Attenborough's Big Birds

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0:00:18 > 0:00:20Birds are masters of the skies.

0:00:23 > 0:00:26There are more than 10,000 species

0:00:26 > 0:00:30and they behave in a huge variety of different ways.

0:00:34 > 0:00:36But of all the birds I've filmed over the years,

0:00:36 > 0:00:40there's nothing that can really compare with these comic characters.

0:00:43 > 0:00:46That's not just because of their great size.

0:00:46 > 0:00:48But because they can't do the one thing

0:00:48 > 0:00:51that birds are famous for doing.

0:00:51 > 0:00:52They can't fly.

0:00:54 > 0:00:59The ostrich, the emu and the rhea, together with two other birds,

0:00:59 > 0:01:01the kiwi and the cassowary,

0:01:01 > 0:01:03are the court jesters of the avian world.

0:01:06 > 0:01:09They're a family with a remarkable success story,

0:01:09 > 0:01:13despite having never flown a day in their lives.

0:01:18 > 0:01:22But exactly how and why did these birds abandon flight?

0:01:23 > 0:01:26It's one of the natural world's great mysteries

0:01:26 > 0:01:29and it's taxed some of the finest minds in science

0:01:29 > 0:01:33from Darwin's time right through to the present day.

0:01:37 > 0:01:40And now, DNA is promising to give us the answer.

0:01:42 > 0:01:44But what is even more exciting

0:01:44 > 0:01:47than the remarkable evolutionary history of these birds

0:01:47 > 0:01:49is their behaviour -

0:01:49 > 0:01:52because if you're a bird that can't fly,

0:01:52 > 0:01:55you have to find other ways of surviving.

0:02:03 > 0:02:05BIRDSONG

0:02:06 > 0:02:10It's said that a bird is three things -

0:02:11 > 0:02:14feathers,

0:02:14 > 0:02:16flight

0:02:16 > 0:02:19and song.

0:02:19 > 0:02:21BIRDS CHIRP

0:02:23 > 0:02:26But what happens if you are a bird which can't fly,

0:02:26 > 0:02:29which doesn't sing...

0:02:29 > 0:02:31HISSING

0:02:32 > 0:02:35..and whose feathers are closer to fluff?

0:02:37 > 0:02:39Well, then you have to come up with

0:02:39 > 0:02:42some pretty unusual ways of surviving.

0:02:46 > 0:02:49This small group of birds are real oddballs,

0:02:49 > 0:02:52with a rag bag of characteristics

0:02:52 > 0:02:54that help them with life on the ground.

0:02:58 > 0:03:01Among their number is the fastest bird on land.

0:03:03 > 0:03:07A bird with the biggest eyes on Earth.

0:03:07 > 0:03:11One has dagger-sharp talons.

0:03:11 > 0:03:13Another, killer thighs.

0:03:16 > 0:03:18OSTRICH HISSES

0:03:21 > 0:03:25Their chicks hatch, ready to run.

0:03:25 > 0:03:27CHICKS GRUNT SOFTLY

0:03:30 > 0:03:33And they all have crazy hair.

0:03:37 > 0:03:40And useless wings.

0:03:42 > 0:03:45This lot couldn't fly even if they wanted to

0:03:45 > 0:03:49because their feathers aren't like those of other birds.

0:03:49 > 0:03:53They don't have barbs that link together into air-cutting vanes,

0:03:53 > 0:03:55like normal wing feathers.

0:03:56 > 0:04:00Nor can they be held neatly and tightly together.

0:04:00 > 0:04:02They are more like a fluffy feather boa.

0:04:06 > 0:04:09Without a role in flight, these feathers act instead

0:04:09 > 0:04:13as warm blankets or insect repellers

0:04:13 > 0:04:16or props in an exotic dance.

0:04:20 > 0:04:24But if you are a bird that hasn't flown a day in its life,

0:04:24 > 0:04:27then beauty isn't enough to survive.

0:04:31 > 0:04:35The first, the fastest and the biggest of all our birds

0:04:35 > 0:04:36is the ostrich.

0:04:36 > 0:04:41OSTRICH BOOMS

0:04:41 > 0:04:45Indeed, it's the largest bird in the world.

0:04:47 > 0:04:51Standing up to 3 metres tall, it weighs up to 150 kilos.

0:04:58 > 0:05:00On the African plains, it lives alongside

0:05:00 > 0:05:03some of the world's most dangerous predators...

0:05:08 > 0:05:09..hyenas...

0:05:11 > 0:05:13..lions...

0:05:15 > 0:05:17..and cheetahs.

0:05:20 > 0:05:22BIRDS CHIRP

0:05:28 > 0:05:32DRAMATIC MUSIC

0:05:33 > 0:05:35Pounding across the plains,

0:05:35 > 0:05:39it uses its powerful legs to run for its life.

0:05:45 > 0:05:47DRAMATIC MUSIC

0:05:47 > 0:05:49Adult birds can run at speeds

0:05:49 > 0:05:53of up to 70km - over 40 miles - an hour,

0:05:53 > 0:05:56covering almost 5 metres in a single stride.

