Nature

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Of all the birds I've filmed over the years, there's nothing that can really compare with these comic characters. 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 ostrich, the emu and the rhea, together with the kiwi and the cassowary, are the court jesters of the avian world because they can't do the one thing that birds are famous for doing -- they can't fly. But exactly how -- and why -- did these birds abandon flight? It's one of the natural world's great mysteries. 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 behavior. Among their number is the fastest bird on land. Their chicks hatch ready to run. One has dagger-sharp talons. Another killer thighs. One is a bird which is heard, but seldom seen. Only in the pitch-black dead of night does it call. This group of birds are real oddballs, but they're a family with a remarkable success story despite having never flown a day in their lives.

Birds chirping

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but thIt's saidamily that a bird is three things --y feathers......flight......and song. But what happens if you're a bird which can't fly, which doesn't sing...

Ostrich hisses

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...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 ragbag 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. One has dagger-sharp talons. Another killer thighs. Their chicks hatch ready to run. 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-catching vanes like normal wing feathers. Nor can they be held neatly and tightly together. They're 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. 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, 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. 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 are 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. In the tropical rainforests of northern Australia lives the most feared of the ratites. Standing at around 6 feet tall, from its dinosaur-like crest to its dagger-sharp claws it has a lethal kick. Cassowaries are fiercely territorial. And one will fight to the death to defend itself or its magnificent emerald-green eggs. This, for most of our big birds, is their main line of defense -- size and strength -- especially for the fastest and biggest of our big birds -- the ostrich. This is the largest bird in the world. Standing around 9 feet tall, it can weigh over 300 pounds. On the African plains, it lives alongside some of the world's most dangerous predators. Hyenas......lions.......and cheetahs. Pounding across the plains, it uses its powerful legs to run for its life. Adult birds can run at speeds of over 40 miles an hour. Covering almost 16 feet in a single stride. 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. This is nonetheless, a remarkable and very rare sight. Most ostriches escape from such attacks. Adult ostriches are powerhouses of strength and agility and are seldom caught by predators. But ratites don't survive on brawn alone. Their success is a story about dedicated dads whose tenacity and endurance 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?

Birds chirping

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Well, they have a few tricks up their sleeve. Including some unusual breeding behavior which sees the male take a starring role. Spring in the Pampas of Argentina, and 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 splendor. As Ratites no longer fly, they have no gland to produce the oil needed to preen their feathers into continuous air-catching surfaces. 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 10 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'll 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.

Rheas hissing

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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. For two weeks now, females have laid their eggs in one shallow communal nest. But 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. 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 had mated with this one male, they move on to another, so increasing the chance that at least some of their young will survive.

Birds chirping, cawing

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

Kiwis screeching

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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 behavior, 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.

CASTRO

For the last 11 years I've been looking at the breeding behavior of kiwi and everything that is associated with it.

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Dr. Isabel Castro is a Colombian expert on kiwis who's lived in New Zealand for the past 25 years.

CASTRO

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 these relatively boring lives. And yet, as soon as we started this project, we started finding out these fantastic things about their intimate life. There has 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.

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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 behavior never filmed before in the wild -- two males fighting. A female calling for her mate.

Female kiwi screeching

CASTRO

Males and females have very different calls. The females have this very coarse, grunty call, as all females should have, you know. And the males have this whistle, beautiful and piercing.

Male kiwi whistling

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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 weighs only about 4 pounds. 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.

CASTRO

They are very naughty kiwi. For a long time we thought that they were really good birds and they mate with one another and one male, one female. But no. They're not like that at all. They do stray a little bit. They do stray.

Female kiwi screeching

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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, and 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. And Maoris used to say the tree roots 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 recognize her own eggs, keeping them at the center 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 gentlemen'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 babysit eggs, which, although small in relation to the ostrich itself, weigh in fact about 4 pounds each -- the largest eggs in the world. 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 omelet 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. 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. In the Australian outback, this male emu's hard work over the past 56 days is about to pay off. He is a father. Like a rhea and a cassowary, he has incubated his chicks alone without any help from the female. Covered in tawny markings, the chicks are known to Australians as Stripeys, although on their heads, the stripes appear a little more like dots. 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 agonizing hours, he makes his choice. Leading the brood to find water, this father helps a new generation of big birds take their first steps. But for one of their 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 some 10 feet tall and weighed half a ton. 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 roc. The roc 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 roc? Well, I was lucky enough to find some pieces of the roc -- 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 was met by the moa of New Zealand, which weighed over 440 pounds. The elephant bird might have been the biggest bird ever to exist, but some think that one species of moa was the tallest. And 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 live had once been part of a super continent 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 continent 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 re-learned 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. It 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 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.

Fly buzzing

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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. All newly hatched ratites emerge from the eggs ready to get up and go almost from the moment that they break free. For large, vulnerable ready-made-meals, this is a shrewd strategy which each of the ratites has evolved in its battle to survive on the ground. These 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. These early days are perilous. Although the ostrich parents have guided their chicks to water, there's still a problem. They might be big birds, but everything around here is even bigger. The chicks could easily be trampled underfoot. Especially as where prey gathers, predators are never far behind. The chicks don't have the option of flying to safety. The lions have unwittingly done the young ostriches a favor. The water hole is now clear. A piece of luck for 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 that it will help us to better understand this family of birds which are surely flightless wonders. This program is available on DVD. To order, visit shopPBS.org, or call 1-800-PLAY-PBS. To learn more about what you've seen on this "Nature" program, visit PBS.org.