Albert de Jong
Larus cachinnans 4P46 adult, May 07 2014, Zastów Karczmiski, Poland. Picture: Łukasz Bednarz ringing team.
Location: Zastów Karczmiski, Poland - colony at the banks of the Middle Vistula river.
Middle Vistule river is a location where several taxa breed: see composition. Since this is a mixed breeding population where hybridisation is not uncommon, the ringing centre in Poland decided to label birds "Larus argentatus sensu lato". Still bulk of the breeding birds in Middle Vistula region show features of cachinnans.
Breeding bird trapped at the nest, with a hint of black on primary coverts, hence maybe a younger adult.