It's a universal dream to fly like a bird.
To soar on wings into the heavens.
But it's nothing compared to the reality.
This is our planet seen as never before.
A bird's eye view.
Theirs is a journey that covers the world...
..filled with astonishing natural events...
..extreme challenges...
..and hard-won rewards.
This is the world on the wing.
It's spring, and tens of thousands of white storks have left Africa
and are trying to reach their breeding grounds a thousand miles away in Europe.
They, like countless millions of other birds,
face many challenges on the journey ahead.
Already, these storks might not make it.
They have been blown off course and out into the Sea of Marmara.
The storks need rising currents of hot air to soar
but these thermals can't form over water.
The sheer effort of flapping their wings is taking its toll.
And the storks are dropping dangerously low.
If a wing as much as touches the water, they will fall in and drown.
They are battling for their lives.
But they have a lifeline.
An outcrop rising from the sea, the Princes' Islands.
Just enough sun-baked rock to create thermals.
They must quickly gain as much height as they can.
In this way, they can use the islands as stepping stones across the sea.
Mainland Europe is tantalisingly close.
They soar upwards one last time.
Then glide the seven miles towards it.
Istanbul - the gateway to Europe for millions of migrating birds arriving from Africa.
They spiral over the city before setting off to re-colonise the continent.
These storks are among the countless millions of birds
that risk their lives to come to Europe to breed.
Many try to choose a less hazardous route into the continent.
Grey cranes cross the Mediterranean at the Straits of Gibraltar.
Here, just 13 miles of sea separate Africa from Europe.
Ahead is the famous Rock of Gibraltar.
Reaching land is just stage one of their goal
as they have an appointment to keep in the far north of the continent.
The cranes don't pass unnoticed.
Barbary macaques were introduced from Africa hundreds of years ago.
Each spring, they witness this mass migration from their original home just across the sea.
Swallows flew the length of Africa to reach here.
Many will travel another thousand miles or more
before they reach their nest sites.
On a good day, cranes can travel 500 miles.
But three days of flying leaves cranes tired and hungry.
The Camargue, Europe's largest river delta, is the perfect place for a spot of R&R.
Below are the Camargue's famous white horses,
a breed that has roamed the marshes for centuries.
Crane families find the best feeding spots by joining other travel-weary birds.
Here, they will take on board the provisions they need for the journey ahead.
They are joined by greater flamingos, fresh from West Africa.
12,000 breeding pairs spend the summer here.
The salty lagoons provide everything they could wish for.
But life here isn't quite as peaceful as they'd hoped.
The flamingos arrive in the breeding season, as feisty stallions try to round up the mares.
Time to find a quieter lagoon.
Fortunately the Camargue has hundreds to choose from.
The cranes can't rest for long, they are bound for Scandinavia
where they have a date to keep with thousands of other birds.
The storks are equally pushed for time.
The first to appear in Europe are males,
racing to reach their nest sites before the females arrive.
Cities are an essential part of their flight plan.
Hard reflective surfaces are better at creating thermals than the surrounding countryside.
Roofs act like storage heaters,
pumping out heat even when the sun's behind a cloud.
Sun-baked roads form a matching highway of hot air in the sky above.
In fact, our urban sprawl now helps the storks migrate.
A warm city benefits birds in other ways, too.
Each winter evening, attracted by the heat of the city,
five million starlings stream into Rome.
Before they roost,
their manoeuvres create nature's greatest aerial display.
Their iridescent plumage is lit up by the setting sun.
But this spectacular performance isn't for fun.
The peregrine falcon is looking for his evening meal
and he's hunting the world's best formation flying team.
Their mesmeric waves confuse the peregrine.
He can't lock onto a single target.
To achieve such synchrony,
each starling shadows seven of his nearest neighbours.
They react 10 times faster than any human pilot.
To stand a chance, the peregrine must up his game.
Despite his best efforts, the peregrine has been outmanoeuvred and outperformed.
For the starlings, city life is just for the winter.
They will soon head for the wilds of Siberia to breed.
Cities aren't always so popular with birds.
Venice was once an area of marshland where migrating cranes could rest and feed.
Now they have to keep on flying.
A mother can help her tired offspring.
Air rising from her wingtips gives a boost to those following in her wake.
As they follow, young birds also learn the route.
Next year they will have to make the journey on their own.
Further along the coast, some marshlands still remain -
a perfect place to stop and recuperate.
Despite Europe's dwindling wild places,
it's still a magnet for breeding birds.
Sand martins fly from South Africa
just to nest in the banks of this river in Hungary.
They are here for the abundant insect life,
but, as their chicks grow, demand outstrips supply.
But in their time of need, the river provides a perfect banquet.
One by one, they emerge.
They are mayflies.
Their moment of glory lasts just three hours.
Just time enough to mate and lay eggs.
They are a "superfood" for the hungry chicks.
As the day ends, the mayflies perform their swansong.
The swallows are so full, they lose their edge and appetite.
But their loss is another's gain.
The biggest challenge for migrating birds is to keep on course.
Like all birds, cranes use the sun as a compass.
Her body clock even compensates as the sun arcs across the sky.
If it's cloudy, she can navigate by the Earth's magnetic field
But despite her state-of-the-art GPS, like us, she prefers to trust her eyes.
From above, the land unfolds like a map
and a river is the perfect line to follow.
Chateau de Chenonceau is a reliable landmark.
The Loire Valley is such a popular route,
50,000 cranes can pass through in a single day.
Many cranes that pass through this valley
still have a thousand miles left to travel.
But the storks are reaching the end of their journey.
They took 50 days to fly from South Africa to their nest sites in this German village.
The first male to arrive prepares to land.
He whiffles, spilling air from his wings to get down quickly.
He then jams on his air brakes
by lowering his legs and flaring his feet.
He's returning to his ancestral home,
a nest that has been in his family for generations.
But he faces competition. Younger males try to claim squatters' rights.
He protects the nest as if it's a family heirloom.
Soon all the arguments are over,
and the males settle down to wait for their mates to arrive.
To fill the time, they start a thorough spring-clean.
They haven't seen their partners for eight months
so it's vital to make a good impression.
He preens himself ready for the grand reunion.
Hopes are high.
But so far, it's just swallows and house martins that are arriving.
They set off from South Africa at the same time as the storks,
but had to flap their wings all the way, instead of gliding on thermals.
Like storks, the males arrive first.
The storks could face an agonising wait for their mates.
Migration is tough and some simply don't make it.
Brent geese avoid all this heartache by flying together,
as one big, happy family.
Mum, Dad and the kids are all joined by uncles and aunts.
The brent geese head northwards,
just as other birds migrating from Africa arrive.
Many flocks spend the winter on the coastal marshes
around Mont St Michel in Northern France.
But in spring, they leave for Arctic Russia.
Many start their 3,000 mile journey
by crossing the English Channel.
Brent geese take a leisurely six weeks
to reach their destination, stopping at least 16 times along the way.
The famous White Cliffs of Dover are their first sight of Britain.
As they leave, swallows are arriving for the summer.
They flew 6,000 miles to return to the farm they were born in.
Like storks, the male has some DIY to do.
Some nests have been in the family for 50 years.
Like all old properties, they need a spot of renovation.
Those good at the job impress the females
and are allowed to mate more often.
The right materials are everything.
Adding a few soft furnishings will improve his chances.
It's the perfect way to feather his nest.
And just in time.
The female arrives and follows him for an inspection.
She's impressed.
For the house-proud couple,
the migration has been a great success,
but not all journeys go according to plan.
London is hardly a top attraction for migrating birds.
But many are forced to make an unscheduled stop,
having suffered flight diversions due to bad weather.
Barnacle geese are among the many waifs and strays
that sometimes end up on the wrong side of town.
Lost birds use their navigational skills to try to get back on track.
For stray barnacle geese,
the nearest UK population is 400 miles north in Scotland.
The shortest route to join them is along the east coast of Britain.
Just over the Scottish border is Bass Rock,
the site of another great migration spectacle.
Gannets have travelled 3,500 miles from West Africa just to be here.
150,000 cram onto this one small outcrop.
They are attracted to the rich North Sea fishing grounds
that surround the island.
The birds form a fishing fleet to be reckoned with.
In one year, these gannets net 8,000 tonnes of fish between them.
The gannets' fishing trips may last four days
and take them 300 miles out to sea.
They can submerge 22 metres in a dive, deeper than any other bird.
They are cushioned from the impact
by air sacs in their throat and breast.
They slice though the water without slowing at all.
Meanwhile, the barnacle geese will travel on north
over the city of Edinburgh.
They prefer to hug the coast
but will move inland when they sense danger ahead.
Falling air pressure warns of an approaching weather front.
It may be safer inland but some storms are impossible to avoid.
THUNDER CRASHES
Thankfully, they're equipped
with the best wet-weather gear imaginable.
Their feathers interlock, creating a watertight seal,
resistant to the driving rain pounding at 40 miles per hour.
It's like water off a duck's back.
But storms aren't the only challenges that geese encounter.
The golden eagle, Scotland's deadliest aerial predator.
The geese whiffle to lose height quickly.
Eagles are formidable hunters.
But suddenly it's the hunter that's under attack.
Crows mob any predator that dares invade their territory.
The geese hightail it.
The eagle gets his comeuppance for once,
put in his place by a lowly crow.
The barnacle geese head northwest along Loch Ness.
Then, just ahead, a gathering of other geese,
exactly what a lost flock needs.
The massed birds are waiting for a weather window
that will allow them to leave for the Arctic.
They use the time to pile on the pounds.
But they have a problem.
