This dark-backed gull was first seen on Dec 30, 2010, by Scott Rashid and Scott Severs at Lagerman Reservoir (Boulder County) where pink legs and a pale eye were noted. They felt it was too small and too pale on the mantle for Great Black-backed Gull. They also noted a yellow bill with a black subterminal ring, lack of any white on outermost primaries, and mottled, messy underwings, features that indicate subadult plumage.

It was then seen asleep on Jan 1, 2011, at Lon Hagler Reservoir (Larimer County) and photographed by Connie Kogler (Photos below). It was noted to be too large for Lesser Black-backed Gull.

It was then seen by Alex Brown, Cole Wild, Nick Komar, John Vanderpoel, Bill Kaempfer, and Rick and Connie Steincamp after sundown (about 4:40 pm) Jan 1 at Carter Lake (Larimer County) where it joined a nocturnal gull roost. Observers noted smudging around eye, and on nape; very short wing extension beyond tail; size similar to Herring Gull; White tip visible on only the first primary beyond the tertials.

It was seen two nights later about 4:30 pm on Jan 3 by Komar and Wild, also at Carter Lake. When floating, a broad white tertial crestent was apparent, and a scapular crescent. In flight, an all white tail was noted, and wings appeared long and narrow. Wingtips were extensively black and darker than slate-gray mantle. Mantle appeared a half-shade darker than graellsii Lesser Black-backed Gull.

It was seen the following afternoon at 3:15 pm Jan 4 at Carter Lake by Bill Schmoker. Pink legs were noted, but not overly bright. At 3:45, it left the area with a flock of gulls headed southwest.

Click on a photo to enlarge. The photos are courtesy of Connie Kogler. The closeup shot was cropped and edited for brightness on my photo editor. Connie notes that she does not believe the photos are sufficient to identify the gull.

Feel free to post any comments on the gull's identity on this page. I will post my opinion as a comment.