The Life of Birds (1998) s01e02 Episode Script

Getting into the air is not easy.
For many birds it is by far the most exhausting bit of the whole business of flight.
But these shearwaters here in Japan have adopted a very labour-saving way.
Whoops! There we go, a labour-saving way of doing so.
They've taken to climbing trees.
This particular tree is by far the most suitable for the take-off, and that bird may have come from as far as 30 or 40 yards away, wandering across the forest floor in order to climb it and get to the launch pad.
There's another.
40 feet up, a bend in the trunk makes a perfect platform for a take-off.
These shearwaters will spend most of their lives in the air.
They are true seabirds.
They only come to land in order to nest.
This particular species is exceptional in nesting in woodland, most of them nest right on the edge of cliffs and all of them get into the air by the simple method of simply falling into space.
The land birds, on the other hand, have much greater problems.
Most of them have to be able to get into the air from the ground with a standing start.
And that takes a lot more energy.
A pigeon begins by jumping vertically upwards.
As it leaves the ground, it opens its wings and sweeps them forward, fanning the air downwards with maximum force.
The second stroke must be equally vigorous, pushing the bird upwards.
If now it leans forward and starts to go ahead.
But the effort involved has been huge.
Birds only a little bigger than a pigeon can't do this twice in quick succession.
And a bird as big as an albatross can't do it at all.
It has to use yet another way of getting into the air.
It taxies, along a runway.
It's a method we use too, in our machines.
For the majority of birds the most exhausting part of flight is now over.
Those shearwaters achieved it by climbing trees, the pigeon jumped and flapped, and aeroplanes and albatross did it by running and creating a flow of air over their wings.
When they do actually get into the air, a bird's flight seems almost effortless.
And when you watch a really superb flyer like these albatross, then they seem to be defying the law of nature.
They are, after all, big heavy birds.
How is it that they can withstand the pull of gravity that keeps the rest of us tied so firmly to the ground? The secret is a wing with a thick, rounded front edge that curves gently downwards towards the back edge, which is very thin.
As thin, in fact, as a feather.
As the bird glides forward, the air flowing under the wing is impeded by the wing's downward curve.
So it becomes slightly compressed and that pushes the wing up.
At the same time, the air flowing across the top of the wing is deflected upwards by the wing's front edge so reducing its pressure.
If the air is moving fast enough, then the slight suction from above combined with the push from beneath will be enough to lift the bird into the air, as it did during take-off, and ample to keep it aloft, as it's doing now.
The trick is to make sure that the air does flow over the wing sufficiently quickly.
Upward air currents can also sustain a bird in flight and that is just what are created when breezes, blowing in from the sea, hit a cliff.
If they are really strong, such up-draughts can be so powerful that they alone will keep an albatross in the air.
0ut at sea, the waves deflect the wind upwards in somewhat smaller gusts and the albatross is so skilful that it can sail on them for hours with scarcely a movement of its wings.
Most birds, however, once in flight, have to create that air-flow across their wings by another method.
They drive themselves forward by flapping.
This knot is 'rowing' through the air, stretching its wings forwards, and beating them downwards.
0n the upstroke it half-folds them, to reduce their surface area and therefore their resistance to the air.
The feathers on its wing slide smoothly over one another so that although the wing is continuously changing shape, its surface remains perfectly smooth and streamlined.
Its body is also streamlined by its coat of feathers, and its feet are pressed against its tail so that drag is kept to a minimum.
This mallard is flying at nearly 40 miles an hour, but its streamlining is so perfect that there is scarcely a ruffle to its feathers.
It's only from behind that you notice the little flicks of the feathers over its tail and the back edge of its wings which show just how fast it's travelling.
To see just how important streamlining is, and how much energy it can save, just watch this osprey as it goes fishing.
To take off again, with the fish in its talons, the bird has to beat its wings with all the strength it can muster.
But even now it is in the air, the fish hanging broadside.
It creates so much drag that the osprey has great difficulty in making any headway at all.
But it knows how to solve the problem.
Gripping the fish with just one foot, it manages to bring its other foot forward.
Now, using both feet, the bird changes the position of the fish so that it faces ahead and its streamlined shape reduces its drag so much that the osprey's wing-beats become almost leisurely.
Flying in formation also saves energy.
