Attenborough's Big Birds Natural World

Birds are masters of the skies.

There are more than 10,000 species

and they behave in a huge variety of different ways.

But of all the birds I've filmed over the years,

there's nothing that can really compare with these comic characters.

That's not just because of their great size.

But because they can't do the one thing

that birds are famous for doing.

They can't fly.

The ostrich, the emu and the rhea, together with two other birds,

the kiwi and the cassowary,

are the court jesters of the avian world.

They're a family with a remarkable success story,

despite having never flown a day in their lives.

But exactly how and why did these birds abandon flight?

It's one of the natural world's great mysteries

and it's taxed some of the finest minds in science

from Darwin's time right through to the present day.

And now, DNA is promising to give us the answer.

But what is even more exciting

than the remarkable evolutionary history of these birds

is their behaviour -

because if you're a bird that can't fly,

you have to find other ways of surviving.

BIRDSONG

It's said that a bird is three things -

feathers,

flight

and song.

BIRDS CHIRP

But what happens if you are a bird which can't fly,

which doesn't sing...

HISSING

..and whose feathers are closer to fluff?

Well, then you have to come up with

some pretty unusual ways of surviving.

This small group of birds are real oddballs,

with a rag bag of characteristics

that help them with life on the ground.

Among their number is the fastest bird on land.

A bird with the biggest eyes on Earth.

One has dagger-sharp talons.

Another, killer thighs.

OSTRICH HISSES

Their chicks hatch, ready to run.

CHICKS GRUNT SOFTLY

And they all have crazy hair.

And useless wings.

This lot couldn't fly even if they wanted to

because their feathers aren't like those of other birds.

They don't have barbs that link together into air-cutting vanes,

like normal wing feathers.

Nor can they be held neatly and tightly together.

They are more like a fluffy feather boa.

Without a role in flight, these feathers act instead

as warm blankets or insect repellers

or props in an exotic dance.

But if you are a bird that hasn't flown a day in its life,

then beauty isn't enough to survive.

The first, the fastest and the biggest of all our birds

is the ostrich.

OSTRICH BOOMS

Indeed, it's the largest bird in the world.

Standing up to 3 metres tall, it weighs up to 150 kilos.

On the African plains, it lives alongside

some of the world's most dangerous predators...

..hyenas...

..lions...

..and cheetahs.

BIRDS CHIRP

DRAMATIC MUSIC

Pounding across the plains,

it uses its powerful legs to run for its life.

DRAMATIC MUSIC

Adult birds can run at speeds

of up to 70km - over 40 miles - an hour,

covering almost 5 metres in a single stride.

DRAMATIC MUSIC

DRAMATIC MUSIC CLIMAXES

This young ostrich hadn't quite developed

the power or agility needed

to escape these speediest of predators.

But it still took the combined skill and experience

of a team of cheetahs, working together,

to bring the young ostrich down.

CHEETAH GROWLS

This is, nonetheless, a remarkable and very rare sight.

CHEETAH PANTS

Most ostriches escape from such attacks.

Adult ostriches are powerhouses of strength and agility

and are seldom caught by predators.

BIRDS CHIRP AND WHOOP

The second of our birds also has size and speed on its side.

But for the biggest bird in South America,

there is danger of a different kind.

LATIN GUITAR MUSIC

This Argentinian rhea has grown big -

indeed, bigger than most of the mammals that live here.

But this male has nonetheless to remain alert...

..from attacks from one of his own kind.

It's the beginning of the breeding season

and males are starting to spar, sizing up their rivals' strength

before the real battle to breed begins.

RHEAS GRUNT

MUSIC CONTINUES

To the winner, TWO females.

But although this fight has been won,

the coming war will doubtless see him forced to defend his gains.

CRICKETS CHIRP, INSECTS BUZZ

DIDGERIDOO PLAYS

Here in the Australian outback

roams the second-largest of our big birds,

the emu.

A nomadic character, he uses his spectacularly elongated legs

and ferocious-looking feet to go walkabout...

..meaning he can cover vast distances

in search of food and water.

BANJO PLAYS

Emu truly are wanderers -

always on the move, following the rains,

they walk hundreds of kilometres.

And when they find water, they take on board all they can.

BIRDS CHIRP, INSECTS BUZZ

But flightless birds in Australia

aren't restricted to the parched outback.

In the tropical rainforests in the north of the country

lives another one.

It stands almost 2 metres tall and has a dinosaur-like crest

and dagger-sharp claws that give it a lethal kick.

