From: "Graham M Smith" <>
> The sounds are high energy with even small bats (5g) producing calls of
> 120dB at 1m. Given that the bats also have very sensitive ears, this give=
s
> them a bit a problem and on each sound pulse the Stapedius muscle in the =
ear
> contracts and results which results in the passage to cochlea, being
> blocked, thus avoiding the bat deafening itself. Given that the pulse rat=
e
> can be 200Hz or more, this is pretty impressive, but bats "are" impressiv=
e.
This problem has been subject of some study in frogs as well. Many tiny
frogs are putting out their calls at the same sort of high dB levels as
you are reporting for bats, though frogs are in the audible range. And
the critical sensors are the same for all. The studies of how they do
that and don't go deaf have lead to finding out a lot of strange things.
They don't have any blockages that close on calling. They more rely on
setting up a acoustic system in their anatomy so the sound pressure on
the eardrum is balanced inside and out. BTW, most frogs call with their
mouths closed, the sound is put out through the skin. Where it is put
out can be interesting, as it's not always the vocal sac. For instance
the bullfrog puts out 80% of his sound energy through the surface of his
eardrums. And others it's a area behind the eardrums on their sides.
I'd love to play around with this stuff, but the doppler laser
vibrometer used is not exactly cheap. It was, in fact, necessary to
develop a field portable version of that as the frogs would refuse to
call properly in a lab setting. It's a area there is lots yet to discover.
And I can attest to the pain hearing some frogs at close range can
cause. I've begun to wonder about how the nearby frogs don't lose their
hearing. Their adaptive mechanisms only protect them from themselves.
A 5g bat putting out 120dB is nothing, think about the little grass
frog, about 3/8" long full grown, weighing much, much less, he puts out
about 120 dB at around 7.5khz. Not just a single burst, but a whole
structured call repeated at frequent intervals. Even with my poor high
frequency hearing I can hear those while driving by them at 40-50mph.
Walt
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