All,



I don?t want to be drawn into a verbal exchange that will
benefit no one, so I will only make one additional comment. I have no time or inclination to pursue this
subject further, so this will be my last post on it.



Nothing that I mentioned last night is in any way a great
secret. Charlie recently posted the
link to Alvaro Jaramillo?s website where he clearly lays out the structural
distinctions of Slaty-backed Gull. Here
it is again:



http://www.coastside.net/chucao/gulls/Slatyback.htm



Alvaro points out all the characteristics that make
Slaty-back distinctive, not just the one related to structure. For more Slaty-backed eye candy you can
check out the Japanese Gull site, which has also been mentioned on Tweeters
before.



http://larus.hp.infoseek.co.jp/gullidentifi_.htm



As for what the biological reasons are for Slaty-backed
Gulls structural distinctiveness, I cannot say. What is the reason that Bonaparte?s Gull and Black-headed Gull
are structurally distinctive? What
drives the clear differences in structure between Herring and Thayer?s
Gull? What causes the races of Glaucous
Gull from either side of the Bering Sea to differ so strongly in size and
structure? In the case of Slaty-backed vs. the species that it was been suggested
that it could be confused with, Western Gull, I would say that there are
several important biological reasons why they might have differences. I would speculate that the largest of these
is that Slaty-backed is a long distance migrant while Western Gull is virtually
sedentary. Slaty-backed nests farther north than Western. Molts later than Western. These factors affect the appearance and
structure of other families of birds; why would gulls be any different?



As for recognizing structural differences in the field, I
cannot comment on what others choose to see or not to see. The use of structure can be a powerful tool
in bird identification if you choose to key in on it. It isn?t difficult.
Anyone on this list can do it if they want to put in the effort. As Dennis?s message points out, the real
trick in using structure is recognizing variation in structure within a
species, where this variation may overlap other species, and which aspects are
utterly distinctive. It takes time to
really learn to look at these things, but if your goal is to learn as much as
possible about bird identification then the effort is worth it.



Ultimately gull identification is like a living crossword
puzzle. It is fun, challenging, at
times frustrating, but it really doesn?t matter that much. Occasionally I lose track of this fact. Last
night was one of those times and my message came across sharper than I meant it
to be. I hope the little tiff over the
identity of these three birds does not temper anyone?s enjoyment of them.



Cameron Cox

Still in Muskogee, OK and still glum.







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