DRAMATIC MUSIC

Cassowaries are fiercely territorial.

And one will fight to the death to defend itself

or its magnificent emerald-green eggs.

Like the rest of his family

in Africa, South America and Australia,

it's a bird which has taken an evolutionary route

very different from that of its aeronautical relatives.

Cassowaries vary greatly in colouration.

So, it's debatable how many species there are.

Probably three.

Another flightless bird lives in New Zealand,

hidden in the forests and only active at night.

It could be called the runt of the litter.

Standing only a half a metre or so tall,

this is a kiwi.

More like a mammal than a bird, it has dense, hair-like plumage

and a very long, very sensitive beak,

which makes up for its tiny and all but useless eyes.

It walks along like a little hobbit, with its arms behind its back.

When, in the 19th century,

tales of the kiwi reached naturalists in England,

they thought them merely figments of early travellers' imaginations.

One of the largest collections of this weird walking family

was amassed by a Victorian English eccentric, Walter Rothschild.

Collectively, these extraordinary birds are known as the ratites,

flightless birds that just grew and grew,

from the smallest - that's the kiwi -

to the largest alive today, the ostrich.

But their ancient relatives were even more impressive.

Enormous birds that would have towered over me,

like the moa from New Zealand

or the elephant bird from Madagascar.

But exactly why did these birds abandon flight?

Well, flying is a very energetic business,

much more so than walking or running,

and birds don't fly unless they have to.

-WAVES CRASH

-Some, like penguins,

gave up flight relatively recently

and took to the water.

But they still have strong wings,

which they use like paddles for swimming.

The ratites are different.

They are the original flightless birds.

And they're the only birds whose skeletons

make them incapable of flight.

Hidden beneath their mass of feathery fluff

is a flat, raft-like breastbone

that lacks the ridge onto which flight muscles can be attached.

In fact, it's this which gives them their name,

from the Latin word, "ratis", meaning "raft".

So, whilst there are other birds which don't fly,

our very special family, the ratites,

stand entirely apart from all the others.

They are the Flintstones of the bird world,

a group whose lineage can be traced back to the time

when dinosaurs walked the Earth.

The dinosaurs once dominated the land,

just as their relatives, the pterosaurs, ruled the skies.

But when, 66 million years ago, both groups were wiped out,

some of the ancient birds seized their moment

and made a bid to dominate the land themselves.

Some, the ancestral ratites, grew big and fat,

with long, strong legs, until one day,

they were too heavy to fly.

Since then, of course, the mammals have fought back

and in most places, THEY won.

But the elephant bird and the moa, now extinct,

survived until a few centuries ago

and five others still flourish across the southern hemisphere.

The ostrich, the emu,

the cassowary, the rhea

and the kiwi.

BIRDS CHIRP, INSECTS BUZZ

The success of the ratites today is largely due to

some bizarre breeding and very complicated relationships.

Males mating with multiple females,

females mating with multiple males,

fathers raising chicks which aren't theirs.

The tenacity and endurance of these dedicated dads

has helped raise generations of walking giants.

So, how do our motley crew ensure the survival of their offspring

when safe tree-top nests are out of the question?

Well, it takes a lot of work.

For the emu in the Australian outback,

the breeding season starts in the winter.

This is when a male needs to be at his heaviest.

DIDGERIDOO PLAYS

Large bodies enable ratites to develop large guts,

so unlike small flying birds,

they can stock up on plenty of plants and seeds.

Soon, he will mate and he will be the one who will incubate the eggs.

During his time on the nest, he won't eat or drink.

So, he's preparing for that by fattening up.

This time of the year is all about finding food

and some enterprising males

even go into town to pick up dinner.

CAR HORN BEEPS

BANJO PLAYS

TRUCK HORN BEEPS

A strange sight - but the locals are used to it.

TRUCK HORN BEEPS

When they are ready to breed,

male ratites start to try and impress females

and they do so with some pretty flamboyant dance moves.

Ratites might not be strong contenders in a beauty contest

but these males certainly know how to move and groove.

From the ostrich to the cassowary,

the males all work hard to show off their best features.

Just HOW hard can be seen on the grasslands of Argentina.

It's spring and the rheas are preparing for the breeding season.

Male rheas, with their distinctive black markings, have broken away

from the flocks in which they spend the rest of the year.

Now is the time for courtship,

when their feathers will be shown off in all their splendour.

