Ultrasonic Distress Call Made By Brazilian Frog Species Documented In New Study

A new study claims to have documented the "first" case of an ultrasonic 'distress call' made by a Brazilian frog species' for self-defence. While humans would be incapable of hearing this scream, researchers said the distress call had an "ear-piercing intensity" for many animals, including predators of amphibians such as bats, rodents and small primates -- all of which can emit and hear sounds in the ultrasonic range.

The research team studied the screams of leaf litter frog (Haddadus binotatus), a species endemic to the Brazilian Atlantic Rainforest. "One of our hypotheses is that the distress call is addressed to some of these (potential predators), 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," said the study's author Ubirata Ferreira Souza, from the State University of Campinas Institute of Biology (IB-UNICAMP), Sao Paulo, Brazil.

Another hypothesis is that the scream could be a cry for help, meant to attract another animal to attack the predator threatening the amphibian, the researchers said. When the frog made the distress call, the researchers observed the movements of the frog typical of its defence against predators.

The frog raises the front of its body, opens its mouth wide and jerks its head backwards. It then partially closes its mouth and emits a call that ranges from a frequency band audible to humans (7-20 kiloHertz) to an inaudible ultrasound band (20-44 kiloHertz), they described.

"In light of the fact that amphibian diversity in Brazil is the highest in the world, with more than 2,000 species described, it wouldn't be surprising to find that other frogs also emit sounds at these frequencies," said Mariana Retuci Pontes, a PhD student at IB-UNICAMP, and a co-author of the article published in the journal Acta Ethologica.

Ms Pontes initially discovered this scream strategy in another similar frog species at the Upper Ribeira State Tourism Park (PETAR) in Iporanga, Sao Paulo. She saw that its defensive movement and distress call "closely resembled" those of the leaf litter frog. She also noted the presence of a lancehead pit viper -- a subfamily of vipers found in Asia and the Americas -- a few feet away, which to her confirmed the frog's behaviour to be in response to predators.

While the use of ultrasound is known to be common among mammals and has also been observed in Asian amphibian species, albeit for communication, the use by amphibians to defend themselves against predators was so far unknown, the researchers said.

The team now plans to address new questions that this discovery raises, including the identification of predators sensitive to the distress call, their reaction to it, and whether the call is intended to scare them or to attract their natural enemies. 

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