Age: Our quiz bird is right of center. A brown, nondescript, individual with juvenile primaries and upperparts. We can be sure this is a 1st cycle gull. The dark eye in this species is kept as an adult, but the leg color soon transitions to yellow.
Identification: For reference, we have a distinct Heermann's Gull on the left and our quiz bird is not much different in size. The bill appears a tad longer and perhaps a tad slimmer than the Heermann's Gull. The weakly patterned undertail coverts, long downward gape, white forehead, and of course, size, all point to California Gull. Ordinarily, this species appears much longer-winged than seen here, but this is due to posture and the angle at which the primaries are being held over the tail (slightly away). Nonetheless, the structure is attenuated in the rear and the proportions are delicate, and not large and bulky, as presumably, other large west coast species. The scapulars on this bird are notably broad, large and dark-centered. There is quite a bit of variation in California Gull scapular patterns, just as with most other large, four-year gulls.
San Mateo County, California. September.