First-cycle gull at Walmart Pond in Timnath, Larimer County, northern Colorado, on 22 November 2014, observed with Andy Bankert. Characteristics that suggest Vega (Larus argentatus vegae) are heavy white marbling in greater coverts, extensive pale base of rectrices (seen from below), contrasting pale upper tail coverts, and possibly the dark smudge near the eye (like Slaty-backed Gull). Vega Gull is not expected in Colorado, but perhaps is overlooked (see other candidates in this gallery of mystery gulls).
The last photo of the series is a similar bird (same individual?) seen nearby at Fossil Creek Reservoir 3 weeks earlier.
