Lords of the Air Life on Earth

White Storks - if you wanted to pick one bird as representative of all birds in the world...

you could do worse than pick the White Stork - a marvellous flier and an intrepid traveller.

This pair have come from Africa to nest in this small town in Bavaria -

they have complicated courtship and greeting rituals and they are devoted parents.

Just as they could stand for all the birds, so this - a stork's feather -

could be seen as a key to everything that is most crucial about a bird.

A feather's a marvellous aerofoil - man has yet to invent anything as strong weight for weight.

It's also an efficient insulator and that too, is important to a bird.

It's a complicated structure.

This feather has hundreds of filaments on either side of the central quill.

They're held together by several hundred thousand microscopic hooks.

The feather is the individual creation of the bird - no other animal possesses it.

And the oldest known feather was found as a fossil in rocks a few miles from here in Bavaria.

It's about 3 inches long, preserved in miraculous detail

and to all intents and purposes, it looks identical with a stork's feather.

That feather had been found by men quarrying this limestone near the town of Solhofen.

The stones have been laid down 150 million years ago, at the bottom of a shallow lagoon.

Its fine, even texture, made it ideal for use in lithographic printing.

The texture also makes it a superb preserver of fossils and the feather tantalised the world of science.

What could it have come from? Immediately there was a huge search mounted in the quarries.

Even now it's almost impossible to resist the temptation of pulling down every boulder you see

then opening it like a book to look at each page to see if it contains yet another fossil.

After nearly a year, in 1851, in this very quarry, they found what they'd been looking for.

A skeleton, a foot long, surrounded by feathers - Archaeopteryx - Ancient bird.

Its skull was missing - but then, another complete skeleton was found.

It had limbs of equal length, so but for the feathers it might have been a four-legged runner.

Its head too, was very reptilian with tiny teeth along its bony jaw.

The front limbs had three toes apiece - each toe ending with a claw.

The tail was supported by a rod, an extension of the backbone running down the middle.

All around are miraculously detailed impressions of feathers.

In some places it's even possible to see the filaments on either side of a central quill.

So those front limbs with claws are not the legs of a lizard, but the wings of a bird.

So perfect are these fossils, we can make a confident reconstruction of the animal.

But could this earliest of birds flap its wings?

Its breastbone had no keel to carry muscles so its wing beats can only have been feeble.

It probably depended for the most part on gliding.

The long toes had a good grasp forwards and backwards.

So it would've had no difficulty perching on branches.

The claws on its wing helped it steady itself.

In all the world today, there's only one creature with claws on its wings - and this is it:

This is the Hoatzin - not an adult but a chick and it only has claws on its wing for a week or so

but while it does, it gives a vivid hint of how the first birds may have moved in the trees.

Maybe ancestors of Archaeopteryx took to trees because of hungry reptiles

roaming below looking for a meal.

The young Hoatzin faces just such dangers today.

Its home in the swamps of Venezuela is haunted by crocodile and caiman,

and reptiles very like them prowled the swamps and forests 150 million years ago.

Although adult Hoatzin don't have claws on the wings, they do have a reptilian look

with glittering eyes, surrounded with scaly skin and an odd, bristly crest.

Nor have they totally mastered flight - they can only cover short distances.

In the branches, they use their wings to help them keep their balance.

But they're true birds, better adapted for flying

than Archaeopteryx ever was.

Fliers must reduce their weight to a minimum.

All birds today, including the Hoatzin have lost the tail of the reptile and have a tail of feathers.

Weight has been reduced in front -

bony jaws and teeth are heavy -

and no modern bird has them.

Instead, they've beaks of keratin, the same horny substance as that from which feathers are made.

Keratin is light and strong and can easily be moulded into a variety of shapes

and turned into the particular tool the bird needs to gather its food.

The Hoatzin has an unusual diet.

It plucks leaves which it regurgitates for its chick.

Often the beak is elongated and used as forceps.

The White Stork can pick up frogs and little fish.

The Shoebill has a heavy-duty version for dragging lungfish from mud.

The Crane has a short pair to pick up seeds and insects.

The butchers among birds have turned their beaks into hooks to tear flesh - Vultures.

