Our Planet

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.

And the health of our planet depends on it.

Migration is the most vital survival strategy.

Whether to feed...

to breed...

...or to find a new home.

And it's not without risk.

This series traces extraordinary journeys

in a world that is changing faster than ever.

And only now are we beginning to understand

that all life on Earth

depends on the freedom to move.

Every year, this land in Botswana is transformed.

These scars are the only sign that it was covered by water

just three months ago.

Then, rich and green.

Now, baked and barren.

This change drives animals to move en masse.

Cape buffalo are marching across the Kalahari Desert

towards the last remaining water.

Groups have come together and formed a mega herd.

The largest in Africa.

All are making the same annual pilgrimage

to one remote marsh.

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.

Finally.

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.

One by one, they casually walk towards him

as if uninterested in a hunt.

In fact, they're falling into position.

The females take it in turns to attack...

tiring the bull.

Now, the heavier males join the fight.

The pride has honed their technique so well

that in just three minutes,

they have defeated their most formidable opponent.

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.

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.

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.

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.

In late March, the days lengthen faster than at any other time.

Sunlight increases, quickly heating the land.

Triggering rainstorms.

The Northern Hemisphere suddenly becomes warmer

and wetter.

Perfect for plants.

The land turns green.

And one animal exploits the boom in plant growth like no other.

A week ago,

this desert locust in Ethiopia

was a shy, solitary creature that moved very little.

Not anymore.

When available food skyrockets,

locusts switch to swarm mode.

They start marching

and multiply ten times faster.

As their numbers explode,

they strip the land bare.

So to find more and more food,

they must keep moving.

The swarm grows.

And grows.

Devouring every plant in its path.

But this is just the start.

On foot, they can only move so far.

To go further,

they must change form.

They grow wings.

Now, with an even larger appetite,

the entire army takes to the sky.

They eat...

and fly.

Eat...

and fly.

They come together to form a super swarm,

the biggest seen in 70 years.

200 billion strong.

every single day.

So if the whole swarm is to feed,

it must move further and faster.

It travels 100 kilometers every single day

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.

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.

In April, day length in the North continues to rise.

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.

Midnight on a remote island off British Columbia.

Underground...

something stirs.

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.

Mum makes contact.

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.

This is the only seabird

that is fed exclusively at sea.

The chicks just need to get there.

They can't yet fly,

so their only way to the ocean

is on foot.

While waiting till nightfall makes sense to avoid predators,

it's a little harder to see where you're going.

And when you're barely bigger than a golf ball,

anything can be an obstacle.

Their way may be blocked by the lowest of logs...

and the smallest of streams.

For some, the journey is over before it has even begun.

But not for this chick.

Finally, the beach.

And it's the last land it will touch for two years.

To find Mother,

it calls into the darkness.

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.

And because the oceans are so productive in summer,

the murrelets can spend virtually their entire lives at sea.

1600 kilometers northwest of Hawaii

lies a remote speck of land,

Laysan.

Home to one of the world's largest seabirds.

The Laysan albatross.

This chick, six weeks old,

will become a supreme long-distance traveler...

...flying millions of kilometers in its 60-year life.

Now, however, at four months old,

it's still flightless

and going nowhere.

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.

Through pouring rain...