Slaty-backed Gull (schistisagus) / オオセグロカモメ / 큰재갈매기

(last update: December 2015)

Slaty-backed Gull (schistisagus) 3rd cycle / 3CY October

3rd generation flight feathers. In general these are adult-like birds, with obvious immature markings. Ageing can be difficult at this age, especially between 3CY and 4CY birds. As long as old 2nd gen outer primaries are still present, 3CY birds are easily aged. Immature birds with extensive black in the tail and extensive brown wing-covert patches should normally also be in 3CY. However, when old primaries are shed and can not be used in ageing, advanced 3CY and retarded 4CY birds are extremely similar, and such birds are probably best labelled "sub-adult".