"Birds are the most accomplished aeronauts the world has ever seen." "They fly high and low." "At great speed and very slowly." "And always with extraordinary precision and control" "But birds are not the only creatures in the air." "There are also small furry mammals, bats, like these in Texas." "They are so competent in the air that they have just made a journey from Mexico, a thousand miles away, simply in order to rear their young in this cave, which is particularly suitable for them as a nursery." "Just now they are flying out to catch their evening meal of insects." "But they had better be careful, because in the skies above them there lurks a creature that can outfly them." "It is, of course, a bird." "A red-tailed hawk." "Bats with their fluttering zig-zag flight are not easy targets, and a hawk needs all its aerobatics skills and powers of concentration if it is to snatch one out of the confusing multitude." "That is one bat that will not return to the roost tonight." "The red-tail lives beside the cave and is well practised in bat-catching." "This prairie falcon, on the other hand, is a visitor, but it's learning fast." "Unlike the hawk, it chooses to eat its meals on the wing." "Bats are latecomers to the skies." "They've only been flying for a mere 60 million years." "The air was first colonised 200 million years earlier still by the insects, but now they can't escape the birds either." "Some insects, of course, have powerful weapons with which to defend themselves." "But a bee-eater certainly knows how to deal with a bee." "A rub against the perch usually discharges the sting." "And if that doesn't, then a sharp nip will squirt the venom harmlessly into the air." "Dragonflies first flew around 350 million years ago and insects had the skies to themselves for 150 million years thereafter." "And then a different kind of animal joined them in the air." "As the dinosaurs dominated the land, so the pterosaurs now ruled the skies." "Pterosaurs had wings of skin, stretched between one enormously elongated finger and their flanks." "They flew over the sea as well as the land." "It seems likely that some roosted on cliffs and launched themselves into the air as gannets do today." "They probably snatched fish from the surface of the sea, and some certainly fell into it." "Their bodies were buried by mud;" "the mud turned to limestone and eventually became exposed in great quarries like this one in Southern Germany." "Today, separating the layers of sediment is just like searching through the pages of a visitor's book that hasn't been opened for 150 million years." "0f course, nearly all of the pages are absolutely blank." "Visitors, after all, were very few." "But every now and again you come across a signature that is unmistakable." "A fish the size of a sardine." "A shrimp, even its antennae perfectly preserved." "0ne of those pioneering dragonflies, nearly six inches across." "And a pterosaur with skinny wings and teeth in its jaws." "With so many superb fossils, people thought that they had a complete list of the visitors to the lagoon." "And then, in the middle of the last century, a signature was discovered that was wholly unexpected and totally amazing." "This is it." "It's a feather." "Its barbs are narrower on one side of the quill, just as they are on the feathers of a modern bird's wing." "This asymmetry is a sure sign that such feathers were used for flight." "But what animal at the time of the dinosaurs could have such a wing?" "The answer was found the very next year in the same quarry:" "a fossil with its feathers still attached to its body." "This is archaeopteryx." "It had three toes armed with claws and long, strong legs." "Clearly it walked and perched like a bird." "But its head was very reptilian with bony jaws." "And in those jaws, teeth." "Its spine was extended into a bony tail, again like that of a reptile." "But on either side of the tail bones, clearly visible, it had those characteristic possessions of birds:" "feathers." "Feathers are made of keratin, as are the scales that many birds still have on their legs, and reptiles all over their body." "A scaly coat must be very hot, so reptiles, like this skink, have to seek shade during the hottest part of the day." "But if the scales became fibrous, they could be fluffed up to let in cooling air during the day, and closed down to trap insulating air for warmth at night." "So it is not difficult to believe that scales eventually became transformed into feathers." "But why should they have become so long that they enabled the animal to take to the air?" "Well, this Australian lizard suggests an answer." "When it is threatened by its enemies, it responds by spreading the great frill it has around its neck." "But if that doesn't scare them off, it runs away, on its hind legs." "If such a reptile had developed feathery scales on its forelegs and then spread them out then it might easily lift into the air and so escape a land-bound predator." "There's another possibility." "Maybe that early reptile did not live on the ground but climbed in the trees searching