The Monkey-eating Eagle from the Philippines.

Others, like the Scarlet Ibis, have long probes that can pick small invertebrates from burrows.

The beak of a Spoonbill isn't a spoon but a sieve which collects small creatures from the water.

A Flamingo's bill is a filter-pump - the tongue's a piston drawing water in and squirting it out.

Coarse hairs on the side prevent mud getting in and hairs inside trap microscopic plants and animals.

Pelicans.

Some dive on shoals of fish - others use their bills as nets.

They fish in teams.

Another fisherman.

Little fish swim into the shade.

The Black Heron provides it with its wings

and then stabs with precision at any fish that's attracted to it.

The beak's not only a feeding tool

it's an essential instrument for keeping in trim the feathers.

They need a lot of maintenance if they're to be kept in good condition.

The beak is used with great delicacy to preen the feathers,

repairing any breaks by zipping up the hooks on the filaments.

Storks, like most birds, have a preen gland on their rump.

They collect oil with their beak and use it to waterproof their feathers.

Waterproofing is specially important for water birds...

and water flows off a duck's back because its feathers are well-oiled.

But being waterproof makes problems.

Below water, unwetted feathers hold air like a silver sheath.

It's very buoyant, so ducks and ducklings must paddle hard

or they bob back.

The business of getting the beak into the mud

is made easier by having the legs back near the tail - all the same, it's hard work.

As well as oiling feathers

many birds, like the Peacock, ruffle them in dust.

The skin beneath the feathers makes an attractive home for parasites like fleas and lice.

This gets rid of them.

Another way is to enlist the help of other insects - ants.

Ants, when irritated, squirt acid and that shifts most insect parasites.

Jays and Crows are addicted to this habit.

By spreading its wings, the bird makes it easy for angry ants

to swarm over its skin between the feathers.

Often the bird enjoys it so much

it goes into a kind of ecstasy.

So, one way or another, birds go to a lot of trouble to keep their feathers in good condition.

In truth, their lives depend on them - and not just for support in the air.

Birds are warm-blooded.

So insulation for their bodies is essential - and nothing does it better than a coat of feathers.

Only a bird in a coat of feathers...

..can live in the coldest place on Earth - the Antarctic in winter.

Some species of Penguin survive at 40 degrees below freezing for weeks on end.

The feathers of adult and chick

are adapted to provide warmth - fine and in a thick mat.

But the feathers of most birds serve another purpose as well - flight.

If beauty comes from perfection, grace a measure of skill,

then a bird in the air must be one of the loveliest sights in nature.

Terns are among the most graceful of fliers, responding to every variation of wind currents

with subtle adjustments to the contours of tail and of wings.

The Tropic bird uses updraughts and works hard to hang in the air to display to its mate.

Ocean-going birds like the Frigate sail on long thin wings - the best shape for efficient gliding.

One of the most skilled gliders of all - the Albatross.

It beats up and down the ocean, supported by the lightest of breezes with only gentle flaps of its wings.

But long wings for easy flight don't make for easy landings.

Having missed its touchdown, the Booby labours to regain speed and avoid a stall and a crash.

The Frigate has similar problems, but solves them successfully.

The Booby has another try.

There are helpful winds to be exploited over land as well as sea.

Above wild, mountainous country, like the Grand Canyon, the sun heats the naked rock.

There are hot currents sweeping up...

so vultures can sail and soar with an economy that rivals that of the Albatross.

Such birds sliding effortlessly though the air, can reach great speeds.

But the airspeed record is held by a much smaller flier...

..the Swift - here it's in slow motion.

One species can reach speeds of 170 kms an hour.

The Swift - most aerial of birds, hardly alighting except to nest, mating and sleeping on the wing...

..flying up to 1,000 kms a day...

..to gather insects from the air.

Others feed on the wing and just as ground feeders have beaks modified for their diets...

..so many of these hunters have beaks specially suited to their own techniques.

What's more, ones that require acrobatic skill to manage properly.

The Skimmer has the oddest.

It's the only bird with the lower mandible longer than the upper - to use it needs perfect control.