As ratites no longer fly, they have no gland to produce the oil

needed to preen their feathers into continuous air-catching services.

But with a little grooming,

their plumage can be very impressive.

This male has managed to secure several females for himself.

Herding them with his outstretched wings,

a male can maintain a harem of anything from two to ten females,

as long as he can keep them close.

He doesn't let them out of his sight,

courting each one in turn.

And the grand finale of his mating ritual...

..this curious head-bobbing dance.

It's hardly a tango.

And the object of his affections doesn't seem particularly impressed.

But despite the lack of encouragement,

he will spend most of the breeding season

herding and head-bobbing to his females,

until they are ready to mate.

Unless, of course...

..this rival male can rob him of his hard-won harem.

Rising up as high as he can,

he puts on a show of size and strength.

This performance has rarely been filmed.

It's a tango of a different, aggressive kind

with plenty of Latin American spirit.

Today, there is someone better than he.

He retreats, leaving the rival male

to take his place on the dance floor.

This male is, it seems, a little more persuasive.

Exactly how ratites mate

was a mystery only solved by scientists

in the last few years.

Most birds don't have a penis.

Instead, both the male and female birds

have an opening called a cloaca.

That certainly helps to streamline the body of a flying bird.

The male ratite, however, is different.

He does have a penis,

and it was once assumed that these large birds

would have blood-based erection systems,

similar to humans.

But in fact the ostrich, emu and rhea

enlarge their penises with lymph fluid.

They also have a few additional muscles to keep everything in place.

While it's known that male and female rheas will mate

with several different partners over the course of the breeding season,

there is much less certainty with another of our ratite family.

On the islands of New Zealand lives an enigma.

The most secretive of our flightless birds.

Hidden in these ancient and mysterious forests,

it only emerges after dusk.

HIGH-PITCHED BIRD CALL

Only in the pitch-black dead of night does it call.

HIGH-PITCHED CALLING

Ratites might not sing,

but their mating calls are certainly piercing.

This is a bird which is heard but seldom seen.

Scientists have to struggle to catch sight of the kiwi,

let alone to understand its behaviour,

even when they work around the clock.

But using infrared light, which the kiwis can't see,

and radio transmitters to track them in the darkness,

the researchers here are slowly piecing together

a picture of this shy bird.

For the last 11 years,

I have been looking at the breeding behaviour of Kiwi

and everything that is associated with it.

Dr Isabel Castro is a Colombian expert on kiwis

who has lived in New Zealand for the past 25 years.

This environment where they are

is completely different than our environment.

They are nocturnal where we are diurnal,

and for many years before we started this research,

people thought that they had this relatively boring life

and yet as soon as we started this project,

we started finding out these fantastic things

about their intimate life.

There have been all sorts of things

that were completely unexpected,

and that made now these birds very extraordinary,

because we didn't know those things before.

Living in complete darkness,

unable to see virtually anything, the eyes of the kiwi

are all but useless,

but - unusually for a bird -

it's got a great sense of smell,

which it uses to find its way around.

By setting up remote cameras,

the scientists have been able to capture behaviour

never filmed before in the wild.

Two males fighting.

KIWIS RASP

A female calling for her mate.

REPETITIVE GUTTURAL CALL

Males and females have different calls.

The females have this very coarse, grunty call,

as all females should have, you know!

The males have these whistles, beautiful and piercing.

REPETITIVE SHRILL CALL

Isabel and her team even managed to film a kiwi family

with a tiny chick.

Kiwis are the only nocturnal ratites

and by far the smallest.

This big bird isn't big at all.

It only weighs about two kilos.

Kiwis never grew big

because they lived alongside the now-extinct moas.

With those giant herbivores already roaming New Zealand,

the kiwi's evolution took an alternative path.

It remained small, became nocturnal and omnivorous.

With nostrils at the end of its beak,

the kiwi sniffs out insects and worms at night...

..and then stays in the safety of its burrow for the day.

Unlike the other ratites, it nests underground.

Until recently, it was thought that kiwis bred in monogamous pairs,

but now DNA analysis has painted a much more complicated picture.

They are very naughty, kiwi.

For a long time, we thought that they were really good birds,

and mated with one another, one male, one female,

but they are not like that at all.

They do stray a little bit.

They do stray.

It seems that breeding is a little more flexible than just one-on-one.

Some birds seem to breed in family groups.

Others may raise young as a pair

even though the chicks might not belong to Dad.

However, it's the males who shoulder the burden of incubation.

The eggs in their care are among the oddest on earth.

