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Dogs bark, birds chirp, and foxes…
well, the jury’s still out on that one.
Nature is full of interesting sounds,
but there are a whole host of them
that our human ears can’t pick up.
But now, thanks to advances in audio recording,
we’re hearing more of the natural world than ever before.
And some of those sounds are giving scientists
a whole new insight into what living
and nonliving things are capable of.
So here are five sounds of nature t
hat come from stuff we never thought could talk.
[intro song]
Generally, we think of plants as pretty silent.
Sure, we may chill out to the sounds
of swaying branches or rustling leaves,
but that’s all wind.
The plants themselves aren’t really making any sound.
At least that’s what we thought.
But in early 2023, scientists set up microphones
next to some potted plants and discovered
that they’re noisier than we gave them credit for.
Specifically, they make a kind of popping noise,
that sounds like this.
[ Popping Noise]
The popping that you’re hearing comes from tomato and tobacco plants,
and they’re not happy.
Specifically, they’ve either been cut
or left without water,
so the plants are stressed.
The researchers who recorded the sounds
think that the sounds come from a process called cavitation.
That’s where tiny bubbles trapped
inside the plants’ water transport system,
or xylem, burst
and release audible shock waves
through the stem and into the air.~
At their loudest, the pops can be around 60 decibels,
That’s loud enough to be heard three to five meters away
In their experiment,
researchers noticed that stressed out plants,
like those that were dry or had been pruned,
let off way more pops than plants
that were just sitting around in their pots
– up to 35 times more.
Plus the dried-out plant pings were slightly different
from the chopped-plant pings.
So much so that a computer program
could tell them apart 70% of the time.
You’re probably wondering
why we don’t hear plants popping all over the place.
Well, the pitch, or frequency,
of these plant cries peaks at between 49 and 58 kilohertz,
which is way outside our hearing range of up to 20 kilohertz.
That recording you heard
has been processed into something we can hear,
because, well we all wanna know what a plant sounds like!
But we’re probably not the ones meant to hear these sounds.
Researchers think that the plants’ pops
might be used to signal to other plants.
That’s because there’s evidence that plants are listening to sounds.
In some studies, plants increase their drought tolerance
after listening to particular, artificially-made sounds.
And in others, plants exposed to the sounds of
birds chirping or bees buzzing germinated more quickly.
So it's possible that the neighboring plants
hear other plants’ sounds of stress
and change how they grow as a result.
Now, we don’t know for sure if plants can hear,
but researchers have proposed
that mechanical receptors on the plant
or on the surface of plant cells
might be picking up the vibrations.
If plants are listening and talking,
whatever that means in the plant world,
there might be others listening in.
The frequencies of the sounds that plants make
also fall right in the listening sweet spot of insects
like moths or mammals like mice.
So whether plants mean to or not,
those creatures might be listening in, too.
The world of plant communication is pretty new
so there are still lots of unknowns,
like exactly why plants might want to talk to their neighbors
or who might be listening.
But scientists are certainly keeping an ear out for answers.
Animals have come up
with all sorts of sexy ways to find a mate.
Some make smelly perfumes,
others build elaborate structures,
and many have some kind of mating call.
It turns out that a particular species of wolf spider,
sometimes known as the drumming sword wolf spider,
is one of these song birds.
Or … song spiders?
These arachnids try to entice far-away females
by making a kind of purring noise, that sounds like this.
[ Spider brushing sound ]
Now, it might not sound all that weird for a spider to purr.
After all, insects like crickets and cicadas
make rasping-like noises too.
But here’s the rub.
Unlike some insects or other animals
that make sound,
spiders don’t have ears,
or any structures for hearing sound!
In fact, most spiders are totally silent.
But the cool thing about sound, though.
It doesn’t just have to be heard,
it can also be felt.
See, lots of spiders create vibrations
that can travel through substrate or along leaves,
but these signals can only travel so far
before they encounter a gap in whatever material
they’re traveling through,
and have to stop.
Unlike those kinds of vibrations,
airborne signals like sound
are less likely to hit one of these physical roadblocks,
which is what lets male wolf spiders cast their mating net
just that little bit farther.~
Their purring can be heard up to a meter away.
And since the ladies can’t hear,
they rely on feeling those vibrations
when they resonate with what’s under their feet.
The whole thing only works
if males are on a surface that jiggles,
like leaves, and a female is on another jiggly surface
so they can feel the sound.
Scientists have analyzed the wolf spider’s song
and found that it actually has two to three distinct parts.
The first verse, the kind of purring,
comes from males rubbing together a pair of extra appendages
called pedipalps to create anywhere
from six to more than 20 short, rapid pulses.~
Then they drop the beat
by making a kind of drumming sound
by striking their abdomen against the ground.
And some males might include a third verse, which sounds like quick, low frequency tics.
This last sound is a bit of mystery and arachnologists
haven’t yet figured out exactly where it’s coming from.
What’s neat is that it seems
only females respond to these acoustic signals,
so the songs might be a way for males to talk only to them.
Since it’s such an unusual example in the spider world,
researchers want to study the wolf spider
and use it as a kind of model
for understanding how sound signaling
might have evolved in different groups of animals.
If you were lying in bed and heard
this sound in the middle of the night,
[ Growling Sound ]
it’d probably be pretty unnerving!
But not so for grey snapper larvae.
These thumps they make in the dark
might just be their way of snuggling up close to one another.
Grey snapper spend about the first month of their lives
floating around in the ocean as tiny larvae,
about the size of a pencil-top eraser.
And scientists recently recorded the larvae making low frequency noises
to each other, both in the lab and out in the wild.
Most of the time, these little larvae were knocking sounds like this.
