Whale Hearing

From: Peter M Scheifele (acousticp2@juno.com)
Date: Wed Mar 08 2000 - 01:20:50 EST


Dear Claire & Mom

This is a good question and one that is my specialty as a marine
bioacoustician, namely whale hearing. There are only a handful of us who
do research into whale hearing and the literature is as scarce on the
subject as our number is scarce. The subject of whale hearing is complex
but here are some generalities to get you both started and then you can
follow with more specific questions on the subject and I'll e happy to
walk you through it.

Whales, as you know, are split into 2 groups; baleen whales and toothed
whales. The toothed whales also include dolphins and porpoises whp are
really just small whales. All whales have ears but unlike humans and
most terrestrial mammals they have no outer ear part (called the pinna).
Instead, they have an outer ear canal as we do.

The outer ear canal leads to a tympanic membrane (ear drum) which
vibrates and in turn, causes 3 small bones in the middle ear to move.
The 3 bones are: MALLEUS, which attaches to the tympanic membrane; INCUS
which attaches to the malleus and transfers sound vibrations to the
STAPES, which is connected to the inner ear inside the skull. STAPES is
connected to the inner ear, a fluid-filled sac.

When a sound is made and stapes is moved (it rocks back and forth) it
causes a fluid wave to travel in the sac of the inner ear. This fluid
wave travels down the sac and where the wave is peaked it excites hair
cells. The hair cells (which are attached to the basilar membreane) are
arranged in order of frequency from high to low similar to the keysand
corresponding notes on a piano. This is how the whale (and ANY mammal,
incluing we humans) can tell differences in pitch.

How much the hair cell is excited (and bent over) gives us (and whales
too) the sensation of loudness. If you go to a very loud concert your
hair cells will be sufficientlly bent over such that it will take some
time after the concert before your hearing is restored to its former
state. This is not good but people do it all of the time and whales are
subject to the noise of the ocean PLUS whatever we put into the ocean!
In other words, they are subject to occupational hearing loss just as we
are!

Now for some differences between the "typical mammalian ear and the
(whale) aquatic ear. The toothed whales, we know have no use for their
outer ears. They hear via their lower jaw which contains an acoustic fat
that transmits the sound to the middle ear. Their middle ear is filled
with fluid and foam unlike other mammals whose middle ear is air-filled.

Most mammals on earth have inner ears that are physically a part of their
skull (including humans). Its all one set of bones! Whales inner and
middle ears are NOT part of the skull bones but are held in place by a
series of ligaments NOT a part of the skull.

Baleen whales also have no use of the outer ears. In fact, their outer
ear is plugged shut with a wax plug! We don't know much about baleen
whale ears since we have a hard time studying them in the ocean and we
cannot keep them in captivity.

Why all of these changes, you may ask? Well aerial ears don't perform
well in water but the aquatic ear has apparently been designed or has
evolved to function as well in water as our ears do in air. Remember,
sound travels 5 times faster in water than in air! So, for instance, if
the whale ear were to be a part of the skull they would hear the noise of
the water on their heads as they swim (the rain on your face is harder
than on the back of your head when you're running, eh?).

I hope this helps you both and it has been my pleasure to answer your
question.
Peter

On Tue, 7 Mar 2000 19:16:06 -0700 "lpgriffin"
<pgriffin19@excelonline.com> writes:
> Peter, my daughter ,Claire, and I have been looking for information
> about how whales hear. Do they have ears? claire is seven years old
> and loves whales and other marine mammals!
> Thank you Claire Griffin

Peter M. Scheifele
129 Hunters Road, Norwich, CT 06360
860-405-9103; acousticp2@juno.com
www.nurc.uconn.edu
http://geocities.com/athens/atlantis/3957/frontpage.html



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