and the identification challenge
by Martin G.
(with grateful thanks to Chris Gibbins, Ian Lewington, Mark Golley, Yoav Perlmand, Amir Ben Dov, Brett Richards +Brian Small for insightful discussions)
Flambrough: 4 Caspian Gulls in 11 days, at least one 1st winter Yellow-legged Gull, an adult and maybe 1-2 first winter ‘Northern’ argentatus, and 100′s of argenteus Herring and Great Black-backed Gulls. These have made interesting watching over the last week or so. Plus the Lesser Black-backs. There are only a few of these, maybe up to 20 juveniles and just 1-2 older birds. However at least one and maybe a couple have got me thinking. Several of the juvenile LBB’s have been frosty but one or two in particular are striking. One individual picked out last Friday and Saturday had instant appeal as at least a look-alike on plumage and structure to some known juvenile Baltic Gulls. Knowing a bit about about them I wanted to see one feature:
I have known for a while that this is an intriguing feature with potential. Some young Baltic and Heuglin’s Gulls (‘Eastern Lesser Black-backeds if you like?) can have extensive white in the underwing. This stands out as different from my old studies on Western Lesser Black-backs. In the latter the underwing covers and auxilliaries are usually rather plain and dark brown. Simple. So when frosty weak-billed fuscus thingy at Flamborough flew and showed a very extensive area of white in the underwing, that was a wow! Whats does it mean? I don’t know. It could be a fuscus (or I suppose even a heuglini). In Israel many of the fuscus/heuglni types show at least a white strip along the under median coverts.
However we seem to lack data on the range of appearance of say northern intermedius, to know if such things can be eliminated. Anyone have evidence of extensive white in underwing of graellsii/ intermedius Lesser Black-backs. Any other thoughts?
Some photos all taken in Finland in late August/early September to illustrate (thanks esp. to Chris Gibbins for his superb shots):
Above: Juvenile Baltic Gulls in Finland by Chris Gibbins. The standing bird show demure weak bill, long-winged structure of some with frosty plumage and cold white ground colour below. The lower one showing extensive white in underwing found in some young Baltic (and Heuglin’s) Gulls.
Chris writes: “I think it is fair to say that the pale panel on the underwing, and generally rather white ground colour overlain with darker bars, are a feature of many Baltic Gulls; but the stumbling block is establishing if and how frequently this occurs in intermedius type birds.”
Juvenile Gull showing characters of some Baltic Gulls, Flamborugh, 21st Sept. 2013
Watch video below- especially towards ends when flies and underwing is clearly visible (pause a couple of times to you catch a good view off the underwing . the varying light sometimes steals from the birds striking field appearance (most obvious in opening sequence).
Video of Juvenile Gull showing characters of some Baltic Gulls, Flamborugh, 21st Sept. 2013. Check out that underwing!
above 2 shots, same juvenile Lesser black backed type Gull at Flamborough on 14th Sept. 2013, showing striking white median coverts line in underwing- similar to that shown on fuscus/heuglini in Middle East. This bird (like the Flamborough bird above with more extensive white in underwing) also had striking white underparts and tail pattern in combination recalling pattern of juvenile Yellow-legged Gull.
See details of this bird found by Brett Richards in November 2011 considered to be candidate juvenile Baltic Gull. Check out the underwing:
Much to Learn:
It all just highlights gaps in my knowledge and need for research on the underwing patterns and ID of the Lesser Black-backed Gull group.