A big bird like a pelican creates a trail of turbulence in the air and this can give a following bird lift.
The effect is at its greatest directly behind a bird's wing-tip, so that is the best place for a following bird to fly.
Pelicans also save some 20% of their energy by mixing flapping with gliding.
Aerodynamically it's more profitable for a bird to time its flaps with those of the bird ahead.
So it is the pelicans who give breathtaking displays of synchronised formation flying.
The most economical way of flying, however, is to draw almost all the energy you need directly from the sun.
As it warms the ground in the morning, the rocks reflect its heat and shimmering columns of air, thermals, begin to rise.
Griffin vultures in Spain now leave the ledges on the cliffs where they have spent the night and launch themselves into the air.
With the thermals rising powerfully beneath their outstretched wings they sail effortlessly upwards.
All they have to do is to make sure that they remain within the column of warm air.
So dozens of them spiral together in tight circles, adjusting their flight with the tiniest movements of their wings and tails.
There can be no more economical flight than this.
The vulture's ability to 'read' the air conditions above their landscape, and detect exactly where the thermals are at their most powerful, seems almost uncanny.
But in recent years, human beings have also mastered it.
When you hit a thermal in a glider, you really feel it.
Your stomach drops beneath your feet.
- 0ohh! - I'm going to roll into the thermal here.
Glider pilots spend a lot of time going around in circles just as birds of prey do, because a thermal's a rising column of air and in order to stay in it you have to turn.
There's nothing to see though, is there? Apart from what's on the ground.
You can't see anything in the air to indicate a thermal Right now there's no cumulus cloud over this thermal But often there is.
If you look over there, you can see all those cumulus clouds.
Underneath most of those there would be a thermal, and that's one of those indicators of lift, that's one thing we look for, and that's what birds look for also when they fly, I'm sure.
Feel that! Now there's a big rocky outcropping.
Just look at that.
Now you can see the altimeter winding up.
Look at that.
- How high could we go with this? - Probably up to 14-15,000 feet with no problem.
- And do the birds go as high as that? - I've seen birds up to 16-18,000 feet.
- They are just out there flying for fun.
- How do you know that? Because how can you see a mouse from 18,000 feet? Not hardly.
And they do all kinds of tricks and aerobatics.
Look at this.
We're really going up now.
The pressure on the wings is actually bending them, isn't it? The spar is slightly flexible, so when you develop more lift, the spar actually bends upwards a little bit.
Very similar to a bird.
Every flight has to end in a landing.
That requires less energy, but perhaps more skill if disaster is to be avoided, particularly if you are a big bird like a pelican.
A swan, one of the heaviest of flying birds, can only come down on the smoothest and most forgiving of natural surfaces; water.
There you can use your feet as brakes.
Albatross are not so lucky.
They have to alight on the ground.
Indeed their landings seem scarcely better than controlled accidents.
Most birds, however, have to come down with much greater precision than that.
They may have to land, after all, on a narrow ledge or a very thin branch.
To do that they have to lower their flaps, put down the undercarriage and put on their brakes so that they lose all air speed at the precise moment that they come alongside their perch.
That requires great judgement and co-ordination.
A Griffin vulture is able to exploit the position of its nest, which is nearly always on the ledge of a cliff.
It descends towards it at speed.
It aims for a point below its nest and then brakes by swooping upwards so that as it arrives at its ledge its forward speed is zero.
Landing into the wind helps any bird by keeping air flowing over the wings and maintaining lift until the last moment.
So, one way or another, birds manage to complete an operation fraught with danger, with virtually total success.
As anyone who has had to pay for excess baggage at an airport knows, if you travel by air, it is important to keep your weight down.
This magnificent golden eagle manages to do that in a most thoroughgoing way.
It's about the same size, I suppose, as a bulldog.
But I couldn't hold a bulldog on my wrist.
But this bird only weights about a quarter as much.
So how do birds manage to keep so light? A beak is not so weighty as the bony jaws and teeth of a mammal like a bulldog or one of the birds' reptilian ancestors.
Its disadvantage is that a bird can't chew.
It can pluck, crush or, like an eagle, tear and rip.
They also have weight-saving features inside their bodies, a skeleton with fewer bones than a mammal's, no tail-bone, one wing-bone instead of five fingers, and a slim pelvis fused to the backbone.
And the bones themselves are not solid like a mammal's, but hollow.
Inside they have a lattice of cross-struts so they are nonetheless very strong.
But the most remarkable weight-saving features of all are those things that only birds possess: their feathers.
They look simple, but in fact they have a very complex structure.
The quills are hollow and very light, yet resilient and extremely strong.
The filaments on either side of the quills are fringed with microscopic hooks that link them to their neighbours so that they all latch together to form a continuous surface.
And that means that if a feather gets damaged or over-strained, it can be repaired instantly.
It can be zipped up.
Not surprisingly, all birds lavish a great deal of attention on their feathers.
After all, their lives depend on them.
And since birds have no hands, they have little alternative but to care for them with their beaks.
But one bird, uniquely, can't do that.
The sword-billed hummingbird has a beak that is so long that there is no way that its tip can touch its feathers.
It has to comb its plumage with one foot while balancing on its perch with the other.
Not easy! A good bath is also important in keeping the feathers clean and in first-class condition.
Most birds take one every day and, watching them doing so, it's difficult to avoid coming to the conclusion that they enjoy it just as much as we do.
Not all birds, of course, can get to water that is deep enough for bathing.
Then, like the quail that lives on dry plains and during the summer seldom finds so much as a puddle, they may have to use dust.
This may not exactly make them cleaner, but it does, apparently, help in dislodging parasites such as lice that nibble their feathers, mites that scavenge bits of dead skin and ticks that suck their blood.
Many parrots and cockatoos grow special feathers that fray at the end into a fine powder.
These feathers are scattered throughout the plumage, and as a bird such as a cockatoo scratches itself at the end of its toilet, the powder is dislodged in clouds and is caught in its ruffled feathers.
Exactly how this powder improves the feathers is not really certain, but it is probable that it helps with waterproofing as well as by discouraging parasites.
Parasites, in fact, are such a problem that some birds are thought to recruit assistants to help in getting rid of them.
Ants! Crows and jays deliberately land on an ant's nest and stir up the colony so that the angry insects come rushing out and swarm all over them.
In their irritation the ants discharge formic acid which is a particularly powerful insecticide.
But we don't really understand this behaviour.
It may be that the birds are stimulating the ants to get rid of their formic acid so that they are more digestible as meals.
Regular, meticulous maintenance is essential for maximum efficiency and safety in the air, and that applies to everything that flies.
Well, that was about 500 miles an hour and of course birds can't equal that.
But nonetheless, before aeroplanes were invented, a bird was the fastest living thing in the air.
The peregrine holds the record.
Diving on its prey it can exceed 200 miles an hour.
It achieves maximum aerodynamic efficiency by sweeping back its wings, like the jet fighter.
Then it accelerates by beating them.
The barn owl, on the other hand, owes its success as a hunter to its ability to fly extremely slowly.
It hunts voles and mice and, to find them in the grass it has to search very intently, and that takes time.
Its wings therefore are shaped very differently from a peregrine's.
They are rounded in outline and much broader which gives the maximum lift at slow speeds.
But the barn owl also has a very special adaptation for this kind of hunting.
The rodents it seeks are often invisible from the air, hidden beneath the matted grass.
The barn owl detects them by the rustling sounds they make.
To do that, it has extremely acute hearing, the sounds being focused by the hair-like feathers of the discs on either side of its head.
But if it is to hear them it has to fly very quietly indeed, and its wings are fitted with silencers.
Fluffy margins to its wing feathers.
So, in the evenings, a barn owl can waft over the countryside as silent as a moth.
This little dot, suspended in the sky, might seem to be the slowest flyer of all.
It's a kestrel It's not, in fact, truly stationary.
It's facing into a gentle wind, so there is a current of air passing over its wings.
And that gives it all the lift it requires.
Silence is not as important for the kestrel as it is for the barn owl, for it hunts by sight.
The wind has dropped a little.
Now, to keep its position relative to the ground it has to flap to keep the air moving over its wings.
It's spotted something, a quick turn into the wind, and a drop; a turn back to face the wind for a stationary check; another quick look; but whatever it was, has gone.
0nly one group of birds can manage to hover for any length of time without the help of a head-wind: the hummingbirds.
Their wings work in a way quite unlike that used by any other birds.
They beat routinely 25 times a second, so fast that they make the humming noise that gives them their name.
It is impossible to see how they operate unless the camera slows them down.
The wings have become, in effect, twirling blades that create down-draughts, rather like those that man produces with his hovering machines.
Helicopters, however, have a very special device, a wheel revolving continuously on an axle.
No bird or any other animal has yet evolved a mechanism that can exactly parallel this.
But hummingbirds have the next best thing: wings which beat in a figure of eight and flick over on the backstroke.
Unlike the wings of other birds, they are symmetrical in cross-section and work equally well with either surface uppermost.
By changing the angle of the beat, the thrust can be directed not only downwards, but either forwards or backwards.
So a hummingbird, steering with its tail, can move through the air in any direction.
Beating wings at such speed, however, uses a lot of fuel Even at rest, hummers need a great deal just to keep their bodies ticking over.
So they have to refuel very frequently.
But their fuel stations, flowers, close at night.
What do they do then? This is a particular problem in the Andes, where the nights can be very cold indeed.
As evening comes on, the hillstar hummingbird makes its way to its regular roosting place, in a cave.
After its regular toilet, it settles down for the night, and in effect turns off all its motors.
Its heart, that in flight contracted a thousand times a minute, slows until its beat is virtually undetectable.
Its body temperature falls dramatically and its breathing seems to cease altogether.
It is doing what a hedgehog does in winter, it is hibernating.
But for a hummingbird, winter comes 365 times a year.
The sun returns, and the temperature begins to rise.
The hillstar starts up its motors.
Its heart beat accelerates, its muscles slowly warm to flying temperature.
A quick pre-flight check.
And it's off again.
At higher altitudes, it seldom gets really warm even at midday.
This is the territory of the giant hummingbird.
It's as big as a thrush.
Great size helps in retaining body heat, but this is as big as a hummingbird can get.
Any larger and it couldn't beat its wings fast enough for this kind of flight.
And this is one of the smallest of all birds, the purple-collared woodstar from Ecuador with a wingspan of scarcely more than two inches.
Small wings are easier to flap, but the smaller they are, the faster they have to move to produce sufficient downwards thrust, and this hummingbird can beat its wings at an astonishing 75 times a second.
It is barely bigger than a moth.
Indeed this moth looks so like a tiny hummingbird that some people in the south of England, where it appears regularly in the summer, think that they have been visited by a real hummer.
The ability to fly gave birds the freedom of the planet.
Rivers, deserts, seas, even mountain ranges are no obstacle to them as they are to land-bound creatures such as ourselves.
They can fly relatively easily and quickly to collect a sudden glut of food.
And that is exactly what has happened here.
I'm in northern Canada.
It's June, the beginning of the short Arctic summer.
The rising temperatures have caused the plants to put out new leaves and roots, and tens of thousands of snow geese have come here to graze.
They nested almost as soon as they arrived and many have already got families.
Even hummingbirds have come up to the far north to collect nectar from the bushes that are now briefly blooming within sight of glaciers.
0n the Arctic coasts, little waders, western sandpipers, are collecting a rich harvest of small worms that are swarming in the mud.
In the middle of the continent, on the prairies, sorghum and other grain crops are ripening in the summer sun.
Dickcissels, relatives of the common sparrow, have come up here to take their percentage.
The warm weather has caused swarms of insects to hatch and they provide the dickcissels with the protein that is essential for the nourishment of their swiftly growing young.
Hawks are also breeding here in the north.
They were attracted by the seasonal abundance of voles and other small mammals, as well as the finches and songbirds that they need to feed their young.
But the superabundance of summer is brief.
By the end of July the days are noticeably shortening.
Many of the trees are preparing to shed their leaves.
The birds that flew up for the summer banquet can no longer stay.
All across the northern hemisphere the story is the same.
From eastern Siberia across Asia and Europe, to the woodlands and tundra of north America, birds are starting to fly south.
The sandpipers are stocking up for the 6,000 mile journey that lies ahead of them.
They eat so voraciously that they will nearly double their weight, putting on layers of fat on their upper thighs and their flanks.
They even shrink their internal organs, partially absorbing them as though they were food reserves and replacing them with more readily available fat.
They must wait for the right weather conditions, and then, when the wind blows strongly from the north, they set off.
Hawks and vultures are also now finding it harder to discover any food.
They too must prepare to leave.
But the weather they require for their journeys is rather different.
They need a good hot day when the thermals are shimmering upwards from the rocks that are still warming in the late summer sun.
As the last thermals of summer start to rise, the birds circle up to great heights, 10,000 feet or more, to give themselves a good start for the long journey ahead.
As they glide southwards, slowly losing height, they will look for another thermal and make for its base so that once again they will be lifted high enough to reach the next.
The snow geese are already on their way, their departure triggered by the shortening days and the dropping temperatures.
They will rely on straightforward muscle power.
They will travel continuously for great lengths of time, both through the day and the night.
The raptors, however, have had to stop to overnight in a roost.
Without thermals they can't travel far.
But the snow geese fly on.
The exertion of continuously beating their wings creates a lot of heat in their bodies, so travelling in the cool of the night does, in fact, suit them.
They navigate by the stars.
If the skies are heavily overcast for long periods they may lose their way, but that is exceptional Day returns and the stars fade.
Now they steer by the sun.
But the sun, of course, moves from east to west during the day, so the fact that they are able to use it for navigation means that they must have internal clocks and know fairly exactly what the time is.
Members of the same family travel together, calling to one another as they go.
And the geese have made it.
0ne of them has been recorded as covering an astonishing 1,700 miles in a mere 70 hours.
These fields in California will be their home until they return north on their spring migration.
The sandpipers have gone even further.
They have now reached Mexico.
But they will spend only a few days here for this is merely a refuelling stop.
They feed intensively, replacing the fat reserves that they have lost.
The raptors, so conscious of the nature of the land beneath them that generates thermals on which they depend, also look to it for their signposts.
They are now passing Mexico's highest mountain, the Pico de 0rizaba.
There are no thermals to be found over the sea, so they are tied to the land, and that means they have to go all the way round the western side of the Gulf of Mexico.
There is, of course, a short cut, directly south across the sea.
Astonishingly, the little ruby-throat hummingbird tackles that 500 mile long journey.
It must necessarily be non-stop for a hummingbird cannot land on the water.
A feeder in Texas provides a ruby-throat with a final top-up of nectar.
Its cruising speed is about 27 miles an hour.
So, if conditions are good, it could make the crossing by flying for a little over 18 hours.
But that is right on the very limit of its endurance.
If even a light head-wind springs up it will perish at sea.
Delphiniums blooming on the Mexican shore await with life-saving nectar.
A ruby-throat arrives after its epic journey and feeds urgently before it runs out of fuel, and it's fatally grounded.
But even now its journey is not finished.
It still has several hundred miles to go and may travel as far as the Panama border.
The hawks and vultures, travelling round the western side of the Gulf, have now reached Panama City.
They came from all over North America, converged on the Isthmus and travelled together down that narrow corridor of land so that now, for the only time each year, they form dense flocks.
Below, on the mud of Panama Bay, the sandpipers are feeding.
This, at last, is the end of their journey.
The mud here will never freeze, the sea will enrich it daily, and each bird returns every year to exactly the same patch.
The raptors rise once more in an immense vortex.
From here they will take their separate ways all over South America, some going as far south as Argentina.
0nly by dispersing widely will each bird find enough prey to sustain itself.
The dickcissels have also travelled down the Isthmus of Panama.
They too have come from all over North America and have been funnelled together into flocks of gigantic size and density.
This surely is the very acme of flying skill.
How they co-ordinate their flight in these extraordinary concentrations, changing direction within it, as if with one mind, is one of the unsolved mysteries of ornithology.
Years ago, they, like the hawks and eagles, would have travelled on south from here and spread over the plains of northern South America to feed on the seeds of wild grasses.
But here in Venezuela, they find great fields of cultivated grain, exactly like they found up in the north.
So they have no need to disperse, but remain together and devastate the crops wherever they settle.
It seems they positively prefer one another's company.
Some of the flocks may be half a million strong.
And man's practice of intensive cultivation allows them to stay and feed together.
At night they select a relatively small patch within a huge field of sugar cane where the whole half million roost, half a dozen birds to a single stem.
Flying, when all is said and done, takes a great deal of energy.
So birds have huge appetites and have to spend much of their lives in an unending search for food to fuel their expensive lifestyle.
Just how they find it, we will be looking at in the next programme in The Life of Birds.