0:06:04 > 0:06:07DRAMATIC MUSIC

0:06:27 > 0:06:29DRAMATIC MUSIC CLIMAXES

0:06:33 > 0:06:35This young ostrich hadn't quite developed

0:06:35 > 0:06:37the power or agility needed

0:06:37 > 0:06:41to escape these speediest of predators.

0:06:44 > 0:06:47But it still took the combined skill and experience

0:06:47 > 0:06:50of a team of cheetahs, working together,

0:06:50 > 0:06:53to bring the young ostrich down.

0:06:53 > 0:06:55CHEETAH GROWLS

0:06:57 > 0:07:00This is, nonetheless, a remarkable and very rare sight.

0:07:00 > 0:07:02CHEETAH PANTS

0:07:02 > 0:07:06Most ostriches escape from such attacks.

0:07:10 > 0:07:14Adult ostriches are powerhouses of strength and agility

0:07:14 > 0:07:17and are seldom caught by predators.

0:07:22 > 0:07:25BIRDS CHIRP AND WHOOP

0:07:25 > 0:07:29The second of our birds also has size and speed on its side.

0:07:31 > 0:07:34But for the biggest bird in South America,

0:07:34 > 0:07:36there is danger of a different kind.

0:07:43 > 0:07:45LATIN GUITAR MUSIC

0:07:51 > 0:07:54This Argentinian rhea has grown big -

0:07:54 > 0:07:58indeed, bigger than most of the mammals that live here.

0:08:06 > 0:08:10But this male has nonetheless to remain alert...

0:08:12 > 0:08:14..from attacks from one of his own kind.

0:08:21 > 0:08:24It's the beginning of the breeding season

0:08:24 > 0:08:29and males are starting to spar, sizing up their rivals' strength

0:08:29 > 0:08:32before the real battle to breed begins.

0:08:36 > 0:08:39RHEAS GRUNT

0:08:40 > 0:08:43MUSIC CONTINUES

0:08:52 > 0:08:55To the winner, TWO females.

0:08:55 > 0:08:58But although this fight has been won,

0:08:58 > 0:09:03the coming war will doubtless see him forced to defend his gains.

0:09:07 > 0:09:10CRICKETS CHIRP, INSECTS BUZZ

0:09:12 > 0:09:15DIDGERIDOO PLAYS

0:09:16 > 0:09:18Here in the Australian outback

0:09:18 > 0:09:22roams the second-largest of our big birds,

0:09:22 > 0:09:23the emu.

0:09:34 > 0:09:39A nomadic character, he uses his spectacularly elongated legs

0:09:39 > 0:09:42and ferocious-looking feet to go walkabout...

0:09:46 > 0:09:49..meaning he can cover vast distances

0:09:49 > 0:09:51in search of food and water.

0:09:53 > 0:09:56BANJO PLAYS

0:10:06 > 0:10:09Emu truly are wanderers -

0:10:09 > 0:10:12always on the move, following the rains,

0:10:12 > 0:10:14they walk hundreds of kilometres.

0:10:26 > 0:10:31And when they find water, they take on board all they can.

0:10:33 > 0:10:36BIRDS CHIRP, INSECTS BUZZ

0:10:39 > 0:10:42But flightless birds in Australia

0:10:42 > 0:10:44aren't restricted to the parched outback.

0:10:50 > 0:10:54In the tropical rainforests in the north of the country

0:10:54 > 0:10:55lives another one.

0:11:02 > 0:11:07It stands almost 2 metres tall and has a dinosaur-like crest

0:11:07 > 0:11:11and dagger-sharp claws that give it a lethal kick.

0:11:11 > 0:11:14DRAMATIC MUSIC

0:11:21 > 0:11:23Cassowaries are fiercely territorial.

0:11:25 > 0:11:29And one will fight to the death to defend itself

0:11:29 > 0:11:32or its magnificent emerald-green eggs.

0:11:59 > 0:12:00Like the rest of his family

0:12:00 > 0:12:03in Africa, South America and Australia,

0:12:03 > 0:12:06it's a bird which has taken an evolutionary route

0:12:06 > 0:12:10very different from that of its aeronautical relatives.

0:12:18 > 0:12:21Cassowaries vary greatly in colouration.

0:12:21 > 0:12:25So, it's debatable how many species there are.

0:12:25 > 0:12:27Probably three.

0:12:30 > 0:12:33Another flightless bird lives in New Zealand,

0:12:33 > 0:12:36hidden in the forests and only active at night.

0:12:37 > 0:12:40It could be called the runt of the litter.

0:12:46 > 0:12:49Standing only a half a metre or so tall,

0:12:49 > 0:12:51this is a kiwi.

0:12:55 > 0:13:00More like a mammal than a bird, it has dense, hair-like plumage

0:13:00 > 0:13:03and a very long, very sensitive beak,

0:13:03 > 0:13:07which makes up for its tiny and all but useless eyes.

0:13:11 > 0:13:15It walks along like a little hobbit, with its arms behind its back.

0:13:20 > 0:13:21When, in the 19th century,

0:13:21 > 0:13:24tales of the kiwi reached naturalists in England,

0:13:24 > 0:13:29they thought them merely figments of early travellers' imaginations.

0:13:36 > 0:13:40One of the largest collections of this weird walking family

0:13:40 > 0:13:44was amassed by a Victorian English eccentric, Walter Rothschild.

0:13:52 > 0:13:57Collectively, these extraordinary birds are known as the ratites,

0:13:57 > 0:14:01flightless birds that just grew and grew,

0:14:01 > 0:14:03from the smallest - that's the kiwi -

0:14:03 > 0:14:08to the largest alive today, the ostrich.

0:14:08 > 0:14:11But their ancient relatives were even more impressive.

0:14:15 > 0:14:19Enormous birds that would have towered over me,

0:14:19 > 0:14:22like the moa from New Zealand

0:14:22 > 0:14:24or the elephant bird from Madagascar.

0:14:29 > 0:14:33But exactly why did these birds abandon flight?

0:14:33 > 0:14:37Well, flying is a very energetic business,

0:14:37 > 0:14:40much more so than walking or running,

0:14:40 > 0:14:44and birds don't fly unless they have to.

0:14:44 > 0:14:47- WAVES CRASH - Some, like penguins,

0:14:47 > 0:14:49gave up flight relatively recently

0:14:49 > 0:14:51and took to the water.

0:14:51 > 0:14:54But they still have strong wings,

0:14:54 > 0:14:56which they use like paddles for swimming.

0:15:01 > 0:15:04The ratites are different.

0:15:04 > 0:15:08They are the original flightless birds.

0:15:08 > 0:15:11And they're the only birds whose skeletons

0:15:11 > 0:15:14make them incapable of flight.

0:15:14 > 0:15:17Hidden beneath their mass of feathery fluff

0:15:17 > 0:15:19is a flat, raft-like breastbone

0:15:19 > 0:15:24that lacks the ridge onto which flight muscles can be attached.

0:15:24 > 0:15:26In fact, it's this which gives them their name,

0:15:26 > 0:15:30from the Latin word, "ratis", meaning "raft".

0:15:31 > 0:15:34So, whilst there are other birds which don't fly,

0:15:34 > 0:15:37our very special family, the ratites,

0:15:37 > 0:15:40stand entirely apart from all the others.

0:15:41 > 0:15:44They are the Flintstones of the bird world,

0:15:44 > 0:15:47a group whose lineage can be traced back to the time

0:15:47 > 0:15:50when dinosaurs walked the Earth.

0:15:55 > 0:15:57The dinosaurs once dominated the land,

0:15:57 > 0:16:01just as their relatives, the pterosaurs, ruled the skies.

0:16:03 > 0:16:08But when, 66 million years ago, both groups were wiped out,

0:16:08 > 0:16:10some of the ancient birds seized their moment

0:16:10 > 0:16:13and made a bid to dominate the land themselves.

0:16:18 > 0:16:23Some, the ancestral ratites, grew big and fat,

0:16:23 > 0:16:27with long, strong legs, until one day,

0:16:27 > 0:16:29they were too heavy to fly.

0:16:33 > 0:16:36Since then, of course, the mammals have fought back

0:16:36 > 0:16:38and in most places, THEY won.

0:16:40 > 0:16:43But the elephant bird and the moa, now extinct,

0:16:43 > 0:16:45survived until a few centuries ago

0:16:45 > 0:16:49and five others still flourish across the southern hemisphere.

0:16:49 > 0:16:51The ostrich, the emu,

0:16:51 > 0:16:54the cassowary, the rhea

0:16:54 > 0:16:56and the kiwi.

0:17:02 > 0:17:05BIRDS CHIRP, INSECTS BUZZ

0:17:09 > 0:17:13The success of the ratites today is largely due to

0:17:13 > 0:17:17some bizarre breeding and very complicated relationships.

0:17:18 > 0:17:21Males mating with multiple females,

0:17:21 > 0:17:24females mating with multiple males,

0:17:24 > 0:17:27fathers raising chicks which aren't theirs.

0:17:29 > 0:17:34The tenacity and endurance of these dedicated dads

0:17:34 > 0:17:37has helped raise generations of walking giants.

0:17:40 > 0:17:44So, how do our motley crew ensure the survival of their offspring

0:17:44 > 0:17:47when safe tree-top nests are out of the question?

0:17:49 > 0:17:51Well, it takes a lot of work.

0:18:01 > 0:18:04For the emu in the Australian outback,

0:18:04 > 0:18:07the breeding season starts in the winter.

0:18:10 > 0:18:14This is when a male needs to be at his heaviest.

0:18:14 > 0:18:17DIDGERIDOO PLAYS

0:18:17 > 0:18:21Large bodies enable ratites to develop large guts,

0:18:21 > 0:18:23so unlike small flying birds,

0:18:23 > 0:18:26they can stock up on plenty of plants and seeds.

0:18:32 > 0:18:37Soon, he will mate and he will be the one who will incubate the eggs.

0:18:43 > 0:18:47During his time on the nest, he won't eat or drink.

0:18:47 > 0:18:50So, he's preparing for that by fattening up.

0:18:55 > 0:18:58This time of the year is all about finding food

0:18:58 > 0:19:00and some enterprising males

0:19:00 > 0:19:03even go into town to pick up dinner.

0:19:03 > 0:19:05CAR HORN BEEPS

0:19:08 > 0:19:10BANJO PLAYS

0:19:24 > 0:19:27TRUCK HORN BEEPS

0:19:32 > 0:19:36A strange sight - but the locals are used to it.

0:19:36 > 0:19:39TRUCK HORN BEEPS

0:19:51 > 0:19:53When they are ready to breed,

0:19:53 > 0:19:56male ratites start to try and impress females

0:19:56 > 0:20:00and they do so with some pretty flamboyant dance moves.

0:20:10 > 0:20:14Ratites might not be strong contenders in a beauty contest

0:20:14 > 0:20:17but these males certainly know how to move and groove.

0:20:20 > 0:20:23From the ostrich to the cassowary,

0:20:23 > 0:20:26the males all work hard to show off their best features.

0:20:34 > 0:20:39Just HOW hard can be seen on the grasslands of Argentina.

0:20:46 > 0:20:50It's spring and the rheas are preparing for the breeding season.

0:21:07 > 0:21:11Male rheas, with their distinctive black markings, have broken away

0:21:11 > 0:21:14from the flocks in which they spend the rest of the year.

0:21:16 > 0:21:18Now is the time for courtship,

0:21:18 > 0:21:21when their feathers will be shown off in all their splendour.

0:21:25 > 0:21:30As ratites no longer fly, they have no gland to produce the oil

0:21:30 > 0:21:34needed to preen their feathers into continuous air-catching services.

0:21:39 > 0:21:40But with a little grooming,

0:21:40 > 0:21:43their plumage can be very impressive.

0:21:51 > 0:21:55This male has managed to secure several females for himself.

0:22:03 > 0:22:06Herding them with his outstretched wings,

0:22:06 > 0:22:12a male can maintain a harem of anything from two to ten females,

0:22:12 > 0:22:15as long as he can keep them close.

0:22:22 > 0:22:24He doesn't let them out of his sight,

0:22:24 > 0:22:27courting each one in turn.

0:22:40 > 0:22:43And the grand finale of his mating ritual...

0:22:50 > 0:22:53..this curious head-bobbing dance.

0:23:02 > 0:23:04It's hardly a tango.

0:23:09 > 0:23:14And the object of his affections doesn't seem particularly impressed.

0:23:23 > 0:23:26But despite the lack of encouragement,

0:23:26 > 0:23:28he will spend most of the breeding season

0:23:28 > 0:23:32herding and head-bobbing to his females,

0:23:32 > 0:23:34until they are ready to mate.

0:23:40 > 0:23:42Unless, of course...

0:23:43 > 0:23:48..this rival male can rob him of his hard-won harem.

0:24:27 > 0:24:29Rising up as high as he can,

0:24:29 > 0:24:32he puts on a show of size and strength.

0:24:34 > 0:24:37This performance has rarely been filmed.

0:24:37 > 0:24:40It's a tango of a different, aggressive kind

0:24:40 > 0:24:43with plenty of Latin American spirit.

0:25:26 > 0:25:30Today, there is someone better than he.

0:25:39 > 0:25:43He retreats, leaving the rival male

0:25:43 > 0:25:45to take his place on the dance floor.

0:25:54 > 0:25:59This male is, it seems, a little more persuasive.

0:26:26 > 0:26:29Exactly how ratites mate

0:26:29 > 0:26:31was a mystery only solved by scientists

0:26:31 > 0:26:34in the last few years.

0:26:37 > 0:26:40Most birds don't have a penis.

0:26:40 > 0:26:42Instead, both the male and female birds

0:26:42 > 0:26:44have an opening called a cloaca.

0:26:52 > 0:26:56That certainly helps to streamline the body of a flying bird.

0:27:01 > 0:27:04The male ratite, however, is different.

0:27:04 > 0:27:06He does have a penis,

0:27:06 > 0:27:08and it was once assumed that these large birds

0:27:08 > 0:27:11would have blood-based erection systems,

0:27:11 > 0:27:12similar to humans.

0:27:16 > 0:27:19But in fact the ostrich, emu and rhea

0:27:19 > 0:27:23enlarge their penises with lymph fluid.

0:27:27 > 0:27:31They also have a few additional muscles to keep everything in place.

0:27:46 > 0:27:49While it's known that male and female rheas will mate

0:27:49 > 0:27:53with several different partners over the course of the breeding season,

0:27:53 > 0:27:57there is much less certainty with another of our ratite family.

0:28:14 > 0:28:18On the islands of New Zealand lives an enigma.

0:28:21 > 0:28:23The most secretive of our flightless birds.

0:28:26 > 0:28:30Hidden in these ancient and mysterious forests,

0:28:30 > 0:28:32it only emerges after dusk.

0:28:51 > 0:28:53HIGH-PITCHED BIRD CALL

0:29:03 > 0:29:06Only in the pitch-black dead of night does it call.

0:29:06 > 0:29:09HIGH-PITCHED CALLING

0:29:16 > 0:29:18Ratites might not sing,

0:29:18 > 0:29:21but their mating calls are certainly piercing.

0:29:23 > 0:29:27This is a bird which is heard but seldom seen.

0:29:27 > 0:29:30Scientists have to struggle to catch sight of the kiwi,

0:29:30 > 0:29:33let alone to understand its behaviour,

0:29:33 > 0:29:35even when they work around the clock.

0:29:40 > 0:29:43But using infrared light, which the kiwis can't see,

0:29:43 > 0:29:47and radio transmitters to track them in the darkness,

0:29:47 > 0:29:50the researchers here are slowly piecing together

0:29:50 > 0:29:52a picture of this shy bird.

0:29:57 > 0:29:59For the last 11 years,

0:29:59 > 0:30:03I have been looking at the breeding behaviour of Kiwi

0:30:03 > 0:30:05and everything that is associated with it.

0:30:07 > 0:30:11Dr Isabel Castro is a Colombian expert on kiwis

0:30:11 > 0:30:14who has lived in New Zealand for the past 25 years.

0:30:16 > 0:30:18This environment where they are

0:30:18 > 0:30:21is completely different than our environment.

0:30:21 > 0:30:22They are nocturnal where we are diurnal,

0:30:22 > 0:30:25and for many years before we started this research,

0:30:25 > 0:30:29people thought that they had this relatively boring life

0:30:29 > 0:30:31and yet as soon as we started this project,

0:30:31 > 0:30:35we started finding out these fantastic things

0:30:35 > 0:30:37about their intimate life.

0:30:39 > 0:30:41There have been all sorts of things

0:30:41 > 0:30:43that were completely unexpected,

0:30:43 > 0:30:47and that made now these birds very extraordinary,

0:30:47 > 0:30:50because we didn't know those things before.

0:30:54 > 0:30:56Living in complete darkness,

0:30:56 > 0:31:00unable to see virtually anything, the eyes of the kiwi

0:31:00 > 0:31:02are all but useless,

0:31:02 > 0:31:04but - unusually for a bird -

0:31:04 > 0:31:06it's got a great sense of smell,

0:31:06 > 0:31:08which it uses to find its way around.

0:31:17 > 0:31:19By setting up remote cameras,

0:31:19 > 0:31:22the scientists have been able to capture behaviour

0:31:22 > 0:31:24never filmed before in the wild.

0:31:26 > 0:31:28Two males fighting.

0:31:28 > 0:31:30KIWIS RASP

0:31:55 > 0:31:58A female calling for her mate.

0:31:58 > 0:32:01REPETITIVE GUTTURAL CALL

0:32:11 > 0:32:13Males and females have different calls.

0:32:13 > 0:32:18The females have this very coarse, grunty call,

0:32:18 > 0:32:20as all females should have, you know!

0:32:20 > 0:32:24The males have these whistles, beautiful and piercing.

0:32:24 > 0:32:27REPETITIVE SHRILL CALL

0:32:36 > 0:32:40Isabel and her team even managed to film a kiwi family

0:32:40 > 0:32:41with a tiny chick.

0:32:58 > 0:33:01Kiwis are the only nocturnal ratites

0:33:01 > 0:33:03and by far the smallest.

0:33:15 > 0:33:18This big bird isn't big at all.

0:33:18 > 0:33:21It only weighs about two kilos.

0:33:24 > 0:33:26Kiwis never grew big

0:33:26 > 0:33:30because they lived alongside the now-extinct moas.

0:33:33 > 0:33:37With those giant herbivores already roaming New Zealand,

0:33:37 > 0:33:40the kiwi's evolution took an alternative path.

0:33:42 > 0:33:46It remained small, became nocturnal and omnivorous.

0:33:54 > 0:33:56With nostrils at the end of its beak,

0:33:56 > 0:34:00the kiwi sniffs out insects and worms at night...

0:34:02 > 0:34:06..and then stays in the safety of its burrow for the day.

0:34:14 > 0:34:18Unlike the other ratites, it nests underground.

0:34:26 > 0:34:31Until recently, it was thought that kiwis bred in monogamous pairs,

0:34:31 > 0:34:36but now DNA analysis has painted a much more complicated picture.

0:34:40 > 0:34:42They are very naughty, kiwi.

0:34:42 > 0:34:45For a long time, we thought that they were really good birds,

0:34:45 > 0:34:48and mated with one another, one male, one female,

0:34:48 > 0:34:50but they are not like that at all.

0:34:50 > 0:34:52They do stray a little bit.

0:34:52 > 0:34:53They do stray.

0:34:57 > 0:35:02It seems that breeding is a little more flexible than just one-on-one.

0:35:02 > 0:35:06Some birds seem to breed in family groups.

0:35:06 > 0:35:08Others may raise young as a pair

0:35:08 > 0:35:11even though the chicks might not belong to Dad.

0:35:16 > 0:35:20However, it's the males who shoulder the burden of incubation.

0:35:20 > 0:35:24The eggs in their care are among the oddest on earth.

0:35:26 > 0:35:29This is a kiwi's egg.

0:35:29 > 0:35:33It's the biggest in proportion to body size of any bird's egg.

0:35:33 > 0:35:35It weighs about a fifth

0:35:35 > 0:35:38as much as the adult bird.

0:35:38 > 0:35:42It's so big, it takes 80 days to incubate.

0:35:42 > 0:35:44The Maoris used to say

0:35:44 > 0:35:48that tree routes would grow over a kiwi's nest.

0:35:48 > 0:35:53This is the egg of another ratite, an ostrich,

0:35:53 > 0:35:59and curiously, it is the smallest egg in terms of body weight

0:35:59 > 0:36:01for any bird in the world.

0:36:04 > 0:36:07These ostrich eggs are unusual in other ways.

0:36:07 > 0:36:12They too are part of an elaborate game of pick and mix...

0:36:15 > 0:36:18..because ostriches are almost like cuckoos.

0:36:18 > 0:36:22Females will lay in the nests of other ostriches,

0:36:22 > 0:36:24but unlike the cuckoo,

0:36:24 > 0:36:26the owners of the nest know about it

0:36:26 > 0:36:28and they don't seem to mind.

0:36:34 > 0:36:37It may help to have a few spare eggs.

0:36:41 > 0:36:45The female seems to be able to recognise her own eggs,

0:36:45 > 0:36:49keeping them at the centre of the nest while rolling out others

0:36:49 > 0:36:53as sacrifices to any predator brave enough to make an attack.

0:36:58 > 0:37:02Up to six female ostriches may lay in a single nest.

0:37:07 > 0:37:09For most members of the ratite family,

0:37:09 > 0:37:11the rhea, the emu and the cassowary,

0:37:11 > 0:37:15incubation is something of a gentleman's club -

0:37:15 > 0:37:17females aren't welcome.

0:37:18 > 0:37:21But the ostrich does things a little differently.

0:37:23 > 0:37:27The male and female take turns at caring for the clutch,

0:37:27 > 0:37:30keeping watch by day and night to make sure

0:37:30 > 0:37:33nothing has a chance to steal the eggs.

0:37:38 > 0:37:42This father-to-be is carefully rolling the eggs to make sure

0:37:42 > 0:37:44the embryo inside gets evenly warmed.

0:37:49 > 0:37:50In the cold of the night,

0:37:50 > 0:37:54he uses his feathers as a blanket to cover his charges.

0:38:07 > 0:38:09Communicating by clacking their beaks,

0:38:09 > 0:38:12this couple share the parental burden.

0:38:20 > 0:38:23They take turns to sit on the eggs,

0:38:23 > 0:38:26which, although small compared to the ostrich itself,

0:38:26 > 0:38:29weigh in fact almost two kilos each,

0:38:29 > 0:38:32the largest eggs laid by any living animal.

0:38:44 > 0:38:49Left unattended, such large eggs soon attract attention.

0:38:53 > 0:38:56These ostrich eggs are giant ready meals

0:38:56 > 0:38:59for a variety of African animals.

0:39:01 > 0:39:04You can't make an omelette without breaking eggs,

0:39:04 > 0:39:08and this jackal has worked out just how to crack one against another

0:39:08 > 0:39:10and so release his lunch.

0:39:33 > 0:39:37The Egyptian vulture has its own ingenious version of smash and grab.

0:39:58 > 0:40:00It's perhaps not surprising

0:40:00 > 0:40:03that up to 90% of ostrich clutches

0:40:03 > 0:40:05are totally destroyed.

0:40:19 > 0:40:25In South America, rheas nest in a similar way to the ostrich.

0:40:31 > 0:40:37For two weeks, females lay their eggs in one shallow, communal nest.

0:40:39 > 0:40:44Each egg is 12 times the size of that of a chicken.

0:40:45 > 0:40:47But unlike the ostrich,

0:40:47 > 0:40:50it's the male who settles down to do all the hard work.

0:40:54 > 0:40:56He alone will incubate these eggs,

0:40:56 > 0:41:01and he does so for more than five weeks, whatever the weather.

0:41:01 > 0:41:05THUNDER CRACKS, HEAVY RAIN

0:41:32 > 0:41:34It's an arduous task.

0:41:34 > 0:41:3865% of males abandon their nests,

0:41:38 > 0:41:41many because they don't have the energy to sustain themselves

0:41:41 > 0:41:43without going away to feed.

0:41:55 > 0:41:59The females, however, never put all their eggs in one basket.

0:42:01 > 0:42:04Once they've mated with this one male,

0:42:04 > 0:42:07they move on to another, so increasing the chance

0:42:07 > 0:42:10that at least some of their young will survive.

0:42:26 > 0:42:28Nesting on the ground out in the open

0:42:28 > 0:42:32means that, inevitably, the eggs are vulnerable.

0:42:38 > 0:42:42From the enormous eggs of the ostrich...

0:42:45 > 0:42:48..to the green eggs of the emu.

0:42:57 > 0:43:02But for one of the relatives, the battle to keep their clutches safe

0:43:02 > 0:43:05was, in the end, lost.

0:43:08 > 0:43:11These are the leg bones of the elephant bird.

0:43:11 > 0:43:13It was the largest of the ratites.

0:43:13 > 0:43:16Indeed, it was one of the biggest birds ever known.

0:43:16 > 0:43:20It stood over 3m tall and weighed half a tonne.

0:43:22 > 0:43:26It lived on the ancient island of Madagascar,

0:43:26 > 0:43:29which I visited over 50 years ago.

0:43:46 > 0:43:49Before Europeans ever went to the island,

0:43:49 > 0:43:50it had a reputation for being the home

0:43:50 > 0:43:53of really strange, fabulous beasts,

0:43:53 > 0:43:56and Marco Polo, 700 years ago,

0:43:56 > 0:43:59believed that it was the home of the fabulous bird, the rukh.

0:43:59 > 0:44:03The rukh, which carried off Sinbad the Sailor, and which was reputed

0:44:03 > 0:44:05to be able to carry off elephants in its talons,

0:44:05 > 0:44:08as this one is doing.

0:44:08 > 0:44:12But Marco Polo had very good reason for thinking that it lived in Madagascar,

0:44:12 > 0:44:16because he heard stories that in Madagascar were found gigantic eggs,

0:44:16 > 0:44:22over two feet long. What else could have laid them but the rukh?

0:44:22 > 0:44:24Well, I was lucky enough to find

0:44:24 > 0:44:28some pieces of the rukh, or elephant bird's egg.

0:44:36 > 0:44:40And even luckier to be given some pieces that looked like

0:44:40 > 0:44:42they might belong to one egg.

0:44:46 > 0:44:48Now, would they fit together?

0:44:55 > 0:44:57These two certainly did.

0:45:05 > 0:45:08At the end of an hour, I had two halves.

0:45:18 > 0:45:22And to my joy, they fitted together perfectly.

0:45:25 > 0:45:28There was a place for even such a tiny fragment as this.

0:45:31 > 0:45:36The egg was well nigh perfect.

0:45:36 > 0:45:40As I held it, I had little difficulty in imagining the country

0:45:40 > 0:45:44as it must have been when great numbers of gigantic birds,

0:45:44 > 0:45:48over ten feet tall, strode majestically through the swamps.

0:45:51 > 0:45:56This is the egg that I brought back from Madagascar all those years ago.

0:45:56 > 0:46:00It's the biggest egg ever laid by anything.

0:46:00 > 0:46:05Bigger by far than even the egg of the biggest dinosaur.

0:46:05 > 0:46:08As you might imagine, it could have made a meal

0:46:08 > 0:46:10for quite a lot of people,

0:46:10 > 0:46:13and that may well be, some people think,

0:46:13 > 0:46:17the reason why the elephant bird became extinct.

0:46:17 > 0:46:21If it wasn't for human beings, the elephant bird might still

0:46:21 > 0:46:23be walking around on Madagascar.

0:46:30 > 0:46:34The same fate met the moas of New Zealand,

0:46:34 > 0:46:38some kinds of which weighed over 200 kilos.

0:46:38 > 0:46:42The elephant bird might have been the biggest bird ever to exist,

0:46:42 > 0:46:46but some think that one species of moa was the tallest.

0:46:47 > 0:46:51Moas, too, were hunted and had their eggs eaten by humans

0:46:51 > 0:46:54until there were none left.

0:46:54 > 0:46:58We know this because of the careful detective work scientists

0:46:58 > 0:47:00have done on their bones.

0:47:02 > 0:47:04It's not the only puzzle

0:47:04 > 0:47:08that fragments of extinct bird like these, of the moa,

0:47:08 > 0:47:10might be able to solve.

0:47:10 > 0:47:14If these birds were flightless, how did they manage to spread

0:47:14 > 0:47:16round the world, from the deserts of Africa

0:47:16 > 0:47:19to the rainforests of Australia?

0:47:19 > 0:47:22It's a conundrum that has puzzled minds for centuries.

0:47:27 > 0:47:31Not that long ago, scientists thought they had the answer.

0:47:31 > 0:47:34All the places in which the ratites lived

0:47:34 > 0:47:38had once been part of a supercontinent called Gondwanaland.

0:47:41 > 0:47:45Perhaps our birds came from one common ancestor, which was

0:47:45 > 0:47:48also flightless, that roamed all over that land.

0:47:50 > 0:47:54Then, millions of years ago, when the continents split up,

0:47:54 > 0:47:57populations of this bird were separated.

0:47:57 > 0:48:00As their homes drifted into new positions,

0:48:00 > 0:48:04the isolated birds adapted and evolved in different ways,

0:48:04 > 0:48:06producing everything from the tiny kiwi

0:48:06 > 0:48:09to the huge extinct elephant bird.

0:48:12 > 0:48:16But ancient bones are telling a different story.

0:48:16 > 0:48:19Scientists have recently been sequencing DNA

0:48:19 > 0:48:22from the bones of extinct ratites

0:48:22 > 0:48:25and compared them with living flightless birds,

0:48:25 > 0:48:28and the results have come as a huge surprise.

0:48:32 > 0:48:35The mighty elephant bird, which should be most closely

0:48:35 > 0:48:40related to the ostrich, turns out to be most similar to the tiny kiwi.

0:48:41 > 0:48:44Not what was expected at all.

0:48:44 > 0:48:47So how could this possibly be?

0:48:49 > 0:48:53Well, an unexpected character is providing some answers.

0:48:57 > 0:49:00A little-known ratite relative, the tinamou,

0:49:00 > 0:49:02that lives in Central and South America.

0:49:07 > 0:49:12DNA has recently revealed that it isn't a distant relative,

0:49:12 > 0:49:14a cousin, say, but instead a sibling,

0:49:14 > 0:49:18smack in the middle of the ratite family tree.

0:49:20 > 0:49:25Which is remarkable, because tinamous can fly.

0:49:27 > 0:49:29Now, if all the ratites and the tinamous evolved

0:49:29 > 0:49:31from one flightless ancestor,

0:49:31 > 0:49:35then the tinamous must have relearned how to fly.

0:49:36 > 0:49:41But there are no known examples of a species of flightless bird

0:49:41 > 0:49:43regaining flight, so this suggests

0:49:43 > 0:49:47that the common ancestor of the ratites and the tinamous

0:49:47 > 0:49:51wasn't flightless at all. He could fly.

0:49:57 > 0:50:00Our birds might not have drifted away from one another

0:50:00 > 0:50:03on the lands in which they live today.

0:50:03 > 0:50:07Instead, their ancestors must have flown across miles of ocean

0:50:07 > 0:50:10to reach the far corners of the world, and only then

0:50:10 > 0:50:13did they independently lose the ability to fly.

0:50:24 > 0:50:26It's an amazing thought,

0:50:26 > 0:50:30but the ratites lost their ability to fly independently

0:50:30 > 0:50:33and on several different occasions.

0:50:36 > 0:50:40Thousands of miles apart from each other on their separate continents,

0:50:40 > 0:50:44each kind of ratite developed into its own flightless form.

0:50:48 > 0:50:51The ostrich and the rhea kept their wings

0:50:51 > 0:50:54and evolved elaborate uses for their feathers.

0:50:57 > 0:51:02The wings of the emu and cassowary became short and tiny...

0:51:03 > 0:51:08..and the kiwi, well, its wings are now all but invisible.

0:51:14 > 0:51:16Although the details are different,

0:51:16 > 0:51:20the demands of living on the ground meant that all the ratites

0:51:20 > 0:51:23evolved in their own way into flightlessness.

0:51:26 > 0:51:30And there's one survival strategy which they all share,

0:51:30 > 0:51:32and which begins when they hatch.

0:51:40 > 0:51:42In the Australian outback,

0:51:42 > 0:51:48this male emu's hard work over the past 56 days is about to pay off.

0:51:59 > 0:52:01He is a father.

0:52:06 > 0:52:10His chicks, like all newly hatched ratites, are able to get up and go

0:52:10 > 0:52:14almost from the moment they break free from their eggs.

0:52:24 > 0:52:27This is an invaluable ability for a chick,

0:52:27 > 0:52:29which is, after all,

0:52:29 > 0:52:32a very succulent mouthful for almost any predator.

0:52:40 > 0:52:44Emu chicks, with their tawny markings, are known to Australians

0:52:44 > 0:52:46as stripeys.

0:53:05 > 0:53:10Their dedicated dad will spend the next six months caring for them,

0:53:10 > 0:53:15by which time they will already have grown to at least half his height.

0:53:15 > 0:53:18That is, if they ever hurry up and hatch.

0:53:34 > 0:53:38The chicks had to work hard to free themselves from the egg shells.

0:53:38 > 0:53:40Now they need a drink.

0:53:45 > 0:53:48Their father must face a tough decision.

0:54:01 > 0:54:04One egg still hasn't hatched.

0:54:04 > 0:54:09If he stays and waits for it to do so, the older chicks may die.

0:54:21 > 0:54:25It's likely that he can hear sounds coming from within

0:54:25 > 0:54:26the unhatched egg.

0:54:31 > 0:54:35Meanwhile, the harsh Australian sun scorches down on those

0:54:35 > 0:54:39of his offspring desperately waiting for their first drink.

0:55:15 > 0:55:19After many agonising hours, he makes his choice.

0:55:34 > 0:55:36Leading the brood to find water,

0:55:36 > 0:55:42this father helps a new generation of big birds take their first steps.

0:56:14 > 0:56:18From South Africa to South America,

0:56:18 > 0:56:22an extraordinary combination of mating behaviour

0:56:22 > 0:56:26and parental care has produced birds which are very special indeed.

0:56:28 > 0:56:30CHIRPING

0:56:39 > 0:56:45These young ostriches will soon grow into the biggest birds in the world.

0:56:49 > 0:56:54Although today, as they take tiny steps across this vast landscape,

0:56:54 > 0:56:56that day seems a long way off.

0:57:00 > 0:57:02The next generation of ratites.

0:57:04 > 0:57:08A reminder of how one remarkable group of birds independently

0:57:08 > 0:57:12seized a moment when there were no predators around to hunt them down

0:57:12 > 0:57:17and set off down various but similar evolutionary paths.

0:57:21 > 0:57:25The only group of birds to have become massive and flightless.

0:57:29 > 0:57:34It wasn't long before some mammals also became big and dominant,

0:57:34 > 0:57:35and when they did,

0:57:35 > 0:57:39the window of opportunity for more birds to do so closed.

0:57:39 > 0:57:43But what an opportunity it was,

0:57:43 > 0:57:47and those birds which took advantage of it are truly remarkable.

0:57:54 > 0:57:58Scientists are currently working to gather still more clues,

0:57:58 > 0:58:03from birds both extinct and living, to add even more detail

0:58:03 > 0:58:06to their amazing evolutionary history.

0:58:06 > 0:58:10We can only hope this will help us to better understand

0:58:10 > 0:58:14this family of birds, which are surely flightless wonders.