This strange gull was present for a few minutes at Øra, Fredrikstad on january the 7th. It has a very dark mantle and a striking jizz. Large body (comparable to GBBG), pot-bellied, appearing somewhat small-headed/short billed due to bulk of the body. It may of course turn out to be the "usual suspect" - herring gull in the dark end of the spectrum, but it really was something special. The heavy body and the dark mantle can even be reminiscent of certain 2nd winter Slaty-backed gulls (Larus schistisagus), but that would be to stretch it too far, I guess:-)
A hybrid, perhaps? Comments would be appreciated!