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.
Experience our planet as never before.
A bird's-eye view.
This is a journey that will embrace the world...
..showing us astonishing natural events...
..extreme challenges...
..and hard-won rewards.
This is the world on the wing.
It's spring in the Gulf of Mexico, in the far south of North America.
Families of snow geese are soon to begin an epic journey
across a continent.
It's a migration made by millions upon millions of birds.
Before they leave,
individual families join thousands of other geese
preparing for the great trek northwards.
They become one of a crowd made up of hundreds of other families.
But this spectacular gathering doesn't go unnoticed.
Out of the heavens soars America's national bird -
an aerial predator of cunning and power.
The parents warn their young, and the message spreads like wildfire.
The bald eagle flushes the birds, checking for signs of weakness.
The panic spreads like a Mexican wave,
but still, among the masses, the families stick together.
As more and more families take to the air,
they create a snowstorm of geese that confuses the eagle.
The massed ranks create a whiteout, impossible to see through.
She must look for easier options.
Overwintering coots are a far better bet.
Unlike geese, they need a long take-off.
They are also weak fliers.
It heads back to the water...
and performs a disappearing act...
..diving two metres below the surface.
But the game isn't up yet.
Another coot dives, but the water's shallow,
and the eagle's pin-sharp vision can see him.
It's a fatal mistake.
The eagle will follow the migrating flocks,
hoping for yet more opportunities.
The snow geese have a tight schedule to keep
if they are to reach the Arctic in time to breed.
It's 3,000 miles away.
They become part of a spring migration across the continent,
one that features millions of other birds.
Brown pelicans are one of America's most charismatic birds.
They breed in the warm waters of Baja California,
but travel north in search of fish.
The brown juveniles are still learning the ways of the ocean.
Their more colourful elders have many secrets to pass on.
The youngsters must learn the habits of every sea creature below.
He soon discovers that some can guide him to a meal.
Humpback whales are the easiest to spot -
they have travelled over 2,500 miles from the Arctic to breed here.
The males announce their arrival by slapping their five-metre long fins.
But this "breaching" is a more spectacular way of gaining attention.
35 tons of blubber make quite a splash!
The pelican soon discovers that these show-offs have nothing to divulge at this time of year.
They are too preoccupied with each other.
Dolphins, on the other hand, are a different proposition.
The youngsters learn that dolphins follow schools of anchovies.
Huge pods form around the biggest shoals.
The pelicans take their cue to dive from the dolphins.
The deeper the fish, the higher the birds dive.
The young pelican is perfectly adapted for plunge attacks.
As he hits the surface,
his legs and wings thrust backwards, forcing his bill around his prey.
His pouch gapes, sucking in ten litres of water
as his upper bill closes the trap.
Brown pelicans leave these pleasant, balmy seas when fishing opportunities arise further north.
Birds of prey arriving from South America have their own appointments to keep.
Many red-tail hawks stop for a bite to eat
at Bracken Cave in southern Texas.
High on the menu are 20 million free-tailed bats
that have just arrived from Mexico to breed.
It's the largest gathering of mammals on the planet.
As the bats leave to feed each evening,
they run the gauntlet of the waiting hunters.
For a rookie hawk that's just arrived, they're quite a challenge.
She has to learn how to catch them.
But she's pitched against the fastest and most agile bats in the world.
They run rings round her.
The sheer numbers are overwhelming, especially for a beginner.
She tries again.
Then again.
Finally, she spots a bat that's strayed from the mass,
and flicks her back claw to hook it.
Impressive stuff, but nothing compared to the real top guns.
These experienced hunters have learnt the best technique,
dive-bombing the bats at over 100 mph.
The best can catch a bat with one talon while still holding another.
The "best of the best" stay for the entire summer,
but most migrating hawks simply use the cave as a drive-through restaurant.
Like hawks, snow geese travel along well-defined routes,
known as flyways.
The Mississippi flyway is the most popular,
as families can drop down any time to rest or feed.
BOAT HORN BLOWS
Youngsters stick close to their parents -
those that are making their first migration will still be learning the way.
The young will only need to make the journey once
to remember it for a lifetime.
But not all routes are quite so easy.
Birds taking the western route have to cross hazardous deserts,
such as the Grand Canyon.
Hawks can use the updraughts rising from the canyon walls
to glide onwards and upwards to more forgiving lands.
The master of these travellers is the bald eagle.
She, too, is exquisitely sensitive to rising air currents.
She is a slope-soarer,
adapted to exploit the uplift created by hills and cliffs.
There is no shortage of uplift here!
