A bat, like many animals,
lives in a different sound world to ours.
(Siren blaring)
Through its ears,
all but the highest sounds simply disappear.
(Hissing)
( # Congregation sing hymn )
A bat may not hear our low-frequency sound
but it can eavesdrop on ultrasonic frequencies
far above our hearing range.
To listen to this ultrasound,
we must slow our world down.
(Music slows )
(Hissing)
In the bat´s sound world,
low frequencies disappear.
But the high frequencies of ultrasound
are revealed.
(Loud hissing)
To the bat, some of our quietest actions
create a cacophony of high frequencies.
(Clattering)
(Trumpets )
Even familiar animals
can enter a sound world unfamiliar to us.
(Growling)
The trumpeting of elephants
is the highest sound they make.
This is the lowest.
(Groaning)
These calls are normally too low for us to hear.
0nly by raising the pitch
can we hear their communication rumbles.
(Rumbling)
A lone male calls to distant females.
This sound is below our hearing.
Known as infrasound,
it can reach herds many kilometres away.
They respond with a call to leave.
Their calls draw them together.
Those left behind rumble in alarm.
As they meet, they greet each other
with a chorus of infrasound.
The sounds elephants hear
are only just below the human range.
But some birds, like guinea fowl, can hear
infrasound at even lower frequencies.
(Thunder rumbling)
Their breeding anticipates the lush, rainy season
and may be prompted
by the infrasonic murmur of distant storms.
(Clicking)
The call of the capercaillie
also contains infrasound.
Both females and other rival males
react to these territorial calls.
Low frequencies
travel further than high frequencies,
so the infrasound component
can reach distant rivals.
The males fight
for possession of the display ground.
In the air,
all sound carries over greater distances,
giving birds even more information
than is available on the ground.
Those birds that can hear infrasound
can tune into frequencies that carry further still.
Winds on mountain ranges generate infrasound
which could carry for tens of kilometres.
Birds may use these auditory guides to navigate
long before the source of the sound
becomes visible.
There are many natural sources of infrasound
which may give the bird information
from different compass points.
From the changing pattern of sound,
a navigating bird may keep track of its route.
The waterfall
produces a whole range of frequencies.
As it recedes, the higher frequencies disappear.
The infrasound that remains
will carry for many kilometres.
The infrasound of deserts, cities and oceans
could all be used as a distant guide.
Even the sounds of storms
could warn of impending danger.
Infrasound may carry through the air
for many kilometres.
But beneath the ocean´s surface,
there are creatures
that create sounds that travel even further.
The blue whale
is the largest animal ever to have lived.
It creates sounds
that only Just enter our hearing range.
(Humming)
In water,
sound travels four times more efficiently.
So these low frequencies
carry even further than they would in air.
They´re helped
by a unique feature of the deep ocean.
Sound channels, created through
variations of temperature and pressure,
allow the sound that enters them
to pass without being scattered or absorbed.
The calls travel for hundreds of kilometres
and reach many other whales.
The sound may help
to keep the scattered herds together.
At one time, the calls
would have travelled across whole oceans
but noise pollution from modern shipping
now limits their range.
(High-pitched calling)
The sounds of the humpback
not only change from year to year,
they even show regional dialects.
The social groups
are led by a female and her calf.
(Growling)
Her escorts compete vociferously
for a position by her side.
The humpback creates the longest and most
complex range of sounds of any animal.
But they´re not the only creatures
to sing in the oceans.
These are the songs of fish.
(Croaking)
Fish like the barracuda are better adapted
to hearing these sounds than we are.
They can only hear low frequencies.
Even so,
they have a complex vocabulary of calls.
The sergeant major fish
protects its purple cluster of eggs
with an aggressive popping sound.
(Popping)
When threatened by the approach of a predator,
the squirrel fish react with sounds of alarm.
(Dull clicking)
There are even fish with courtship calls.
The toadfish.
The cowfish.
0thers have a whole repertoire of sounds.
A male bicolor damselfish attempts
to entice a female to his nest in the rocks.
As she loses interest,
so his calls and movements change.
(Aggressive clicking)
To a predator, the most significant sounds are
those made by the movements of shoaling fish.
From one of the noisiest places on earth...
to one of the quietest.
The desert at night.
The fennec has the largest ears of any fox.
The veins inside
bring the blood supply to the surface
and help cool the fox during the day.
Because of the heat,
most desert animals are active only at night.
The fox´s huge ears
are now used to gather sound.
(Rustling)
They respond to the slightest rustle.
These large ears are not the only aid to hearing.
The internal ear has an enlarged chamber
to help amplify sound.
The North American kangaroo rat
has similar specialised hearing.
It too has an enlarged chamber
to its internal ear
to enhance its sensitivity.
The smallness of the external ear
is no real handicap.
It is acutely aware of the sounds of predators.
Although alerted by the rustle of scales,
the kangaroo rat is in no hurry to escape
for its hearing can outwit the rattlesnake.
Even in total darkness, it can hear
and instantaneously react
to the sound of the final strike.
(High-pitched calling)
The hearing of frogs
is tuned to the call of the males.
That of the coqui is unique.
(Whistling)
Each sex hears differently.
To a female, the world must sound like this.
(Muffled high-pitched whistling)
She hears only part of the male´s call.
Males hear the other part.
