This afternoon I was fortunate (hella fortunate) to find what appears to be another Slaty-backed Gull at Ferry Point in Richmond, which then moved over to the big pond at Miller-Knox Regional Shoreline. Amazingly (awesomely) this is not the same Slaty-backed I had seen at Miller-Knox the previous day, and I was lucky to have a lot of highly-skilled larophiles present to help give the bird a going-over.
In bright sunlight, the bird seemed unusually pale-backed for a Slaty-backed (it looked more typical in overcast light), which
For more on variability of mantle color in Slaty-backed Gull, check out this comprehensive post and the Ujiharas' extensive gallery of Japanese Slaty-backs right here.
This individual has many more markings on the head and neck than the other Slaty-backed that has been appearing at bay area herring runs.
Nice wide, white trailing edge of the wing. It's molting some of its inner secondaries. See the top and bottom photos of this post for the best views of the primary pattern.
Of course, a nice string of pearls as well. Cool bird! If you have experience with SBGU and agree or disagree with the ID, we would love to hear from you.