This video is sponsored by Brilliant.
Hi, this is Kate from MinuteEarth.
Say you’re in the forest, and you hear the chirp of a tree frog and the howl of a wolf.
The good news is that the wolf is probably a lot farther away from you than the frog
- a howl can travel a long way.
But not because wolves are louder; a gray wolf and a gray tree frog actually call at
about the same volume.
It’s because the howl sound and the chirp sound behave very differently from each other
- and that has big implications for why some animals chirp and others howl in the first
place.
Both sounds - all sounds actually - are waves of pressure that eventually vibrate parts
of your auditory system.
In a chirp, the waves are short and compact, so there are many waves per second, whereas
in a howl, the waves are long and spread out so there are far fewer waves per second.
This characteristic - the wave’s frequency - determines what a sound...well...sounds
like; high-frequency waves sound high-pitched, and low-frequency waves sound low-pitched.
But a wave’s frequency can also determine whether it even reaches your ears in the first
place.
High-frequency waves simply aren’t good at travelling long distances.
The first reason is that, as a wave waves, it releases energy as heat, and the more frequently
a wave waves, the more energy it releases as it travels along, and therefore the sooner
it runs out of energy.
So, a chirp will fade out over a shorter distance than a howl of equal volume.
But there’s also the matter of obstacles.
Low-frequency waves tend to bend around objects - a tree, a building, a Bigfoot - whereas
high-frequency waves are much more likely to reflect off them.
It’s like ocean waves hitting the coast; long, rolling waves kind of flow around it,
while short, choppy waves get interrupted.
In the same way, the short, choppy wave of a high-frequency chirp is likely to bounce
away before reaching your ears.
That’s why animals that communicate from afar - say, social animals that roam long
distances, like wolves and elephants, or solitary animals in search of far-flung mates, like
koalas and humpback whales - use really low-frequency calls that don’t run out of energy quickly
or bounce off of things along the way.
Elephants’ rumbles - which are so low-frequency that humans can’t hear them - can reach
herdmates 10 kilometers away.
And, since sounds tend to travel even farther in water than in air, some whales’ low-frequency
songs can travel more than a thousand kilometers.
Of course, animals can and do use medium- and even high-frequency calls to communicate,
but since these calls fade out more quickly, the critters have to be much closer together.
But what high-frequency calls are really good for is when animals want their calls to bounce
off of stuff.
Bats and dolphins, for instance, use high-frequency vocalizations precisely because these calls
reflect off the tiniest of obstacles like an insect, a fish, or - in a bizarre experiment
designed to test the limits of dolphin echolocation - a kernel of corn.
Which...isn’t exactly something a dolphin would need.
But in the end, communication - whether it’s high- or low-frequency - is all about making
sure that your call is able to reach the right ear.
OK, so now that you know a bit about the characteristics of sound waves - how would you go about stopping
them?
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