01x02 - Love and Rivals

[bunniefuu]

The natural world

is filled with sound.

But so far,

we've been hearing only part of it.

New audio technology now captures

sounds that we can't even hear.

For some animals,

sound is the key to finding a mate

..to impress others

..and to warn off the competition.

A British woodland in spring.

The air is filled

with the sound of bird song.

It's a sound that brings

a lot of people a lot of pleasure

including me.

And all these birds

are singing for two reasons

one - to establish a territory,

and two - to attract a mate.

Song travels well

in an open woodland.

But making yourself heard can be more

challenging in a noisier environment.

And there is one creature here

that has risen to that challenge.

This delightful little bird

is a white-throated dipper.

For most birds of its size,

living beside streams

is rather a dangerous place.

Feathers, when they are wet,

on a bird of this size,

aren't much good for flying,

but the dipper

knows how to deal with that.

As it searches for food

between the rocks,

it stops frequently to cover its

feathers with oil from a preen gland

so that they stay waterproof and dry.

Reaching your food underwater

is just one of the problems

faced by the dipper.

Another is how do you send messages

above the noise of the fast-flowing

stream by which you live?

But the dipper has a way

of dealing with that as well.

It's the breeding season

..and this male uses his voice

to find a partner.

To our ears,

his singing can hardly be heard

above the sound of the water.

But eliminating

the sounds of the river

reveals a surprisingly complex

and melodious song.

Most of the dipper's notes

are higher-pitched

than the noise of the water.

This allows others

to hear his song more easily.

He has attracted

the attention of a female.

Only males in peak condition

can sing complex tunes like this.

His song has impressed,

and his new mate will stay with him

for the rest of the year

and help him defend this territory.

Six weeks later,

and the pair have been busy.

Concealed behind the waterfall

is their nest.

To ensure a steady supply of food

for the chicks,

the pair have to defend

their stretch of river from others.

And its their song

that acts as a warning to rivals.

Together,

they present a united front.

For any intruders,

the message is loud and clear.

Keeping the chicks well-fed

is crucial,

and not just for their growth.

It's needed to develop

the part of the brain

responsible for learning song.

So, they will, one day,

become proficient singers,

like their parents.

Two weeks on, and all three chicks

have fledged successfully.

These youngsters have had

the best possible start in life

..thanks to their parents

and their song.

When it comes to finding a mate,

power, not melody,

is sometimes needed.

Autumn in

the Rocky Mountains of Canada.

This bugling call of the elk

marks the change of season

and the beginning of the annual rut.

This bull is in his prime,

and over the next six weeks,

he will push himself close to death

in order to mate.

The females will only accept

the largest and strongest male.

And his success will depend on

the power of his voice.

Stretching his vocal chords,

he produces a high-pitched shriek

through his nose.

It travels over a mile

and announces his presence

to distant females.

At the same time,

he makes a guttural groan

..which signals his size and strength

to nearby males.

The deeper his voice,

the bigger and stronger he is.

And he backs it up

with a physical display.

His goal is to gather

as many females as possible

to ensure that his genes

are the ones that are passed on.

Now he switches

to a different call

..a low 'glunking' sound

to encourage the females to join him.

A successful bull can attract

up to 20 females in one season.

Chemical cues,

detected with his tongue,

tell him which cows are fertile.

But retaining so many females

is easier said than done.

A rival enters the arena.

Their bugles signal

that they are equally matched.

There's only one way to settle this.

He must stand his ground

or surrender his females.

These battles can result

in serious injury, even death.

For the moment, at least,

his legacy is secure.

On the vast grasslands of Alberta,

it takes teamwork to get noticed.

Every spring,

male sharp-tailed grouse gather

on traditional breeding grounds

..practising for their most important

performance of the year.

And they have a remarkable array

of musical instruments

at their disposal.

Feet are stamped,

and tail feathers rattled,

to produce a rhythmic beat.

A low cooing sound,

amplified by inflatable air sacs,

provides the accompanying tune.

And it's all to attract the attention

of the females.

The more males, the louder and more

impressive their performance.

But sometimes, tensions boil over.

They need to stop squabbling

and work together.

Their combined song and dance

has attracted a female.

Time for the synchronised finale.

They all freeze.

She takes the opportunity

to assess each male.

Now she's looking for

the fastest tail rattle.

And a sound

like the popping of a cork

..which females find irresistible.

Their display will help her find

the fittest male in the group.

And this one

has caught her attention.

But not everyone

is sticking to the dance routine.

A young, over-enthusiastic male

is ruining the performance

for everyone.

She's seen enough.

And she's off.

Today didn't go as planned.

But tomorrow, they'll have

the chance to do it all over again.

