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video! As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. 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
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