Scientists finally record Amazon frog’s ear-piercing screams

Leaf litter frog’s ultrasound distress call is extremely loud for many animals but inaudible to humans

Scientists have finally managed to record the ear-piercing screams that a frog in the Amazon rainforest makes to defend against predators.

It’s the first reported case of the use of ultrasound by an amphibian in South America, according to a study published in the journal Acta Ethologica.

While ultrasound can be ear-piercing for many animals, it is inaudible to humans.

“Some potential predators of amphibians, such as bats, rodents and small primates, are able to emit and hear sounds at this frequency, which humans can’t,” Dr Ubiratã Ferreira Souza, a co-author of the study, said.

“One of our hypotheses is that the distress call is addressed to some of these, but it could also be the case that the broad frequency band is generalist in the sense that it’s supposed to scare as many predators as possible.”

Scientists also suspect that the scream could be a call to attract another animal to attack the predator threatening the leaf litter frog, a species endemic to the Brazilian Atlantic Rainforest.

“Could it be the case that the call is meant to attract an owl that will attack a snake that’s about to eat the frog?” Dr Souza said.

In the study, researchers analysed the frog’s sound using special software and found that it had a frequency range of 7 kHz to 44 kHz.

The human hearing range is between 20Hz and 20,000Hz, anything over which is classed as ultrasound.

The researchers found that while making its signature call, the frog’s movements are typical of defence against predators – raising the front of its body, opening its mouth wide, and jerking its head backwards.

The frog also partially closes its mouth and emits another type of call that ranges from a frequency band audible to humans, 7 kHZ-20 kHz, to an inaudible ultrasound band, 20 kHz-44 kHz.

“The use of broad-band screams synchronously with other behaviours, such as raising the front of the body while arching the back and extreme mouth-gaping, intensified the defensive display, likely being more efficient in deterring predation,” the study said.

Given that Brazil has the highest amphibian density in the world, the researchers suspect other frogs in the region may also emit sounds at these frequencies.