Original subtitles

...watched as a family of wild Chinese elephants

slept, exhausted after an epic 400-kilometre journey.

Forced from their ancestral forests by the worst drought

on record, the family had gone in search of a new home.

Having travelled through huge swathes of farmland,

there was still no sign of them stopping.

But what they did next surprised everyone.

Crossing under a five-lane highway, the family approached the city of Kunming.

Within days, the elephants had reached the city limits.

And they quickly found themselves in a frightening new world.

Scared and disorientated, the family had no choice

but to turn around and begin the long march home.

Remarkably, despite the damage they caused, the elephants were not just

tolerated by the local people, but helped.

With hundreds of thousands of dollars spent guiding them safely home.

After almost two years and more than a thousand kilometres on the road,

the weary caravan arrived back in the southern forests, where the drought had eased.

Against all odds, this part of the family's story had a happy ending.

But it showed that when animals are faced with dramatic

change, the urge to move away can be overwhelming.

Our planet, travelling around the sun, is tilted.

And in January, this means it's summer at the southern end.

Though, at the bottom of the world, that isn't always of this.

Even in the summer's peak, temperatures in Antarctica barely rise above freezing.

But with 24-hour daylight, there's now just enough

warmth to melt the sea ice around the continent.

And that is important for Gentoo penguins, who need to reach land in order to breed.

For the last few weeks, their lives have been driven by a 30-kilometre daily

commute to their feeding grounds out at sea.

Now, with bellies full, they're heading back to their chicks.

After a day in the water, it takes a while to get their land legs back.

Gentoo's need rocks free of ice on which to lay their eggs and raise their young.

So, the home straight is often an uphill waddle to the wind-blown cliff tops.

Their chicks had to be kept in a sheltered place.

They were hatched eight weeks ago and are now nearly fully grown.

In Antarctica's short summer window, they're

right on target to fledge before winter returns.

The chubbier the chick, the greater their demand for food.

And some parents seem reluctant to indulge them.

But there is value in this behaviour.

By making the chicks work for their meal, the

adults are able to assess their strength...

their stamina...

and their coordination.

The prospect of food entices the chicks down to the water.

Though not quite into it.

It seems that even for a penguin, the first step into cold water requires...

a little courage.

But it just takes one to lead...

for others to follow.

Shallow, sheltered pools are a safe way of testing their waterproof coats.

And with the summers so short here, they'll need them very soon.

They'll need them very soon.

They'll need them very soon.

Before long, the seas around Antarctica will be covered by ice once more.

So the young chicks must head for open water now, if they are to feed.

But they're nervous.

And for good reason.

Who wants to share the water with a three-metre leopard seal?

And not just one of them, but three.

Like their namesake, they hunt by ambushing their prey.

And gentoo chicks make easy targets.

But regardless of the danger, the penguins' need to feed is great.

And they're not afraid of the cold.

Gentoo's are the world's fastest penguins.

If they can avoid being ambushed, they have a chance.

The young penguins stick together for safety.

But in the confusion, a chick becomes separated.

It's now one-on-one.

The penguins' only hope is to rely on its great agility and stamina.

So the longer the chase, the better its chances.

This very lucky young penguin can now join the others.

And the open ocean awaits.

In February, the northern end of the planet points away from the Sun.

So in the Arctic midwinter, darkness is almost

continuous, with the only light coming from the aurora.

These ethereal displays are created as electrically charged particles from the

Sun collide with the Earth's magnetic field.

This is the time when countless animals begin

their long journeys to these northern regions.

5,000 kilometers to the south, snow geese have just started their annual migration.

Led by the older, experienced adults, they follow the thaw as it spreads

northwards and fly from the Gulf of Mexico to their breeding grounds in the Arctic.

They will reach the tundra just as the long days of summer

create the perfect conditions in which to raise their chicks.

They use natural landmarks like lakes and rivers to prevent them straying off course.

But today, the world beneath them is very different

from the one over which their ancestors flew.

Where there was once endless savannah, there's now industrial farmland.

But that is not necessarily a bad thing for the geese.

To reach the Arctic, the flocks need to refuel regularly along the way,

so the fields of America's breadbasket country have become vital pit stops.

This near-endless supply of food has meant that the snow geese population,

and their population, has doubled in the last 50 years.

But there's a cost to becoming one of the world's most numerous goose.

Not everything in this modern world is as it seems.

A quarter of a million are shot each year.

Snow geese have to run the gauntlet of hunters along much of their route.

But sandwiched between two of America's migratory

flyways lies a patch of wetland where they're protected.

Missouri's lowest bluffs.

It's one of the most important stop-off points on their long journey north.

How long they will stay depends on the weather.

In February, icy winds blowing down from the Arctic can cause snow to fall.

With temperatures to suddenly fall and

if it's freezing here conditions will be far worse where they're headed.

So for now all flights north are suspended.

They may be snow geese, but they don't seem to be at home on the ice.