(Low-pitched whistling)
Males hear only the territorial sound,
females the sound of courtship.
The sound of courtship
has also shaped the hearing of these insects.
But before they hear anything at all, the pupae
must break through the surface and transform.
These feathery antennae
are the ears of the male mosquito.
The male lives only to mate.
So its antennae
are tuned to the sound of the female.
0nce dry and mature, he begins his search.
(Whirring)
Through his antennae,
the world may sound like this.
(Muffled voices )
The buzz from the female´s wings coincides
exactly with the male´s restricted hearing.
The female attracts many males,
all enticed by the sound of her wings.
Because of their smaller size,
the male´s wings beat twice as fast.
Their higher pitch
avoids confusion in this aerial courtship.
The chira spider listens for wing beats too.
But it also reacts to other sounds
at the same frequency.
(Voices )
Instead of using a web,
it mimics the smell of the female moth
to lure the male towards it.
As the male hovers
in search of the phantom female,
the spider tracks the sound of every movement.
In darkness,
many animals use sound to find their prey.
The barn owl´s facial ruffs of tightly-packed
feathers funnel sound into its ears.
0ne ear is lower than the other
and angled differently.
This helps the owl
to pinpoint the slightest noise.
(Rustling)
It can locate the position of a sound
better than any other creature.
Its brain creates a sound map
of the area in front of it.
The owl uses this to memorise
the position of the last sound it heard.
Sound is the only guide
as it orientates its claws.
(Mouse squeaks )
(Cat miaows )
A cat can detect ultrasound
above our hearing range.
(Miaows )
At these frequencies, some of the quietest
animals appear surprisingly noisy.
(Snapping)
The peacock butterfly uses ultrasonic clicks
to startle predators.
The bush cricket uses ultrasound for courtship.
The female responds to the call of the male.
Her return call is almost instantaneous.
They hear this high-speed conversation
through ears on their legs.
As the male moves towards her,
the calls continue.
There is just a 30th of a second
between the call and the reply.
This makes the bush cricket
the fastest communicator of any animal.
Beehives are sometimes filled with the sounds
of another ultrasonic courtship.
(Fast tapping)
These wax moths breed in abandoned hives.
As they attempt to attract the female,
the wing-fanning males
create an ultrasonic cacophony
at the limits of even the cat´s hearing.
(Miaows )
As a rule, the smaller the animal,
the higher it can hear.
The high-pitched squeak of a rat
is actually the lowest sound it makes.
(Squeaking)
Most of its calls are ultrasonic
to match its hearing range.
When touched by an adult, young rats use
ultrasonic calls to prevent accidental attack.
At this age, the young easily lose heat
if they stray from the nest.
So they use ultrasonic cries
to attract the mother.
The rat uses sound in another remarkable way,
one that relies on echoes.
(Men´s voices )
Using echoes, even humans can gain
an impression of the size of a chamber.
In a similar way, a rat uses echoes
to help judge distance.
Before it jumps,
it makes this audible sniffing sound.
(Sniffing and squeaking)
From the returning echoes,
it gains an impression of the size of the gap.
The rat´s echo location is crude,
but a few animals
have found ways of improving the technique.
The caves of Kenya are home to some of
the largest roosts of rousettus fruit bats.
Although their eyesight is good,
in the blackness of the cave,
they rely on echoes to find their way around.
As they fly into darkness,
they begin to click their tongues,
a sound we can hear.
From the echoes,
they gain a crude impression of the cave walls.
As it approaches a wall, the bat clicks
at a faster rate to gain more information.
Although relying totally on sound, the bat must
process this information to form an image.
The sound pitch is coarse, as sound reflections
pick up less detail than light.
To improve the picture, it would need
to use higher ultrasonic frequencies.
As it leaves the cave, vision takes over again.
To find a system that rivals vision, we need to
look at the fruit bat´s insect-eating relatives.
The European pipistrelle
improves its sound picture
by using the higher frequencies of ultrasound.
For us to hear these calls,
we need to slow them down.
Each ultrasonic pulse
sweeps the frequency range.
(Squeaking)
The complex call creates a more detailed picture
than the one from the simple
low-frequency click of the fruit bat.
As they near their prey,
they too speed up the pulse rate.
(Waves crashing)
(Clicking)
The dolphin has developed
the ultimate sound-imaging system.
Instead of using frequency chirps like bats,
the dolphin and other toothed whales
produce a stream of intense, sharp clicks.
They use them for both navigation and hunting.
The sounds are focused into a beam by the
dome-like forehead known as the melon.
The lower Jaw acts as a directional ear,
picking up the returning echoes.
Focused into a beam, up to a thousand pulses
per second are directed at the fish.
As the lower Jaw picks up the echoes,
it gathers information
about size, speed and even body structure.
Ultrasound penetrates like an X-ray,
revealing even the swim bladder.
The dolphin
may have even more startling powers.
Like this animal.
The pistol shrimp´s claw
is a unique sound weapon.
It uses these clicks to stun.
The sounds are produced
in the hinge of its claw as it snaps shut
and can be heard over a kilometre away.
The effects at close range can be devastating.
The repeated blasts
literally knock its prey senseless.
It is believed
that dolphins too may possess this power.
As they near a fish,
they can increase the sound bursts.
The effect is stunning.
0n our next Journey,
Super Sense explores the world of smell.
