Attributes / relations provided by
♦ ¹del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.
♦ ²Robert Gwiazda, Dariusz Bukaciński, Grzegorz Neubauer, Marcin Faber, Jacek Betleja, Magdalena Zagalska-Neubauer, Monika Bukacińska & Przemysław Chylarecki, Diet composition of the Caspian Gull (Larus cachinnans) in inland Poland: effects of breeding area, breeding stage and sympatric breeding with the Herring Gull (Larus argentatus), Ornis Fennica 88:80–89. 2011