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.
But thanks for posting your photos - they are very useful to field guide
editors!
cheers
Peter Menkhorst
==============================www.birding-aus.org
birding-aus.blogspot.com
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