With the lake's margins frozen, the birds become concentrated in the center.

The busier it gets, the less room there is for maneuver.

And that suits another visitor.

Bald eagles come here from across North America.

And they time their arrival to coincide with that of the snow geese.

The geese are far too big to be snatched on the

wing, so the eagles use a different hunting strategy.

Flying at the flock, they scare the birds into the air.

The tighter the geese are packed, the better it is for the eagles.

In

their panic, geese collide with one another and limbs are broken.

Injured birds are left high and dry on the ice.

Not able to escape underwater.

All will remain vulnerable for as long as this cold snap lasts.

Their onward migration still blocked by ice and snow.

Back in the Arctic the Sun is slowly beginning to strengthen.

But in late February its rays still barely show above the In such frigid conditions,

there's little to eat and most animals retreat southwards or shut down altogether.

But this one does neither.

A lynx, the most northerly cat in the world.

It's well protected from the cold, so it doesn't retreat.

But it may have to travel huge distances to find food.

One was even recorded walking more than 3,000 kilometres in just one year.

Further than anyone thought possible.

This cat relies almost entirely on just one kind of prey.

And right now, there are very few.

There's a few around.

Snowshoe hares.

Spotting one is only half the challenge.

Lynx need to eat every few days, so his search never ends.

He's in luck.

He has detected another scent.

The hare holds its nerves.

And trusts its camouflage.

The lynx can't outpace its prey over a long run, so he needs to get close.

A meal at last.

As the Earth's northern hemisphere tilts back towards the sun, bringing the longer

days of March, pronghorn antelope start their annual migration.

Their journey will take them far.

From the snowy plains of southern Wyoming to the lush

valleys of the Rocky Mountains, where they will give birth.

But today, their path has changed beyond recognition.

And to start with, they have to find a way through oil and gas fields.

A male tries his luck.

Pronghorn are cautious.

Especially when encountering humans.

So far, so good.

Now, for the rest of the herd.

Go!

Over the next couple of months, they will travel 200

kilometers to reach their carving grounds in the north.

A journey that gets more challenging every year.

Fences that were designed to keep livestock in

are equally effective at keeping pronghorn out.

But this is the route their ancestors took.

So they persevere.

And

this is the route they will follow.

Recently, one pronghorn crossed nearly 150 fences on its migration north.

But pronged horns and barbed wire can be an unhappy combination.

But pronged horns and barbed wire can be an unhappy combination.

And fences are far from the only problem.

More perilous are the highways that now cut across their path.

They may be the fastest land animal in the Americas.

But they can't always dodge a car.

The changes brought by the last 200 years have reduced pronghorn numbers by over 90%.

But there is some good news.

The pronghorn's loyalty to ancestral roots has made it

possible to build overpasses at key crossing points.

And that has almost eliminated road deaths in the area.

As the herd continues north, they reach the real Wild West.

Here, they must face not human-made obstacles, but natural ones.

The snow is now melting, showing that they're on schedule to

reach their carving grounds just in time to give birth there.

But the seasonal changes also bring problems.

Ahead lies Wyoming's Gros Ventre River, now swollen with meltwater.

The pronghorn must cross it to get to their breeding grounds, but they seem nervous.

Not about the river itself, but what predators may be hiding on the opposite bank.

In the water, their speed over land will be of little relevance.

But predators such as wolves and cougars have now been hunted almost to extinction.

So the chances of an attack here are slim.

It's just that the pronghorn don't know that.

It still pays to be cautious.

It's got them this far.

Several weeks after setting off, they at last reach their breeding grounds,

the fertile valleys of the Rocky Mountains.

Mexico's Baja Peninsula doesn't experience the cold winters of the north.

So the mild temperatures of its seas at this time of the year make it an excellent

seasonal retreat for one of the world's greatest long-distance travellers.

Grey whales.

It's mid-March, and six weeks ago, this female gave birth here.

The sheltered waters are warm and free from predators.

It's an excellent nursery.

But such perfection comes at a cost.

There's no food for this mother, and she's been here since December.

So as soon as her calf is strong enough, she will lead him 8,000 kilometres north

to their feeding grounds in Alaska's Bering Sea.

The longest migration made by any mammal.

Fortunately, her youngster is growing fast.

Nourished by more than 200 litres of milk a day, the one-tonne baby is full of energy.

Luckily, mother knows just the place for him to let off steam.

And this is it.

A shallow sandbar in the middle of the lagoon.

And it's clearly the place to be.

As the tide rolls in over the shallow bank, it creates a gentle current.

Attracting whales from across the lagoon.

It's the calf's first introduction to whale society.

And he seems a little shy.

Best stay close to mother.

The sandbar is a good place to practise the swimming

skills he'll need for the long journey north.

Jellyfish are carried along with the current, but he swims against it.

Using it like an underwater treadmill to build up his stamina.

Every year, over 1,000 grey whales migrate to this one lagoon.

But not all are females with calves.

