.
[music abates]
It sweeps across country after country...
and most astonishing of all,
it even crosses the Red Sea.
It's the first time a swarm clears the Himalayas and reaches Tibet.
[music intensifies]
Everywhere it goes,
it brings chaos.
It will keep moving until the changing seasons bring drought.
For when their food finally disappears...
so will they.
[music fades out abruptly]
[solemn drumbeat reverberates]
[metallic percussive sound reverberates]
In April, day length in the North continues to rise.
[subdued expectant music playing
The increase in sunlight warms the oceans,
creating vast algal blooms
and a sudden abundance of food.
For one animal, this is the moment to travel.
[music becomes suspenseful]
Midnight on a remote island off British Columbia.
Underground...
something stirs.
[whimsical music playing]
[chirruping]
This ancient murrelet chick has only just hatched,
yet it's about to face the toughest journey it will ever make.
She hasn't had her first meal
and urgently needs food.
[warbling]
Mum makes contact.
[chick chirruping]
[warbling]
Across the island, hungry chicks emerge from their burrows
following their parents' calls.
But if they're expecting to eat now,
they're going to be disappointed.
[music intensifies]
This is the only seabird
that is fed exclusively at sea.
[music abates]
The chicks just need to get there.
[peeping]
They can't yet fly,
so their only way to the ocean
is on foot.
- [quirky dramatic music playing] - [peeping]
[chicks peeping]
While waiting till nightfall makes sense to avoid predators,
it's a little harder to see where you're going.
[squeaks]
[soft thud]
And when you're barely bigger than a golf ball,
anything can be an obstacle.
- [thuds] - [music stops abruptly]
[chirps]
[music reprises]
[all chirping]
Their way may be blocked by the lowest of logs...
and the smallest of streams.
[peeping]
[music abates]
For some, the journey is over before it has even begun.
[muffled cheeping]
[music reprises]
But not for this chick.
[optimistic music playing]
Finally, the beach.
And it's the last land it will touch for two years.
[chirping]
To find Mother,
it calls into the darkness.
[gentle piano music playing]
[chirping]
[chick peeping]
Together again.
But the chick has still not eaten.
To reach the nearest food,
they paddle nonstop
for a remarkable 70 kilometers.
Here, Mother can finally dive
to collect the chick's first meal of krill.
But this is just a pit stop.
The pair paddle a further thousand kilometers.
It's a month-long migration to the rich northern seas
where they can feast.
It's probably the longest journey made by any newly hatched bird.
[music becomes rousing]
And because the oceans are so productive in summer,
the murrelets can spend virtually their entire lives at sea.
- [single piano key plays] - [metallic percussive sound reverberates]
1600 kilometers northwest of Hawaii
lies a remote speck of land,
Laysan.
Home to one of the world's largest seabirds.
[whimsical music playing]
The Laysan albatross.
[quacks, beak clacks]
This chick, six weeks old,
will become a supreme long-distance traveler...
[music becomes comical]
...flying millions of kilometers in its 60-year life.
Now, however, at four months old,
it's still flightless
and going nowhere.
[whimsical music playing]
Unlike the murrelet,
it depends on food being brought to it
by its parents.
But they could be fishing up to 3,000 kilometers away.
So it may be waiting a while.
- [comical music playing] - Through pouring rain...
...blasting winds...
and baking heat.
[music intensifies]
[music ends]
Every bird crossing the horizon brings hope.
- [shrieks] - [expectant music playing]
An albatross.
But the wrong kind.
A black-footed.
[music intensifies]
Though she has almost certainly brought food.
[clucking]
Starving, the Laysan chick tries its luck.
[shrieks]
- [squealing] - [shrieks]
Clearly, for this mother, it's family first.
[peeps, beak clacks]
[beak clacking]
[somber music playing]
But what looks like a lifeline...
[peeping weakly]
...could be a death sentence.
[peeping stops]
Across the island, chicks are dying.
