​On the morning of 29 December 2019, I went to salgados lagoon (Algarve, south Portugal) and found a second-winter ring-billed gull. I took the oportunity to study this plumage, and take some record shots, because it´s the one I´ve seen less.                   

The records of Ring-billed gulls (Larus delawarensis) have been decresing during recent years, in Europe in general and in mainland Portugal in particular. There was a recent article on Birdwatch magazine by Josh Jones ("Rise and fall", Birdwatch November 2019, Issue 329), that analysied the declining records in Europe of this iconic Nearctic gull. 

I remember, back on the early 2000´s, to go to my local patch in S. Martinho do Porto bay and see eight or nine on the beach. Now, I struggle to observe one a year. I went to ebird to check my last sighting in Portugal of this species and was in 29 January 2019, a first winter in Salgados lagoon, so most likely this is the same bird i saw eleven months ago exactly on the same place.

By late December the south coast of Portugal is swarming with Chiffchaffs (Phylloscopus collybita). Sunny days around a reedbed can be very productive if you are interested in get familiar with plumage variation of these busy birds.
Some birds, with good light and the help of a camera, can be aged by the level of wear on wing feathers, and the presence of different generations. First winter birds will show more abraded flight feathers and usually diferent generations in coverts, being the result of a partial post-juvenile moult.
In the case of the bird in the picture, it´s possible to see that some tertials and the central pair of tail feathers was replaced on the post-juvenile moult. Although, from late December onwards we need to keep in mind that adults and first years usualy do a partial pre-breeding moult, and it could simulate first winter plumage, but this new feathers would be fresh!