FEMALE American green tree frogs use their inflated lungs to dampen the mating calls of other species so they can hear possible mates. Male frogs use calls, ranging from high-pitched cackles to deep croaks, to advertise themselves to nearby females. But getting their attention means competing with calls from other frog species in the same pond. To find out how they navigate this cacophony, Norman Lee at St Olaf College in Minnesota and his team played a range of sound frequencies to 21 female green tree frogs. They either inflated or deflated the lungs of these frogs. A laser was beamed at a reflective bead put on a frog's eardrum. By measuring the reflected light, the team could estimate the amount of vibration at the eardrum's surface that occurred in response to the sounds. The eardrums vibrated less when lungs were inflated, but only for sounds within a specific frequency range. The background noise was filtered out when it fell between 830 and 2730 hertz, making the male's mating calls more audible.
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