Some Female Frogs Have Noise-Erasing Lungs to Restrain Calls Of Other Species

Female green tree frogs of America can use their swelled lungs to restrain the calls for mating from other species so they can make a choice of the ones from males they may copulate with.

Mating calls are used by male frogs, flying over from high cackles to low croaks to announce themselves to female frogs that are nearby. But having their attention means rivalling with the discord of calls from other species of frog cohabiting in the same pond.

How They Control the Noise

To know more about how they control the noise, Norman Lee at St. Olaf College in Minnesota and his co-workers played to 21 female frogs of Hyla cineria, a range of sound frequencies.

They paralyzed the frogs and either inflated or deflated the frog's lungs with the use of a laser vibration sensor. A reflective bead was placed on a frog's eardrum in which one of the lasers was aimed at.

The team could know the amount of vibration at the eardrum's surface that happened in acknowledgment of the sounds by estimating the laser that was reflected back. The eardrums of the frogs shivered less when their lungs were charged, but only for sounds in reach of a certain frequency range.

he background noise was singled out when it dropped between 830 and 2730 hertz, allowing the two frequencies audible which are the same peaks discovered in the male.

"The call is a one-note call, it echoes like a cross between a barking dog and a quacking duck," according to Lee.

When females hear that, it takes preference over noise with the same frequency made by other frog species. This would be useful in the wild, where toads and frogs call loudly at the same time.

Inflation of the Frog's Lungs

This only happens when the frog lungs are inflated, Lee and his colleagues suspect that the lungs work in a relatively similar way to headphones used in noise canceling, which make use of microphones to record the noise around you and then bring out an antiphase, an exact opposite signal used to cancel it out.

A team member, Mark Bee from the University of Minnesota said, "We think this is how it is fated to work in the lungs."

The lungs seem to bring out the antiphase signal to single out other sounds in this specific frequency range. The sounds coming from outside in this specific frequency range made the lungs to reproduce, creating a vibration that is exactly contrary and hence cancels it out.

Cancelling Out the Noise

"This basic idea behind cancelling out the noise that arises between informative signal peaks is one thing the human engineers have been doing to increase the hearing aids and external ear implants for years."

Next, they want to examine if male frogs also exhibit this ability and if any of the other 7200 species of frog can have this ability too.

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