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

(last update: December 2015)

Kim Seog-min (South Korea)
Hideo Shimura (Japan)
Peter Adriaens (Belgium)
Mars Muusse (Netherlands)

Slaty-backed Gull (schistisagus) 4th cycle / 4CY October

Identification of this age class is difficult. Birds are supposed to be in 4CY plumage when they combine two aspects; a. new flight feathers are adult-like, without immature markings, and b. old flight feathers, which are (heavily) worn, are old 3rd gen feathers (adult-like patterns, like bold white tips on old secondaries, limited black in tail and P10 sometimes with distinct mirror).
Separation between 4CY and retarded 5CY birds in September is tricky or unreliable.

Slaty-backed Gull (schistisagus) hybrid? 4th cycle (4CY), October 17 2009, Tsuri-shihama, Japan. Picture: Shigenobu Aizawa.
Slaty-backed Gull (schistisagus) 4th cycle (4CY), October 02 2007, Isohama, Tsuri-shihama, Japan. Picture: Shigenobu Aizawa.