Apart from the wind,
the canyon appears to offer little for such a water-loving bird.
But the gorge was carved out by water.
And here, the mighty Colorado still flows.
It has sustained life in these deserts for the last 17 million years.
It still feeds the eagles that are travelling through.
Just 85 miles further east lies Monument Valley.
It has no obvious attractions for migrating birds at all.
Even so, many snow geese taking the western route
pass over it as they travel north.
Like their Mississippi counterparts,
the adults recognise the landscape features,
and guide their young through.
But geese needing food or water face more of a challenge out here.
Unlike the Mississippi, the desert offers no food or water at all.
From the goose's perspective, this is a hard land to cross.
Geese must flap hard and fast to stay aloft
and push onwards to the fertile lands that lie further north.
But like the walls of the Grand Canyon,
the huge sandstone buttresses deflect air upwards.
It's just the help a family needs.
Migrating geese appreciate these free rides,
using them to join other flocks flying overhead.
On the West Coast, pelicans are also on the move.
They must keep to a strict timetable
if they are not to miss a great feeding event.
They say, "A wonderful bird is the pelican,
"his bill can hold more than his belly can".
While it's true he could swallow five kilos of fish in one gulp,
these rays are way out of his league.
They trawl for tiny shrimps using their mouths as a net.
They are also known as Devil rays,
and at times they appear to display supernatural powers.
It seems they too can fly!
Why they indulge in such weird aerobatics is anyone's guess.
But the pelican's aerial perspective
reveals that the jumps happen around the edge of the shoal.
Perhaps they panic the shrimps into the mouths of the other rays.
Or maybe they're just showing off!
But the rays' aerobatics won't delay the pelicans.
They are heading for one of the most bizarre natural spectacles in North America.
The youngsters follow the adults as they navigate
to a very special beach in the Sea of Cortez.
They are right on time.
The tide has reached its highest point.
The sea now reveals its prize.
An entire shoreline, carpeted in gulf grunion.
The adult pelicans know exactly when the grunion will arrive,
passing on this knowledge to the youngsters travelling with them.
The grunion surf ashore, and the females burrow backwards,
laying their eggs in the exposed sand.
The males then coil around to fertilise them.
They are laying their eggs out of the reach of aquatic predators,
above the high tide mark.
Their young will hatch on the next spring tide and return to the sea.
These fish out of water should be a doddle for a pelican to catch.
But they're missing the right tools for the job.
Their bills are too unwieldy to scoop the grunion from the sand.
The pelicans are relegated to fishing in the surf zone
as the orgy goes on behind.
Not the easiest place to fish, especially on a rough day.
But as the fish make their getaway, the pelicans seize their chance
and go back to what they know best -
plunge diving on to their prey.
The marshlands of South Carolina are the setting
for another strange fishing story.
One that involves a very talented pod of dolphins.
They are closely watched by a flock of great egrets,
who have become experts on the dolphins' behaviour.
As the dolphins manoeuvre, the egrets shadow them,
leap-frogging from one spot to the next.
Their cue is the moment a dolphin pops to the surface,
checking the position of the nearest mud bank.
The egrets are poised and ready for action.
Then it happens.
The dolphins drive the fish shoal ashore.
As the fish flounder, the dolphins scoop them up.
But the egrets also pile in.
This is the only place in the world where dolphins "strand feed" like this,
and the local birds have learnt to make the most of it.
As the tide drops further,
the dolphins search for more fish shoals.
Strangely, the dolphins always use their right sides to push ashore.
Their bellies flush pink with the excitement of it all.
The young dolphins pick up this technique from their parents,
as do the egrets that follow them.
Many no longer fish for themselves,
and totally rely upon the dolphins' cast-offs.
The egrets are living proof of birds' extraordinary ability
to adapt to the opportunities on offer.
Snow geese taking the Mississippi route pass over Nebraska.
Here, over the last 150 years,
natural grasslands have been transformed into America's grain belt.
From the goose's perspective, the changes are a major improvement,
and now the snow geese population is booming.
It is increasing at an incredible 5% per year
as farmers grow crops that the geese can eat on their migration.
Many of the birds that touch down here
will have been flying continuously for three days.
They would have travelled 800 miles, burnt over 3,000 calories
and lost a third of their body weight to reach here.
The first priority is to top up their lost reserves.
But even best-laid plans are at the mercy of the weather.
An overnight snowfall can blanket everything.
They have no option but to move, even on empty stomachs.
But flying burns calories,
and many of the migrating geese are pretty much running on empty.
