Secret World of Sound with David Attenborough (2024) s01e02 Episode Script

1
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.