Category
📺
TVTranscript
00:00I'm several hundred feet up in the air. Up here I might encounter perhaps a flying insect,
00:22now I haven't seen one yet, or maybe even a baby spider clinging to a gossamoth thread of silk,
00:28which is their way of getting around. But by and large, this is the kingdom of the birds.
00:38The first birds flew about 150 million years ago. They spread around the globe and evolved into a
00:48multitude of different kinds. Aerial acrobats.
00:58Stealthy hunters.
01:04And some of the fastest creatures on the planet.
01:10Their extraordinary skill enabled them to surpass Earth's original flyers, the insects.
01:19But there is a vast kingdom that the birds do not control.
01:22The night skies.
01:26These are ruled by very different creatures. Flying mammals. Bats.
01:36And in one spectacular place, these two populations of the night and the day collide.
01:44Bats.
01:46Bats.
01:48Bats.
01:50Bats.
01:52Bats.
01:54Bats.
01:56Bats.
01:57Bats.
01:57Bats.
01:58Segovia
02:18This is Segovia in central Spain.
02:21Some of the inhabitants of this gorge allow us to see very clearly how birds as a group
02:31have become so versatile in the air through the ability to change the shape and the size
02:37of their basic flying mechanism, the wing.
02:41And there's a wonderful example of that just over here.
02:48You may think that birds are much the same when it comes to flight, but in fact different
02:53species need to fly in their own particular way.
02:58This vulture is an airborne scavenger.
03:03It feeds on the bodies of dead animals.
03:08So it needs to spot any fresh carcass very quickly and get to it before others claim
03:13it.
03:16Like most birds, it has superb eyesight.
03:21So it climbs high in the sky, constantly scanning the ground below for hours at a time if need
03:28be.
03:32To fly in this highly specialized way, it has evolved a very distinctive kind of wing.
03:43To get up close to some of the many vultures that live in this area, I'm visiting a place
03:48where they're regularly fed by conservationists.
03:56These are griffin vultures, one of the largest of all vulture species.
04:02Each one can weigh up to 11 kilos.
04:06Lifting an 11 kilo body high into the sky takes a lot of energy.
04:13The vultures don't supply that energy directly themselves.
04:21A clue of how they do so comes from observing their behavior at the start of the day.
04:30Those vultures roost and nest on ledges up there.
04:38They're not early risers.
04:40That's because they rely on the sun to get airborne.
04:44As the day warms up, patches of bare rock reflect the heat of the sun, forming columns of rising
04:51hot air known as thermals.
04:54And the vultures know exactly how to exploit those thermals to be carried high in the sky
04:59with the minimum of effort.
05:08They have wings that have been shaped over millions of years to catch as much of that
05:16rising air as possible.
05:20They're huge, very broad, with a span of over two meters.
05:33But riding thermals may not be as easy as it looks.
05:47A thermal is quite a narrow column of rising air, and to stay within it, a vulture has to
05:52make quite sharp turns, and that can lead to disaster.
05:58In a tight spiral, a vulture's inside wing travels a shorter distance than its outer wing.
06:06And if we were to measure the speed of this inner wing, we would find that it moves much
06:11more slowly through the air.
06:13This means it generates less lift.
06:16So little, in fact, that the vulture could easily stall and drop from the sky.
06:24It avoids that by having special control over the feathers at the ends of its wings.
06:32They can be splayed so that they separate.
06:37As a result, each feather acts as a small extra wing, and together they increase overall lift.
06:46This enables the vulture to turn in a tight circle, and so hold its place in a thermal and
06:53soar upwards.
07:00Using this technique, a vulture can climb to a height of a kilometer above the ground with
07:04scarcely a flap of its wings.
07:07And then if it spots food down below, it can switch its flying technique and descend at speed.
07:14A dead animal, once found, makes an easy meal, except for the fact that there are rather a lot
07:32of diners, but other meat-eating birds have even greater problems.
