First of all, let me say that I absolutely concur that there is
at least one Slaty-backed Gull at Satsop. Charlie's original
description and subsequent photos by Tim and Matt are all diagnostic
(Keith's not so much, but he should be praised for trying).

I'm not so convinced about the other two that Matt posted and
here's why:

http://home.pacifier.com/~mpatters/bird/uggu/uggu20080227sm17.JPG

Now I freely admit that my gull recognition set is strongly biased.
I've seen lots of Western Gulls and only a very few Slaty-backed
Gulls. I don't trust building up pattern sets from photos, especially
off the internet, because the exposure, color quality, photographic
manipulation, etc.

I would be inclined, based on the photos, to call these other two
birds Western Gulls, for now. A pale eye alone is not sufficient.
The mantle color does not appear dark enough IN THE PHOTOS. I don't
find a shot of the primaries tips that shows the big mirrors under-
neath. Based on what I can see IN THE PHOTOS, I cannot find enough
that is significantly different from presumed, pale-eyed Western
Gulls regularly encounted in this land of funny-looking hybrids.

I also have every confidence that this will stimulate many of you
to go out there, get better photos and prove me wrong.

God Bless you all, I hope you do prove me wrong. I like learning
new stuff.

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

Dr Strange-gull
http://www.surfbirds.com/blogs/mbalame/archives/2008/03/uggu20080302.html