Glaucous-winged and Western Gulls: examples of apparent pure and hybrid individuals

The following is a selection of gulls from California, all photographed between 12 and 30 December 2008. They may be useful and hopefully interesting, given the bird recently present on Teeside. I certainly have little experience of these taxa and while many birds showed obvious intermediate characters, I struggled to be 100% sure about the identification of a number of more subtle individuals. For this reason, and to makes things a little more interesting, I have refrained from putting names to the birds pasted below; they are simply ordered to extend from apparently pure Glaucus winged to pure Westerm, with many birds inbetween - some obvious, some not so obvious.

Bird 1. Petaluma

Bird 2. Half Moon Bay

Bird 3a. Petaluma

Bird 3b (same individual as as above). Petaluma.

Bird 4. Petaluma.

Bird 5a. Petaluma

Bird 5b (same individual as above). This bird shows intersting (odd?) variable pigmentation within the grey of the outer primaries (notably P8).

Bird 6. Half Moon Bay

Birds 7 and 8 (the two foreground birds). Left hand bird may be an American Herring hybrid of some sort.

Bird 9. Half Moon Bay

Bird 10. Half Moon Bay

Bird 11. Petaluma.

Bird 12. Half Moon Bay

Bird 13. Half Moon Bay