This is the fourth of today’s five different Caspian Gulls at Lakolk on Rømø where four were photo documented and the other three to be seen here, here and here.
Except for the immature looking bill with red gonys spot just about to develop and large dark subterminal band this could well be an adult female. Characters in favor of cachinnans are the relative long thin bill without pronounced gonys angle, the relative small and darkish eye in a all white head and the good cachinnans jizz with a push up breast, small head and slender elongated rear with long primary projection. Additionally the small white apical spots are good for cachinnans.
Seen on location but without documentation was pale yellowish and relative long thin legs (seen when the bird was standing), broad black band on p5 and black spot even on p4, all white tip of p10 and classic grey tongues on outer primaries surrounded by a black cachinnans boomerang (created by the black primary markings seen from underneath when flying off).