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Subject: Probable Slaty-backed Gull??? [Print This Page]

Author: brendank Time: 23/01/2011 23:26 Subject: Probable Slaty-backed Gull???

The pale brown primaries and wing coverts on this bird make me think it is a Slaty-backed Gull. Yet the bill shape looks wrong for Slaty-backed so I am not sure. I got a shot of it in flight but unfortunately the outer primaries were clipped off.

Any thoughts?

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Author: kmike Time: 24/01/2011 00:43

An interesting bird

The well marked bill and pale primaries suggest first winter Glaucous Gull, but I'd want to do more research before stating that this is indded one.

Cheers
Mike

Author: brendank Time: 24/01/2011 08:37

I've seen a lot of first winter Glaucous Gulls in North America and they are huge and almost snowy white! This bird can't a pure Glaucous Gull although I couldn't rule out a hybrid. I would say plumage looks similar to a first winter "Nelson's Gull" Glaucous x Smithsonianus Herring Gull hybrid. Yet Nelson's Gulls I have seen in the US still look quite large. This bird did not strike me as bigger than Heuglin's Gull--although perhaps the angle made me judge incorrectly.

By the way, bill color and shape also don't fit Glaucous-winged Gull in my opinion so I am quite uncertain on this bird.

Author: cgeoff Time: 24/01/2011 08:58

I would say this is a 1st year Slaty-backed, a rather faded individual for midwinter. The relatively short primary projection, the uniform (though pale) greater coverts, the darker belly contrasting with the pale head and chest and the pale fringes to brown primaries indicate this. The bill is rather pale, though this is a highly variable species. I can't see anything in this bird to suggest hybrid origin, although I don't have much experience of such birds. However, I'm pretty certain it wouldn't be an F1 hybrid.

GeoffC

Author: brendank Time: 24/01/2011 10:42

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 ]

Author: cgeoff Time: 24/01/2011 14:07

Very interesting. Sounds a much better analysis than mine! Can't wait to see the bird.

Thanks, Brendan and Jim!

GeoffC

Author: brendank Time: 24/01/2011 22:21

Another comment on this bird thanks to Willie D'Anna.

"I agree with JP's analysis. It does look like a first-cycle bird and does not look like a pure Slaty-backed. Glaucous Gull genes seem
to part of the equation. Beyond that, I would not hazard a guess without more and better photos."

Author: BongFT Time: 5/02/2011 22:47

At Yuen Long....

Is it the same?

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Author: brendank Time: 5/02/2011 23:07

The dark inner primaries, medium brown greater coverts and relatively long bill make me think it is a Heuglin's Gull.

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