This is a kiwi's egg.

It's the biggest in proportion to body size of any bird's egg.

It weighs about a fifth

as much as the adult bird.

It's so big, it takes 80 days to incubate.

The Maoris used to say

that tree routes would grow over a kiwi's nest.

This is the egg of another ratite, an ostrich,

and curiously, it is the smallest egg in terms of body weight

for any bird in the world.

These ostrich eggs are unusual in other ways.

They too are part of an elaborate game of pick and mix...

..because ostriches are almost like cuckoos.

Females will lay in the nests of other ostriches,

but unlike the cuckoo,

the owners of the nest know about it

and they don't seem to mind.

It may help to have a few spare eggs.

The female seems to be able to recognise her own eggs,

keeping them at the centre of the nest while rolling out others

as sacrifices to any predator brave enough to make an attack.

Up to six female ostriches may lay in a single nest.

For most members of the ratite family,

the rhea, the emu and the cassowary,

incubation is something of a gentleman's club -

females aren't welcome.

But the ostrich does things a little differently.

The male and female take turns at caring for the clutch,

keeping watch by day and night to make sure

nothing has a chance to steal the eggs.

This father-to-be is carefully rolling the eggs to make sure

the embryo inside gets evenly warmed.

In the cold of the night,

he uses his feathers as a blanket to cover his charges.

Communicating by clacking their beaks,

this couple share the parental burden.

They take turns to sit on the eggs,

which, although small compared to the ostrich itself,

weigh in fact almost two kilos each,

the largest eggs laid by any living animal.

Left unattended, such large eggs soon attract attention.

These ostrich eggs are giant ready meals

for a variety of African animals.

You can't make an omelette without breaking eggs,

and this jackal has worked out just how to crack one against another

and so release his lunch.

The Egyptian vulture has its own ingenious version of smash and grab.

It's perhaps not surprising

that up to 90% of ostrich clutches

are totally destroyed.

In South America, rheas nest in a similar way to the ostrich.

For two weeks, females lay their eggs in one shallow, communal nest.

Each egg is 12 times the size of that of a chicken.

But unlike the ostrich,

it's the male who settles down to do all the hard work.

He alone will incubate these eggs,

and he does so for more than five weeks, whatever the weather.

THUNDER CRACKS, HEAVY RAIN

It's an arduous task.

65% of males abandon their nests,

many because they don't have the energy to sustain themselves

without going away to feed.

The females, however, never put all their eggs in one basket.

Once they've mated with this one male,

they move on to another, so increasing the chance

that at least some of their young will survive.

Nesting on the ground out in the open

means that, inevitably, the eggs are vulnerable.

From the enormous eggs of the ostrich...

..to the green eggs of the emu.

But for one of the relatives, the battle to keep their clutches safe

was, in the end, lost.

These are the leg bones of the elephant bird.

It was the largest of the ratites.

Indeed, it was one of the biggest birds ever known.

It stood over 3m tall and weighed half a tonne.

It lived on the ancient island of Madagascar,

which I visited over 50 years ago.

Before Europeans ever went to the island,

it had a reputation for being the home

of really strange, fabulous beasts,

and Marco Polo, 700 years ago,

believed that it was the home of the fabulous bird, the rukh.

The rukh, which carried off Sinbad the Sailor, and which was reputed

to be able to carry off elephants in its talons,

as this one is doing.

But Marco Polo had very good reason for thinking that it lived in Madagascar,

because he heard stories that in Madagascar were found gigantic eggs,

over two feet long. What else could have laid them but the rukh?

Well, I was lucky enough to find

some pieces of the rukh, or elephant bird's egg.

And even luckier to be given some pieces that looked like

they might belong to one egg.

Now, would they fit together?

These two certainly did.

At the end of an hour, I had two halves.

And to my joy, they fitted together perfectly.

There was a place for even such a tiny fragment as this.

The egg was well nigh perfect.

As I held it, I had little difficulty in imagining the country

as it must have been when great numbers of gigantic birds,

over ten feet tall, strode majestically through the swamps.

This is the egg that I brought back from Madagascar all those years ago.

It's the biggest egg ever laid by anything.

Bigger by far than even the egg of the biggest dinosaur.

As you might imagine, it could have made a meal

for quite a lot of people,

and that may well be, some people think,

the reason why the elephant bird became extinct.

If it wasn't for human beings, the elephant bird might still

be walking around on Madagascar.