When the lower mandible strikes an object, the beak snaps shut.

There may be more to it than that.

The furrow in the surface of the water sparkles and attracts surface-feeding fish.

Having made one run, the Skimmer turns and flies back along the same course.

Perhaps to collect anything that has taken the lure.

In the Andes live other birds with superb aerial control and extraordinary beaks to manipulate.

The Datura plant is rich in nectar and humming birds love it.

But those with normal-sized bills can't reach the main supply at the top of the tubular blossom,

even when they cling to the flowers with their feet.

The Sapphire-Wing has a longer bill.

Even this can't reach the depths of the flowers.

What's needed is this -

the beak of the Swordbilled hummingbird

longer than its entire body.

The flying control has to be total

to manoeuvre this huge instrument, and it is.

Slow motion shows its expertise at keeping its bill perfectly steady

in relation to the blossom,

even while its body moves in all directions.

Slowed right down, you can see how the wings move to enable the bird to hang in the air.

The bird tips its body vertically so air currents from the wings are driven downwards.

Each wing's so jointed, it beats in a figure of 8 and gives lift on both forward and backward beat.

Their arms are short and close to the body,

so they actually fly with their hands.

So with the help of feathers

birds have mastered all manoeuvres in the air.

The stork flies up from Africa to Europe in spring to nest,

often on the same site it's used many times before.

The male usually arrives first and proclaims his ownership of the site.

The nest's refurbished - no matter how big it is, the bird improves it with sticks and a fresh lining.

This display is not only a notice of possession, but is also an invitation to a mate.

BILLS CLATTER

Once they've come together, the ritual's carried out again and again strengthening bonds between them.

The sound of the bill-clatter is an integral part of the display.

The Nightingale also needs a mate and a nesting site...

but its feathers are drab, its habits retiring, and it claims them with a song

a song that penetrates the thickets where it lives.

Song, like bright feathers, conveys a third message - identity.

A relative of the nightingale - the Blackcap.

He makes his species clear with that distinctive patch of black on his head.

But he produces a quite different, and very characteristic song.

The Grasshopper Warbler relies almost entirely on song.

A rival is singing and he must answer.

This looks a Grasshopper Warbler and birdwatchers and birds can't be sure it isn't till it sings.

It's a Willow Warbler.

So with song and dance, identities are established, territories claimed and the pair bond made.

All is set for the business of reproduction.

Feathers are well suited for display.

They're light, can be easily erected into fans and crests, and some birds

like the Kori Bustard, have exploited that potential to an extraordinary degree.

When male meets male on the African plains, they argue over territory with feathers.

The female Great Bustard is neatly camouflaged and unobtrusive

but her mate inflates himself in a most spectacular fashion.

One family excels in the shape,

colour and beauty of its feathers - New Guinea's Birds of Paradise.

The Superb bird has an iridescent sheen on its chest

and a roll of feathers it can open like an umbrella.

The Six-Wired birds carry six naked quills on their heads, each ending in a black pennant.

The males display on the ground, clearing special dancing floors, which they keep meticulously clean.

The female hasn't his splendour.

The male's life in the breeding season is devoted to dancing - she mates with one of the dandies.

She rears the young by herself,

while he continues to strut on his court.

The Magnificent bird has two quills

and three capes of different colours.

He too, displays on the ground and strips the leaves so he can dance in a pool of light.

Other Birds of Paradise display in the branches.

Males don't acquire plumes until they're older and moult at the end of the breeding season.

So mostly they're like their drab females.

When dressed for the dance however they spend a lot of time grooming and preening themselves.

They lavish as much care on their display feathers as they do on the utility ones - those for flight.

Females visit the display trees to select partners

but males display whether they are there or not.

Each species - this is a Lesser bird - has its own dance

its own way of showing off its finery to the best advantage.

The Emperor of Germany's bird begins by fluffing up the plumes beneath its wings

but has developed a most surprising climax to his performance.

Count Raggi's bird throws his plumes over his back in a quivering fountain of red.

But the most remarkable display is that of the Bluebird.

As he quivers, he sings as extraordinary and unbirdlike a song

as comes from any bird.

