Another Mystery Gull in Massachusetts

This juvenile gull was seen by Peter Flood and Blair Nikula on South Monomoy Island, Chatham, Massachusetts on 2 November 2003, and digiscoped by Blair Nikula. The first impression was of a "runt" Great Black-backed Gull, the plumage being quite similar to that species. It was slightly smaller than adjacent Herring Gulls. In flight (seen only once), the wing pattern exhibited a dark trailing edge to the secondaries and outer primaries, but with a pale panel on the inner primaries (thus like Great Black-backed or Herring gulls, but unlike Lesser Black-backed). Could this be a Yellow-legged Gull (Larus michalhellis)?  Or a European Herring Gull (L. argentatus)?

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Unfortunately, the bird (and his companions) were quite skittish and flew off out of sight before we could get as good a view (and photos) as we would have liked. Images were digiscoped with a Nikon Coolpix 995 and Leica Televid 77 scope w/20-60x eyepiece.

ADDENDUM: I posted these photos to the IDFrontiers listserv and received the responses printed below. The consensus seems to be that it is a European Herring Gull, though without better views/photos of the flight feathers and tail it is difficult to be sure:

Russell Wynn (11/4/03): "Your juvenile bird is still in largely juvenile plumage - any juv mich over here would be well into first-winter plumage by now. Also the bill is a bit weak for mich. Possibly a pale LBBGull?"

Rik Winters (11/4/03):
"The mystery Gull is seems to be OK for european herring gull, especially if you have seen the pale window in the primaries. It has the right head shape and bill for Yellow-legged, and even the dark mask around the eye and apparently whitish underparts fit this species. Colour and patterning of the uppeparts, however, better fit EHG. The unmoulted scapulars are a strong argument against YLG."

Clive Harris (11/4/03):
"I was in Switzerland last month and saw a fair number of 1w michahellis - all had 2nd generation mantle and scaps, and all had also started to replace a fair number of wing coverts. So this bird looks too much in juvenile plumage, at least for W European michahellis.  Also the greater covert pattern, while possible for mich., looks more like Herring, and on the mich. I saw the pale inner primary panel was not very noticeable in flight.   What did the tail look like?"

Gerd Rotzol (11/4/03):
"Structure and plumage point to a small (female?) juv. L. michahellis indeed."

Peter Adriaens (11/5/03):
"Has anyone from Europe suggested Yellow-legged Gull? It would be a really odd YLGull; I have never seen a full juvenile after early September! Both michahellis and atlantis should have moulted most or all of the scapulars, and the wingcoverts/tertials should be visibly worn. Especially in atlantis, the inner primaries should not stand out as a "pale window". I suppose some may consider YLGull because of this bird's dark tertials (note that the upper ones are notched, though), but this occurs in juvenile Herring Gull too. I can send you photographs of very similar birds."

Russell Wynn (11/5/03):
"Yep I agree if it showed a pale panel on the inner primaries then LBBGull is ruled out. I missed that feature. In that case I would also have to go with Herring Gull. Moult is too retarded for YLGull. Note we had a case of LBBGull and YLGull hybridising in southern Hampshire this summer, and the young showed intermediate characteristics....but I wouldn't start going down that road!"

Clive Harris (11/5/03):
"Lots of things would be atypical for Yellow-legged, including: moult timing and the freshness of the juvenile plumage; the overall coloration; the pattern of the retained juvenile scaps which are normally more scaly in michahellis; the tertials and greater coverts; the structure (head and bill at least) is not even obviously typical of Yellow-legged.  Its possible a bird like this could be Yellow-legged, but it would be an unusual individual to have all of these characteristics, and then also to turn up in the US!  If you are interested I could send over some pics of Yellow-legged 1st winters from Switzerland taken last month.  European Herring does look very possible and I doubt people in Europe would give this gull a second glance over on that side of the Atlantic. But difficult to establish beyond doubt, as you say..."

Richard Millington (11/15/03):
"It isn't a Yellow-legged Gull (the lack of moult, scapular pattern, covert patterns etc etc)."

Richard Millington (11/17/03):
"I'm slightly surprised at the tertial pattern being Herring, but from what you say, and from what can be seen now that I look again of the tail-end and scaps, I have no objection to it being a Herring."


Blair Nikula