The same fate met the moas of New Zealand,

some kinds of which weighed over 200 kilos.

The elephant bird might have been the biggest bird ever to exist,

but some think that one species of moa was the tallest.

Moas, too, were hunted and had their eggs eaten by humans

until there were none left.

We know this because of the careful detective work scientists

have done on their bones.

It's not the only puzzle

that fragments of extinct bird like these, of the moa,

might be able to solve.

If these birds were flightless, how did they manage to spread

round the world, from the deserts of Africa

to the rainforests of Australia?

It's a conundrum that has puzzled minds for centuries.

Not that long ago, scientists thought they had the answer.

All the places in which the ratites lived

had once been part of a supercontinent called Gondwanaland.

Perhaps our birds came from one common ancestor, which was

also flightless, that roamed all over that land.

Then, millions of years ago, when the continents split up,

populations of this bird were separated.

As their homes drifted into new positions,

the isolated birds adapted and evolved in different ways,

producing everything from the tiny kiwi

to the huge extinct elephant bird.

But ancient bones are telling a different story.

Scientists have recently been sequencing DNA

from the bones of extinct ratites

and compared them with living flightless birds,

and the results have come as a huge surprise.

The mighty elephant bird, which should be most closely

related to the ostrich, turns out to be most similar to the tiny kiwi.

Not what was expected at all.

So how could this possibly be?

Well, an unexpected character is providing some answers.

A little-known ratite relative, the tinamou,

that lives in Central and South America.

DNA has recently revealed that it isn't a distant relative,

a cousin, say, but instead a sibling,

smack in the middle of the ratite family tree.

Which is remarkable, because tinamous can fly.

Now, if all the ratites and the tinamous evolved

from one flightless ancestor,

then the tinamous must have relearned how to fly.

But there are no known examples of a species of flightless bird

regaining flight, so this suggests

that the common ancestor of the ratites and the tinamous

wasn't flightless at all. He could fly.

Our birds might not have drifted away from one another

on the lands in which they live today.

Instead, their ancestors must have flown across miles of ocean

to reach the far corners of the world, and only then

did they independently lose the ability to fly.

It's an amazing thought,

but the ratites lost their ability to fly independently

and on several different occasions.

Thousands of miles apart from each other on their separate continents,

each kind of ratite developed into its own flightless form.

The ostrich and the rhea kept their wings

and evolved elaborate uses for their feathers.

The wings of the emu and cassowary became short and tiny...

..and the kiwi, well, its wings are now all but invisible.

Although the details are different,

the demands of living on the ground meant that all the ratites

evolved in their own way into flightlessness.

And there's one survival strategy which they all share,

and which begins when they hatch.

In the Australian outback,

this male emu's hard work over the past 56 days is about to pay off.

He is a father.

His chicks, like all newly hatched ratites, are able to get up and go

almost from the moment they break free from their eggs.

This is an invaluable ability for a chick,

which is, after all,

a very succulent mouthful for almost any predator.

Emu chicks, with their tawny markings, are known to Australians

as stripeys.

Their dedicated dad will spend the next six months caring for them,

by which time they will already have grown to at least half his height.

That is, if they ever hurry up and hatch.

The chicks had to work hard to free themselves from the egg shells.

Now they need a drink.

Their father must face a tough decision.

One egg still hasn't hatched.

If he stays and waits for it to do so, the older chicks may die.

It's likely that he can hear sounds coming from within

the unhatched egg.

Meanwhile, the harsh Australian sun scorches down on those

of his offspring desperately waiting for their first drink.

After many agonising hours, he makes his choice.

Leading the brood to find water,

this father helps a new generation of big birds take their first steps.

From South Africa to South America,

an extraordinary combination of mating behaviour

and parental care has produced birds which are very special indeed.

CHIRPING

These young ostriches will soon grow into the biggest birds in the world.

Although today, as they take tiny steps across this vast landscape,

that day seems a long way off.

The next generation of ratites.

A reminder of how one remarkable group of birds independently

seized a moment when there were no predators around to hunt them down

and set off down various but similar evolutionary paths.

The only group of birds to have become massive and flightless.

It wasn't long before some mammals also became big and dominant,

and when they did,

the window of opportunity for more birds to do so closed.

But what an opportunity it was,

and those birds which took advantage of it are truly remarkable.

Scientists are currently working to gather still more clues,

from birds both extinct and living, to add even more detail

to their amazing evolutionary history.

We can only hope this will help us to better understand

this family of birds, which are surely flightless wonders.