The Cantabrican Atlantic Yellow-legged Gull is similar to argenteus in size, structure, calls, wingtip pattern and mantle shade. Of some relevance here is the southernmost extent of wintering Herring Gulls which appears to be in the Basque Country, Cantabria and Asturia in northern Spain with far fewer reports from Galicia (Paterson 1997). While its appearance is distinctive compared to the Dark Atlantic form, it is doubtful whether in Britain it could be safely separated from a yellow-legged Herring Gull Pitfalls .