07:41They pursue living prey, and one such hunter has become one of the fastest of all living creatures.
08:01To watch one of the fastest of all flying animals, I've come to Italy and the city of Rome.
08:12There's a bird that flies over these roofs that finds its prey not on the ground but in the air.
08:20And it owes its success to its speed.
08:23In fact, it's said to be the fastest moving animal on earth, the peregrine.
08:33Peregrines hunt other birds.
08:37Many different kinds of birds now live in cities, attracted by the food and shelter that
08:42are so easily found here.
08:47And a tall building like this is an ideal lookout for a hunter.
08:55Flying prey can move in any direction it chooses, so a hunter has to be both fast and agile if
09:01it's to get a meal.
09:04A peregrine's wings have a very special shape.
09:10They're pointed and swept back.
09:16If wings have a blunt end, air will swirl over that end, forming trails of turbulence.
09:24These act like brakes slowing a bird down.
09:31But pointed wings shrink that edge and so reduce the turbulence.
09:36Pulling the wings back towards the body makes the bird even more streamlined.
09:42And speed is crucial to a peregrine's success.
09:48It also has acute vision that enables it to spot prey over a mile away.
09:55And for the peregrines that hunt in Rome, these birds are prime targets.
10:02Starlings.
10:07They, too, are fast fliers.
10:10And their smaller size makes them even more maneuverable.
10:23So, to catch a starling, a peregrine must be even faster.
10:27And in order to gain speed and surprise, it attacks them from above.
10:36First, it climbs.
10:43When it sees a group of its potential prey, it turns, dives, and accelerates by beating its wings.
10:54The starlings are still unaware of the danger hurtling towards them.
11:09The starlings are still unaware of the danger hurtling towards them.
11:15Finally, the peregrine draws its wings back.
11:22This is called the stoop.
11:25A superb streamlined shape that slices through the air.
11:30Now, it can reach speeds of over 200 miles an hour.
11:39As it nears its target, it opens its wings to slow its descent and makes its final lunge.
11:45The starlings, in fact, are an abundant source of food for the peregrines.
12:00They come into the city in the winter attracted, no doubt, by the warmth in order to roost.
12:19Every evening, at dusk, the starlings start to arrive.
12:26And they have a remarkable way of defending themselves against peregrines.
12:32One that relies on their ability to fly together in tight formations as a flock.
12:38And here they come, vast numbers of them, tens of thousands, hundreds of thousands.
12:48It's like a great black hailstorm, a blizzard of birds.
12:53And now some start to fly closer together and perform far more complex manoeuvres.
13:21Look how these great flocks come together, form a cloud, veer away, then split.
13:32It's a quite extraordinary piece of aerial navigation.
13:40We're still unsure exactly why they perform these elaborate dances,
13:44but they're often triggered by the arrival of a predator.
13:48And today is no exception.
13:52Because over there, on one of those buildings, I've seen a peregrine.
13:57Coming in in great numbers like this is in itself a defence, because if you're surrounded by tens of thousands of others,
14:03well, it's a good chance that the peregrine won't get you.
14:07But the aerial ballet is part of a more complex defensive strategy.
14:10When a peregrine does attack with its wings drawn back in its stoop,
14:13the starlings, flying in their tight formation, coordinate their escape.
14:19Instead of scattering in different directions when a straggler might be picked off,
14:25they stick together even when they make the sharpest of turns.
14:27Even when they make the sharpest of turns.
14:28Recent studies analysing the flight paths of these romans
14:32have a very complex defensive strategy.
14:34When a peregrine does attack with its wings drawn back in its stoop,
14:37the starlings, flying in their tight formation, coordinate their escape.
14:42Instead of scattering in different directions when a straggler might be picked off,
14:48they stick together even when they make the sharpest of turns.
14:54Recent studies analysing the flight paths of these roman flocks
14:58have now revealed how they manage to do this.
15:05Each individual starling is constantly tracking the movement
15:09of up to seven of its close neighbours, even if they drift far apart.
