(ANIMALS HOOT AND CHATTER)
The natural world is filled with sound.
(THUNDERCLAP)
But so far, we've been hearing only part of it.
(CHITTERS)
(GROWLS)
(CHIRPS) (BUZZES)
New audio technology now captures sounds that we can't even hear.
(DEEP, RESONANT RUMBLING)
For some animals, sound is the key to finding a mate...
(CHIRPS)
..to impress others...
(CHIRPING, WHISTLING)
(RUMBLING, POPPING)
..and to warn off the competition.
(BELLOWS)
(ANIMALS CHIRP AND CALL)
(TWEETS)
(CHIRPS, CHITTERS)
(SINGS)
(BIRDS CHIRP AND WHISTLE)
(SINGS, CHIRPS)
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.
(BIRDS SING AND CHIRP)
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.
(WATER RUSHING, SOFT CHIRPING)
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.
(ARTICULATED CHIRPS)
Most of the dipper's notes are higher-pitched
than the noise of the water.
(MELODIC CHIRPING)
This allows others to hear his song more easily.
He has attracted the attention of a female.
(ELABORATE CHIRPING)
Only males in peak condition can sing complex tunes like this.
(SINGING)
His song has impressed,
and his new mate will stay with him for the rest of the year
and help him defend this territory.
(COMPLEX CHIRPING)
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.
(SINGS)
Together, they present a united front.
(SINGING)
For any intruders, the message is loud and clear.
(ELABORATE CHIRPING AND SINGING)
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.
(CHIRPING)
These youngsters have had the best possible start in life...
..thanks to their parents and their song.
(SINGS)
When it comes to finding a mate,
power, not melody, is sometimes needed.
(HIGH-PITCHED CALLS)
(RESONANT CALLS AND GRUNTS)
Autumn in the Rocky Mountains of Canada.
(SNORTS)
(HIGH-PITCHED CALL)
This bugling call of the elk marks the change of season...
and the beginning of the annual rut.
(DEEP VOCALISATIONS)
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.
(BELLOWS)
At the same time, he makes a guttural groan...
(RESONANT BELLOW)
..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.
(BELLOWS, CALLS)
His goal is to gather as many females as possible...
to ensure that his genes are the ones that are passed on.
(BLEATING)
(HIGH-PITCHED CALL)
(DEEP, RESONANT VOCALISATIONS)
Now he switches to a different call...
(VOCALISATION CONTINUES)
..a low 'glunking' sound to encourage the females to join him.
A successful bull can attract up to 20 females in one season.
(DEEP VOCALISATIONS)
Chemical cues, detected with his tongue,
tell him which cows are fertile.
But retaining so many females is easier said than done.
(HIGH-PITCHED CALL)
A rival enters the arena.
(BELLOWING)
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.
(HIGH-PITCHED CALL)
For the moment, at least,
his legacy is secure.
(RUMBLING)
On the vast grasslands of Alberta,
it takes teamwork to get noticed.
(COOING)
(RESONANT RATTLING)
Every spring,
male sharp-tailed grouse gather on traditional breeding grounds...
(RATTLING)
..practising for their most important performance of the year.
(CLUCKING, RATTLING)
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.
(CLUCKING, RATTLING)
And it's all to attract the attention of the females.
The more males, the louder and more impressive their performance.
(COOING, RATTLING)
But sometimes, tensions boil over.
(CLUCKING)
They need to stop squabbling and work together.
(RATTLING)
Their combined song and dance has attracted a female.
(CLUCKING)
Time for the synchronised finale.
They all freeze.
She takes the opportunity to assess each male.
(RATTLING RESUMES)
Now she's looking for the fastest tail rattle.
And a sound like the popping of a cork...
(POPPING)
..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.
(CLUCKS)
She's seen enough.
And she's off.
(RATTLING)
Today didn't go as planned.
(CLUCKS)
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.
(HIGH-PITCHED SHRIEKS)
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.
(THUNDER RUMBLES)
(WIND HOWLS)
(CRACKLES)
(THUNDERCLAP)
Within hours, the rains flood the ground...
and temporary pools appear.
The thunder sends shockwaves through the ground...
(THUNDERCLAP)
..which trigger an annual uprising.
Breaking free from their underground vaults,
desert frogs and toads emerge to breed.
(CROAKS)
(CACOPHONOUS CROAKING)
They will have just one or two nights to find a mate.
And there are hundreds of frogs in this one pool.
(CROAKING CONTINUES)
Not only that,
at least five different species are all trying to make themselves heard.
(CROAKS)
How is a female to find a male of her own kind?
(CROAKING)
The answer, it seems, lies in their voice.
Each species has its own distinctive call.
(CROAKING, CHIRPING)
(DEEP, RATTLING CROAK)
(GROANS)
And now we can see just how the females do it.
A specialised acoustic camera shows sounds
of different frequencies in different colours...
(GROANING, CROAKING, CHIRPING)
..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.
(CROAKING)
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.
(CROAKING, CHIRPING)
She tunes into the calls of her own kind of male.
(CROAKS RHYTHMICALLY)
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.
(RUMBLING)
Frogs aren't the only ones
to use their voice under the cover of darkness.
(RESONANT HUMMING)
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.
