Secret World of Sound with David Attenborough (2024) s01e01 Episode Script

1
The natural world
is filled with sound.
But so far,
we've been hearing only part of it.
The most advanced audio technology
can now record sounds
that we can't even hear.
For some animals,
sound is the key to survival.
They use sound to hunt
..and escape.
Sound can make the difference
between life and death.
It's time to open your ears
to life
as you've never heard it before.
Dawn on the African savanna.
It's the best time of the day
for lions to broadcast their message.
As the sun rises,
cold air is trapped near the ground.
Because it's denser than warm air,
it allows sound to travel further
before dissipating.
It's a declaration to other prides
of his ownership
of these hunting grounds
..and the key to his
and his pride's survival.
It's one of the greatest
acoustic displays of power in nature.
He can be heard
up to five miles away.
But even this isn't far enough
to reach the boundaries
of their territory.
It spans over 150 square miles.
To defend an area
as immense as this,
the pride must roam and roar.
But some members are too small
to get very far.
This pride is protected
by three brothers.
Together, they head off on patrol.
A lion's roar sends a clear message
to other prides.
But sound can also be used
in more subtle ways.
This garden is filled with the sound
of the buzzing of bees.
It's a sign that the plants have been
successful in attracting pollinators
with their brightly-coloured flowers
and seductive smells.
The buzzing sound
we associate with bees
is a by-product created by
the beating wings as they fly.
But some bees
take advantage of their buzz,
and use it,
in a surprisingly sophisticated way,
to get to a supply of food
that others can't reach.
One such bee lives underground.
These are buff-tailed bumblebees.
For the colony to survive,
each worker must collect
as much pollen as she can
with which to feed their young.
Searching for it
is a constant preoccupation.
It's spring in England
..and she is not the only one
in search of food.
Competition for pollen and nectar
is high.
And poppies are putting on a show.
Packed full of pollen,
they flaunt it at the top
of long filaments called anthers.
These flowers are a free-for-all
..and everyone
is seeking a share of the bounty.
But she doesn't need to compete
with other species
if she can find
a particular kind of flower.
She's found
what she's been looking for
..a type of nightshade.
Its flowers are less striking
and, unlike poppies,
its pollen is locked up
inside long yellow anthers.
The only way for it to escape
is through tiny holes.
The bumblebee holds the key
that unlocks this treasury of pollen.
Sound.
Locking in her wings,
she uses her flight muscles
to vibrate her whole body,
buzzing up to 370 times a second.
This sonic assault
blasts the pollen loose.
She then grooms the pollen
down into sticky sacs on her legs
and flies off to the next flower.
Very few species
can buzz-pollinate in this way,
so bumblebees have nearly exclusive
access to the nightshades' pollen.
The bee's pollination buzz
is higher pitched
than that made during flight.
It's the same frequency
as the musical note D.
She's like a living tuning fork.
Some buzz pollinators
can vary their pitch,
fine-tuning it
to suit different flowers.
So pollen is released
in the most efficient way.
Fully loaded,
she returns to the hive.
She has successfully used sound
to help secure the pollen
her colony needs.
We tend to take bees for granted
but it's not just plants
that depend on them, we do too.
Many of our crops rely on pollinators
like bees and other insects.
Worryingly, bee populations,
together with those
of many other insect pollinators,
are in serious decline
around the world.
And with their numbers plummeting,
both the natural world and our own
food supplies are in danger.
Bees need our help
and without them
and the sound of their buzz,
the future for us all
would look bleak.
Sound provides the key
to this partnership
between bumble bees and plants.
But not all relationships in nature
are as harmonious.
The Bahama Islands in the Caribbean.
The sand flats here are the home
of garden eels and razorfish.
But there is trouble in paradise.
The sound of approaching danger.
It's a cue to hide.
A mixed groups
of spotted and bottlenose dolphins.
Their whistles and squeaks are part
of their continuous conversations
..with a range of frequencies
seven times greater than ours.
To hunt for food, they must split up.
Each dolphin
needs 15 kilograms of fish a day.
But, thanks to their rowdy arrival,
there isn't a morsel in sight.
The hunt is on.
The bottlenose dolphins
now switch from whistles
to bursts of fast clicks,
up to 200 per second.
These high-frequency clicks
are sent out like a sonar beam
through an organ in the forehead
called a melon,
with which
they can scan the ocean floor.
When the beam of sound
hits a fish hiding beneath the sand,
it's reflected back,
revealing its location.
Using echolocation,
the dolphins are able
to create a visual map
of what is hidden
under the sea floor.
Some of these clicks
are ten times higher
than the sounds our ears can detect.
High-frequency sounds
are most effective at close range,
enabling the dolphins to pinpoint
their prey with great precision.
But there is more to these
pirouettes than meets the eye.
Scientists have recently discovered
that bottlenose dolphins
favour their
right side when scanning the seabed.
The right side of the head
usually produces the sonar clicks.
And the right side is also better
at detecting the returning echo.
The only evidence that there has been
a sonar search here
are small craters in the sand.
Dolphins use sound with great effect
to find their food.