[music becomes more somber]
There is now so much plastic in our oceans
that it reaches even the most remote islands on Earth.
Carried here by the currents.
The parents mistake small floating pieces for food
and bring it to their young,
accidentally killing them.
- [beak clacking] - [music intensifies]
It's almost certain that every chick on the island
has plastic in its stomach.
[cheeps softly]
Those that are fed too much starve to death.
Laysan albatross are in the greatest danger.
They consume more plastic than any other seabird.
And it's getting worse each year.
[music becomes rousing]
[music abates]
At last, after nearly three weeks at sea...
the chick's father returns.
[whimsical music playing]
[shrieking]
Having spent so long apart,
they need to renew their bond.
[chirping, beak clacking]
[chick peeping, beak clacking]
This could be the last meal the chick is ever given.
And almost certainly contains plastic.
[tense poignant music playing]
[chick chirping]
[distant chirping]
Its father returns to a life traveling the Pacific.
And the chick is left to its fate.
But it's not over for him yet.
[tense music playing]
Albatrosses normally throw up hard-to-digest parts,
like squid beaks and bones.
Ejecting lighters and bottle caps, however, is more of a challenge.
[music intensifies]
[music crescendos]
[cheeps, clacks beak]
But this chick...
is a survivor.
- [whimsical French music playing] - [cheeping]
And with that,
he is one step closer to takeoff.
In a few weeks, on the right wind,
he will finally be able to make his big debut
as one of the greatest ocean travelers.
[music fades out]
The course of our tilted planet through space
affects one place more than any other.
[disquieting classical music playing]
Summer in the North.
The Arctic now faces the sun
and is bathed in round-the-clock daylight,
melting an ocean covered in ice.
[music becomes rousing]
To survive in this shifting world,
life must move with it.
[snorts]
[music becomes menacing]
[music abates]
[growling]
This young polar bear's home changes so much each year
that he can't keep to a limited territory.
Instead, he must roam for thousands of kilometers
in search of seals.
[quirky string music playing]
But every summer, as the ice begins to melt,
he must spend less time walking...
and more time swimming.
[music becoming dramatic]
Now, for almost eight hours a day.
[snorting]
He can smell prey from 30 kilometers away.
[music abates]
So he knows that this bearded seal is nearby.
[seal snorts]
[tense music playing]
[sniffing]
The seal is unaware of the danger.
[croaks softly]
And the bear needs to keep it that way.
[music intensifies]
[music continues]
[croaks]
[music becomes chaotic]
[music fades out]
[snorts]
The success rate of hunting from the water is very low.
[gentle classical music playing]
[sniffing]
[music becomes suspenseful]
[music abates]
Maybe third time will be lucky.
[sniffs]
[music continues]
[music intensifies]
[music becomes chaotic]
[music fades out]
[stillness]
[subdued music playing]
This young bear has yet to master the art of stalking from the sea.
But it's important that he does.
He may have to rely on it more and more each year.
[yawns]
Our climate is warming.
[poignant music playing]
And nowhere is this having a greater effect
than in the Arctic.
This year, the temperature climbs
to a staggering 38 degrees Celsius...
melting sea ice faster than ever.
And one Arctic animal is affected more than most.
[music continues]
To feed,
walrus need a combination of a shallow seabed,
abundant clams,
and ice floes on which to rest.
[walrus rasping, snorting]
But there are now fewer places to do so.
[music abates]
Making each summer more difficult than the last.
[music resumes]
Especially so for a new mother.
[calf chirping]
[mother rasps]
Three days ago, she had to leave the herd to give birth on her own.
And since then, she hasn't left her calf's side.
- [calf grunts] - [mother growls]
Nursing mothers need nearly twice as much food.
But they can't leave their calves alone while they themselves feed.
So she must go in search of others
to help her care for her young.
A newborn walrus is able to swim from day one.
But he's not yet strong enough to travel far.
So, for his first journey,
he hitches a ride.
