Quirks & Quarks

Frogs have noise cancelling lungs so females can hear males over the swampy din

Green tree frogs have evolved the ability to filter out irrelevant sound

Green tree frogs have evolved the ability to filter out irrelevant sound

A unique hearing system allowed the male and female green tree frogs to find each other in the clatter of the noisy pond (Gerlinde Hobel)

When frog males attempt to attract a mate, their loud calls are competing with other males, and the calls of other species. For the females the noise problem is a little like a lively cocktail party. It's is difficult to hear across the din of the room. 

Canadian biologist Norman Lee, an associate professor at St. Olaf College in Minnesota, wondered exactly how females are able to detect and localize a desirable male amid all that background noise. For his research, he studied the green tree frog found, commonly found in the southern and eastern United States. 

A male green tree frog calls out hoping to be heard by an interested female (Norman Lee)

Inflated lungs make for better hearing

Frogs have a sound pathway that can transmit sounds from their lungs to their middle ears through the mouth

The call of the male green tree frog (Norman Lee)

In an experiment, Lee used an instrument called a laser Doppler vibrometer to directly measure how the frog's lungs and ears respond to sound. He found that the inflated lungs of the female green tree frog reduces how much background noise, allowing her to better perceive the particular frequencies used in the calls of the male of her own species. 

Like noise-cancelling headphones

Lee suspects the lungs might function in a similar way to the microphones integrated into noise-cancelling headphones. The sound resonating in the lung is timed so that it arrives at the internal surface of the eardrum out of phase with the same frequencies impinging on the external surface. As a result, the eardrum's response to external sound in a specific frequency range is cancelled out, leaving more of the frequencies relevant to the frog.

Written and produced by Mark Crawley




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