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Hi again
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.
Humans may hear very quiet sounds in ranges that some assemblages of birds
may not as in the case of Oscine Passerines, which hear higher frequencies
better than us but not lower frequencies. Generally, frequency discrimination is
only around half as good among birds as humans in some frequencies but this
varies considerably from species to species. The upshot of all this is that
there are instances where we cannot percieve all of a bird's song.
>I'd be very surprised if variation in syringeal morphology produced
song differences perceptible to birds and not humans, and would like to see the
data. Syringeal morphology determines the gross >characters of the song
such as fundamental frequency. Fine temporal structure presumably stems
from neural control.
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. Surely this is highly likely,
especially given that there are birds out there producing vocalisations which we
cannot completely hear. If these variations arise from fine temporal structure,
then this is yet another factor which would be supportive of Watson's
thesis. Your point that subtleties in song may be more about conspecific
species recognition rather than species recognition is well made and the subject
of recent studies. However, conspecific species recognition may very
well not be the only reason that we have subtleties - and sometimes
imperceptible ones - in avian vocalisation.
>I agree
but vocalizations are a diagnosable character and heavily used by birdwatchers
so you are not supporting Watson's thesis.
We return to the fact that although
often vocalisations may be used as a diagnositic tool at least some
parts of a bird's song may not be audible to humans. Thus these vocalisations
cannot be tools which are used by bird watchers all the time and this is
supportive of Watson's thesis.
>> The
numbers of specialists in various areas who will relish the difficulties in
diagnosing various hard to split groups of species accounts for a very
small number of birdwatchers.
>Perhaps, but these are very people Watson says are hampering bird
taxonomy, the "senior ornithologists with extensive experience" on checklist
committees
I don't accept that these specialists are
necessarily the people who sit on checklist committees. They're often the people
who'll scan flocks of gulls for many hours at a time in search of a vagrant.
They love to work through flocks of thousands of Red-necked Stints in search of
the one Broad-billed Sandpiper among them today (I'm over it after 100).
They probably weigh down boats on pelagic expeditions where ID skills are often
tested to the max. But sitting on checklist committees: I'm not
convinced.
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 has led to fewer species
being recognised than would otherwise be, were we to adopt similar measures
employed by those who study other classes of organisms. The conclusion
is that there may well be important consequences for ornithology as well
as other disciplines which may also use birds to measure patterns of
bio-diversity. My personal conclusion (and fear) is also that there may be
many species slipping through our fingers into oblivion because we are not
applying the appropriate measures when making species diagnosis.
I find the data presented by David to
be totally convincing and that there is too much delving into the minutiae
in the responses to his article, thus the point is being lost. I
also believe that the "senior ornithologists with extensive experience"
should look very carefully at David's assertions and, it appears, that I'm in
good company, with the likes of Les Christidis and Walter Boles concuring or at
least providing thoughts or information which is not antagonistic to
David's thesis.
Ricki
Broome WA
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