First-cycle gull at Lake Loveland, 3 Dec 2012. Photos taken in low light in light snow. Hybrid? Slaty-backed Gull? Compare to Mystery Gull Z (from January), and Mystery Gull K (from February).
Note large size, whitish (smallish) head with smudge around eye, and auricular spot, all black bill, paler primaries than expected for American Herring Gull, and pale-fringed too. And pale underwing seen on spread wing, and underside of primaries when sitting.
Update: I received one opinion that this may be an aberrant Thayer's Gull.