These are among the largest feathers and the most spectacular - the Peacock's feathers.

They're still something of a mystery - Darwin was baffled

by the sheer perfection of such feathers as these.

Are they just to help him compete?

Or to impress the Peahen?

There are people who think we've some way to go before we know the answer to questions like those.

This is one characteristic of the reptiles, birds never abandoned - laying eggs in nests.

Every other vertebrate group has species that retain eggs in the body and give birth to live young.

Some fish, amphibians, reptiles and all mammals, but not a single bird does - the reason's obvious.

It would be a severe handicap for a bird to fly with the weight of this or a whole clutch

for as long as it takes for it to hatch.

Much better to lay it in a nest as soon as it forms - but that makes the eggs very vulnerable.

Birds go to a lot of trouble to protect their eggs and their nests.

The peahen nests in undergrowth and foregoes the display feathers of her mate so she's well camouflaged.

Some waterbirds such as the Giant Coot in Chile, lay eggs on islands of vegetation.

Beyond the reach of nest robbers.

Other birds, like the Oropendolas from South America, achieve inaccessibility

by weaving bottle nests on branches.

On the pampas of South America, the Oven birds build with mud.

It's shaped like a local oven and when finished has a tiny entrance which foils most intruders.

Longtailed Tits weave a domed nest of cobwebs and moss...

fill it inside with downy feathers and camouflage it with lichen.

The Sparrow is an untidy builder and makes use of sticks, including those from other nests.

In Iceland, there are great colonies of Arctic Terns.

The shores where they nest provide little building material and no cover whatsoever.

So they dispense with nests and do their best to deflect intruders by diving at them.

The safety of their eggs depends largely on their camouflaged shells.

Inside the eggs, developing chicks like parents, have warm blood

and if they get chilled, they die.

The Eider Duck, which also breeds in Iceland, develop special downy feathers on the breast

and with them, builds one of the warmest of all nests.

Man himself has yet to devise anything more luxuriously warming than eider down.

The colour of eggs varies - and so does the size.

This is the smallest of all, laid by a Hummingbird and no bigger than a pea - and this is the biggest.

It's the largest egg it's possible to have - the shell has to be thick to hold two gallons of liquid.

If it were any bigger, it might have been so thick the chick might not be able to hammer its way out.

This egg was found here in the thorn forests of Madagascar.

It was laid by a giant flightless bird, the biggest ever, like the Ostrich - about 10 feet tall.

It was the Elephant bird and was alive up to 200-300 years ago, but now, alas, extinct.

Birds have to work hard keeping them warm in the cold or protecting them from the sun.

When the eggs hatch, they must collect food for the growing and perpetually hungry young.

Soon these storks will fly - but where exactly will they go?

To find out, stork-chicks all over Europe have been ringed.

The rings are light and aluminium with an address,

so anyone finding the bird will know where it was hatched and reared.

The young storks flap their wings, exercising the muscles that will sustain them in the air,

while their parents collect daily supplies of frogs and fish.

In 60 days, young and old depart.

The chicks have most of the skills of flying the very first time they launch into the air.

Some surprising results have come from ringing storks in this town in southern Germany.

Many make their way to Africa going east round the Mediterranean by way of Istanbul.

The town lies on a fork in the migration route - others go west across the Straits of Gibraltar.

As they head south they become more concentrated.

These journeys make great demands on a bird's strength.

Many rely on upward-rising thermal currents produced when the sun heats the land.

If you can get high, you can glide effortlessly for great distances.

Thermals don't occur over the sea so birds gain as much height as they can before crossing the Med.

Near Gibraltar and Istanbul they soar round and round in up-currents climbing higher and higher.

Those that arrive in the evening, roost.

After the sun's gone, there are no more thermals and it's better to wait till morning.

The Straits of Gibraltar in spring and autumn are visited by thousands on the way to or from Africa.

Nearby mountains and the Rock warming in the sun

produce strong up-currents of air - and Africa lies only a few kilometres away across the Straits.

A Kestrel, resting on its journey.

Honey Buzzards from much of Europe congregate here and share thermals with Storks.