But in other places,
a quieter approach
is the key to a successful hunt.
In the forests of Manitoba
in Canada,
the great grey owl
is a master of silence.
Specially-adapted flight feathers
allow him to approach silently.
His prey is hidden
under a blanket of snow.
Voles.
Finding them in this vast,
snow-covered landscape
seems an impossible task.
To combat the extreme cold,
he must catch seven voles a day.
His ears will be
his most effective weapon.
Voles need to feed continuously
or they will freeze to death.
They constantly dig tunnels
to find new food supplies
..unaware of the danger above.
Hidden under a face
covered by feathers,
the owl's ears are positioned
at slightly different levels
on either side of his head.
Sound will hit one ear
before the other,
allowing him to pinpoint his prey
with great accuracy.
His acoustic arsenal
doesn't stop there.
The large facial ruff,
formed from feathers that are
particularly stiff and dense,
help to amplify sound
and funnel it towards the ears.
Through half a metre of snow,
the sound of scampering feet
is inaudible to us.
But it's loud enough for him.
With the help of a specialist camera
equipped
with 60 highly-sensitive microphones,
we can reveal
what the owl is hearing.
The camera visualises
where the vole is beneath the snow.
And he's off.
This time he's missed.
Despite his acute hearing,
hunting in snow is a challenge.
The snow not only muffles sound,
it bends it too.
While it appears
as if the vole is here,
it's actually over there.
The only way to defeat
this acoustic illusion,
is for the owl
to get directly above the vole,
where sound is no longer distorted
by the snow.
As he flies,
he tracks the sound as it changes.
The closer he gets,
the less the sound is bent.
Directly above the vole,
he can pinpoint his target.
The great grey owl's hearing
is its key to securing a meal.
For others,
it's crucial to avoid being eaten.
In the Arizona desert,
it's the height of summer.
Daytime temperatures
are over 40 degrees Celsius.
So it's best to be active at night.
Filming under infra-red lights
with a specialist camera
..we can see everything.
But to a kangaroo rat,
it's nearly pitch black.
In the dark,
her most valuable ally is sound.
Her mission tonight is to collect
as many seeds as she can.
But food is scarce
..and competition fierce.
And, in the dark,
it's hard to spot danger.
Her ears are 90 times
more sensitive than ours
and hollow spaces in her skull
act like an echo chamber,
amplifying the faintest of sounds.
But she has
another problem tonight.
Wind.
She might not hear a predator
until it's too late.
This time, it's just a stick.
But, in the darkness,
she's right to be cautious.
Snakes can pick up
the sounds of scampering feet
through their lower jaw.
She's made it
to her favourite feeding spot.
But she's not alone for long.
She warns him to stay away
by drumming her foot on the ground.
He can decipher her size and strength
from her signal.
He drums back.
It's a battle of beats.
Stalemate.
There's only one
way to resolve this.
Dinner time at last.
She hears something.
Just out of striking range,
she drums again
..this time to alert the snake
it's been spotted.
But just to be sure
Message received.
While kangaroo rats
use the ground as a drum
to drive their enemies away
others are summoned
by seismic sounds.
Amboseli National Park in Kenya.
It hasn't rained here
in nearly a year
..and the dry season
has turned into a severe drought.
For elephants,
the situation is desperate.
With no food or water
for miles around,
the matriarch
must wait for a message
..a sound that will travel
through the ground.
If it arrives,
it will guide them from disaster.
The young calves
are especially vulnerable.
Their mother's milk will dry up
if rain doesn't arrive soon.
A hundred miles away,
a storm has broken
..and the elephants have heard.
Not with their ears
..but with their feet.
The sound of the storm
sends low-frequency vibrations
through the ground.
The herd picks up the vibrations
through a network of nerves
in the fatty pads of their feet.
By lifting one foot,
they can make better contact
on the ground with the other.
It's the message the matriarch
has been waiting for.
She gives a low "let's go" rumble.
It's echoed by her sisters.
The journey ahead is treacherous
..but the sound of the storm
will be their guide.
Finally,
after two days on the move
..they've made it.
Their ability to detect sound
a hundred miles away
has saved the herd.
Elephants aren't the only ones
who respond to the sound of rain.
But sometimes
sounds can be deceptive.
In Vancouver, in Canada,
it's also raining.
Underground the soil
is teeming with earthworms.
Some rise to the surface
in search of food or mates.
But if the ground isn't wet enough,
they risk drying out.
Sound helps them
pick the opportune moment.
As the rain hits the ground,
it creates vibrations
that travel down into the soil.
They are picked up by sensitive
nerve cells in the worm's skin.
As they rise,
the tumultuous pitter-patter
is music to their senses.
But it is also a sound
that can seal their fate.
Worms aren't the only ones
on the move.
Outside the city, a flock of gulls
are co-ordinating their
morning departure from the roost.
Thanks to the rain, they've got
a special meal on the menu today.
Worms!
But by the time they arrive,
the downpour is over
..and the worms
are already retreating.
Dining options look scarce
..but the gulls have a crafty trick.
For it to work,
they must find their rhythm.
Paddling creates vibrations that
likely mimics the sound of rain.