While grouse

benefit from joining forces,

others must find a way

to stand out from the crowd.

In the deserts of Arizona,

temperatures can soar

above 40 degrees Celsius.

Rain hasn't fallen here

for several months.

But things are about to change.

Within hours,

the rains flood the ground

and temporary pools appear.

The thunder sends shockwaves

through the ground

..which trigger an annual uprising.

Breaking free

from their underground vaults,

desert frogs and toads

emerge to breed.

They will have just one or two nights

to find a mate.

And there are hundreds of frogs

in this one pool.

Not only that,

at least five different species are

all trying to make themselves heard.

How is a female to find a male

of her own kind?

The answer, it seems,

lies in their voice.

Each species has

its own distinctive call.

And now we can see

just how the females do it.

A specialised acoustic camera

shows sounds

of different frequencies

in different colours

..and reveals that each species

favours different notes and rhythms,

allowing females to pinpoint males

of their own kind.

When it comes to mating,

it generally makes sense

to stick with your own species.

But desperate times

can lead to desperate measures.

On the other side of the valley,

the rains have been less plentiful,

and the pools here

are dangerously shallow.

This plains spadefoot

needs her young to develop quickly

before the water disappears.

It's a race against the clock,

and the calls of

two different species are deafening.

She tunes into the calls

of her own kind of male.

But surprisingly, she sidesteps them.

The pulsing call

of a Mexican spadefoot

has attracted her attention.

He belongs to a different species,

but, remarkably, she can still

mate with him if she so chooses.

And in this case, she does

and for a specific reason.

His tadpoles will develop faster

than those fathered by her own kind

and give her young a chance to reach

maturity before the pond dries up.

It's an unusual practice

but an effective one.

And in an unpredictable

and warming climate,

solutions like this

may help ensure their survival.

But her decision comes at a price.

Only female offspring produced

from this liaison will be fertile.

But she's ensured that at least

some of her genes are passed on.

Frogs aren't the only ones

to use their voice

under the cover of darkness.

On the Pacific Coast

of North America,

the night air resonates

with an eerie hum.

It's a sound

that baffled people for years.

It coincides with the arrival

of a fish from the open ocean

..a plainfin midshipman.

For the next three to four months,

this male will risk his life

in the shallow intertidal zone.

He's searching for a suitable spot

to make a nest.

This one looks ideal.

Time for some housekeeping.

One final mouthful

..and it's complete.

But the females

are still in deeper water.

He needs a way

of attracting their attention.

The onset of night is his cue.

By vibrating muscles

attached to his swim bladder,

he produces a low-frequency hum

that travels well through water.

And he's not alone.

He's joined by dozens of others.

The sound reaches

a staggering 110dB -

as loud as a lion's roar

..giving rise to the mysterious drone

that once puzzled the people

who lived on these shores.

This sound is loud enough

to be heard by the females.

Guided by the hum,

a female arrives, swollen with eggs.

The harmonics produced

by each male are slightly different,

like a sonic fingerprint,

and help him stand out

from the crowd.

His song has drawn her this far,

but now his nest is under scrutiny.

It's to her liking.

Hovering upside down,

she lays her eggs on the roof.

The next morning, she has gone.

The male alone will protect the eggs

for the next three months.

During this time, he won't feed

or leave them unattended.

A crablooking for a snack.

He sends a warning growl

..and a grunt.

The crab finally gets the message.

But the biggest challenge he faces

comes with the daily changing

of the tides.

Midshipman fish

are adapted to breathe air,

but the low tide

leaves him defenceless.

With no means of escape,

it's now down to luck.

On this tide, he's made it.

If he and his eggs can survive

the hazardous months ahead,

he will have helped father the next

generation of midshipman singers.

Sound travels well underwater.

On land, however,

it is often deflected,

or absorbed, by the surroundings.

Thick rainforests

pose a particular challenge.

The dense vegetation

acts as a sound barrier

..and despite the many voices,

most messages don't travel far.

In the forests of Southeast Asia,

however, there is one animal

that knows exactly how

to make its message heard

..a yellow-cheeked crested gibbon.

He moves to a higher position

where the canopy is less dense.

Unobstructed by trees,

his call carries

for over a mile across the forest.

And he's not alone.

His partner and baby are close by.

The female now joins in

with her own song.

Together, their duet

sends a message to other gibbons.

It's a declaration

that this patch is taken,

and the fruiting trees within it.

Their calls spark responses

from other pairs,

each protecting their own territory.

It's a noisy but effective

early-morning roll call

to establish the order of the forest.

While gibbons sing

over the forest canopy

..deep within the forest, some

animals use the plants themselves

to transmit their messages.

