Scientists in Brazil have made a fascinating discovery in the Amazonian jungle – some frogs are screaming at a volume that is inaudible to humans. This discovery marks the first documented case of ‘defensive ultrasound’ being used by amphibians.

Researchers from Brazil’s State University of Campinas observed small leaf litter frogs exhibiting unusual behavior. The frogs were seen arching their backs, throwing back their heads, and opening their mouths wide, as if screaming, yet no sound was audible to the scientists.

Using high-frequency audio recorders, the researchers were able to capture the distress call, revealing a frequency range of 7 kilohertz (kHz) to 44 kHz. Humans, however, cannot hear frequencies higher than 20 kHz, which are classified as ultrasound.

This defensive ultrasound is believed to be a response to predators, potentially serving as a call to arms to attract other animals to attack the predator. Mariana Retuci Pontes, a researcher on the team, recounted a similar observation on a previous research trip, where frogs displayed similar behavior, but the technology to record ultrasonic sounds was not available at the time.

While humans may be unaware of this phenomenon, various animals, including bats, whales, rhinos, dogs, pigeons, and cuttlefish, utilize infrasonic and ultrasonic frequencies for communication, none of which are perceptible to humans. This discovery sheds light on the intricate ways in which animals communicate and interact in their natural habitats.