for food, as today the little flying lizard of Borneo does." "It now glides from tree to tree." "It has developed wings that are flaps of skin supported by elongated ribs." "If that early enterprising reptile with feathery scales did have specially long ones on its arms, then they too would have enabled it to glide from tree to tree." "Maybe its arm muscles were even strong enough to allow it to make a few flaps to help it on its way." "Archaeopteryx was certainly well-equipped for climbing, for its wings still carried three fingers, each ending with a hooked claw, ideal for clinging on to twigs." "And there are birds today with very similar ones that give a clear hint as to how it might have used them." "These are young hoatzin, sitting on their nest in a South American swamp, still guarded by their parents." "A hoatzin chick has an adventurous disposition and starts clambering about when it's only a few days old." "The hooks on its front limbs are obviously very useful in keeping it secure until such a time as they become feathered and reliable wings." "0ne can imagine that archaeopteryx used them in much the same way and for much the same reason." "Sometimes, however, there's a disaster." "There are dangerous reptiles in the swamp:" "snakes and caiman." "But those claws on the wings are once again invaluable." "Mother returns." "She has been feeding on leaves and will have a full crop." "Maybe there will be some for the chick." "The hoatzin, of course, like all modern birds, doesn't have bony jaws with teeth like archaeopteryx, but a lightweight beak." "When did that important change take place?" "Well, this fossilised bird has a beak, and it was found in China recently." "It's only a little younger than archaeopteryx, so it seems that the change took place quickly." "And it must have made flight much more efficient for it prevented a bird from being nose-heavy and significantly reduced its overall weight." "By 50 million years ago, the dynasty of birds was firmly established." "At that time, a great lake lay here in Central Germany." "It's long since dried out, and the layers of mud from its floor have turned into shales." "Excavations like the one that's going on here have revealed just how varied the birds had become." "This one has been set in yellow resin to make its details quite clear." "It had a horny beak, a fully feathered wing, a long feathered tail with no bony support and long legs." "It probably looked like a rail" "0ther fossils from these shales show that several families of modern birds were already established." "This was a water bird, possibly an ancestor of today's jacana." "It would have found plenty of insects among the floating leaves on the lake." "There were birds with powerful chisel-like bills, perhaps woodpeckers, that even in this early period had started excavating insects from trees nearby." "Another inhabitant of those prehistoric woods had a stubbier, more all-purpose beak, rather like finches do today." "There were tall birds with long powerful legs that hunted for small reptiles on the ground as the South American seriama does." "And there was a gigantic vulture with a wingspan of over 20 feet, bigger even than that of the Andean condor and probably the biggest flying bird that has ever existed." "There were even birds which, judging from their skeletons, were as agile in the air as their probable descendants, the frigate birds." "So by 50 million years ago, several families of modern birds were well established." "The rule of the reptiles was now really over." "Not only had pterosaurs disappeared from the skies, dinosaurs had gone from the ground." "So the dominance of the land was up for grabs." "There were two contenders:" "the mammals and the birds." "The biggest mammal to be found from this lake in Germany was a primitive horse." "It was no bigger than a spaniel" "But the biggest bird was very different." "That was the lower part of its beak, and this was the upper." "If its skeleton still lay here, you would have to dig a huge pit to extract it." "This bird was immense." "It has been named, with good reason, the terror bird." "Its wings were tiny but it had long and powerful legs." "Flightless birds of a comparable size still exist and can give us some idea of what it looked like." "This, the ostrich, is the biggest and heaviest bird alive today." "It is probably not closely related to those monstrous feathered hunters of prehistory, but together with the emu of Australia and the rhea of South America, it belongs to a very ancient family of birds that abandoned flight a very long time ago." "It relies for its defence on speed and, in the interests of its efficiency as a runner, its toes have been reduced to two." "If pursued, it can sprint at over 40 miles an hour." "But although it is now flightless, it still has many of the physical characters evolved by its ancestors that enabled them to fly." "It still has feathers and they are still placed on its wings in much the same position as those on the wings of a flying bird." "But they are now useless for flight." "Their filaments have