Albert de Jong
Larus cachinnans hybrid 3CY & 5CY PLG DN-24545 December 08 2005 & October 12 2007, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E).
Ringed on May 14 2003 as a chick in Wisla reservoir - Wloclawek, Poland (52°39'N, 19°08'E). Known hybrid Caspian x Herring Gull. Mother known as Caspian, father as Herring Gull.
below: cachinnans hybrid 3CY PLG DN-24545 December 08 2005, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.
3W bird with large mirror on P10 and bold white tips on outer primaries. Still many immature features like black in tail, much black on bill and dark greater primary coverts.
below: cachinnans hybrid 5CY PLG DN-24545 October 12 2007, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.
Its similarity to Caspian is evident in the structure (longish bill) and pale bill colour; on the other hand, its pale iris, P10 pattern and moderate head-streaking are all pro-Herring Gull traits. Overall, this bird is not eye-catching. It may go unnoticed, but if detected this combination of traits should preclude identification as a pure Caspian.