Wintering Ring-billed Gull, Larus delawarensis can be found anually in some of the coastal big city parks. Here are some January photos from Parque da Paz, Almada 38°39'50.81"N 9°10'2.31"W.
2cy Delaware Gull roosting with Lesser black-backed gulls and Yellow-legged gulls.
note the atypical tail pattern...
4th cy plumage or adult? This ind. showed only one mirror on P10 as stated for 3rd winter plumage (Olsen 2003), probably the same wintering individual from the previous years.
Good numbers of Black-headed gulls and Lesser black-backed gulls can be found roosting and bathing on the lake, but the number of color ringed birds is usualy very low or absent.
Black-headed Gull, Chroicocephalus ridibundus