It's a world of sound

that we can't hear

..but is clear to those that can.

A male treehopper.

Only half an inch long,

it lives in an acoustic world

entirely unlike our own.

But with a special laser vibrometer,

we can now hear these sounds.

He shakes his abdomen

a hundred times a second

to produce a low sound

that vibrates through the stem.

It's a courtship song that spreads

through every part of the plant.

A female receives his message

through her legs

loud and clear.

She's ready to mate,

and she answers back.

But she could be anywhere

on the plant.

To find her, he needs to keep

the conversation flowing.

Using her sound to navigate,

his direction of travel is determined

by whether it hits

his front or rear legs first.

He must be quick.

Her signal may be picked up

by other males on the same plant.

But this crossroad

is proving hard to read.

He checks for directions.

Now the signal is coming from behind.

He's taken a wrong turn.

His detour has cost him

valuable time.

Found her at last.

But he's too late.

Another male has beaten him to it.

However, there are plenty more

treehoppers in the forest.

Most animal calls

are encoded in their DNA.

But some can enhance their repertoire

in other ways.

A starling.

Ah! Ooh, and a hungry one at that.

They are, in fact, one of

our most accomplished singers.

And they not only have

their own songs,

but they can also mimic

the songs of other species.

And it's all done

in order to impress the females.

And they're not the only bird

that can imitate others.

The forests of Eastern Australia

are home to one of nature's

most accomplished mimics

..the superb lyrebird.

And this mound of earth is his stage.

This modest performance

won't be enough.

Female lyrebirds are fussy

and demand more complex songs.

But he has a solution.

He listens carefully

to the sounds around him

..and mimics them perfectly.

He can learn the songs

of over 20 different birds.

And he's not only a mimic -

by stringing the songs together

in his own way,

he's also a composer.

No two lyrebirds

sing exactly the same tune.

With age,

his songs become more intricate

and give him greater success

with the females.

But the lyrebird's world

is changing,

and urban settlements have replaced

much of its natural home.

And with it have gone

many of the songsters

that he relied on for his tunes.

Luckily, this bird is a virtuoso.

A car alarm

..a camera shutter

..and even a crying human baby.

This soundis anyone's guess.

But it's done the trick

and got him noticed

..a female.

He may have

an unusual choice of tunes,

but they add to his repertoire,

and that's all matters.

If she is impressed,

she'll choose him to father

the next generation

of master songsters and mimics.

Many of the sounds we hear in nature

are the voices of animals.

But some creatures are so quiet,

they appear to be making

no sound at all.

We wanted to film one of these -

the treehopper.

But how do you record

the sound of a creature

we ourselves can't even hear?

Dr Rex Cocroft is a biologist

at the University of Missouri.

He's fascinated by creatures that

communicate using just vibrations.

There are at least

200,000 species out there

singing in ways

that are silent to us.

And that's way more songs than

if you add up all of the birds,

and the fish and the whales,

and the frogs out there. So

the majority of animal sounds are

ones that we don't actually hear.

Which makes them

a challenge to study.

But a special sound-recording device

solved the problem.

It's called a vibrometer

and uses a laser beam to detect

the slightest vibrations

on the surface of an object.

By amplifying these sounds,

the vibrometer allowed Rex to listen

in on treehopper communication.

This little treehopper

sounds like a tap-dancing monkey.

Another one sounded like

an owl laughing at its own joke.

One male treehopper

sounded like a clucking hen.

Another one

sounded like a woodpecker

followed by a tiny car honking.

Oh, my gosh.

I was just lost at that moment.

There was no going back because

I heard these wonderfulsounds

that were right there

in one small plant.

Let me put this here.

And how high do you want this?

Rex's discovery proved irresistible

to our film crew,

led by Director Nalini Crack.

Nalini wants to record

the courtship duet of a treehopper.

Helping her is Vikrant Palan

from Polytec,

with his company's

most advanced vibrometer.

Yeah.

Getting there. Yeah.

Good, good, good. Good, good.

Nalini has placed a female

on the stem of the plant.

Let's try putting a male on there

and see if we can get him calling.

The male song

will vibrate through the stem.

If the female answers,

he'll follow her call.

Go on, little guy.

Here he goes.

Yeah, that was it.That was it?

That was him.

Yeah.

Wow! Oh, my God!

But his vibrations

aren't having the desired effect.

She doesn't want him.

She's not into it.

Oh, wow.

Finally, his love song is answered.

It's amazing.

These insects that sing silently

are just as magical in their way.

We're only just

beginning to understand

the secret sounds

of nature's smallest creatures.

The story of sound continues

..as baby animals attempt to survive

in a perilous world

with the help of their voices.