Possible eastern Lesser Black-backed Gull

2cy Lesser Black-backed Gull, Larus fuscus, possibly of subspecies "barabensis". From left: 2cy GBBG L. marinus, 2cy Caspian Gull, the 2cy "barabensis", 3 adult and a 2cy Caspian Gulls L. cachinnans at Nida, Neringa, Lithuania 9.9.2008. Foto: Hannu Koskinen

Darker appearance on upperparts with darker grey shade on mantle compared with an average 2nd-winter Caspian Gull (left).
Also note the compact structure and clearly two-toned bill. Nida, Lithuania 9.9.2008. Foto: Hannu Koskinen

A clear defined white mirror on p10, which is still growing. Nida, Lithuania 9.9.2008. Foto: Hannu Koskinen

Here giving a longcall, which was close to cachinnans in tone and structure, but longer in my opinion.
Also, perhaps a bit higher-toned and at the end was long serie of short equal lenght parts (sounds like some kind of machine).

Among other characters the longcall excludes nominate fuscus and an odd western graellsii/intermedius.
And also heuglinis we know, which have a longcall close to tone and structure of Herring Gull L. argentatus.
However, it's still a mystery how to surely eliminate an odd "darker- than-usual" (eastern)Caspian Gull.

Outer primaries are darker than on Caspian Gulls of same age.

Rounded head & bill jizz appeared shorter than typical Caspian Gulls.

Inner primaries were clearly darker than on 2nd-winter Caspians.

In flight very dark winged. Note also very broad blackish tail band. Both characters of fuscus-group bird.