Signals and Songs The Life of Birds

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BIRDSONG

It's spring in Sweden.

Fieldfares are ferrying meals of worms to their ravenous chicks.

They nest in colonies, up to 30 or 40 in a group, and that helps a lot with defence.

There are plenty of raiders around.

This is one.

It's a young raven. He's after a nestling.

A fieldfare has spotted him and sounds the alarm. STRIDENT CHIRPING

Others take up the call, and the defence force assembles.

The raven now knows that he's been spotted, but he's hungry.

The fieldfares, screaming with anger, converge on their enemy.

Now threat turns into direct action.

They mob him.

Intimidated by the commotion, the raven retreats.

But the fighters press home their attack. The raven is brought down.

They bomb him with their droppings.

RAVEN CAWS

Soiled feathers soon become waterlogged.

That could be crippling, even fatal.

Thoroughly cowed, the raven retreats.

The colony is saved, thanks to its members' highly effective system of communication

between themselves AND with their enemy.

The messages proclaimed by those Scandinavian fieldfares could hardly be misunderstood, even by us.

The first were calls to arms.

The second were battle cries designed to intimidate the enemy.

But alarm calls aren't always so easily recognised by outsiders.

Sometimes it's better to sound the alarm more surreptitiously.

And that is something that birds in an English wood do very well.

HIGH-PITCHED, SINGLE CHEEPS

That sound is a general alarm call. It's short and very high-pitched.

That makes it difficult to locate the bird that makes it.

It's a great tit. Half-hidden among the leaves, he continues sending furtive signals to his family.

But all the birds around get the message.

An enemy would find it very hard

to detect where that sound is coming from.

Another warning. HIGH-PITCHED, QUIET, SINGLE CHIRPS

This time it's from a robin.

He's telling his mate to stay still until the danger has passed.

And that's the blackbird's version. HIGH-PITCHED, GENTLE CHIRP

The begging cries of nestlings could put them in danger.

A male chaffinch tells them to keep quiet. REPEATED, SHRILL CHIRP

They do as they're told.

So this surreptitious call is like an international distress signal understood by everyone.

SERIES OF REPEATED, STRIDENT CHIRPS

That's a different kind of message.

That's not one that's sent surreptitiously to others. It's aimed directly at me.

It's a warning to tell me that I've been spotted.

I'm too near this blackbird's mate who is sitting on her nest.

His calls are almost continuous and much lower pitched

because he wants to be located so as to distract me away from her.

Sound is not the only way to spread the alarm or intimidate an intruder.

Some birds do the same thing visually.

Most of the time, this sun bittern is well camouflaged and unobtrusive,

even less conspicuous than the jacanas and cayman that also haunt the river's edge, here, in Venezuela.

The river is continually bringing edible bits and pieces within range,

and the sun bittern lives on them. But it has competitors.

A hawk in the branches above has spotted something.

So has the sun bittern. But the hawk gets there first...

..and collects it.

A second hawk arrives. If the sun bittern is to get anything, it will have to frighten the others off.

So it transforms itself.

A ferocious, hissing, two-eyed monster that doesn't exist is saving the day.

The hawk tries again.

But this startling display convinces the hawks that the bird down there is dangerous. They give up.

There is, of course, an alternative signal.

Instead of saying, "I am here and extremely formidable," you could say, "I'm not here at all."

That, of course, is a straightforward lie,

but there's a bird in these Brazilian forests that tells the most convincing of lies.

Finding it is not easy. Indeed, I'm sure I've walked past one many times. But this time, we're lucky.

It's sitting on the tree trunk. It's a potoo,

a kind of nightjar.

It hunts for insects at night so it needs to rest during the day.

It relies on the visual match between its feathers and the tree trunk to protect it from disturbance.

The only thing that could give it away are its beak and its eyes.

Now I'm getting quite close,

so it decides to improve its disguise even further.

It does that by changing its posture and closing those giveaway eyes.

Now it's no more than the stump of a broken branch.

You might think it would be a dangerous thing to do -

to shut your eyes just when danger approaches.

But, in fact, although its eyes are shut, it can still see me.

There are two hitches in its eyelid. Its night-vision eyes are so sensitive that it can still see.

As it watches me going away, it relaxes and returns to its doze.

Most birds, of course, rely on their ability to fly to keep them out of trouble.

So, as you walk through an English wood, they, too, vanish.

But establish their confidence, and they will soon come back.

And then you can see that they use their plumage to send very different messages.

One finch meeting another needs to know whether it's the same species.

If it is, it could be a rival, either for a mate or for territory. If it isn't, it can be ignored.

So finches, with such similar body shapes,

wear uniforms that make plain who they are.

And what works for other birds

will also work with us, provided we know the code.

