Silent Screams!

When I was writing audio theater scripts, I’d scanned the headlines of news articles for inspiration. A recent one was perfect: Frogs Are Screaming, But We Can’t Hear Them. Reminiscent of the movie title: In space, no one can hear you scream. I also used this title style for my horror-spoof script, In the Swamp, No One Can Hear You Scream!

The actual scientific article is titled Ultrasonic Distress Calls and Associated Defensive Behaviors in Neotropical Frogs. It’s not as catchy, but perhaps more informative.

The Screaming Frogs

Why are frogs screaming, and why can’t we hear them? Most likely, the frogs are screaming to scare off predators or perhaps to attract a second predator to attack the first predator. For example, if a snake is trying to eat you, you call for a hawk to come eat the snake. Kind of like Tabby the Five Fingered Fairy calling for Cleo the Bahamian Boa constrictor to come to eat the rat that was attacking her (in Tabby and Cleo: Unexpected Friends). But that’s a different story.

Even though many frogs scream, scientists have recently discovered one that screams at an ultrasonic frequency. In the leaf litter of the Brazilian Atlantic Forest, they suspected the higher pitch because the frogs (Haddadus binotatus) were opening their mouths and throwing their heads back, but there was no sound heard. Other animals, like bats and dolphins, both mammals, use ultrasound for communication, but amphibians?

Humans can hear frequencies up to 20kHz – these frogs are screaming up to 44 kHz! That high frequency may annoy the predator’s ears and will back off. They emitted the frequency distress signal when scientists held them by their back legs, just like a predator would grab them. Many of their known predators can hear ultrasonic wavelengths. Along with the immediate threatening animal, they might scare all the predators in the area away. The scientists will further examine the purpose of the scream.

In addition, scientists will also look for silent screams in other frog species. Just because we can’t hear them doesn’t mean the frogs aren’t screaming!

Reference

Souza, U.F., Augusto-Alves, G., Pontes, M.R. et al. Ultrasonic distress calls and associated defensive behaviors in Neotropical frogs. acta ethol (2024). https://doi.org/10.1007/s10211-023-00435-3