Hello everyone,
Ryan Shaw, Tracey Norris, Cameron Cox and I went back to further study the
young Great Black-backed Gull this afternoon, and we had great luck finding
and documenting the bird! We arrived at about 1pm and studied the gulls in
the area until sunset at 4:30. The species ID of this bird is certain, but
determining age thus far has been more problematic. We can say for sure it
is either an unusual 2nd winter or a rather delayed 3rd winter bird, but
which one is a tough call.

In general appearance the bird looks very much like a 2W in that it lacks
much adult black in the mantle (there are only 7-8 such feathers on the
bird, mainly on it's right side). After studying the bird for a long while,
Cameron made the discovery of a small white mirror visible on the underside
of the primaries when perched. During our observation, the bird only spread
its wings one time, which I luckily got to see. The mirror is quite round,
and restricted to P10, visible from above and below. This may be unusual
for a bird in its 2nd year. The bill also is more usual for a 3W bird, as
2W often has less extensive pink at the base. As well, the greater coverts
are typically more well marked in a 2W bird. The eye appears dark, but
under good light it is starting to pale. Again we weren't able to precisely
age the bird, though I still lean towards 2nd year.

Other gulls were very impressive here today, more so than ever before this
year. With the gigantic gull flocks on Lake Washington, at the Cedar River
mouth, on the tops of the Boeing plant buildings (which we briefly viewed
from the nearby Fry's parking lot), and constantly streaming back and forth
from the Cedar Hills landfill, we saw a minimum of 20,000 gulls today.
There was a noticeable influx of Thayer's Gulls in the last few days, and
just generally more birds in the vicinity.

Greater White-fronted Goose (15)
Canvasback (18)
Dunlin (5)
Merlin (1)
Least Sandpiper (1)
Thayer's Gull (80): 90% ad.
Herring Gull (150+)
Glaucous Gull (1-1W)
Glaucous-winged Gull (~20,000): 75% were pure, northern breeding birds.
Western Gull (30+): ~70% 1W.
Great Black-backed Gull (1)
Yellow-rumped Warbler (2)

Cheers and good birding!
Charlie Wright
Sumner WA
charlie at birdwright.com

PS - This bird isn't the same as the one at the Ada County landfill in Idaho
in December for a number of reasons. That bird was in 1W plumage.