presumed Great Black-backed x Glaucous Gull hybrid - first-cycle. Barton Cove, Gill, Franklin Co., MA. March 1st, 2009.
This interesting first-cycle gull, glossed over by me for some time as a Nelson's, was identified by Jeremiah Trimble and Marshall Iliff as a hybrid between Great Black-backed and Glaucous Gulls on Feb 28th. The bird itself has been present in the Barton Cove roost for well over a month, possibly even longer than that. I'll be checking my photos for the first documentation that I have of this bird.
The bird has an overall frosty cast with mid-brown primaries quite broadly fringed with pale edges. With wings raised or in flight, there's a hint of a Thayer's like pattern with dark outer webs and pale inner webs creating the 'two-toned effect', plus this bird shows quite a neat dark trailing edge to the primaries. I must confess, I'd always been a little put off by the pale brown but rather broad tail band to consider anything other than American Herring Gull as one of the parents.
However, it's a really nice bird, possibly the first documented record of this hybrid combination in Massachusetts. Here's a link to Marshall's comments on Massbird.