15:16This is the hidden glue binding the flock together.
15:22And it can also help the birds to communicate among themselves.
15:27A bird that turns to evade a predator triggers a ripple
15:32that passes through the overlapping networks in milliseconds.
15:36And that causes the whole flock to turn as one.
15:50As the light finally fades, the flock suddenly descends into the trees
15:55that will be their roost for the night.
15:58The peregrine's sharp eyesight doesn't operate nearly so well in the dark.
16:02So now the starlings are safe.
16:07Until tomorrow, that is.
16:136,000 miles away in South America,
16:16there are other birds with a very different skill.
16:20And they also find their food on the wing.
16:24In the cloud forests of Ecuador, there is a plentiful supply of a type of food
16:33produced by plants to attract flying animals.
16:38Nectar.
16:42Around 130 million years ago, plants recruited insects
16:46to transport pollen from one flower to another by bribing them with a sugar-rich drink.
16:55Birds, when they first evolved, were unable to collect it
16:59because there was seldom something solid nearby on which they could perch.
17:03Then, around 30 million years ago, a kind of bird appeared that had no need of such a perch.
17:16Hummingbirds.
17:21They could hover.
17:22They do so by beating their wings extremely swiftly, so fast, in fact, that they make a humming noise.
17:41The largest hummingbird beats its wings around 14 times a second.
17:56But some tiny species are able to do so 80 times a second.
18:11To fly in this extraordinary way,
18:16hummingbirds have changed the structure of their wings and the way they beat them.
18:22Here in Ecuador, scientist Doug Altschuler is working to analyze exactly how they do so.
18:32Hummingbirds are remarkable animals.
18:34They have extreme adaptations in physiology and anatomy.
18:37And they also have a very unique behavior.
18:40They can hover.
18:42And the approach that we've taken is to study
18:45how those physiological and anatomical adaptations determine their hovering ability.
18:53Using high-speed cameras, he records the mechanics of their flight in minute detail.
18:58He can slow down the action by around 40 times and so observe exactly what's taking place.
19:15Most birds flap their wings up and down, but hummingbirds flap theirs more like insects.
19:21They twist their wings around between strokes and so can generate lift when flapping both forwards and backwards.
19:36Doing this at high speed puts a huge strain on their wings.
19:44So to withstand it, the wings have a special structure.
19:48The hummingbird wing is very stiff and undergoes few changes in shape as it rapidly beats back and forth.
20:05They owe this stiffness to a modification of the bones.
20:08The arm bones have shrunk, but the bones of the hand have elongated and support most of the wing surface.
20:22Twisting this wing at the shoulder and at the wrist produces the hummingbird's distinctive wing beat.
20:28Doug is also investigating one of the great mysteries of hummingbird flight.
20:40Their ability to move sideways in mid-hover.
20:46Hummingbirds are able to track flowers that were moving back and forth in the wind.
20:51And this was something I always wanted to know more about.
20:53To replicate the swaying motion of a flower, Doug places a reservoir of nectar on a mechanical slider.
21:06Before long, he has a volunteer.
21:08Amazingly, it manages to track sideways to keep up with the slider and still feed.
21:24The bird is exploiting an unexpected feature of its wing beat.
21:29Not the flapping itself, but the twist at the end of each stroke.
21:33During hovering flight, as the wings come forward, they rotate symmetrically, so the forces remain in balance.
21:40But if they instead rotate differently, such that one wing rotates before the other, then the forces are no longer in balance.
21:48And this asymmetry can be sufficient to push them to one side or the other.
21:51So a combination of modified wing bones and precise control of wing motion gives hummingbirds the aerial agility they need to collect nectar.
22:05And they need plenty of it.
22:09Hovering burns a huge amount of fuel.
22:12All hummingbirds have to constantly top up their tanks with high-energy nectar.
22:18And when supplies are low, competition can be fierce.
22:28Now, their flying skills are put to a very different use.
