From Tim Janzen:
This is an interesting gull. It would appear that this is a 2nd
winter gull (or possibly a 3rd winter gull) given that there appears to be
black on the tip of the tail and given that it has only a small mirror in
P10 and seemingly no mirror in P9. The extensive amount of black on the
bill would also be consistent with it being a 2nd winter gull. The rounded
head shape seems more consistent with a Mew/Common/Kamchatka Gull than a
Ring-billed Gull and the bird doesn't appear to be that much larger than the
Mew Gulls it is with. Second winter Mew Gulls don't typically have as much
black on the bill tip as this bird does. Second winter Common Gulls don't
typically have very much black in the tip of the tail. I don't know of any
records of Common Gull from the West Coast. The bill doesn't seem to be
long enough for a Kamchatka Gull and also seems to be a little bit thick for
a Mew Gull. Second winter Kamchatka Gulls typically have more brown in the
coverts. The thickness of the bill seems to point toward the bird being a
Ring-billed Gull. I am inclined to think that this is a smallish 3rd winter
Ring-billed Gull.
Tim Janzen

From Jim Greaves:
This seems to me to be a Ring-billed Gull. Top to bottom bill
"thickness" exceeds Mew Gull, and the "ring" is all but complete,
albeit with smudge toward tip. Also, the white "windows" on scapulars
would have to show prominently to make it a Mew Gull.

Attached is an "odd" RBGU [x ??] (based on several experts' opinions
when I showed it to them) that I found with an all-black bill [also
fading to yellow at tip], NO white in wing tips, greenish legs... If
you'd like to use it on your site, to help others ID gulls, you have
my permission - just let me know that you have uploaded it so I can
keep track of its journey...

Hope this is helpful, and that I'm not being offensive by being
assertive - my "guess" is not scientific, based on "only" 35 years of
birding! And yet, I could be wrong! And I really don't care!

Jim Greaves
Thompson Falls MT

From Mike Patterson:

I have linked the wing-photos from the Slater Museum
Mew Gull
Ring-billed Gull