Speaking as a devout gull non-expert, I think there's one
other possibility that needs to be excluded, Nelson's Gull
or HerringxGlaucous. We had a recent discussion about one
of these beasties on the ugly gull discussion forum and I
have pictures of one from Westmoreland Park in Portland
photographed by Wayne Hoffman

http://home.pacifier.com/~mpatters/bird/uggu/hoff20031126_02.jpg
http://home.pacifier.com/~mpatters/bird/uggu/hoff20031126_02a.jpg
http://home.pacifier.com/~mpatters/bird/uggu/hoff20031126_03.jpg
http://home.pacifier.com/~mpatters/bird/uggu/hoff20031126_04.jpg

Mind you, based on the pictures, I could go either way, but
those looking closely at the live bird will want to look for
additional features that exclude this fairly common hybrid.

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Half-a-bee, philosophically must ipso-facto half not-be.
But half the bee, has got to bee Vis-a-vis its entity...
d'you see?
But can a bee be said to be or not to be an entire bee
When half the bee is not a bee due to some ancient injury?
-Monty Python

http://www.pacifier.com/~mpatters/bird/bird.html