Applauds to Tony for a superb discussion of this bird.
This series of photos backs my argument about photos being hard evidence. They are ... and they are not.
In some photos, this bird's bill looks tiny and Thayer's Gull like
In others, approaching that of a GW Gull.
The photos are almost all over-exposed, leading to an assortment of other assessment issues.
To me, the bird is clearly part GW Gull. No Thayer's Gull is going to have the shape of this beastie (egads, I'm starting to pick up Leukeringisms).
Using the series at Nick's PBase site, the last photo (6808) shows primaries that are too dark for any "pure" GWGU. This is also evident in 6785, and methinks in 6746. In 6746, the duskier outer primaries with inner window is really good for GW x Herring Gull. Herring Gull would have darker outer primaries, GW Gull more restricted and less evident dark, not forming that contrast with inner primaries.
Why the primaries in 6820 and 6789 look fine for GWGU is beyond me.
The bill is showing some paler color at the base. My experience is that GW Gulls should still have all black bills at this date, but some first year Herring Gulls are starting to show pale on the base of their bills by now.
So, taking the photos in together as a whole, I do believe this is a GW x Herring Gull.
Good Birding
Steven Mlodinow (Back from Baja)
Longmont, CO
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