It's a dance of deception.
The worms rise once again.
They can't resist
the rhythmic rain dance.
Another shower
brings an acoustic climax.
The rainy season
will last all winter,
so worms are on the menu
until spring.
For these gulls,
the cunning use of sound
helps them win an easy meal.
But in other parts of the world,
the stakes are higher
for both predator and prey.
As night falls
on the African savanna,
the air is filled
with sounds of a formidable hunter.
On the other side of the territory,
the females of the pride
are preparing to hunt.
Over 30 strong,
they must make a kill every night.
Close by, a hyena den.
The adults must also head out
to find their next meal.
Hyenas will often steal
if the opportunity arises
..even from their deadliest foes.
But separated from the males,
this pride is vulnerable.
For a successful heist,
the hyenas rely on sound.
First,
the lionesses need to make a kill.
With a noisy family in tow,
that can be tricky.
Wildebeest have gathered
together for safety.
In the darkness,
they have to rely on their hearing.
The lioness
makes a stealthy approach
..but there is a problem
A porcupine is a playful distraction
for the youngsters.
The sound of shaking quills
is a warning
..and the wildebeest
have heard the commotion.
They have blown it for her.
They will take the rattle of shaking
quills more seriously next time.
The pride
have detected another opportunity.
A warthog burrow.
The sound of their feast
carries far in the cool night air
..and the hyenas have heard.
But there are too many lions here
to steal this meal alone.
She will need the full force
of her clan.
She sends a message
to rally her troops.
Directed at the ground, her message
resonates further and faster
than it would through air.
Even with numbers now on their side,
sound is critical
if they're to steal this meal.
Calling unites the clan.
They must approach
as a tight-knit group,
making as much noise as they can.
The noise of the battle
has alerted more lions.
It's game over for the hyenas.
The brothers have returned.
After a successful night,
the pride is well fed.
Some will spend the day dozing.
But for others,
it's time to reaffirm
the prides' ownership
of their territory.
We are only
just beginning to understand
the many ways that animals use sound.
For us,
the sound of the natural world
is a source of peace
and tranquillity.
For other animals,
it's a tool they have to master
in order to hunt and survive.
- Yep.
- It is so cold out here.
I think just over here
to the left looks pretty good.
OK.
We have picture.
Our film crew have come
to Manitoba in Canada
in search of the great grey owl.
Yeh, that looks like
a promising spot.OK.
I think there were
some owls here last week.
But, like many of our shoots,
we rely on the work of others
who've come before us.
For years, scientists have wondered
exactly how the owl penetrates the
layers of snow that conceal its prey.
Biologists Chris Clark and Jim Duncan
are on a mission.
This is excellent.
There's a plunge hole right here
where the great grey hit the snow.
They are armed with a special tool.
I'll grab the battery.
OK.
An acoustic camera.
This version
has 40 sensitive microphones
that pinpoint sound, while a tiny
camera films its exact location.
It should allow them to see exactly
what the owl is hearing.
This camera is wonderful
because it visualises
where the sound is coming from.
So I'm able to look and see,
how does the environment
affect the sound.
Snow is a formidable barrier.
For the vole,
it's a cloak of invisibility.
To the owl, it's an obstacle that
must be overcome by hearing alone.
52cm?
Yeah.
The researchers
bury a speaker under the snow
which will play the sound
of a foraging vole.
They will bury it
at different depths
and use the acoustic camera to see
how the snow affects the sound.
The speaker is now visible
in the camera view.
This black thing right here,
that's the speaker.
And the acoustic camera,
that blob of colour,
is localising the sound
coming from the speaker.
But the playback
from the snow-covered speaker
reveals a surprise
- the snow dramatically alters
the location of the sound.
That metre stick
is above the speaker
and there's a blob of colour
where the acoustic camera
perceives the sound
to be coming out of the snow.
It's amazing. The snow is bending
the path that the sound is taking.
As a result, if an owl were to try
to localise the sound of the vole,
from where it hears the sound, it
would miss and hit the wrong spot.
But Chris realises there is a way
for the owl to overcome this problem.
As the owl is coming in,
it's listening to pinpoint
the location of the vole.
Because of the snow,
it sounds like the vole is here
..when it's actually there.
But as the owl gets closer,
it starts to overcome the effect
that snow has on the sound.
For the first time Chris realises
why, at this point in its attack,
the great grey owl hovers.
The acoustic camera reveals that
it's now in the perfect position.
The sweet spot for the owl
is when it's right above the prey.
Directly above the vole,
the snow doesn't bend the sound
so the owl can pinpoint
exactly where the vole is.
Only then does the owl plunge.
It's completely amazing that
these owls can localise their prey
just by listening.
I love doing this kind of research
and, through that,
understand the natural world
and the amazing things
that species
like the great grey owl are doing.
For decades,
researchers had believed
that there was more to discover about
the great grey owl's acute hearing.
Now they've finally uncovered
the complex ways
it uses sound
to hunt its prey in snow.
Alrighty.
As the story of sound continues
..we reveal how animals use sound
to fight off competition
..and use songs
in their quest to win a mate.