lost their hooks so they can no longer be zipped together into an unbroken blade." "Instead they are loose and fluffy." "Their only function now is as insulating blankets, to keep out the cold at night and the heat during the day." "0striches have become grazers, the bird equivalent of antelope or horses." "But unlike them, they not only pick up leaves." "They swallow all kinds of other things as well, and for a very good reason." "Just as they inherited feathers from their flying ancestors, so they also inherited a lightweight, horny beak instead of a heavy jaw laden with teeth." "And without teeth, they need another way to grind up their food." "A pebble can help them do just that." "Down it goes into a muscular compartment of the stomach, the gizzard, a kind of mill where bits of vegetation are churned around and ground into a digestible pulp." "But while some birds were abandoning flight, some mammals were becoming formidable hunters." "0striches with their superb eyesight and tall necks are able to keep a sharp lookout for approaching danger." "The cheetah has to calculate very carefully whether it's worthwhile chasing something... ..and an ostrich, usually, is not." "It is so very fast, and even if it's caught, it has little meat on it compared with a similar sized mammal" "But birds that can't run are a tempting target for hunters everywhere." "If they couldn't fly, they wouldn't last long." "Flight has certainly enabled birds to colonise the entire globe." "But the compulsion that drove them into the air in the first place, and has certainly kept most of them there ever since, was probably safety." "Even so, the cost of flying is high." "Flapping wings takes a lot of effort and if there is no need to do so, birds save their energies." "Those that live here on the Galapagos Islands, isolated in the Pacific, have no natural enemies from which to escape, so some birds don't bother to fly." "Have a look at these cormorants, for example." "At first sight, they look like many another cormorant sitting on cliffs round the world." "But these wings are stunted and tattered." "This bird could never get into the air." "Its feathers now serve only to keep it warm in the water." "It's for that reason alone that it keeps them well-oiled." "It is scarcely any better at walking than it is at flying." "0nce in the water, however, it's a very efficient mover indeed." "The position of its legs right at the back of its body that made it so clumsy on land is ideal for propelling it through the water at speed and helps it to catch all the fish it needs." "For the Galapagos cormorant, flight has become an irrelevance." "0ther island birds have reacted in a similar way." "This is New Caledonia in the western Pacific, and this is its special bird, the kagu." "Its ancestors must certainly have arrived here by air, but since New Caledonia had no ground predators until recently, they gave up flying and today the kagu is virtually flightless." "It finds all its food on the ground in the leaf litter." "It's been here so long that it's difficult to be sure exactly who its ancestors were, but they were probably herons." "Rails are a very widespread family of birds." "Wherever there is a big swamp, you are likely to find one." "0n the continents, they tend to lurk shyly in the undergrowth to keep out of trouble." "But some, somehow, have also managed to reach a great number of islands and there they seem to have no fear at all." "This one, it's a weka, has also become flightless because of its isolation on an island." "But its island is immense." "It's 1,000 miles long, if you discount a narrow arm of sea that crosses it in the middle, and it contains mountains over 12,000 feet high;" "it's New Zealand." "The first land-living mammals to get here were human beings and they didn't arrive until a mere 1500 years ago." "So here you can still glimpse what the world would have been like if the birds had won that battle with the early mammals and now ruled the earth, for here they once did." "Many of New Zealand's birds flew here from Australia, 15,000 miles away across the sea to the west." "They started to do so millions of years ago, and they are still doing so today." "So if you know Australian birds, you will recognise quite a lot, particularly those that are relatively recent arrivals." "The New Zealand pigeon is not all that much different from Australian ones." "The saddleback, on the other hand, must have been established here for much longer for it has changed so much that no one is quite sure what family it belongs to." "The tui has similarly mysterious origins." "No other bird has a costume to compare with its lacy cape and that little white throat bobble." "The kaka is clearly a parrot." "There are lots of parrots in Australia so it's not surprising that some of them in the past should have found their way here." "Most of these birds have still not learned that mammals are dangerous." "This saddleback is a fully wild bird and certainly hasn't seen me before." "But look how trusting it is." "This is a New Zealand robin." "It's no relation to the