[ knocking sounds ]
But sometimes,
they’d make these grumbling, growl kind of sounds too.
[ Growling sound ]
Researchers think the fish might be making these sounds
by moving a muscle connected to their swim bladder.
Kind of like beating a drum, just, inside their bodies.
And while we knew the adult fishes make these sounds too,
these recordings were the first time researchers
have heard such young fish making noise.
Plus, the adults only make these noises when prompted with a jolt of electricity,
so these spontaneous noises are especially intriguing.
The larvae were beating their tiny drums mostly at night,
so researchers think that the sounds might be
to help them stay close to each other
when it’s dark and they can’t see each other.
‘Cause sticking together when you’re pint-sized
is a pretty good strategy if you want to make it in the big wide ocean.
Plus, generally,
sound is a really useful form of communication underwater,
since sound waves travel faster in water than in air
and can travel farther than other signals,
like light or smell..
Which is great when you’re just a tiny floating speck.
Speaking of drumming, there are even smaller organisms
that have percussive talents.
Drum roll please, for… bacteria.
In 2022, researchers discovered that E. coli can make a
rolling, rumbling sound
when they’re placed on an ultrathin sheet of graphene.
It sounds like this.
[ Rolling Sound ]
These double-layered graphene sheets were
circular and taut and pretty much acted the same way drums do to make sound –
by vibrating that taut surface –
except on a really, really tiny scale.
Instead of a drumstick, it’s their movement across the surface that makes the noise.
For some of the bacteria,
that came from flicking their tiny whip-like flagella
to scoot along,
but bacteria that didn’t have flagella
still made noise as they moved,
even without a built-in drumstick.
Now, obviously E. coli are microscopic,
so they don’t exactly make a big ruckus.
The way researchers were able to hear this drumming
is by measuring how much the drum moved using a laser
and then converting that vibrational signal into an audible one.
And how much and how loud those bacteria drummed
could tell scientists something about how active they are.
See, the more they move around,
the more noise they make,
so how loud the drumming is can tell scientists
how active the bacteria are.
Scientists used this fact to test
how susceptible the bacteria were to antibiotics.
When they exposed different groups of bacteria
to several types of antibiotics,
those bacteria that were resistant kept on drummin’,
while those that weren’t were killed off.
So scientists think they could use the drum method
to check for antibiotic resistance at the level of a single bacterium.
But some bacteria don’t just make noise by accident, they actually sing.
In an experiment from 1998, scientists recorded
what they call sonic emissions coming
from plates of Bacillus subtilis bacteria.
They then played tones that were the same frequency
as the sounds made by B. subtilis over a speaker
to a group of bacteria from another species,
Bacillus carboniphilus.
They saw that B. carboniphilus
was able to grow in inhospitable conditions
when played the sound, but not when it was silent.
The songs were spurring on their growth.
Several other experiments since then have shown
that bacteria grow better
when they’re played different sounds,
which makes them think that sound somehow regulates the growth between cells.
But they’re not really sure how that regulation happens,
why or even how bacteria sense the sound in the first place.
Like, they’re probably picking up each other’s songs
from feeling the vibrations caused by that jiggling,
but other than that,
these organisms’ musical talents are a bit of a mystery.
So between the percussion and vocals,
we’re about halfway to starting an all-bacterial band soon!
Unlike the other noise-makers on our list, this last one isn’t living.
But the noise it makes is so bizarre and mystifying
to researchers that we had to include it in this list.
These sand dunes….. burp.
Sand dunes, like these in Death Valley National Park in the US
or these in the Gobi desert in Asia,
regularly let off booms and burps,
that sound like this.
[ Low frequency boom ]
It happens when the dunes avalanche,
either naturally or when disturbed by others,
like, say, a bunch of researchers shuffling along the slope.
Scientists have recorded and classified both types of sound
and have found that booming is generally a
low, long note somewhere around 85 hertz.
The burps on the other hand are short
and at a different frequency,
although dunes can belch a whole range of notes.
But how the dunes make their booms and belches
has been a bit of a mystery that’s plagued researchers
dating all the way back to Charles Darwin.
As of 2015,
the mystery has been solved
thanks to a clever array of sound recording device
s and several years of making recordings.
Turns out,
it all comes down to the physics of how the sand slides down the slope.
See, steep and long dune slopes consist of different layers,
each moving at a different speed.~
As the sand in the surface layer tumbles,
it creates a P-wave,
where some sand squeezes close together
before spreading apart again.
As these waves travel down the slope,
they overlap or interfere,
which amplifies them.
The sand in the layer about a meter and a half
below the surface moves more slowly
than the rest,
and acts as a kind of guide for sound waves to travel along.
Not all sand dunes are capable of
making these booming noises.
Shorter, less steep dunes don’t boom
because there isn’t enough sand for these different layers to build up.
On the other hand, those quicker burps happen for a different reason.
Dunes belch because of a slow-moving, rolling wave of sand
called a Rayleigh wave, which moves along the surface.
Imagine an ocean wave moving towards the shore,
where each crest has swirling particles inside it.
In the burping sand dune,
those particles are tiny grains of sand.
And although they’re swirling in a kind of backwards ellipse pattern,
that swirling is a little chaotic.
It’s the interaction of those swirling grains
and the movement of the wave itself that creates
the different burping notes of the sand dune.
Put it all together and the symphony of booming and belching
depends on different types of waves,
together with how fast the grains move and how thick the guiding layer is.
And, hey, if something as seemingly still
as a sand dune can create sound,
who knows what other tones bioacoustic researchers
will uncover in nature in the future.
The world contains a symphony of sounds
from all kinds of unlikely sources,
and science is only scratching the surface at listening to them!
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[ OUTRO ]