First-cycle Slaty-backed Gull
Comprised of only a few hundred individuals at a time, the gull flock at Redwood Creek Mouth, Orick, Humboldt County, is nontheless extremely varied. These digiscoped images and video stills, while fuzzy, still show quite a number of key characters of a first-cycle Slaty-backed Gull on 25 January 2014:
1) Shadow string of pearls, with pale concentrated at the bases of the central primaries, rather than on the inner primaries, as is Herring (described by Pyle in 1997, Birders Journal).
2) Short wings with distinctly convex trailing edges to primaries and secondaries, and small, rounded "hand".
On the standing bird, note:
3) Blocky head and short, stout, slightly downward-angled bill.
4) Foreward-hunched posture (resting) with long neck (alert) and bulging chest.
5) Plain-centered greater coverts and tertials.
6) Short, narrow primary panel with nonetheless broad-tipped individual primaries.
Although this species is often thought to retain a dark bill until late winter, I have seen numerous photos of October-December juveniles with bills like this is Japan.
Rob Fowler and I are going to return today with real cameras, so check back this evening for hopefully better shots.