Many are large males that make the long journey here in the hope of finding a mate.

Females with young are definitely not interested.

Though that doesn't put off this amorous male.

And swimming away only seems to encourage him.

Rejection is clearly hard to take when you've

travelled half the length of the planet.

It's hard to get here.

Now,

he seems to take out his frustration on the

calf, forcing him down, away from the surface.

Finally, the male gets the hint.

It's time for the pair to head north.

Since arriving three months ago, the female has lost a third of her body weight.

So now she must begin the long trek back to her feeding grounds.

Her youngster will need luck to complete the journey.

One in three grey whale calves never reach their destination.

The Earth's tilt drives all migrations.

But even at the equator, where the tilt has little seasonal

effect, there are some animals that are constantly on the move.

Army ants.

Every day, each runs the equivalent of a human marathon in order to collect food.

These particular ants specialise in capturing the larvae of other insects.

Workers loaded with their prey are helped to cross gaps

in the leaf litter by others forming living bridges.

They are also known for their ability

to feed themselves.

Trails of pheromones lead them to their temporary headquarters.

A bivouac.

A nest built entirely from the bodies of the ants themselves.

Hidden behind this living wall lies the control centre of the colony.

The queen and her most recent young.

The whole bivouac has hung here for the last two weeks.

But that is about to change.

Day turns to night and a signal ripples through the colony.

A chemical cue coming from deep within the bivouac.

The message is clear.

It's time to move.

These little insects have large appetites.

And having cleared the surrounding forest of living

prey, they must now move and find new feeding grounds.

Following one of the main foraging trails, workers transport the newly hatched larvae.

While soldiers guard the edges.

There could be as many as half a million ants in this colony.

And none will be left behind.

The reason they proceed under the cover of darkness now becomes clear.

The queen herself is on the move.

She's bigger than any other individual.

And for the past two weeks, she's been laying an

egg every minute or so and therefore unable to move.

She's now able to travel.

Now, with her reproductive duties temporarily

suspended, she's able to move to fresh hunting grounds.

This is the only time she's ever visible out in the open.

And the queen is not the army's only important traveler.

In a rare event that only happens every few years, supersized larvae appear,

carried by the workers.

These are the young males and future queens who will

soon leave this colony and establish their own dynasties.

Before daylight returns, the army makes camp.

They will continue to travel every night until they reach fresh hunting grounds.

By then, the queen will be ready to lay more eggs and add more workers to her empire.

Back in the north, the mother gray whale and her

calf are now four weeks into their epic migration.

Since leaving, the youngster has put on over a thousand kilos.

But his mother hasn't eaten for months.

And there's still a lot of ocean to cross before

she can begin her banquet in the Bering Sea.

They keep close to the coast, using visual cues to guide them.

She's made this journey many times during the last

30 years, and a lot has changed since her first trip.

Still, she doesn't shy away from human attention.

And the calf appears to positively relish the limelight.

The crowded Californian coast seems a million

miles from their sheltered bay in Mexico.

And it's only going to get busier from here on.

Soon, the pair reach the port of Los Angeles, the biggest in North America.

Nearly 2,000 ships use it every year.

The constant engine noise disrupts the underwater soundscape, disorientating the

whales and increasing the risk of a collision.

Scores of whales die every year in ship strikes in these waters.

This gray whale was one of the unlucky ones.

Mother and calf have avoided the busiest shipping lanes.

But the most dangerous part of the trip lies just ahead.

Monterey Bay.

35 kilometers of open water.

Staying close to the shore here would cost valuable time.

So she leads her calf across the deep water of the bay.

But it's a risk.

She knows what's out there.

She goes into stealth mode.

Stopping her regular contact calls and surfacing as infrequently as possible.

Orca.

They know these waters well.

And they are on the hunt.

Mother and calf have been discovered.

An adult gray weighs ten times as much as an orca and can be a formidable opponent.

So the pod circle warily, looking for a chance.

They don't want her.

They want her calf.

They surge up onto his back and force him underwater, trying to drown him.

Supported by his mother, he has survived the first attack.

But he's been wounded.

And now the pod call in their reinforcements.

A massive five-ton male.

Boasted by this extra muscle, the orca switch to an all-out attack.

There's little your mother can do.

At full ramming speed, it's like being hit by a bus.

The outcome is inevitable.

This mother will have to continue her journey alone.

For many animals, the instinct to move is overwhelming.

Despite the dangers.

But for every trip that ends in tragedy, countless millions reach their destination.

Allowing them to reap the rewards of better conditions and fresh opportunities.

And these migrations are crucial for others, too.

However,

we have now changed the planet.

Cutting off ancestral roots,

and impacting even the most remote corners of the globe.

But there is hope.

We know more about these journeys than ever before.

And with our help, many animals are now

overcoming the challenges of our modern world.

For a healthy and connected planet, we must preserve the freedom to move.

And if we do, the vital journeys of each and

every animal will continue for years to come.