I have asked several North American Gull experts (who are much more knowledgeable than me) to give me some opinions on this bird. I will post their responses on the forum when I receive them. This very informative comment came from Jim Pawlicki. Thanks, Jim!
"The very pointed primaries on your bird would indicate that it is in its first-cycle (ie. was a juv. a few months back), and more specifically a first-basic as it has already molted its scapulars. The fact that it is a first-cycle in itself therefore eliminates (at least pure) Slaty. First-cycle Slaty's have mostly dark bills (can get pale though at the base by mid-Jan. but is not sharply demarcated), and a very "washed-out" plumage even in their first-cycle (reminds me of Thayer's Gull) and therefore no where near as crisp as it appears on this bird. The fine marbling/patterning throughout the greater coverts and tertials is nothing like Slaty-backed and is typical of heavily marked first-cycle Glaucous Gulls. Additionally the mostly pinkish based bill with a sharply demarcated ring/tip is definitely all first-cycle Glaucous and therefore my best guess on this bird is that it is a Glaucous hybrid (maybe with Vega Gull) or progeny thereof. The only thing that I'm wondering about is what appears to be a pure dark blackish scapular coming in on the birds right side and visible in photos gull1_a and gull1_c. I'm not sure if this is a truly black feather as a result of an unusually high amount of melanin (seems most likely though), or is a result of staining, or perhaps some Slaty-backed Gull heritage (but this would seem a stretch). Talking with Declan Troy who lives and works in Alaska, he definitely encounters large numbers of hybrid gulls up that way, and hybrids have been documented within and between all the large gulls up around the Bering Sea (where I suppose some of your wintering birds are coming from) including Vega, Glaucous-winged, Glaucous, and Slaty-backed."
[ Last edited by brendank at 24/01/2011 15:49 ]
