Secret World of Sound with David Attenborough

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 colored 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 glues the pollen down into sticky sacks 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 nightshade's 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 bumblebees 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 razor fish.

But there is trouble in paradise...

...the sound of approaching danger.

It's a cue to hide.

A mixed group 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 on 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 seafloor.

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 favor 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 meter 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 visualizes where the vole is beneath the snow.