Most bird-watchers do.

A grey-blue cap and reddish cheeks identify a chaffinch.

A brown head and grey collar - a hawfinch.

A completely green head - a greenfinch.

A black cap and red cheeks - a bullfinch.

And a red face and forehead - a goldfinch.

So every finch knows whether another is a rival or not,

and there are no pointless quarrels.

In the forests of Indonesia, hornbills also use colour codes.

Several species have predominantly black and white plumage.

This one, however, the pied hornbill,

has yellowish areas on its white wing patches.

These are not accidental smudges.

This bird uses make-up.

With its beak, it squeezes a yellow oil from a giant preen gland on its rump.

It uses that oil to paint on those yellow blotches.

And not just on its wings. It adds yellow patches to its neck, though they are more difficult to put on.

Even its huge bill owes its yellow colour to the preen oil.

Different kinds of hornbills paint themselves different colours.

Whether these cosmetics are used

just for appearances' sake, or whether they have an additional purpose, we don't know.

But one thing is quite certain -

birds take a lot of care over their appearance.

All birds have to have good eyesight to navigate at speed through the air,

but, in particular, they have excellent colour vision.

That enables some species to have the most gorgeous uniforms.

This bottle of artificial nectar can attract some of the most spectacular.

The particular glory of hummingbirds

are their bibs and breast-shields.

Their colour is not pigment, but an optical effect created by refraction, like the colours of oil on water.

They're particularly attracted by red, which is why I've got red artificial flowers on this bottle.

They can also see in ultraviolet,

and that's a colour that lies beyond the range of the human eye.

It's been discovered that many of their feathers reflect ultraviolet,

so it's likely that these brilliant costumes are even more vivid in their eyes than they are in ours.

Many birds that seem plain are almost gaudy in ultraviolet light.

Starlings, for example, have a sheen to their plumage,

but that has an ultraviolet component that makes them appear much more vivid to one another.

Blue tits, in our eyes, are one of the more colourful garden birds.

But in ultraviolet, they're much brighter still.

Their crests are particularly vivid and much brighter in males than females.

To them, the sexes look different. To us, blue tits all look the same.

Most of us think that budgerigars are unusually colourful birds.

But ultraviolet radically changes the character of their costume.

Their feet glow.

And the spots on their cheeks, which are not particularly prominent to our eyes, positively blaze.

Indeed, a budgerigar's full-dress uniform is dramatic in the extreme.

Uniforms not only indicate an individual's regiment,

but his rank within that regiment.

Male sparrows have black bibs,

but the size varies. The more vigorous birds have bigger bibs

and, therefore, higher ranks.

Sparrows forage in flocks. When there's lots of food in a small area,

you might expect lots of quarrels. But there aren't.

This is a private with no badges.

This one is somewhat senior - a sergeant, perhaps.

A captain.

And the colonel.

There could be disputes, not only over food,

but over amenities like dust baths.

The privates are squabbling among themselves.

But watch what happens when a corporal steps in.

Junior ranks retreat.

Or when a corporal gets too close to a sergeant.

A sergeant, however, gives way to a captain.

And no-one should think of parting a colonel from his lunch.

A quick flourish of his insignia is quite enough.

Among birds that don't live in flocks,

there is no need for the ranking system to be so multi-layered.

Moorhens may mingle,

but each pair has its own territory.

Their badges are the red beak and head shield, and white tail patches.

Rivals assess one another's strength by the size and brilliance of those head shields.

If they feel their ranks are equal,

they may not want to contest the boundary,

and they display the white tail patches to indicate that the confrontation is being broken off.

But here, the male on the right is standing upright.

He reckons he's the senior and he wants to enlarge his territory.

The time for sending messages is over. This quarrel can only be settled by physical violence.

Birds can get badly injured in these battles, but they have to be fought

if a senior bird is to establish and retain his rank.

Eventually, the junior bird surrenders.

A new line has been drawn. They won't need to fight again as long as it's not overstepped.

Communication by visual signals, however, has one major limitation.

Except in completely open country,

they only work at close range. In forests, sound signals travel much further.

So if a bird, in order to get enough food, needs a large territory,

it's likely to declare its claims with sound.

There are, of course, many different ways of making a noise,

and knocking on a resonant tree trunk is one of them.

Here, in Patagonia in South America, two knocks on a tree trunk has a very particular meaning -

at least among birds. If I do it, I might even get an answer.

TWO, DISTANT, RAPID KNOCKS

TWO KNOCKS IN REPLY

It's a Magellanic woodpecker, one of the largest of all woodpeckers,

and he thinks he's heard a rival.

He comes in for a closer look.

And here's his mate to support him.

Now she joins in the dispute.

He's now on my tree.

His mate is even closer.

I've stopped knocking, so it seems to them that their rival has gone.

All is well.

There's another drummer in the bird world -

Australia's palm cockatoo.

His beak is no good as a drumstick so he uses a wooden one.

HOLLOW KNOCKING

HARSH BUZZING

And that noise, too, is made mechanically - by an African broadbill.

It makes its call in the same way as children do when they blow across a blade of grass.

But, instead of grass, the broadbill has specially strengthened and shaped wing feathers.

Of course, most of the sounds made by birds come from their throats.

The calls and songs that you hear in a tropical rainforest, however,

are very different from those you might hear in a European woodland. And there's a reason for that.

The leaves in a rainforest have shiny surfaces that reflect sound.

So a complex call up here would have its notes slurred and confused.

As a result, birds that live up here

tend to have calls that are simple, short and, often, very, very loud.

CLEAR, PIERCING CALL

That's the loudest of all from a bare-throated bellbird.

HIGH-PITCHED WHISTLES This is a close rival - a screaming piha.

Toucans must also be close to the top ten.

REPETITIVE, HIGH-PITCHED CALL

All these birds call from high up in the canopy.

Lower down, where foliage is less dense, the calls can be different.

For one thing, they can be longer.

ONE LONG CALL ON A FALLING NOTE

That's a curassow.

And this - a wattled guan.

LONG, WHIRRING CALL

A longer call, of course, can contain more notes.

PIPING, MELODIC CALL A kagu in New Caledonia. This is a female.

Her mate, some distance away, is listening.

The family wandered apart as they foraged. They want to get together.

Her son has also heard the message.

So the adult pair are reunited and they greet one another, as usual,

with a visual display.

But their son is still out there somewhere.

And, once again, the family group is complete.

The calls of the kagu can be heard half a mile away.

But some birds need to communicate over even greater distances.

The best way to do that is with very low-pitched notes.

THROATY, FROG-LIKE CALL

An American bittern.

LOW-PITCHED, HOLLOW GULPING

An air sac in his chest acts as a resonator, so he starts by gulping in air and pumping it up.

CALL ECHOES IN DISTANCE

This call carries for over two miles, even through the thickets of reeds.

When the performance is over, the air sac slowly deflates.

If you can get out of the reeds, then your calls are less impeded.

The Australian musk duck does just that in order to broadcast his messages.

The smooth surface of the water also helps to reflect the sound far across the lake.

HOLLOW, TAPPING CALL

The flap on his chin is a visual signal for any birds that come over for a closer look.

However, if calls are directed to neighbours nearby,

then they can become very elaborate.

This red bishop makes an almost constant stream of high-pitched notes as he hops around.

You can't get much more elaborate than this.

RAUCOUS, SQUEAKY TRILLING

The extraordinary display of the oropendula includes one of the strangest songs of all.

So how do birds do it?

How, for example, can canaries sing continuously for minutes on end?

Slowing the singer down, which also lowers the pitch of the notes, allows us to see what's happening.

Between notes, it takes mini-breaths to replenish its air supply.

In full song, it may do so 30 times a second,

A bird's voice box can also produce two different notes simultaneously.

It's not high in the throat like ours, but deep in its chest.

Low notes come from one side,

high from the other.

By alternating between high and low notes, even short songs can carry very complex messages.

And this is the champion.

RAPID, MUSICAL TRILL

The cowbird uses over 40 different notes in his songs.

Some of them are so high that they are beyond the hearing of many of us. Again, if we slow the action down,

we can hear what's going on.

The left side is producing the low notes...

MELLOW WARBLE

..and the right, the high.

HIGH-PITCHED PEEPS

Others are made by combining the sounds higher up in the throat.

It may take a cowbird two years to learn his song properly.

It's important that birds should get their calls exactly right

for they can be as significant in proclaiming identity as a uniform.

Indeed, if a bird has a shy and retiring disposition

and lives in a secluded place like this English woodland,

then its voice may be the only way that it can be recognised by another bird or, indeed, by a bird-watcher.

There are two kinds of warblers here. This is a chiffchaff,

fuelling up after its long flight from Africa.

And this is a willow warbler. To me, it looks virtually identical.

But wait until they sing.

This is a chiffchaff. BRIEF, TWO-NOTED PEEPS

MELODIOUS SONG WITH LONGER NOTES And this, a willow warbler.

There's no mistaking who's who as long as you can hear their calls.

But a bird's call can tell another bird

more than just what kind of bird it is that's singing.

This patch of bush on a small, offshore, New Zealand island belongs to a male saddleback.

He's held it throughout the year and he knows who his neighbours are because their calls vary slightly

and he can recognise each one individually. And there he is.

Throughout the day, he keeps in regular contact with his neighbours.

HIGH-PITCHED CHEEPS AND CHATTERING

They each answer his call,

and he can distinguish between them

in the same way that we distinguish between regional dialects.

A northerner.

A southerner.

And someone from the east coast.

If the right call comes from the right place,

then he knows that his territory is safe from intruders and he can go back to feeding.

But if the call is from a saddleback that he doesn't recognise,

and if, as well as that, it comes from a completely new place, then he will react in a very different way.

And, of course, it's quite easy for me to make that happen.

I'm going to play him a recording of a saddleback from a different island.

His response is swift and very aggressive. STACCATO CHIRPING

He comes down for a closer look.

He gives another warning.

This is a serious challenge to his territory. It can't be tolerated.

Now, since his rival seems to be somewhere close by,

he makes a visual threat, displaying the brown patch on his back.

He's ready to fight, if only he could find who it is he has to fight.

That's enough. We'll leave him in peace.

MUTED, SWEET BIRDSONG

To many of us, however, this is the most delectable of natural sounds.

It's an hour before dawn. It's spring. This is an English woodland. And all around - the dawn chorus.

It's so familiar that, perhaps, we take it for granted.

But there's a lot we don't know about it still.

As first light brightens, different kinds of birds, one by one, join the choir.

CALLS MINGLE AND ECHO

Why should they all sing together at this time?

Wouldn't it be better for some to sing later by themselves?

And that's not the only puzzle.

Why should it happen at this time of day?

Well, at dawn, it's still quite cold.

Insects are not yet up and about.

For many birds, there's nothing to eat. So they might as well sing.

PROLONGED, RAPID TRILL

WELL-ARTICULATED MELODIOUS SONG

DRAWN-OUT, HISSING CALL

SWEET, FLUTE-LIKE CALL

There's another possible reason.

It's usually quite calm at dawn and, with no wind,

these messages will travel far and still be recognisable.

The chorus is the equivalent of our early morning news - only broadcast in 50 different languages at once.

By listening to it,

this wren knows which of his neighbours is still alive.

He knows where they are.

And if there are any new males on the scene.

Each kind of bird listens to its own particular section of the sound spectrum.

The song thrush broadcasts in the mid-range.

The wood pigeon's calls are somewhat lower.

Smaller birds, like the firecrest, use the higher frequencies.

These springtime messages from male birds not only say,

"This is my patch." They also say to passing females, "Come and join me."

HIGH-PITCHED, RAPID TRILL

Robins have now extended their usual songs to carry this additional message.

The male chaffinch has done the same. CLEAR, MELODIOUS CALL

He may sing this song over 500,000 times in a season.

By late spring, migrants have arrived from southern Europe and Africa and are adding to the chorus.

RAPID, METALLIC TRILL

A wood warbler.

CLEAR, RINGING CALL A pied flycatcher.

And a redstart.

SWEET, MELANCHOLY SONG

His mate, like many, will be impressed by the originality and complexity of his song.

The male sedge warbler can produce 50 different notes and never sings the same song twice.

He's like a jazz singer - continually improvising.

Different males develop different singing styles.

And this is, perhaps, the most lyrical of all European songsters.

COMPLEX, MELLOW SONG A nightingale.

He may have 300 different love songs in his repertoire.

And he will sing for a mate all through the night.

What bird has the most elaborate, the most complex, the most beautiful song in the world?

I guess there are lots of contenders, but this bird must be one of them -

the superb lyrebird of southern Australia.

MELODIOUS CHIRRUPING

WHOOPS AND WHISTLES

He clears a space in the forest to serve as his concert platform.

To persuade females to come close and admire his plumes, he sings the most complex song he can manage.

He does that by copying the songs of all the other birds he hears around him, such as the kookaburra.

RAUCOUS CACKLING

It's a very convincing impersonation.

Even the original is fooled.

He can imitate the calls of at least 20 different species.

He also, in his attempt to outsing his rivals, incorporates other sounds that he hears in the forest.

CLICK That was a camera shutter.

CLICK And again.

And now a camera with a motor drive. CLICK, WHIRR

WHOOPING, WAILING CALL

And that's a car alarm.

And now the sounds of foresters and their chain saws working nearby.

WOOD CRACKLES AND CHAIN SAW BUZZES

SAW CUTTING THROUGH WOOD

That wonderful performance is only one example

of the extent to which male birds will go in order to attract a female.

The range and sheer extravagance of their courtship displays can be quite astonishing.

And the range of relationships between male and female that these displays lead to

is also much more varied than you might suppose.

And it's that, the most crucial stage in the life of any bird,

that we'll be looking at in the next programme.

CLICK, WHIRR

Subtitles by Mary Easton BBC Scotland - 1998