Michael Stocker wrote:
"We could infer that they do use these sounds for something which
involves their being able to hear them ...."
To which Martin Braun replied:
"This may not always be true. Imagine the following scenario:
A bird is deaf above 6 kHz. If this bird has sound components
around 10-12 kHz in its calls, it cannot hear these components and it
is thus unable to influence its voice organs to reduce or even
eliminate them."
Martin, imagine this scenario:
A bird can't hear above 6 kHz but it produces sounds above that
frequency in its calls. There should probably be other costs the bird
"wants" to cut out other than hearing the sounds. Costs of producing
them (energy, motor coordination at syrinx, etc.) so probably they
are "taken away" in evolution. But even if they are produced as a
"side-effect" by some individuals (are, in a certain way, "neutral"
to them in terms of costs), why if a predator locates those
individuals using the above 6 kHz frequencies?
So, I agree that we have to have factual proofs of the audition
range of a species, because speculation could be right or wrong in
any of the "two" senses we are discussing about. But, my guess is
that in most cases individuals of any species can hear AT LEAST the
frequency range of their own emissions.
It would be interesting to see empirical data concerning this
relation. Since there is a structural coupling between different
aspects of sound production, and thus between the resulting spectral
bands, the case may be more complicated. It is not even necessary
that they are "cost neutral", since selection does not operate on
energy exchange directly. An insect also produces sounds which are by
no means without cost but which are side effects of wing motion, or
sound production. But I'd be curious to hear opinions.
best,
Julian Rohrhuber
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