European robin and, if anything, it's even braver." "The New Zealand bush is full of food, of one kind or another." "And as the birds once had it all to themselves, some were able to adopt diets and ways of life that elsewhere were claimed by mammals." "The kokako eats much the same thing as squirrels: fruit and leaves and insects." "European squirrels run along the branches." "Asian squirrels, using a skinny parachute stretched between their legs, are able to glide as well." "And that is very much how the kokako gets around in the trees." "Having glided down to the lower branches, it runs back up them and jumps from one to the other." "So if the kokako, up in the trees, feeds in the same way as a squirrel might do, what lives and feeds like a mammal on the ground?" "The leaf litter in these forests is full of food of one kind or another." "There are earthworms and insects and beetle larvae." "In any other land there would be some small native mammal that was burrowing around seeking that food." "But not here in New Zealand." "Here there's something quite different." "You will only see it after dark." "It is, of course, a bird, but what an extraordinary one." "The kiwi." "It's territorial and calls stridently to proclaim its ownership." "It finds its prey by smell, uniquely its nostrils are on the tip of its beak." "It's found a worm." "But once it drops it, its eyesight is so poor that it can't see it and it has to smell for it, with its beak." "Its tiny vestigial wings are invisible, buried in its plumage and it has lost all sign of a tail" "If the kiwis live in a patch of forest close by the sea, then in the evening they may come down on to the beach to look for these:" "Sandhoppers." "They love them." "And that will give us a chance, a rare chance, to see them out in the open." "To do so properly, we have to use our special starlight camera." "The kiwi is hunting along the strand line where there are lots of hoppers feeding on the decaying seaweed." "Its sense of smell is so acute it can pick out the largest juiciest hoppers deep in the sand without even seeing them." "0ur starlight camera can see much better than I can." "I need a torch to see this extraordinary creature properly, but it doesn't seem to mind." "Its feathers are just filaments, so that it almost looks as though it is covered with coarse fur." "Probing sand with your nostrils is all very well, but it does clog them up, and so you need to blow them clear every now and then." "It's nocturnal and furry:" "It finds its way around by smell." "It lives in holes and digs for worms and grubs." "It's a bird equivalent of a badger." "But there's plenty of other food to be found in the New Zealand bush." "Here on the forest floor, there are lots of leaves." "They may be a bit twiggy and coarse but they are food nonetheless." "What could have browsed on these?" "Well, not far from here, bones like this have been dug up." "It's obviously a leg-bone, and at first sight you might think it was a leg-bone of a mammal, say perhaps, a cow." "But when you look at it closely you can see that it's got a honeycomb structure." "It's a bird bone, but the bone of a very big bird indeed, as we know from the rest of its skeleton." "It had just three toes." "Its pelvis and its spine lead up to an extraordinarily long neck." "This bird stood over six feet, two metres tall." "The first human settlers on these islands saw these giants alive and called them moas." "Among them were the tallest birds that ever existed, that weighed over 200 kilos, 400lbs." "There were about a dozen different species of varying size and weight." "Up on the high moorlands, there were smaller species with thicker feathers to keep them warm." "The absence of mammals didn't mean that the moas had no enemies." "They were hunted by, of course, another bird." "An immense eagle that could manoeuvre through the patchy forest." "The only prey that was abundant enough to sustain such a giant were other birds and it's probable that it was able to tackle even the biggest moa." "Its talons were certainly long enough to stab right through a moa's flesh and into its pelvis, as some of the bones show." "Nevertheless, the moas survived for a million years or more and spread all over New Zealand." "But eventually mammals did reach these remote islands." "Apart from bats which flew here, the first to arrive were those most dangerous of all, human beings." "They hunted the moas for meat and soon they had hunted them to extinction." "But a different kind of flightless bird does still survive, up in these high mountains." "Like so many of New Zealand's native birds that had abandoned flight, it had no defence against the alien mammals that Europeans brought with them and that soon escaped and ran wild." "Rats ate their eggs and killed the chicks, and cats and stoats massacred the adults." "There was a giant flightless coot that was originally very common." "But it got scarcer and scarcer and by the middle of the nineteenth century, it was thought to be totally extinct." "And then, just 50 years ago, someone in these remote valleys found