These animals can hear everything - Jakob Christensen-Dalsgaard
The world is always abuzz with sounds,
many of which human ears
simply can't hear.
However, other species
have extraordinary adaptations
that grant them access
to realms of sonic extremes.
And some of them don’t even have ears—
at least, not like we typically imagine.
To understand how the animal kingdom’s
best listeners do it,
we need to know the rules of their game.
When an object in a medium
like air or water moves,
it sends out physical waves.
The basics of hearing involve structures
that vibrate in response to these waves
and excite sensory cells,
generating signals that nerves transmit
to the brain,
where they’re processed.
But despite the assemblage
of sound-absorbing and -amplifying
structures in our ears,
many noises are too quiet
for us to detect.
Owls, however, have some workarounds.
Our external ears funnel sounds inward—
but many owls use their whole faces
to do this.
Their ears,
hidden beneath a flap of feathers,
have eardrums proportionally much larger
and more sensitive than humans’.
And because many owls ears
are positioned asymmetrically,
sound waves reach them at different times.
This slight delay helps their brains
determine the direction
of the sound’s source.
And great grey owl wings have
especially thick velvety coatings
and long feather combs and fringes,
which are thought to help reduce
their flight sounds.
So, while hovering,
they can go undetected
and concentrate on the subtle sounds
of their prey.
All these adaptations enable
a great grey owl to hear a vole
tunneling under 18 inches of snow—
and make a fatal strike.
Other animals are almost all ears,
like the aptly named long-eared jerboa,
which is the animal kingdom’s largest ears
in proportion to body length.
These sizable sound-collectors help
the jerboas sense low frequency noises—
and keep cool by radiating heat.
Fennec foxes use
their large, swiveling ears
to rapidly home in on activity
beneath Sahara sands,
while bat-eared foxes can
pick up savanna sounds
as slight as termites crawling
and munching on grasses.
Ogre-faced spiders, meanwhile,
might not have ears in the traditional
vertebrate sense,
but their legs are covered by receptors
sensitive to sound waves
as soft as those generated
by mosquito flight.
This allows them to catch airborne prey—
even after being blindfolded
by scientists.
Lots of different features also help
animal ears hit especially high notes,
like the extra hard, stiff middle ear
bones of toothed whales;
like dolphins and sperm whales,
which efficiently propagate
high-frequency vibrations.
Indeed, some toothed whales and bats
emit sound pulses around 200,000 hertz
and listen for the reflections.
These high-frequency wavelengths—
more than 10 times higher
than what we can hear—
are small enough to generate
strong reflections from objects
as tiny as the insects
many bats are after,
which would be missed altogether
by lower ones.
But many insects are also
in on the conversation—
and vigilant to ultrasonic onslaughts.
The greater wax moth can register
the highest frequencies
of any animal recorded—
up to 300,000 hertz,
thanks to thin, vibration-sensitive,
eardrum-like membranes on their abdomens.
In fact, hearing organs have
evolved independently
more than 20 times among insects.
Katydids sense ultrasonic sounds
with their front legs;
certain hawkmoths can hear
with their mouthparts;
a parasitic fly registers cricket chirps
from organs behind its head;
and the praying mantis has just one
hearing organ,
which sits smack in the midline
of its thorax.
But how low can animals go?
Well, baleen whales emit sounds
around 14 hertz,
the deepest among mammals.
These vibrations can travel
thousands of kilometers.
And they get picked up by other
baleen whales—
possibly via their skulls,
which conduct the vibrations
along to their ear bones.
Snakes pick up ground vibrations
by way of their jawbones,
which connect directly
to their middle ear bones.
And Namib Desert golden moles regularly
stick their heads into the sand,
which likely helps them use their large,
club-like middle ear bones
to sense low frequency activity
in mounds more than 20 meters away.
So, odds are: if a tree falls in a forest,
someone’s bound to hear it.
