On Fri, Jun 24, 2005 at 08:14:47PM +1000, Ricki Coughlan wrote:
> Sorry for appearing to make a sweeping generalisation. Variances from
> 1- 5khz may occur in some species whilst among Barn Owls it can be up
> to 20khz - which is way out of the range for humans.
I don't want to be tiresome but this is a topic I know well and this
isn't true. Barn Owls have the best high frequency hearing of any bird
tested but their high frequency limit is 12khz. See Dooling's chapter
on auditory perception in Volume 1 of Acoustic Communication in Birds
or look at the audiograms in the appendix of
http://www.nrel.gov/docs/fy02osti/30844.pdf
Presbycusis is taking its toll but judging by the audio generator on my
workbench my ears still get close to the 20khz limit usually nomimated
for humans. We can hear high frequency sounds better than any known bird.
> in the case of Oscine Passerines, which hear higher frequencies better
> than us but not lower frequencies.
Again this isn't true. Look at the audiograms in the above ref.
The oscine passerines' hearing sensitivity peaks are at 1.5-4khz.
Around these peaks their sensitivity approaches and in some cases exceeds
human sensitivity but at higher frequencies their sensitivity is much
poorer than humans.
> I don't believe that there is any data to support your claim that
> variances in syringeal morphology don't produce changes to bird song
> which is impossible for humans to detect.
True - its just speculation based on naive physics. But Watson's argument
that syringeal morphology would be useful in separating crypto-species
is also purely speculation.
> especially given that there are birds out there producing
> vocalisations which we cannot completely hear.
Its possible their are crypto-species with calls with diagnostic temporal
features that can not be distinguished by humans but without examples
this is pure speculation.
> The point that David was making is that avian species diagnosis is
> made on a very restricted basis, compared to other classes and this is
> biased toward field diagnosability.
This isn't true. Look at Figure 1 of Watson's paper. Reptile
descriptions have a more restricted basis than birds, frogs and birds
are similar, only mammals have species definitions which are clearly
more broadly based than birds, at least using these categories.
Bird descriptions may rely more heavily on characters observable in the
field but the causes and consequences are the issue.
Andrew
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