something like this." "This is the dropping of a takahe and here, the severed stems of tussock grass on which it's been feeding." "It's still here." "And here is her nest." "She's sitting tight, hiding her brilliant red bill so that she is not conspicuous." "Indeed, when only her lovely moss-green back is visible, she is well camouflaged from her only native enemy, a bird of prey, circling overhead." "0nly about forty pairs of takahe survive today in the wild." "So the eggs she is sitting on are very precious." "This high country was probably not the takahe's original home." "Most of the population in the last century lived at lower altitudes and there they had lush vegetation to feed on in the warm swamps." "But most of those were drained and turned into farmland." "So now these high empty valleys, only recently scraped down to the rock by glaciers, are the takahe's last refuge and there is little to eat up here, except tussock grass." "Extracting something nutritious from tussock is not easy." "The takahe's technique is to pull up a whole stem and then nibble just the bottom inch or so." "That's where most minerals and sugars are and it's the only bit tender enough to be easily cut." "At first the chick doesn't know how to do this and has to be fed." "It will stay with its parent for a whole year." "0nly then will it be strong enough and skilled enough to feed entirely by itself." "Now it's summer, but when winter comes, life will be even tougher." "Then the pools freeze over and the tussock has no fresh shoots, even if they could be reached beneath the snow." "Then the takahe is reduced to digging for tubers in the freezing earth." "So the birds' continued survival up in these barren moorlands is by no means assured." "0ne other flightless bird found refuge from mammals in these high mountains;" "and in many ways, it was the most extraordinary of all." "It was a giant parrot, the kakapo." "It lived in very much the same way as rabbits do." "It created tracks through its territory generation after generation, trudging along here and feeding by plucking these grasses and eating the succulent base." "This particular path runs under this bush and continues upwards along the highest edge of this narrow ridge." "The track leads to this shallow bowl, and there are others like it spaced out along the track." "They were excavated by the male kakapo whose territory this was." "He would dig them out;" "and then in the night, he would come here and, crouching low, make a deep booming call which echoed out across these valleys, summoning the females to come to him." "But there were no females seen after the 1970s up here." "0ne lone male continued trudging up here and calling." "But in vain." "And in 1985, his call was heard no more." "And then when hope was almost gone, a new population of kakapos was discovered on the southernmost island, Stewart Island." "They too were being harried by cats and stoats, so the survivors were caught and taken to three small cat-free islets." "There were only 61 of them." "The kakapo's survival was on a knife-edge." "A male, after slumbering all day in his burrow, emerges for his evening meal" "His hearing is acute, he listens for danger." "He's following his regular track that will lead him to the highest slopes of his mountain." "A female has clambered up into the top of the bushes, looking for fresh shoots and fruit." "Her dappled green plumage camouflages her against attacks from falcons, but even so, she won't dare to venture into the topmost branches until it's dark." "Nightfall, and now we need our starlight camera to see what's happening." "By midnight the male has plodded his way right to the summit of his mountain." "He has reached one of his bowls from which his calls could echo out over the valley below." "He begins to tidy it up." "The female has found what she wants up in the branches." "She will need all the most nourishing food she can find if she is to produce an egg." "Even at the best of times, she will not be able to accumulate enough bodily reserves to lay every year." "The male begins to inflate air-sacs on his chest that will act as resonators and so amplify his calls, sending them booming out across the valley." "There are probably only 12 fertile female kakapos left alive." "In the first 10 years after they were moved to the safety of their new homes, only three chicks were reared." "But then in the last two seasons, seven young kakapo were successfully hatched." "Maybe the species will come back from the brink of extinction after all." "0f course, only a minority of New Zealand's birds have become flightless." "Most, like these handsome spotted shags, have retained that characteristic talent of birds, the ability to travel by air, and worldwide, birds have exploited that ability to an extraordinary degree." "Some can make journeys of over a thousand miles without coming down to earth." "Some can fly to altitudes of over 25,000 feet." "Some can even fly backwards." "How they manage to get into the air and sustain themselves there is what we will be looking at in the next programme."