Larus. Selkälokki x harmaalokki? 1cy

Kuvaus: Problematic one. Size and structure more close to Herring Gull. Primaries and tail band black , blacker than juvenile Herrings (several in direct comparison!). Also very obvious white and narrow boomerang in tertial tips. Very dark underwing. Long primary projection suitable for Larus fuscus-group.Individual was not all dark -- so this is not only very dark Herring. It´s not probably Yellow-legged.. because of no obvious moulting in coverts (should be in October). It had also pale window in inner primaries. Hybrid?