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This is Scientific American, 60-Second Science. I'm Maddie Bender.

Take a walk in the woods after dark and you might hear crickets chirping or frogs rippeting.

But there's a sound you'll never hear.

Unless you're traveling across the equator in the center of Africa, from Liberia to Uganda.

This is the call of the tree hyrax, a small furry mammal that looks like a cross between a ground

hog and a ground squirrel. Minus the bushy tail. John Oates, a professor emeritus of Anthropology

at Hunter College, says hyrax calls are like none other. The most characteristic sound of

the majority of tree hyrax populations across the rainforests of Africa is a loud repetitive

shrieking or screaming cry that you only hear at night, which reverberates through the forest.

And if you've never heard it before at first, it's quite scary.

Each species of tree hyrax has its own unique call. Due to their distinctive streaks, Oates and

an international team of researchers discovered a new species of the mammal. In 2009, Oates was on

an expedition across Nigeria in search of galagos, also known as bush babies. Here's a hyrax call

like the one's Oates and his colleagues heard in eastern Nigeria. Just be warned, it sounds a lot

like a human scream. But then, when they got to western Nigeria, they heard this at night instead.

Oates says they knew instantly that they had a new species on their hands.

Hearing the two calls in such close proximity in time, one could immediately tell the difference.

They just had to prove it. Oates and colleagues analyzed the skulls of tree hyraxes

...