22:33To fight off rivals.
22:34Fight off rivals.
22:35Fight off rivals.
23:04Fight off rivals.
23:09So, different birds adapted their wings to fly in highly specialized ways.
23:16Some began to hunt the Earth's first fliers, the insects.
23:22And in that battle, there is now no real contest.
23:35But because most birds rely for so much of their success on their exceptional eyesight,
23:43there is one major habitat that is largely closed to them.
23:47Not a place, but a time.
23:50The night.
23:58In the British countryside, however, there is a bird that can fly in the dark.
24:05And it's a very skillful hunter.
24:10The barn owl is one of only a very few birds that can hunt at night.
24:29And one of its favorite meals is a field mouse.
24:32But first, it has to find it in the dark.
24:39A mouse is extremely alert to the approach of a predator.
24:49But the barn owl has wings specially adapted for stealth.
24:55And senses that can penetrate darkness.
24:58It's eyes are very sensitive in low light.
24:59But even if the mouse is out of sight, it's still not safe.
25:00The owl's hearing is also very acute.
25:01Those two discs on its face channel sound into its ears.
25:02The owl's hearing is also very acute.
25:03The owl's hearing is also very acute.
25:04Those two discs on its face channel sound into its two ears, which are on a slightly different
25:07level.
25:08On the head.
25:09The owl's hearing is also very acute.
25:10The owl's hearing is also very acute.
25:11The owl's hearing is also very acute.
25:15ETH
25:24and the owl's hearing
25:26And a crow is sometimes because it was very safe.
25:27The owl's having is just accurate which they have around those.
25:29The owl's hear Thus the owl's hearing has beenquele,
25:34the owl's hearing is also very acute.
25:37enables the bird to pinpoint the source of the sound,
25:40whether it's in the air or down on the ground.
25:44But in order to hear that sound,
25:47its wing beats have to be very, very quiet.
25:51And the way it achieves that, we can see
25:54when it goes hunting.
26:07The key reason for its silent flight lies in the nature of its wing feathers.
26:22Along the back edge, their fringe is frayed and tatty.
26:28Most birds' wings have a hard edge, and this can cause quite a loud noise.
26:34The source is turbulence produced when air flowing over the wing
26:38rubs against its surface.
26:40When this swirling air meets a hard back edge,
26:44the sudden drop-off hugely amplifies the noise.
26:49But the barn owl's tatty feathers avoid that.
26:53By creating a softer edge, they cushion the turbulent air
26:57and so reduce noise.
27:04So, silent flight allows the owl to hear its prey
27:12and conceals its approach.
27:15But to position itself for the kill,
27:21it needs to fly extremely slowly.
27:24And to achieve that, it has particularly broad wings.
27:28This slow, silent approach leaves a field mouse little chance of escape.
27:58On nights when there is thick cloud or no moon,
28:09even an owl's sensitive eyes struggle.
28:18But there are creatures that have such highly specialized senses
28:22that they're able to navigate in total darkness.
28:26Among insects, there are some moths whose elaborate antennae
28:31are able to pick up the sense of food or a mate.
28:38And there are those nocturnal animals,
28:40the last group of flying creatures to appear on Earth, the bats.
28:45To see how they battle with the insects for dominance of the night skies,
28:51were heading into the rainforests of Borneo.
29:11Many bats find their food not by sight or smell,
29:15but by using a very different and highly advanced guidance system.
29:21One way to find them is to search for their ideal home.
29:25A place like that deep black cave beneath me.
29:32If you fly at night, there's no better place to spend the day
29:36than in a cave like that.
29:38This is Gomanton.
29:47The cave is a vast network of underground tunnels
29:53and cathedral-sized caverns.
29:55It was carved out by streams of water over millions of years.
29:58And now it's home to a remarkable community of cave-dwelling specialists.
30:00The cave is a vast network of underground tunnels
30:01and cathedral-sized caverns.
30:02The cave is a vast network of underground tunnels
30:03and cathedral-sized caverns.
30:04It was carved out by streams of water over millions of years.
30:09It was carved out by streams of water over millions of years.
30:19And now it's home to a remarkable community of cave-dwelling specialists.
30:24To find the creatures I'm looking for,
30:39I'm being winched high up towards the ceiling,
30:42where the towering walls make ideal roost sites for flying animals.
30:47These little birds flying past me are swiftlets
31:01that have made their nests on the walls of the cave.
31:05They are active during the day,
31:08and they leave the cave to hunt insects.
31:11The bats that I'm interested in are farther behind me in the semi-darkness,
31:18and they're asleep now during the day.
31:22The bats are scarcely the size of mice.
31:25Their wings are constructed with very long fingers,
31:29and they hang by their feet from the rock.
31:34Although there are a few at the back there,
31:36deeper in this cave they exist in huge numbers.
31:41To find their roosts, we're heading still deeper into Gumanton Cave.
31:52A huge black dune fills the back of one of the main chambers.
31:57It's made up entirely of the droppings of the vast numbers of bats
32:01hanging above in the darkness.
32:04To see them fly, we must wait for dusk.
32:21The great tropical island of Borneo contains many huge caves,
32:25and one of the biggest is Gumanton.
32:30High on the rocky cave ceiling above me,
32:33hidden in the darkness,
32:35there are vast numbers of bats.
32:38You can get some idea of how many there must be
32:41because of this huge dune behind me.
32:44That's formed of their droppings.
32:47And if you see little moving glints on the surface,
32:53that comes from an army of cockroaches
32:56which are chewing their way through the back droppings
32:59to extract the last particles of nutriment.
33:02Some people think there are a million bats up here in this cave.
33:17It's impossible to see them in the gloom,
33:20but special night-vision cameras can reveal them,
33:25densely packed crowds hanging from the ceiling.
33:28They're tiny eyes are adapted to low light,
33:35but they cannot penetrate the blackness.
33:39Millions of years ago, however,
33:41these bats evolved an extraordinary guidance system
33:44known as echolocation, or sonar.
33:52A bat produces extremely high-pitched sounds in its throat
33:56and then projects them forward.
34:01We have slowed the sounds down,
34:03but can still only hear them
34:05by converting them to lower frequencies.
34:10They bounce off the walls as echoes
34:12and are detected by the bat's huge ears.
34:18These are in constant movement
34:20and enable the bat to map its surroundings
34:22with remarkable precision.
34:36But these bats not only need to find their way in the dark,
34:39they also need to find their food.
34:43Night-flying insects.
34:46And among them are moths.
34:47Locking on to these moving targets
34:52is a supreme test for the bat's echolocation system.
34:58As one homes in, its sonar beam switches into attack mode,
35:02increasing the rate of its pulses.
35:04This enables it to precisely pinpoint
35:17the location of its prey.
35:22But the bats don't have it all their own way in the darkness.
35:25A team of scientists in Borneo has discovered
35:31that there is another creature here
35:33that uses sound as a weapon.
35:36I'm going to go set up the tent.
35:37Cool.
35:39Everything's set up here?
35:40Yeah, everything's ready to go.
35:41Awesome.
35:42This tent acts as an enclosed flight arena
35:46in which every movement and sound
35:48can be recorded in minute detail.
35:52With these cameras and ultrasonic microphones,
35:54we can see how these interactions unfold
35:57and hear how they unfold.
36:01The team play recordings of bat sounds to moths.
36:05This reveals a remarkable ability.
36:09Here in Borneo, we recently discovered
36:11that hawkmoths respond to these echolocation cries
36:15with their own sounds.
36:19Oh, lots of sound production.
36:20Hawkmoths do it with the tips of their abdomen,
36:23with modified genitals.
36:24They rub the genitals against the inside of the abdomen
36:27and reply to this bat attack.
36:29The moth is tethered to keep it in range
36:31of the cameras and microphones.
36:33Then a bat is released.
36:35The moth is tethered to keep it in range
36:37of the cameras and microphones.
36:40Then a bat is released.
36:42As the bat approaches the moth,
36:54its sonar pulse switches to attack mode.
37:00But now the hawkmoth responds,
37:02sending its own rasping sound back with astonishing effect.
37:07At the last moment, the bat appears to lose track of the moth
37:12and fails to catch it.
37:14We've shown that these moth sounds
37:17actually jam the bat's sonar.
37:19They interfere with the returning echoes from the insect
37:23and causes the bat to miss the moth.
37:29The team has discovered that insects are fighting back
37:33in the ongoing battle for the night skies.
37:39But there are, of course, plenty of other flying insects
37:43with no such defenses.
37:46And they live in vast numbers in the forests
37:49outside Comantong Cave.
37:53So every evening, as dusk arrives,
37:57the bats leave the safety of their secluded home to hunt.
38:02And now the bats are beginning to use their echolocation skill
38:11to fly out from their roosts in the depths of the cave,
38:15coming close to the ceiling and then whizzing out
38:18through this little entrance here.
38:27They don't collide with the roof.
38:29They don't collide with one another or even with me.
38:32All through that metro location.
38:33There they go.
38:34But this is just a trickle.
38:47The main exodus is taking place up a chimney
38:50that's deeper in the cave.
38:56To watch close up the way the bats achieved their million-strong mass
39:01departure, I'm being hauled up 200 feet into the funnel,
39:05which serves as one of the cave's main exits.
39:10At the top, there is a gaping hole.
39:16And now the bats are preparing to leave.
39:19They've assembled in a relatively small chamber close to the exit
39:32and are flying round and round in a great swirling crowd,
39:36waiting for daylight to fade.
39:41And now off they go.
39:43And now on the door, let's go.
39:45And now on the roll.
39:45Coming up in the top of the 10th of the cave,
39:46Let's go.
39:47Well, the big hole.
39:47This is the景色.
39:47We're carrying the view of the big hole.
39:49And now this is the next one.
39:50And let's go.
39:51Let's go.
39:51Let's go.
39:51Let's go.
39:52Let's go.
39:53Let's go.
39:54Let's go.
39:58Let's go.
39:59Let's go.
39:59Let's go.
39:59This brief hour of dusk
40:28is the moment when the two communities,
40:30the day fliers and the night fliers,
40:33may encounter one another in the air.
40:37Outside, danger awaits.
40:40Hunters belonging to that other great group of animals
40:44with which they share the skies, birds.
40:51Hawks, eagles, and kites.
40:58They are why the bats were reluctant to leave,
41:04and why they now do so in one continuous torrent.
41:08There is safety in numbers.
41:13But some will pay the price.
41:16The End
41:18The End
41:20The End
42:22The way that different animals have colonized the skies is surely one of the most remarkable
42:30stories in the natural world.
42:36First to do so over 320 million years ago were the insects.
42:44They had no competition for about 100 million years.
42:50But then much larger flying animals took to the air, reptiles, the pterosaurs.
43:00Around 70 million years later still, one branch of the dinosaurs acquired feathers, and that
43:07enabled their owners to get airborne.
43:10The birds had arrived.
43:12And lastly, about 60 million years ago, the night skies were invaded by mammals, the bats.
43:22And here, in Comantan Cave, the three surviving groups of fliers, insects, birds, and bats,
43:32are still locked together in an ongoing evolutionary struggle.
43:43So, the battle for the supremacy of the skies, that started over 300 million years ago,
43:49still continues every day around the world.
43:53Fascinating stuff there.
44:03And there's some real gems to be unearthed tomorrow at 8 in Show Me Your Garden.
44:08It's brand new on Sky 1 HD, and you can catch up with the latest episodes on demand.
44:12Next up though, more from Sir David Attenborough as we go behind the scenes in more Conquest of the Skies.