Any young now have to rely on their parents' knowledge of the area -
without food, they simply won't make it.
In San Francisco Bay,
the young pelican reaches the end of his journey.
The Golden Gate Bridge spans waters teeming with some of the most diverse marine life on the planet.
Pelicans only make short migrations,
and for many, it's the end of their journey.
In fact, the prison island of Alcatraz
is named after the old Spanish word for pelican.
Throughout their travels, pelicans have learnt to find food
by watching other animals or using their ingenuity.
But here, the going is easy.
He can either catch fish in the bountiful waters of the bay
or scavenge on waste discarded by fishing boats.
He can even partner with Californian sea lions.
Like dolphins, they help find and corral the shoals.
With plenty of food to be had,
more than 1,000 sea lions laze around without a care in the world.
It's a carefree end to the pelicans' journey,
but it is the beginning of another.
These are California gulls,
a bird that lives on his wits around the harbours of the Californian coast.
But despite their love of the seaside,
each spring they hear the call of the wild
and all 65,000 of them up sticks and leave.
They head 200 miles inland to a barren salty lagoon known as Mono Lake.
Here, towers of calcium carbonate rise from the lake surface,
creating a surreal landscape.
It makes a stark contrast to the comforts of the gulls' usual home
along the San Francisco seafront.
Even the water is poisonous -
a caustic chemical brew of alkaline salts.
Despite its lack of amenities, the gulls flock here in their thousands.
Each morning, they wait for an event that happens as the day warms up.
Suddenly, the shoreline fills with vast clouds of brine flies,
billions of them.
For the gulls, it's a feast like no other.
As the flies gather to breed and feed, they turn the sand black.
His technique is anything but sophisticated -
he just opens his mouth and runs.
It may look inefficient,
but each fly contains seven calories.
He just has to catch 60 a day.
Here, the living is easy
so the gulls come here each summer to raise their families.
Food is also top priority for snow goose families.
When snow covers everything, there is none to be found.
YOUNG GEESE SQUAWK
But mother geese know exactly where to go.
In fact, thousands of snow goose families have exactly the same idea.
The marshes of the Platte River Basin
offer plenty of natural food,
even in bad weather.
Two million geese take refuge here
as they wait for the weather to change for the better.
But where geese gather,
so do the eagles.
The youngsters keep close to their parents,
hiding among the masses.
As before, the eagle's tactic is to divide and conquer,
harassing and fragmenting the flocks to single out the weaklings.
But healthy snow geese are ambitious targets
and there are thousands of other waterfowl on offer.
Mallards are certainly worth a try.
The eagle encourages others to join the hunt.
EAGLE CRIES
They pick out any weakened by the ordeals of the journey.
MALLARD QUACKS
With so much prey around, the eagles can relax and socialise.
They even start to play with their food.
Missed!
The youngster sees if he can do better.
Anyone can have a go.
Locking talons is a popular tactic.
Tackling is allowed
and soon everyone piles in.
Even scraps are used for passing practice.
These games are all about establishing relationships
and perfecting combat skills.
Bald eagles are the most social of all eagles.
By playing games,
the young birds learn survival skills from the adults.
The sport passes the time
as all the birds wait for the weather to change.
As the days go by,
all along Nebraska's Platte River,
there is an air of excitement.
The weather has changed in their favour.
It's time to check out.
100,000 snow geese launch themselves into the air.
And that's just a start.
Two million birds are soon on the move again.
Many families head on north over the Badlands of Dakota.
The barren landscape soon gives way to natural grassland.
The prairies stretch for hundreds of miles
and provide grazing for the largest land mammal in America.
The bison attract a very different flying traveller,
cowbirds.
As the bison migrate,
the cowbirds travel with them.
Like cuckoos, they even lay their eggs in other birds' nests,
so they never have to stop moving.
They rely on the bison to stir up insects.
They know their every move...
..and when it's wisest to keep out of the way.
A dust-bathing bison is a force to be reckoned with
but the cowbirds risk their lives to grab fleeing insects.
BISON SNORTS
Males fighting over females are a frequent occupational hazard.
But the birds are experts on bison behaviour
and know just how to dodge the battling beasts.
The bisons' collisions are like a car crashing at 30 mph.
Wisely, the birds stay out of the impact zone.
These one-ton beasts and their feathered friends
once numbered millions.
But the same landscape changes that have helped the snow geese prosper
have given the bison and cowbirds little space to roam.
On the East Coast, in Delaware Bay,
another animal migration takes place
just as it has done for aeons of time.
Over one million shore birds arrive from South America
to take part in this extraordinary event.