Spring is the time of mad March hares
and the geese are bang in the middle of their boxing ring.
Females don't pull any punches fending off over-eager males.
Boxing hares are a sign that the geese should leave.
With a fair wind blowing,
the mad March hares kick-start the goose migration.
The race to the high Arctic is on.
Ahead lies a non-stop, 1,500-mile sea crossing.
The decision to leave is the most important they make.
Getting the forecast wrong could cost them their lives.
Once at sea, the nearest land is 400 miles to the northeast in Scandinavia.
Even these far reaches of Europe
attract birds that over-wintered in Africa.
Many ospreys make the northern forests of Finland their summer home,
travelling over 4,000 miles to get here.
Good fishing ponds are scattered throughout the forests,
making it a popular place to nest.
Brown bears are here for the fishing too.
It's an angler's paradise.
There's always one that gets away!
BEAR GROWLS
Success this time.
GROWLING AND GRUNTING
It's this superabundance of fish
that makes their 45-day journey here worth all the effort.
BIRD CHIRRUPS
BEAR GRUNTS
Ospreys have favourite feeding perches
which they return to time and again.
BEAR GROWLS
A mother bear knows just where they are...
GROWLING
..and so do cubs.
GRUNTING
But ospreys are messy eaters.
They usually leave a few scraps behind.
It's the perfect snack
for a hungry bear.
For the osprey, there's plenty more fish in the pond.
Further south, the bulb fields of Holland bring a patchwork of colour
to a landscape reclaimed by man from salt marshes.
In the past, cranes would have stopped here to breed.
Now they just keep on travelling.
In Europe, migrating birds have to be adaptable.
Until recently, windmills adorned the landscape.
It's now wind turbines instead.
Although wind farms can be dangerous in bad weather,
birds are usually canny enough to avoid them.
Mother cranes have no problem steering their families safely through the hazards.
They have an appointment to make and they must keep them moving.
CRANES HONK
They travelled 3,000 miles
to reach a very special patch of marsh in Sweden.
They join thousands of other families
that have also made the rendezvous on time.
This is the most important social event in the cranes' calendar.
For the parents, it's a place to renew their vows.
HONKING
They call in unison, a synchronised duet that gets them in the mood.
But the youngsters are also searching for a soul mate.
This young female seems free.
Time for a young male to make his move.
He must dance to win her heart.
She's hard to impress.
He will have to raise his game if he's to be taken seriously.
HONKING
Good dance moves demand practice and determination.
He rehearses his vertical leaps, hoping to impress.
Her interest is piqued.
His efforts pay off.
Now an item, they dance together.
Their synchronised routine ties the knot.
Their enthusiasm is infectious. It triggers a mass dance-off.
The happy couple leave the party early
to start their new life together.
And the dance goes on without them.
Barnacle geese fly continuously for days to reach the Arctic Ocean.
It's hard work.
For every breath they take, their wings will beat three times.
Once the fat reserves are gone, they will start burning muscle.
The last few miles are the hardest but the destination is in sight.
The Svalbard archipelago, midway between Norway and the North Pole.
Europe's furthest wilderness may look a barren wasteland to us
but it's paradise for the geese.
24 hours of daylight provide all the grazing time they need
as they prepare to mate and lay eggs.
Back in the stork village,
the return of the females hasn't gone to plan.
The males are still waiting.
When weather conditions are bad, whole flocks can get lost at sea.
But things are looking up.
The girls are back in town.
The males can't contain their excitement.
CLATTERING OF BEAKS
She remembers the location of her nest and drops down to greet him.
CLATTERING OF BEAKS
Together at last, they clatter a greeting.
In Africa, they spent eight months apart.
Now they must get to know each other again.
Back on Svalbard, the barnacle geese
are already experiencing a baby boom.
But this attracts a rare visitor.
And chicks make a tasty snack.
Mothers desperately shepherd their young to safety.
A lost chick is the first to go.
THEY HONK
And then another.
The geese launch a counter-attack but they can't manoeuvre easily.
HONKING AND GRUNTING
A hungry polar bear can wipe out an entire colony.
They desperately need reinforcements.
Nesting Arctic terns join the aerial assault, united by a common enemy.
Their plan is to make the bear's life a misery.
CHIRRUPING
More join the attack.
HONKING
The bear's irritation starts to show.
BEAR GROWLS
Skuas join the combat mission.
Faster and more aggressive, they drive home the attack.
BEAR GROWLS
Working together, the birds have saved the colony.
Although meeting polar bears is an increasing problem,
by nesting in the Arctic, the geese avoid human disturbance altogether.
But storks are among the many birds that deliberately seek us out.
They raise their young among us, in the very heart of Europe.
Like so many birds, they have managed to prosper
in a continent that we have changed more than any other.
Next time, condors and macaws will take us on an extraordinary journey
to discover the hidden secrets of the South American continent.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk