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.