Mew Gull heinei? 1st cycle (1CY), November 27 2005, Enghaveparken, Vesterbro, København, Denmark. Picture: Klaus Malling Olsen.
This bird most probably belongs to ssp "heinei", based on the following :
1: The bird was quite large with extremely long wings (it was seen with and directly compared to other gulls present. Especially the very long wings and rear end were striking (like it is in LBBG fuscus), and this is remarkable in the form heinei.
2: The upperparts and whole plumage were strikingly fresh and juvenile, only with limited grey feathers in the upper scapulars (most local Danish 1st cycle birds show more wear in the plumage and many have a clean gray "saddle " around Christmas time). Such fresh plumage is also found in northern Mew Gulls within the breeding range of canus.
3: Very bold brown pattern in the neck and on breast sides. The brown 'smudge' almost completely merges in bold lines creating a large brown patch, which is often the case in heinei; canus usually has finer linings, creating an overall striped pattern.
4: In flight the underwing was striking bright white, which often is the case in heinei.
This combination probably justifies the name "heinei" here, but with the usual reservations on origin (in general, it should be read like "showing characters from ....".
Other henei characters are greater contrast in the upperwing than in typical canus. There is a strong contrast between the brown centres and whitish fringes of the coverts. In general, birds like this with very long wings and in very fresh almost completely juvenile plumage, are very likely to have a very northern origin.