When it comes to getting around, pretty much all animals rely on sight to figure out what’s
around them, where their next meal is, and what obstacles might be in their path.
Light from luminous sources like the sun bounces off the objects around us, and some of it
enters our eyes, allowing us to see.
But what happens when there’s not enough light to see by?
A few animals have evolved a versatile technique that uses SOUND, rather than light, to build
a picture of their surroundings.
The technique is called echolocation, and it’s the source of success for animals in
the air, on the ground, and under water.
But how does it work?
Some of the most famous echolocators are bats.
The saying ‘blind as a bat’ is a bit of a misnomer, because bats have perfectly good
eyesight.
But their twenty-twenty vision doesn’t do them much good when it comes to hunting in
the dark.
Instead, they let out a series of very high pitched clicks or squeaks.
These are so high-pitched that they’re beyond the range of human hearing, which is known
as ultrasound.
Now, sound travels as a compression wave through the air, like this…
And, just like light, when the sound waves hit an object, in this case it’s my hand,
it bounces back
And it’s that bounce-back that we know as an echo, and bats and other echolocators are
specially tuned to the properties of the echoes to get a good idea of their surroundings.
Special muscles in the bat’s throat allow them to make ultrasound clicks up to one hundred
and ninety times every second.
And their ears are specialised with folds that makes them super-sensitive of the direction
of any sounds around them.
The speed that an echo returns to them tells them the distance to the nearest object.
If it comes back quickly, the object is closer, because the sound hasn’t had to travel as
far.
The intensity of the returning sound also gives an indication of the size of the object.
If it is small, some of the sound waves will go past either side, and the returning echo
will be just a whisper.
And, if the right ear receives the echo before the left ear, the bat can know that the object
is to the right of them, and vice versa.
Bats can even figure out the direction that an insect is moving from the change in pitch
of the returning echo.
If it’s moving towards them, the sound waves get squashed up and become higher in pitch.
If it’s moving away, the returning echo will be lower pitched.
This is known as the Doppler effect, which we experience when an ambulance sounding its
sirens speeds past us.
Putting all of this together means a bat can figure out the size, location, proximity,
and motion of their prey with pinpoint accuracy, processing the information from the echoes
automatically like we process the information from our eyes.
But, while bats may be the master of the dark skies, the waters belong to the odontoceti
– that’s toothed whales like dolphins, sperm whales and orcas.
This group of marine mammals have also harnessed the power of echolocation to navigate and
hunt in deep, dark, or murky waters.
Sound actually travels more than four times faster in water than in air, making underwater
echolocation a fast paced and deadly affair.
Dolphins let out ultrasonic clicks by pushing air through their nasal passage.
These last just a hundred microseconds, that’s a ten thousandth of a second, but can help
them locate objects as small as a can of tuna from a distance equivalent to the length of
two football pitches.
The sperm whale also owes its successes, as well as its massive head to echolocation.
The bulk of its head is filled with a special waxy substance called spermaceti.
The whale generates sounds at the front of the head, and the sound waves travel back
into the head to be reflected off a plate on their skull that’s shaped like a satellite
dish.
This focuses the sound waves into a narrow, powerful beam for more accurate pointing.
Some male sperm whales can produce audible clicks that are as loud as 230 decibels, much
louder than a jet plane, which help them to hunt at depths of more than a kilometre, far
beyond the reach of sunlight.
While these animals have evolved to be masters of their art, the wonders of seeing with sound
aren’t beyond the reach of humans either.
Daniel here is blind, but has taught himself to echolocate, and it’s been helping him
to get around independently for over forty years.
He clicks his tongue against the roof of his mouth, and listens for the echoes coming back,
then just like the animal echolocators, he’s able to form a picture in his mind of the
landscape around him.
--These trees are very high.
The trunk is actually fairly uniform, it’s almost like a pole—
And it really is a picture.
Studies have shown that when blind people echolocate, they’re activating the visual
parts of their brain, just as if they were seeing with their eyes.
But it’s not only blind people who can benefit from echolocation.
The principle has been turned into some pretty useful technology.
Sonar is used by ships to navigate, find fish shoals, and even search for shipwrecks.
It works just the same as animal echolocation, as sound waves are sent down into the water,
to be reflected off any objects there.
The time it takes for the echo to come back tells you how far away the fish, submarine,
or ocean floor is.
And on a smaller scale, ultrasound scans use exactly the same method to create images of
foetuses developing in the womb.
Echolocation really is amazing, so why not try it yourself.
The next time you find yourself in a dark room…
Ow!
That might take some practice!
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And, I’ll see you soon…or should I say hear you soon?!
No.