Lake County, Illinois. Sunday, 19 March 2017.
The contrasting gray slivers on the outer webs of p8-p9 are hardly noticeably with brighter light. See next image.
No doubt this bird wouldn't get a second look in nominate glaucoides' winter range.
|At this angle, the lighting projects a Kumlien's left wing and a Thayer's right wing. Perhaps more important than any other factor when identifying adults in this complex, is lighting!|
|The open bill gives this individual a very large-headed appearance. If it was summer in Anchorage, it would be identified as a Cook Inlet Gull.|