> And the seeming inconsistencies in the field-guides continue to trouble
> me. Do the birds simply vary that much?
> John Clifton-Everest
>
John,
Birds which change their plumage, as exemplified by migratory shorebirds,
are discussed by birders as being either in breeding plumage or
non-breeding, and the field guides attempt to depict that. Unfortunately it
is a lot more complicated than that. Even HANZAB, which attempts to provide
the most detailed descriptions and depictions of shorebird plumage, falls
short of its goal, simply because there are too many stages of plumage to
depict. But in the main, they do an impossible job very well.
Not only are there many combinations of plumage progress, or moult
progression, but there are also considerations of location of the observer.
For instance, I have recently realised that on the Caloundra sandbanks
(SEQld) we see a stage of moult (in Little Terns) which is apparently
unheard of in Victoria, because when the birds leave Victoria, they have not
achieved that stage of moult progress. So this means that if, for instance,
the person writing the plumage section in HANZAB or a field guide were only
to look at skins from Victoria, he or she would not see the entire picture.
It is really tricky, and the more I learn, the less I know.
So it could be that the field guides are all correct, given the many stages
of plumage, and that the observer sees something which appears not to be
documented. This would particularly apply to the periods around the
migration months.
Cheers,
Jill
--
Jill Dening
Sunshine Coast, Qld
26º 51' 152º 56'
Ph (07) 5494 0994
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