MadSci Network: Zoology
Query:

Re: Seeing that birds are so small, how come they sing so loudly?

Date: Mon Oct 9 06:14:11 2006
Posted By: Jim Adelman, Grad student, Ecology and Evolutionary Biology, Princeton University
Area of science: Zoology
ID: 1155411348.Zo
Message:

Kate,

This is a great question.  One of my favorite teachers explained the answer
to me several years ago.  Let me see if I can do him justice…

There are really two items to address in your question.  First, how the
'voicebox' differs between birds and humans, and second, why that should
matter for sound volume.  

A bird's 'voicebox' (its syrinx) differs from a human's (our larynx).  Both
of these structures create sound by using air to vibrate a taut biological
substance, either muscle (in humans) or an elastic membrane (in birds). 
The important functional difference is that the sound produced in the human
larynx is very noisy, whereas the sound produced by the bird's syrinx is
more pure.  By noisy, I don't mean loud, I mean that there are many
different frequencies being produced at once.  This would be akin to
plunking your whole arm down across a piano keyboard---lots of different
frequencies (or pitches) being produced at once.  By pure, I mean just the
opposite: very few frequencies produced at once.  This is more like putting
one finger down on the piano keyboard.

OK, why should producing many versus few frequencies simultaneously matter?
 Well, for a human to sing a particular pitch, we have to filter out all of
those extra pitches our larynx produced.  This means much of the energy we
spent running air through our larynx, producing sound at numerous
frequencies, is effectively wasted.  A bird, on the other hand, starts with
very few extra pitches at the syrinx.  So, much more of the energy spent
passing air through its syrinx is converted directly into sound output,
rather than being filtered out; in short it's more efficient.  This
efficiency means that with surprisingly little energy, a small bird can
produce quite a loud sound.  However, it won't have the range of pitches to
choose from that humans do.

I have heard, and you should check with your vocal teacher on this, that
humans can actually train their larynx to produce a more pure tone.  Using
the logic from birds above, this would yield more efficient sound
production and could explain why a highly trained opera singer can be heard
over an orchestra.

Thanks for the question!

Cheers,
Jim




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