They time their visit to the highest spring tides.
It's now that thousands of bizarre, prehistoric creatures
emerge from the ocean.
Horseshoe crabs.
Like the grunion in Mexico,
they too aim to lay their eggs out of the reach of predatory fish.
It's a plan that worked millions of years ago, before birds evolved
but now the secret's out
and the crabs suffer the consequences.
Sanderlings and sandpipers are first to gather on the strand line.
They are like kids playing dare with the waves
as they pluck the freshly-laid eggs from the sand.
They gorge themselves silly.
They have a journey of 2,000 miles ahead of them.
If the sanderlings' onslaught wasn't bad enough for the crabs,
then the ruddy turnstones arrive!
Their rather unfortunate name
actually refers to their reddish plumage.
But turnstone is a good description.
They really do leave no stone unturned
as they search for eggs missed by the manic sanderlings.
Dunlin have longer bills
and can afford to take their time.
They probe for eggs that were successfully buried by the crabs.
In this battle for the beaches
the crabs suffer huge losses.
Hundreds upturned by the waves find it impossible to right themselves.
But for all this carnage,
the horseshoe crabs are great survivors.
Only a few eggs need to escape
to allow enough young to return to the beach in future years.
The birds now head northwards,
satisfied by an egg breakfast that will last them the journey.
Snow geese travelling up the East Coast of America
pass one of the greatest cities in the world.
They've covered two-thirds of their journey
in a little more than two weeks.
New York is a busy crossroads for travelling birds.
Over 250 migrating species still pass through each year
even though their marshlands have been replaced by real estate.
Although things ain't what they used to be,
the Big Apple does give some help to the exhausted snow geese.
The buildings act like the buttresses of Monument Valley,
channelling wind upwards
and giving geese a much-needed boost as they move inland.
CAR HORNS, SIRENS
Now they will continue into Canada
and onwards to their breeding grounds.
EAGLE CRIES
Bald eagles, also heading north,
spread out across the vast forests,
never straying far from water.
EAGLE CRIES
They head for melt-water streams and estuaries,
as this is their best chance for a meal.
One particular event draws eagles like no other.
It also attracts grizzly bears.
BEARS GRUNT
The soaring eagle gets the first sight of what's to come -
thousands of sockeye salmon
on the starting blocks for a race up the river to breed.
The eagle bides his time
as the bears lay claim to the best fishing spots.
Younger eagles watch from the sidelines, anxious to learn.
BEAR GROWLS
Around 15,000 fish create the critical mass
that fires the starting pistol.
Once one goes, they all do.
As the river fills with salmon, the bears go wild.
But the eagles hold back.
They're happy to let the bears do all the hard work.
The cubs are torn between stuffing themselves or catching more.
An eagle seizes the moment.
But she must eat fast.
Mother bear doesn't like others stealing her breakfast.
But the bears don't just compete with eagles.
Arguments over feeding rights keep tempers running high.
BEARS ROAR
The eagle spots another opportunity.
As she eats, she uses her wings to hide the fish
but she has just seconds to spare.
BEAR CUB YOWLS
Finally, the bears are stuffed,
eating just the fatty skin and leaving the rest,
much to the birds' delight.
And the eagle finally gets to eat in peace.
It's time for the eagles to move on.
They've got one more appointment to make.
All the snow goose families are nearing the end of their journeys.
Some pass over Niagara Falls on the border between the USA and Canada.
Further west, others cross the border
and head right for the heart of the tundra.
As the geese catch up with the retreating snow,
they stop one last time.
But hungry bald eagles have gathered here too,
anticipating the snow goose's arrival.
Maybe now, they will finally get to feed on their favourite prey,
especially as the exhausted geese are at their most vulnerable.
The young eagle buzzes the geese.
This time he's found a sitting duck...
..a youngster weakened by her long flight.
GEESE HONK
The snow goose fights back.
She even grabs his tail.
But the eagle puts his training into practice.
GOOSE SQUAWKS
A remarkable escape.
Or is it?
The snow goose survives against the odds.
And the young eagle returns to the classroom.
Like all birds, he will never stop learning.
As the weather clears, the geese make the final short hop
onwards to their Arctic breeding grounds.
They have travelled 3,000 miles to reach here.
It's only now that the young leave their parents
to raise chicks of their own.
The bond with their mother that guided them across North America
is now formed with their own offspring.
They will learn from her the many secrets known only to birds.
CHICKS SQUEAK
In the next journey across a continent,
we will fly with vultures,
flamingos and fish eagles
as we experience a bird's-eye view of Africa.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk