Original subtitles

On a clear spring morning like this, the dawn chorus is at its peak.

There are surely few more enchanting natural soundscapes than this.

But this avian choir does not sing for us.

These are songs of seduction and weapons of war.

Males are defending territories and attracting mates.

Singing is dangerous.

It reveals the bird's location to predators.

But it also offers a huge reward -

the chance to attract a female and

pass on genes to the next generation.

That, Charles Darwin said, is why song evolved.

It was an example of what he called sexual selection.

But, today, new discoveries are transforming those long-held ideas.

For this programme,

I've chosen some of my favourite recordings from the natural world

that have revolutionised our understanding of song.

There are seven recordings of it

that have particular interest for me.

Some are lovely,

some are surprising,

and one almost broke my heart.

But all of them broke new ground.

I've recorded many sounds of the natural world over the years...

..and I've learned that there is, perhaps surprisingly,

no scientific definition of song.

We tend to use the word

to describe sounds that seem, to our ears, beautiful.

It is, in truth, a somewhat whimsical label,

but it has been attached to some of nature's greatest marvels.

Just listen to this.

Each of my seven chosen songs was recorded in my lifetime.

The oldest was made when I was five.

The most recent, just a few years ago.

None is closer to my heart than the first one...

..which I made back in 1960.

Recording audio in the field in remote parts of the world

was almost unheard of.

There was certainly no money in the BBC budget for a sound recordist,

but I did manage to get hold of a very rare thing indeed -

a battery-driven portable tape recorder -

so that I could record sounds myself.

It was a cumbersome piece of kit, but cutting-edge at the time,

and I was determined to use it to record a singer

that no-one had ever recorded before.

Madagascar's largest lemur, the indri.

This noise was no bird call.

I had never heard anything like it before.

It must be the voice of the indris.

Using my new equipment,

I made the first-ever audio recording of the indri.

But could we also capture them on camera as well?

The song was so loud that it seemed impossible

that the animals could be more than 20 or 30 yards away,

but where were they?

Until now, no-one had even managed

to photograph a living one, let alone film it.

Infuriatingly, the bush was so thick

that I could see no sign of them, whatever.

So the question was, how could we get close enough

to get a clear view of them without frightening them?

"Well," I thought, "what about doing it the other way around

"and trying to persuade them to get closer to us

"by playing their calls?"

And they did exactly what I hoped they would do.

They called in return, came down close to us,

stared at us, still calling.

I was thrilled -

we had recorded their song and filmed them singing.

But why had this trick worked?

Well, because they thought that the song I was playing

meant a competitor was close by,

and their response was to sing.

And this suggested one thing.

There are such things as battle songs.

Songs that say, "Get out, this is my territory!"

It seemed to be a clear example

of Darwin's theory of sexual selection.

A male singing to defend his breeding patch.

But this was still just guesswork.

We suspected that songs could be weapons of war,

but it was the next recording that proved it.

This is the song of a male great tit.

A call, a very simple song.

It was recorded by a scientist

who's been a pioneer in understanding animal song.

Professor John Krebs.

He was the one who proved for the first time

exactly why my playback trick in Madagascar had worked.

Spring 1975.

Back then, John was a young lecturer at the University of Oxford,

researching the birds in woodland just outside the city.

First, he plotted the territories of all the pairs of great tits.

Next, he recorded the songs of the males.

Female great tits do not sing.

Then, on a particular morning in February,

I came out with mist nets to catch the birds,

and I caught all the pairs of birds that were in the woods.

Now there were no great tits,

just empty great tit territories.

In some, John replaced the great tits with loudspeakers

that played the sounds of the birds that he had temporarily removed.

If the song was a "keep out" signal,

then new great tits would avoid these patches.

Other territories were left silent.

No speakers, no great tit song.

New great tits should realise these spaces were empty and available,

and settle there quickly.

But how would John know that it was due to a great tit song

that newcomers had been deterred?

Perhaps any sound would have had the same effect.

So, in some territories, he played a recording of a tin whistle.

He could have chosen anything,

as long as it sounded nothing like a great tit.

And then I watched to see what happened,

and new birds came into the wood,

because this is a prime breeding area,

so birds love to come here to breed.

John discovered that the first territories that were taken

were the silent territories,

and the ones with the tin whistle.

Crucially, the territories in which the great tit song was played

remained empty of new great tits.

By looking at the detail of that pattern of settling,

I was able to show experimentally

that song is an effective "keep out" signal.

Professor Krebs' predictions were exactly right.

Song was a "keep out" signal to other great tits.

For the very first time, there was scientific evidence

that song was being used to intimidate rivals,

just as I had seen with the indris in Madagascar in the '60s.

How astonishing that it was only in 1975

that this was proved for the first time.

The song of the great tit had made history.

Open a window in spring,

and these are the singers that serenade us.

Songbirds.

They make up about half

of the 10,000 species of birds in the world.

Five of my sevens songs are sung by them.

Birds have the most advanced vocal organs in the entire natural world.

We have our voice box at the top of our windpipe,

but their equivalent is at the base of theirs -

it's an organ called a syrinx.

They're the only creatures on Earth to have one of these,

and the syrinx of the songbird

is the most complex of them all.

As breath passes through it,

muscles contract and vibrate,

creating the sounds we call song.

It can produce different notes

from the left and right sides simultaneously.

It's like having two voice boxes that can operate at the same time.

So this is how songbirds can perform

such unparalleled feats of vocal gymnastics.

But working out WHY they do is far more complex.

Each note lasts just a tiny moment and then disappears.

That presents anyone who wants to study it with a problem.

But there are two relatively recent inventions

that have helped us to capture songs.

It was with a gun mic like this, inside its windshield,

that John Krebs caught the fleeting sound of the great tit.

But it was the ability to take that recorded sound

and then turn it into a visual picture

that enabled us to analyse that sound

and reveal its full complexity.

This is an animation of the male great tit song,

generated by a machine called a spectrograph.

It changes the song into an image that's possible to read.

Slowed down, we can see that the great tit song is relatively simple.

It's composed of two notes - one high and one low - repeated.

What we hear is very similar

to what we can see on the spectrograph.

But compare that to the song of the male wren.

What we hear is not what the bird hears.

Birds live on a different timescale,

at a different pace from us.

And they can hear details in their song

that are impossible for us to hear.

It's only when we use a spectrogram that these details are revealed

A trill...

..a connecting note...

..another trill...

..and then a rapid burst of trills at the end.

Now we can see that there are perhaps 100 notes

or more in a song that may last only a few seconds.

What the spectrograms show are these songs are far more complicated

and complex than we could possibly have imagined.

But why complicate things so?

The calls of the indri and the great tit

worked perfectly well.

The answer, of course, is sex.

That is the reason why so many birds have such complex mating songs.

Females seem to prefer them.

The more intricate and detailed the song is,

the better the male's chances.

And my third song helps to explain why.

It's a recording of a nightingale that is my next chosen song.

This is a male singing for a mate.

Just as with the great tit, the females do not sing.

But they are the ones the males are singing for.

So why do they prefer more complex songs?

It's a question that has puzzled scientists for centuries.

Charles Darwin's answer was that the females

have an aesthetic sense.

After all, human beings appreciate beauty.

Why shouldn't other animals do so too?

But the question Darwin didn't answer was

WHY should the females have an aesthetic sense?

Here on the streets of Berlin, we might just find the answer.

Spring attracts over 2,000 nightingales to this city each year.

They flock to Berlin because it's filled with green space,

much of which has been left untamed.

And it's these wild places that they love.

In one of its most popular parks, a male nightingale.

He, like the other males, arrived from Africa a few weeks ago

and has spent his time singing to defend a breeding patch.

But tonight, when the lights go out, he will change his tune

because the females have arrived.

Nightingales migrate at night, and when the females fly in,

under cover of dark, they are met with songs of seduction.

Dr Conny Landgraf made our recording of the nightingale's song.

So right now, there's one... Oh, no there is a second male.

So it's already two males in a vocal contest.

What the females do is that they do not take the first male that comes

their way, but they prospect and inspect different male territories.

And this is like a speed dating that is actually

going on in the middle of the night.

Each male sings his heart out and the females listen.

Time's up!

What does the next potential mate sound like?

Time's up again.

Does the next one have a better song?

Nightingales have extremely large song repertoires, up to 250 songs.

And also they are able to produce really challenging

syllables and phrases, thinking of trill or bass elements.

So these are very fast, repeated single notes.

So this is remarkable.

The more complex his song,

the more beautiful it seems to the female.

But why? Does the female have an aesthetic sense,

as Darwin suggested?

Conny and her team set up an experiment to find out.

First, they recorded males singing at the beginning of spring.

Then they set up cameras to record nightingale nests

later in the season.

Male nightingales play a crucial role in feeding chicks.

What we found in the end was that there was indeed

a very strong correlation between his song

and feeding rates at the nest.

So it's like a promise that the males give to the females

to be good fathers.

So, for example, a male could be saying,

"Hey, there, I'm a healthy, strong man,

"I know this area and all the best feeding places very well,

"so come settle down and mate with me."

Females, Darwin said, chose the males with the most beautiful

songs, and my third recording has demonstrated why.

Better singers are better fathers.

Songs can be a promise of devoted parenthood.

There are some songs that it's impossible for me

to imagine life without.

Songs that accompany our daily lives.

It's one of the most characteristic sounds, and to my ear

is one of the most delightful of the English winter -

the song of the robin.

These are the songs that Charles Darwin

would have listened to as a boy.

And much of our research into song has centred on British species.

Indeed, for much of the last century, we thought birdsong

originated here in northern latitudes.

But what if Darwin had been raised on the other side of the world?

Would his theories about song have been different?

The forests of Australia.

Out here, scientists are in the process of changing

many of our old ideas about song.

They found fossil and DNA evidence of early songbirds,

which show that this, in fact, is where song began.

It was here in Australia that the ancestors

of all songbirds first evolved.

Song number four is from one of the original songbirds'

most remarkable descendants.

And it's one that amazes me every time I hear it.

It was recorded in the forests just outside Melbourne,

and it was the first time that wild birdsong had ever

been broadcast in Australia.

The song of the lyrebird, in my view, is one of the most complex

and beautiful in the whole of the natural world.

And what gives it its complexity

is the talent that a lyrebird has

for mimicry.

Crimson parrot.

The kookaburra.

The descendants of that lyrebird, I'm happy to say,

are still singing in those forests,

and I've been lucky enough to listen

to one of them myself.

It was the 1990s when the BBC series Life Of Birds took me to Australia.

I wanted to film a lyrebird who was the most astounding mimic.

To persuade females to come close and admire his plumes, he sings

the most complex song he can manage,

and he does that by copying the songs of all the other birds

he hears around him,

such as the kookaburra.

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

He also, in his attempt to out-sing his rivals, incorporates other

sounds that he hears in the forest.

That was a camera shutter.

And again.

And now a camera with a motor drive.

And that's a car alarm.

And now the sounds of foresters and their chainsaws working nearby.

Since this remarkable clip was broadcast, millions of people

have watched it online.

Scientists have discovered a lot more about lyrebird song

since that recording was made.

That particular bird was accustomed to the presence of human beings

nearby, but much wilder birds produce something

even more fascinating.

Sunrise, Sherbrooke Forest, today.

One voice in the dawn chorus

is louder than any other - the male lyrebird.

It's the breeding season and they're busy trying to attract mates.

Clearing undergrowth from the forest floor creates

an arena for his mating display.

Once the stage is set, the show can begin.

It's unlike any other in the natural world.

Since I heard this song,

scientists have analysed it and broken it down into parts.

Song A comes first.

Now song B, a loud low shriek, which alternates with song C,

a quiet, very soft clicking sound.

A female arrives.

But no, she loses interest.

What he does next will need to be even more impressive.

Few have analysed the grand finale of the male lyrebird song

more intensively than Dr Anastasia Dalziell.

She and her team were the first ones to film it properly.

We thought no-one's going to believe us until we've actually filmed it.

It's really not like anything else that has been described previously

in birds or any other animals.

It was by studying the recordings from their remote camera

that the team were able to understand the real secret

of the male lyrebird song.

And it's this footage together with our own that enables us to show

this remarkable behaviour on television for the first time.

Having sung A, B and C and been rejected, the male now

begins Song D.

So this final song,

it's the sound of a flock of small birds mobbing,

reacting to a stationary or a hidden predator like a snake.

And this was totally bizarre.

So why is he imitating a flock of birds?

Well, a predator means danger.

So at the sound of an alarm call, the female freezes.

The forest is no longer a safe place.

Now the male takes advantage of her panic.

He jumps on top of her to mate.

It's hard for us to see her under his feathers,

and it's hard for her to see out from under them.

He's doing everything he can to disorientate and confuse her.

The male is actually telling her a big fib -

don't leave me because out there, there's a hidden predator

that you haven't seen.

To put it another way, it's like saying,

"Baby, it's dangerous outside.

"Come back here with me where it's nice and safe."

The lyrebird is, in fact, a bird that tells lies.

His song is an acoustic illusion.

Up to now, scientists have thought

that song was an honest signal from the male.

But it seems song can also be manipulative and false.

Not far away, in the Blue Mountains near Sydney,

scientist Victoria Austin is studying the female lyrebird.

What she's listening for

is something very few people have heard.

So what I'm doing now is just preparing my recorder

because we're about to head to a nest and we're hoping to be able

to record the female lyrebird that resides in that area.

The female lyrebird is the opposite of her flashy mate.

She's secretive.

When she is seen, she's often mistaken for a juvenile male.

To most people, she's invisible,

but Victoria knows how to find her.

This old nest suggests that she may be nearby.

And there she is.

This rarely heard sound is her whistle song.

In Darwin's theory of sexual selection,

males sing to attract females, and females drive the evolution

of song by preferring ever more complex songs.

The females themselves do not sing.

Yet here we are listening to a female lyrebird singing.

So what is the function of her song?

Well, the female raises her chicks alone.

The male plays no part, so it's extremely important

for her to maintain her territory and the food within it.

She uses song to let everyone know that it's her patch.

And Victoria is also researching

whether song helps her in other ways.

In the last few years, she's been recording their songs

across the Blue Mountains.

This is one of them - a female mimicking a goshawk.

It's very accurate.

If you were to play this call alongside an actual goshawk,

it'd be very difficult to tell the difference, if you were able

to tell the difference at all.

So what is the purpose of this perfect impersonation?

She's using it to deceive predators into thinking she's more dangerous

than she actually is.

She is just as talented as the more famous male.

So the biggest purpose of what we're doing working

with these female lyrebirds is to dispel this long-held myth that only

recently was shown not to be true,

and that is the idea that female birds don't sing,

or that it's very rare.

And that's just simply not the case.

This surely challenges Darwin's theory,

as does my next revolutionary song.

My fifth song was also recorded in Australia.

It, too, like the song of the female lyrebird, has rarely been heard.

It's important because its existence changes our idea

of what song actually is.

This is a fairly common Australian bird called a fairy wren.

We filmed these birds for a BBC series back in the 1990s.

We went there to film it because it's extremely promiscuous.

Both male and female will mate with many different partners.

But what few people realised at the time, and I certainly didn't,

was that it's not just the male that sings.

The female does, too.

This is Canberra Botanical Gardens.

Professor Naomi Langmore was the scientist

who made our fairy wren recording.

She was one of the first to realise the significance of female song.

The male fairy wren, with glorious, iridescent blue and striking

black plumage is rather difficult to miss.

So where is the female?

Well, not at the top of a perch like the male,

but instead here, hiding in the bushes.

She is comparatively rather dull - a drab brown.

Because females are often less flashy and eye-catching than males,

it's very easy to miss female song.

But sing she does.

Just as male song is used in competition with other males,

female song seems to be in competition with other females.

But why didn't we hear her before now?

Is it really just because she's less noticeable than the male?

In the history of the study of birdsong,

most research was done in the northern hemisphere, in Europe

and North America, and in those regions,

female song is comparatively rare.

And so researchers working in those regions generalised

from what they were observing in their local birds and assumed

that male song was the norm throughout the world.

A male-biased view of birdsong had,

to an extent, deafened us to female song.

So when I was doing my research, it was basically assumed

that it's the male that sings and the female doesn't.

Maybe that's because most of the scientists were males

who were studying birdsong.

But now there's a new generation of female scientists coming through

studying birdsong all around the world

and discovering that actually female song is very common

and occurs in more species than not.

And it's only now that they're properly being heard.

Naomi and her colleagues have discovered that in 64%

of all songbird species, females sing.

And that, in the distant past,

the ancestors of all songbirds

would have had both male and female singers.

When birdsong began, perhaps all female birds sang.

So why don't all female birds sing today?

The answer is migration.

Male migrants like the nightingale arrive in their breeding grounds

before the female. They set up and defend the breeding

territories, so the females don't need to sing.

In species that don't migrate, like the lyrebird and fairy wren,

then often the females will have their own territory.

And they will sing to defend it.

This female song challenges the way scientists have thought about

sexual selection for the last hundred years.

This recent discovery is a paradigm shift.

It's extremely exciting,

and it really forces us again

to reconsider what we think of as birdsong.

Birdsong was fundamental to the formulation of Darwin's theory

of sexual selection,

and the discovery that females sing as well

makes us challenge that theory.

Because our perception of birdsong has been biased

towards the northern hemisphere,

we have been unaware of some of the most thrilling bird songs

on the planet, but that view is changing.

Our understanding of song is continually developing,

and all the time we're learning new things.

It's a mystery that needs real research to unravel it,

and we're still learning.

How exciting it is to think of the discoveries

that are about to be made about birdsong.

This next ground-breaking recording reminds us just how thrilling

those new discoveries could be...

..because it revealed to us an entirely different world of song.

Few animal songs are more beautiful than the ones that are recorded

on this disc, and yet had it not been for recent technological

advances, we would never have known that such songs existed.

The waters off the coast of Bermuda.

US Navy engineers are using underwater microphones called

hydrophones to listen for enemy submarines.

This is what they pick up.

It's not a submarine or indeed any kind of man-made noise.

I'll always remember the first time I heard those songs.

It brought back to my mind the stories of sailors

in the old sailing ship days

out at sea in their bunks,

hearing those wonderful, eerie sounds resonating through the ship.

It didn't come, of course, from a mermaid, but something perhaps

even more extraordinary - a gigantic creature weighing many tonnes.

A whale.

Almost unbelievably, this was the first time that anyone had ever

identified the sound of a whale.

When biologist Dr Roger Payne heard it, he was thrilled.

It was back in 1967 about that I met a fellow named Frank Watlington,

who became a great friend,

and he played a sound to me of humpback whales.

It was the most beautiful thing I had ever heard from nature.

The first time I ever went swimming with a whale that was singing,

it's such an incredible experience, it's completely shattering.

It feels like, when you get close to one, that something

has put its hands on your chest and is shaking you

until your teeth rattle.

My first thought was, I wonder if I can stand this, I wonder

if this is actually going to kill me somehow.

The question was, would we call these sounds songs?

Some were short, like birdcalls,

but others were longer,

some up to half an hour.

Speeded up, this is what they sounded like.

They sounded like birdsong.

Roger called them songs.

In the late 1970s, I too went swimming with humpback whales.

I remember seeing this creature below me and then hearing its song.

It was thought they sing for the same reason as birds -

males singing to rivals and potential mates.

But no-one has ever seen a female listening.

In truth, no-one really knows why whales sing.

But one thing is certain - the sound of their song saved them from us.

In 1970, Roger released an album called Songs Of The Humpback Whale.

At the time, we had been killing whales,

mainly for their oil, for centuries.

We were very close to exterminating them out of sheer greed.

Then we heard their song.

Whole bunches of people in several countries began making organisations

to save the whales and the Save the Whales movement was born,

and in many ways that was sort of the beginning

of the conservation movement.

The conscience of the world was woken by this song of the whale.

We heard it just in time to save them.

But for my next and final singer,

there was no such reprieve.

There are few songs more haunting than this.

It's a male Hawaiian 'o'o bird calling for a mate.

But is he singing into silence?

Habitat destruction

and the introduction of invasive species have decimated

many Hawaiian songbirds, including the 'o'o.

It may well be that by the time this recording was made,

there were no females left alive.

It's the sound of a male singing for a mate who no longer exists.

The 'o'o has since been declared extinct.

He was the last of an entire bird family found nowhere else on Earth.

Now gone.

There is no more dramatic reminder of this loss than this sound.

And how many more songs have we lost in other parts of the planet?

Here in Britain, it's estimated that 38 million birds

have disappeared from our skies in the last 60 years.

One in five gone.

Climate change, habitat deterioration

and the resulting decrease in food and other resources

are thought to be the main factors

behind this catastrophic decline.

It's now up to us to decide how many more songs

we will allow

to fade into silence.

These songs enrich our lives, too.

They're surely amongst the loveliest in the universe.

And without them, our lives would truly be impoverished.

And what is lost when the songs fall silent is more than just

an enchanting operatic backdrop to our own lives,

because for the creatures that sing them, songs are far more than that.

They are a weapon of war...

..a serenade, a promise of parenthood, a daring deceit...

..or perhaps something even more astonishing

that we are yet to discover.

Each one a marvellous example of the spectacular survival strategies

that animals have developed in order to stay alive.

That is why I'll never cease to wonder at

the beautiful sounds

we call song.

Few sounds of nature are more beloved by this nation

than that of the nightingale.

And there's one more recording of it that I have memories

of listening to as a child.

It was made by the BBC two years before I was born, in May 1924.

It's a cello accompanied by a nightingale.

In this country, it was ground-breaking.

It is, in fact, the first live broadcast of any wild animal song.

The idea came from a celebrated cellist called Beatrice Harrison.

One night when I'd been playing for hours,

I suddenly heard the note

of the most heavenly bird,

and it struck me how lovely it would be if he could be broadcast.

The nation held its breath while Beatrice played.

It was the first time that the wild world of nature

came straight into your living room.

Perhaps a million listeners tuned in to that first broadcast.

It was so popular, the BBC made it an annual event.

The performance became so celebrated that Beatrice was asked to recreate

it for a 1943 film with Sir Laurence Olivier.

It was far from the first time, of course, that the nightingale

had made a cultural appearance.

The nightingale has inspired poets and musicians for ages, and perhaps

the most famous poem of all is by John Keats.

Thou was not born for death, immortal Bird!

No hungry generations tread thee down,

The voice I hear this passing night was heard

In ancient days by emperor and clown.

Keats wrote those lines in Hampstead in London,

but he wouldn't hear a nightingale there today.

There are no nightingales in London now.

In fact, we've lost over 90% of nightingales in this country

in the last 50 years.

What a tragedy.

The causes are still not fully understood...

..but habitat deterioration probably played a significant part.

In one small corner of Britain, however, there is a place trying

to provide the nightingale with a safe haven.

The Knepp Estate in West Sussex - 3,500 acres that was once farmland.

But the soil here wasn't suited to modern-day intensive agriculture.

Since 2001, it's been left to nature.

There aren't many rewilding projects in Britain as pioneering as this.

Wildlife now thrives here...

..including some of the country's rarest species.

This, for many of Britain's best-loved songbirds,

is an ideal place for shelter and food.

The nightingale is one of many species found at Knepp.

Here, dense, almost impenetrable thorny scrub

provides their ideal nesting site.

Today, it's late spring and one nest of chicks is being ringed.

This makes it possible to gather vital information that can help

monitor population numbers.

There are estimated to be more than 40 nightingale territories

in this area of the estate.

Back when it was intensively farmed,

there were only nine.

Few places in Britain have nightingales increasing

in such numbers.

It gives us hope, perhaps, that the British countryside

could once more be filled with the nightingale's

beautiful and iconic song.

How wonderful it would be if each of us could say we've heard the songs

of the Earth and we've saved them.