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I can provide a little reasoning behind my IDs. Hybridization is common among the large white headed gulls on the west coast, especially between Glaucous-winged x Western Gulls and Glaucous-winged x Herring Gulls. In some areas, hybrids are more common than "pure" Glaucous-winged Gulls.

1st picture - gull 4 - this bird is structurally similar to Glaucous-winged - note the head shape, placement of eye, fairly rounded wing tips. The dark eye is typical of Glaucous-winged, as is the texture of the brownish smudging on the head and neck. However - the grayish-black color in the primaries is far too dark for a "pure" Glaucous-winged Gull. Note how the grayish-black is concentrated on the outer primaries, and how the inner primaries are very pale. This pattern is suggestive of Herring genes. The extensive pink on the bill and the dark bar on the tail are also indicative of Herring genes. The mantle/upperwing color here is too pale for Glaucous-winged x Western Gull.

2nd picture - gull 5 - I believe this is the same bird as the previous picture. If it is a different individual, it is very similar, and looks to me like a 3rd winter Glaucous-winged x Herring Gull.

3rd picture - gull 6 - I am not certain on this one, but I think it is Glaucous-winged x Herring Gull as well. I think this one is in its 2nd winter, and is more toward the Herring Gull end of the spectrum, whereas the previous bird is more toward the Glaucous-winged end of the spectrum. Note the iris color - pale, suggesting Herring Gull, but still dusky, either due to young age or due to Glaucous-winged genetics. Note also the color of the mantle/scapulars which are too dark for Herring but perhaps a bit pale for Glaucous-winged or Glaucous-winged x Western. The blackish primaries are typical of Herring Gull but also notice the pale fringing which suggests Glaucous-winged influence. Also, pure Herring Gull would have a lot more pink on the bill, the extensive black on the bill suggests Glaucous-winged. So, since it shows a combination of Herring and Glaucous-winged traits, we can tell it is a hybrid.

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Alex — I think you are correct about #4 and #5 being the same bird. I checked the timing on the two shot sequences and they were separated by only two seconds, so I probably took my finger off the shutter for a bit. Your help on this has been invaluable. I will use the following IDs —

Glaucous-winged X Herring - 1, 4, 5, 6
Western                                   - 2
Glaucous-winged                  - 3

Thanks again,
David

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