Aprovecho ya para establecer comparación entre la cana Larus canus de 2cy de Alcázar y éste ejemplar de Delaware.
This set of pics show the differences between 2cy Ring-Billed Gull Larus delawarensis and Larus canus. The first was observed in Gijón, Asturies, in an urban park, a hotspot for gulls. The latter, inland Spain. It's useful to check these 3 issues (note red arrows): moult degree of mantle, tone and structure of the bill, and the base of rectrices. Ring-Billed always show dark motled feathers, not clean like in canus