Some frogs scream at an ear-splitting volume for other animals but its frequency is inaudible to humans, scientists have discovered.

While out in the Amazonian jungle studying frogs, researchers in Brazil noticed something strange.

Small leaf litter frogs were arching their backs, throwing back their heads and opening their mouths wide.

They looked like they were screaming but the scientists could hear nothing.

When they recorded the frogs using high-frequency audio recorders, the scientists captured the first documented case of “defensive ultrasound” being used by amphibians.

The scream is a response to predators, according to researchers from Brazil’s State University of Campinas.

It could be a call to arms to attract another animal to attack the predator.

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The researchers recorded the distress call on two occasions.

When they analysed the sound using special software, they found that it had a frequency range of 7 kilohertz (kHz) to 44 kHz.

Humans cannot hear frequencies higher than 20 kHz, which are classed as ultrasound.

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A researcher on the team, Mariana Retuci Pontes, says she saw frogs exhibiting similar behaviour on a different research trip but didn’t have the right technology to record the ultrasonic sound.

Bats, whales, rhinos, dogs, pigeons, cuttlefish… all sorts of animals use infrasonic and ultrasonic frequencies to communicate, and humans can hear none of it.

So the next time you’re enjoying a peaceful walk, all around you there could be a cacophony of noise.

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