These invasions of "tourists" infuriate local residents.

Some days Short-toed Eagles can't get the lift they need.

They fly round the Harbour and local gulls mob them.

Sometimes they drive them into the water and they can't take off again - another hazard of migration.

A Black Kite on its way to Africa after breeding in Europe.

September in Gibraltar is a marvellous place for a birdwatcher,

as travellers meet at this migration crossroads.

The best place to watch is from the top of the Rock.

It's coming to the end of the day and it's been a good one for the migrants.

Parties of big birds, 30, 40 or 50 strong, have been passing the Rock...

gathering to get a last lift from a thermal in Europe

so they can glide down across the Straits to Africa 12 miles away.

How did they find their way here?

Some undoubtedly use geographical landmarks and come along the coast.

Others use prominent river valleys - but that can't be all there is to it.

Young birds that have never made the journey manage it alone.

So presumably, they have some kind of inherited map in their minds.

Others use the sun in some way - they can cross large expanses of sea and featureless land.

But the sun has a major drawback as a navigational aid - it moves.

So, to find your way by it, you must know what the time is.

So these birds must also have a clock in their minds.

But in the evening

the sun goes down and it gets dark,

you may no longer be able to see landmarks - what happens then?

The answer can be found here in the Air Traffic Control Tower at the Rock.

Gibraltar's important to defence in Western Europe

and watch is kept by radar on aircraft movements around it.

But radar can show flocks of birds as well as aircraft.

In autumn and spring the information from these screens,

about the sky at night is spectacular indeed.

A few hours of an autumn night can be condensed to a few seconds.

The number of birds crossing into Africa can be estimated from the mass of dots moving south-west.

On this night up to 200,000 birds at one time are represented on the screen.

It's estimated 5,000 million cross the Mediterranean each autumn.

How do they find their way?

Some birds fly by the stars

and if you release them in a Planetarium

where artificial stars have been twisted around, they fly by those.

Other birds are sensitive to electro-magnetic waves.

So it appears a bird must not only have a map, a star chart and a clock

but a compass in its mind.

The fact is there's a great deal we don't know about bird navigation.

Gibraltar's a half-way stage for most migrants -

Arctic Terns hatched in July are here in September.

They've still 10,000 kms to go before reaching their destination.

Shearwaters move in a different direction,

migrating east and west between the Mediterranean and the Atlantic.

They're great travellers - one was back in its nest in Wales after crossing the Atlantic in 12 days.

This Arctic Tern has reached the southern tip of South America.

It left the Arctic at the end of its summer when the sun never set,

it's flying to an Antarctic summer.

So it sees more daylight than any other creature.

The African plains are the target for Storks.

By the end of September, they're among game

as they were among herds of dairy cows a few weeks earlier.

So flight, birds' great achievement has carried them not only to all parts of the world

but makes them the greatest of animal travellers.

Yet, most surprisingly

some species have abandoned it.

There's no doubt ostriches' ancestors could fly.

It still has a beak instead of teeth and jaws,

and feathers in patterns needed for flight.

Now the feathers are used only for display.

The feathers no longer support the bird in the air, so the hooks on the filaments have disappeared.

The feathers have a soft fluffiness that is found to be alluring by other creatures.

Why should the ancestral ostrich have given up flight?

Well, it's a demanding business.

If there are no predators to drive birds into the air, it's easier to remain on the ground.

That happens today on islands and it happened once to ancestral ostriches.

Ostriches belong to one of the most ancient of bird families.

They appeared 50 million years ago

when dinosaurs and other giants had only recently vanished.

The position of ruler of the world was vacant

and it seems that birds like that, made a bid for it.

There was one

a flightless bird in America with a huge bill which could have killed any animal around.

Even looking at ostriches

you see how dangerous they might be if they suddenly acquired a taste for red meat.

They could outrun me and one kick from those legs could knock me over and rip me open.

But that bid for supremacy failed - there was another, unobtrusive creature around at the time...

that also had warm blood but was descended from a different group of reptiles from the birds...

and it insulated its body, not with feathers, but with fur.

That was the creature whose descendants would inherit the Earth,

that was the first mammal.

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