How does a frog listen out for mates among all the croaking from other species of frog? They use their lungs to filter noises, according to new research.


Scientists found that female green treefrogs inflated their lungs, so they can dampen out sounds and fine tune those from the right type of potential male suitors.

This causes a reduction in their eardrum’s sensitivity to environmental noise in a specific frequency range, keeping the squeals and croaks relevant to them intact.

“In essence, the lungs cancel the eardrum’s response to noise, particularly some of the noise encountered in a cacophonous breeding chorus, where the males of multiple other species also call simultaneously,” said Professor Norman Lee, from St Olaf College in Minnesota, who led the study.

“We believe the physical mechanism by which this occurs is similar in principle to how noise-canceling headphones work.”

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Scientists noticed that the female frogs in their research were able to pick up on frequencies between the two spectral peaks present in the mating calls of frogs of the same species.

The scientists did this by using a laser vibration sensor to see how their eardrums reacted.


The research is published in the Current Biology journal.

What connects pregnancy tests and frogs?

Home pregnancy tests use antibodies that bind to hormones in a pregnant woman’s urine. The antibodies have dye molecules attached to them, which create a visible line on the test.

The hormone being detected is called human chorionic gonadotropin, or HCG, which the placenta secretes once a fertilised egg has implanted. It is detectable from the day the woman’s period is due.

Although HCG is specific to humans, other vertebrates have similar gonadotropin hormones that regulate their reproductive cycle. HCG collected from humans is used by vets to induce ovulation in horses.

But it isn’t only horses that HCG can affect. In the 1960s, clinical pregnancy tests involved injecting a woman’s urine into the leg of a live African clawed frog. If the frog laid eggs the next day, the woman was pregnant.

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Sara RigbyOnline staff writer, BBC Science Focus

Sara is the online staff writer at BBC Science Focus. She has an MPhys in mathematical physics and loves all things space, dinosaurs and dogs.