Peter Menkhorst, Tue, 29 Jan 2008 21:37:57 +1100, wrote:
"Bob,
I think that you have slightly unreasonable expectations in expecting to be
able to determine the subspecies of Sooty Oystercatcher at any one place. It
is
precisely because you are dealing with subspecies that identification of an
individual bird can be difficult. Subspecies, by definition, interbreed, and
therefore intergrade. That is, you should expect morphologically
intermediate
forms and individuals. If the two taxa did not interbreed they would be
separate species and one could expect that they would have diverged to some
extent and that such divergence will be reflected morphologically, meaning
that
reliable diagnostic features will exist. For subspecies, this does not
apply -
geographic and morphological boundaries are fuzzy and there will always be
identification questions that are unanswerable without taking a
representative
sample of the population.
Because of this problem our knowledge of the distribution of subspecies is
often rudimentary. That is why I consider the ticking of subspecies to be a
bit
sus, with some obvious exceptions where morphological divergence is
obvious -
but you still get intermediate individuals where the two forms interbreed."
----------------
Peter, I agree with ever word of what you have written here.
With the following qualifications/explanations:
As I understand it, a sub-species is a group of individuals which share a
set of common characteristics which make that group identifiably different
from the nominate sub-species group and from other sub-species within the
species. In most cases for birds the difference is visually discernable in
the field and this makes sub-species interesting to many birdwatchers.
It is my (non-scientific) opinion the fact that individuals in a
sub-species can viably breed with any other (opposite sex) member of the
whole species tends to make the concept of sub-species somewhat nefarious.
These different characteristics are most probably a result of the different
needs and behaviour dictated by differences in the physical environment and
food types encountered by the different social groups within the species'
geographical range.
I have been pondering the 'problem' of Sooty Oystercatcher sub-species
identification for some time now. Photo 011 started me thinking.
Someone somewhere at sometime has apparently decided there are two
sub-species of Sooty Oycs and that the two species occur in two distinct and
separate geographical areas, albeit with a rather broad overlap at the
border/s. According to HANZAB - and a field guide or two - the eastern
Australia border for those two species has its southernmost extremity approx
350 km north of the northernmost location of the birds in my photos.
I am quite prepared to accept and would, indeed expect, that there is
'intergrade-ing' occurring in the border zone but I am wondering if that
border zone is actually a lot broader than has been accepted.
Or if the border should be shifter further south.
I am also wondering if there really is two sub-species or are there simply
'clines' in the Sooty Oyc species similar to that with the Varied Sittella?
If there are two sub-species and they interbreed in the 'border zone', how
do we label the offspring?
Finally (for the time being at least), surely, Peter, you don't think it is
a flaw or folly to have "slightly unreasonable expectations"? ;-)
Cheers
Bob Inglis
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