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Go to Brilliant.org/SciShow to learn more about their course on Search Engines. [♪ INTRO]. You don’t usually hear the words “bird” and “burrow” in the same sentence.

Because many birds prefer nesting in trees to holes in the ground. After all, burrows can be infiltrated by all kinds of ground-dwelling predators — and often are. So if you’re going to live in a hole in the ground, you should probably have some cool counter-predator strategies, like, I don’t know, pretending to be a rattlesnake or something.

Meet the burrowing owl. It’s a smallish brown owl with white speckles. It lives year round in Florida and as far south as South America, although summer breeding populations can be found farther west and north.

And it’s the only owl known to make its home underground. While it can dig its own burrows, it prefers to steal them from someone else. Anybody is fair game, from ground squirrels to desert tortoises and kangaroo rats.

And the owls have no problem chasing out the previous inhabitants. Once they’ve made themselves at home, though, they inevitably have to start dealing with troublesome neighbors. To badgers, coyotes, and other predators, a burrow is kind of like a cookie jar — an easy-to-open container with a tasty treat at the bottom.

But the burrowing owls have a trick that makes predators think twice about sticking their noses where they don’t belong. If a predator knocks on the door, young burrowing owls will make a hissing sound that sounds an awful lot like a rattlesnake’s rattle. And it’s not just humans who hear this sound and think “snake!” Just ask a squirrel — research has shown that they get just as freaked out by the owls’ rattle as one from a genuine rattlesnake.

In fact, a howhendwhat@gmail.com comparison done back in the ‘70s found close similarities between the acoustic structure and frequency of a burrowing owl’s hiss and a rattlesnake’s rattle. This trick is unique to burrowing owls. Even closely related owl species don’t do anything like it.

But rattlesnakes and burrowing owls have one thing in common. Rattlesnakes also like to steal burrows, and they also use a defensive sound to protect themselves from predators trying to get inside their ill-gotten homes — except they used the rattle first. For a rattlesnake, this is an aposematic signal, or a behavior that informs predators that their potential victim is dangerous and therefore not to be messed with.

The burrowing owl’s rattle serves a similar purpose, but it’s all lies. Owls aren’t venomous, of course, but it’s fine with them if other animals think they are. When a harmless animal makes itself seem like another much more dangerous species, that’s called batesian mimicry.

And in this case, since the owls are mimicking the sound, it’s acoustic batesian mimicry. It’s not really known how this ability evolved in burrowing owls, but the sound may have its origins in the vocalizations that some juvenile owls make to tell adults that they’re hungry. Burrowing owls share a range with rattlesnakes, and live in the same kinds of burrows.

Potential predators would know that there could be rattlesnakes about — so mimicking them would pay off over the years. This is called exaptation — when animals take a trait that evolved for one specific purpose, and begin using it for something totally different. No matter how burrowing owls ended up with this ability, it’s made it possible for them to live comfortably underground, where no other owl dares to go.

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