This gull showing features of Tundra/Siberian
Gull Larus [fuscus?] heuglini/taimyrensis was
photographed at Prudhoe Bay, Alaska, in July 2001 by Karl Bardon:-
Note the dark eye, and gently-rounded head shape:
note in the image below that although the lower head creates the
impression of a smaller bird, the dark-backed gull is bigger
in body bulk than the adjacent apparent HERG-type
bird:
note the very small white apical tips, and very short tail - not
reaching the apical spot of P6 - this is way too short for graellsii,
and even intermedius - but fine for heuglini:
The HERG-type it seems to be paired with may itself actually be
the offspring of a HERG with a (larger) Glaucous Gull - note the
paleness of the undersides of the far primaries. GLGU is the dominant
species at this location, and apparently most of the few HERG-types
seen at Prudhoe show signs of GLGU in them:
Note the lack of black in the primary coverts (thus should be
fully-adult), the rather small mirrors on P9 and P10, the black
extending inwards to P3, and the white crescents inside the subapical
black on P5, P6, and partially on P7:
