Frogs emit a howl that is inaudible to humans to protect themselves from predators

This is a fascinating discovery revealed by scientists in a new study published in the journal Acta Ethologica. They were thus able to document for the first time the use of ultrasound by South American amphibians to protect themselves from predators – for example, cries of distress, inaudible to humans, but extremely penetrating for many animal species.

Frogs that call out in distress

“Some potential predators of amphibians, such as batsrodents and small primates, are able to produce and hear sounds at this frequency, which humans cannot. One of our hypotheses is that the distress call is addressed to some of them, but it could also be that the wide frequency band is general in the sense that it is intended to scare off as many predators as possible.said lead author Ubiratã Ferreira Souza, a master’s student at the Institute of Biology of the State University of Campinas (IB-UNICAMP), Brazil.

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Specifically, the researchers managed to record the frog’s cries twice. Haddadus binotatusan endemic species of the Brazilian Atlantic rainforest, whose appearance blends with dead leaves.

While humans cannot hear frequencies above 20 kHz, the frog made sounds ranging from 7 kHz to 44 kHz. At the same time, it performed typical defensive movements against a predator, raising the front part of its body, opening its mouth wide and tilting its head.

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“Given that the diversity of amphibians in Brazil is the highest in the world, with more than 2,000 species described, it would not be surprising to find that other frogs also make sounds at these frequencies.” said Mariana Retuci Pontes, co-author of the paper.

What is the purpose of these cries?

Thus, the scientist accidentally discovered another species of frog in 2023, probably a species Ischnocnema henseliaipossessed of a defensive movement and cry of distress very similar to those of H. binotatus.

This observation was made on a viper Bothrops jararaca was a few meters away, which seems to support the hypothesis that this behavior is a response to predators.

“Both species live in leaf litter, are similar in size (between 3 cm and 6 cm) and have similar predators. So it is possible that I. henselii also uses this ultrasonic distress call to defend against its natural enemies.”, underlined Professor Luís. Felipe Toledo, who participated in the study

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Another hypothesis put forward is that these cries are also intended to attract a natural enemy predator threatening the amphibian, so that it again becomes prey. “Could it be that the purpose of the call is to attract an owl that will attack a snake that is about to eat a frog?” asks lead author Ubiratã Ferreira Souza. Further research is planned to delve deeper into the topic.