(DRONING HUM)
By vibrating muscles attached to his swim bladder,
he produces a low-frequency hum
that travels well through water.
(HUMMING CONTINUES)
And he's not alone.
(CHORUS OF HUMMING)
He's joined by dozens of others.
The sound reaches a staggering 110dB -
as loud as a lion's roar...
(HUMMING CONTINUES)
..giving rise to the mysterious drone
that once puzzled the people who lived on these shores.
(DRONING HUM)
This sound is loud enough to be heard by the females.
Guided by the hum, a female arrives, swollen with eggs.
(DRONING HUM)
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 crab...looking for a snack.
(GROWLS)
(GRUNTS)
He sends a warning growl...
(GROWLS)
(GRUNTING)
..and a grunt.
(GRUNTING)
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.
(HOOTING, CHITTERING)
The dense vegetation acts as a sound barrier...
..and despite the many voices,
most messages don't travel far.
(DEEP CHIRPING)
(HOOTS)
(CHIRPS)
(CHIRPS SQUEAKILY)
(CHITTERS)
(HIGH-PITCHED CROAKS)
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.
(HIGH-PITCHED HOOTING)
Unobstructed by trees,
his call carries for over a mile across the forest.
(HIGH-PITCHED HOOTING CONTINUES)
And he's not alone.
His partner and baby are close by.
The female now joins in with her own song.
(HIGH-PITCHED HOOTING)
Together, their duet sends a message to other gibbons.
(HIGH-PITCHED HOOTING)
It's a declaration that this patch is taken,
and the fruiting trees within it.
(HIGH-PITCHED HOOTING)
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.
(DEEP, RESONANT RUMBLING)
He shakes his abdomen a hundred times a second
to produce a low sound that vibrates through the stem.
(DEEP, RESONANT RUMBLING)
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.
(DEEP, RESONANT RUMBLING)
But she could be anywhere on the plant.
To find her, he needs to keep the conversation flowing.
(DEEP, RESONANT RUMBLING)
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.
(DEEP, RESONANT RUMBLING)
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.
(RUMBLING)
(CHIRPING)
Most animal calls are encoded in their DNA.
But some can enhance their repertoire in other ways.
(CHIRPS AND SINGS)
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...
(CHIRPS)
(MIMICS MECHANICAL SOUND)
(CHIRPS)
..the superb lyrebird.
And this mound of earth is his stage.
(MIMICS MECHANICAL SOUND)
(CHIRPS)
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...
(MIMICS ANIMAL HOOTING)
(MIMICS HOOTING AND HOLLERING)
(CONTINUES HOOTING)
..and mimics them perfectly.
(HIGH-PITCHED SINGING)
(IMITATES BIRD SONG)
(CHIRPS)
(IMITATES CHIRPING)
He can learn the songs of over 20 different birds.
(SINGS)
And he's not only a mimic -
by stringing the songs together in his own way,
he's also a composer.
(WHISTLES, CHIRPS)
(MIMICS MECHANICAL SOUND)
No two lyrebirds sing exactly the same tune.
(CHIRPS, HOOTS)
With age, his songs become more intricate
and give him greater success with the females.
(HOOTS, CHIRPS, SINGS)
But the lyrebird's world is changing,
and urban settlements have replaced much of its natural home.
(HORNS HONK)
And with it have gone many of the songsters
that he relied on for his tunes.
Luckily, this bird is a virtuoso.
(ALARM WAILS)
A car alarm...
(IMITATES ALARM)
(IMITATES CAMERA SHUTTER CLICKING)
..a camera shutter...
(BABY CRIES)
..and even a crying human baby.
(IMITATES BABY CRYING)
(WAILS)
This sound...is 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.
(CHIRPS)
If she is impressed, she'll choose him to father
the next generation of master songsters and mimics.
(HOOTS, CHIRPS)
(HONKING, CHIRPING)
(ANIMALS CALL AND HOOT)
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.
(TREEHOPPER CHIRPING AND TAPPING)
This little treehopper sounds like a tap-dancing monkey.
(RHYTHMIC HOOTING)
Another one sounded like an owl laughing at its own joke.
(RHYTHMIC HOOTING)
(CLUCKING)
One male treehopper sounded like a clucking hen.
(CLUCKS)
(TREEHOPPER RATTLING)
Another one sounded like a woodpecker...
followed by a tiny car honking.
(HONKS AND RATTLES)
Oh, my gosh. I was just lost at that moment.
There was no going back because I heard these wonderful...sounds
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.
(DEEP, RESONANT RUMBLING)
(GASPS)Here he goes. Yeah, that was it.That was it?
That was him. Yeah.
(DEEP, RESONANT RUMBLING) Wow!Oh, my God!
But his vibrations aren't having the desired effect.
She doesn't want him. (LAUGHS)
She's not into it.
(DEEP, RESONANT RUMBLING)
(FEMALE TREEHOPPER RUMBLES) Oh, wow.
Finally, his love song is answered.
(LAUGHS) 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...
(CHIRPING)
..as baby animals attempt to survive
in a perilous world...
with the help of their voices. (CHIRPS)(YELPS)
(HOWLING)
(WHISTLING, CHIRPING)
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