[music becomes whimsical]
With fewer ice floes each year,
they must swim further to find help.
And until then, his mother can't feed.
Even when they do find others,
the ice must be low enough for the calf to climb out.
[rasps]
Too high.
[rasping]
[growling]
This looks just right.
But with suitable ice in short supply,
space is very limited.
- [attacker growls] - [mother grunting]
[both snarling]
[roaring]
[snarling, roaring]
- It's not the welcome they needed. - [calf softly grunting]
[poignant music playing]
Even when there's enough ice,
without anyone to help, she is unable to feed
and must stay with her calf.
- [calf barks] - [mother rasps]
Their search must go on.
The calf will depend on her for the next three years.
Wherever she goes,
they will go together.
[music intensifies]
In the next decade, the summer sea ice could disappear altogether.
If that happens,
even for the Arctic's most seasoned travelers,
there may be nowhere left to go.
[music intensifies]
[music fades out]
In late June,
the North feels the full impact of the Earth's tilt
and receives more daylight than at any other time.
And, in one corner of the Pacific,
this creates the greatest opportunity of the year.
[somber music playing]
For six months,
Alaska's Bering Sea appears lifeless and empty.
Then, one day in June...
all that changes.
Humpback whales arrive
after a month-long voyage...
for the biggest event in their calendar.
Thousands of them.
[music becoming dramatic]
Across the Pacific,
other travelers are also on their way.
Sooty shearwaters race to get there in time...
flying 1,000 kilometers a day nonstop.
The occasion is so important,
they come from the other side of the world.
At 65,000 kilometers,
it's the longest animal migration on Earth.
[music intensifies]
A million of them join the whales.
All have come to feed.
[music intensifies]
It's one of the greatest gatherings of life on Earth.
Here, five months ago,
there were just seven hours of light a day.
Now, there are 17.
The change triggers an explosion in the numbers of plankton and krill.
For the whales, it may be the only time they feed in the entire year.
Over the summer,
each scoops up 900 tons of food.
They all have just 90 days to eat as much as they can.
Soon, the days will shorten
and bring an end to the great feast.
Then, every one of them will return south.
The opportunities brought by our tilted planet's journey
can be enormous yet fleeting.
[music abates]
After a month of long summer days,
temperatures in the North Pacific are reaching their peak.
An ocean predator detects the change
and sets a new course.
[suspenseful music playing]
A tiger shark
on a thousand-kilometer odyssey across the Pacific.
Guided by the Earth's magnetic field,
she swims in a straight line towards her target...
Laysan Island.
And she's not the only one.
[music intensifies]
This species makes some of the longest journeys of all sharks.
And hunts a bigger range of animals than any other.
Including even
birds.
[music abates]
The Laysan albatross chick hasn't eaten
since he was abandoned by his parents two weeks ago.
[whimsical French music playing]
To find food,
he must now leave the island.
[chirping]
But the world's largest seabirds need a lot of lift.
[music fades out]
That could come at any moment.
In July, the high ocean temperatures generate tropical storms at sea...
bringing wind to Laysan
and the young albatross a ticket out of here.
[dramatic string music playing]
The breeze continues to build
until there's enough to lift even an albatross.
And the black-footed chicks are always first to go.
[music intensifies]
[chirping]
[music abruptly ends]
A chick's first flight is never a long one.
[disquieting music playing]
And here, it's often their last.
[music becomes dramatic, fades out]
[chirping softly]
The tiger sharks have arrived.
[menacing music playing]
[music intensifies, abates]
[squawking]
And they are very effective.
[music reprises]
[music fades out]
For the young albatross, it's not exactly encouraging.
- But it's now... - [quirky dramatic music playing]
...or never.
If he reaches the open ocean,
he may not touch land again for five years.
But there is no room for error.
[music intensifies]
Time to throw caution to the wind.
[music builds]
Time to fly.
[music crescendoes]
[music fades out]
[theme tune playing]
[music crescendoes]
[music ends]