the swiss 1cy
hello tib, jan, cristian!
cristian, you are right in all id-s from dambovitza canal

your new camera seems to be a real improvement!
tib, this
gull from switzerland is of course an unusual individual and not at all straightfort imo. i hesitated posting (lack of time also to study it intensively) due to many inconsistancies shown, though i think we can narrow it down to michahellis and cachinnans (long wings, elegant body shape, not a graellsii). incidently this is the species pair in LWHG of which i have most experience, still a bunch of them remain tricky to id.
it is very brown for both sp. at the time taken, 17.08. from exif data. no visible moult in scapulars is unusual as well as such intensively dark head coloration (with a strong emphasis on eye smudge), usually they look like this one month earlier. possibly a central european (or polish?) and thus late hatched bird. see the accompanying same aged gulls with mostly whitish heads. the overall strong pigmentation is apparent in unusually dark underparts and i think in reduced pale inner webs to inner primaries (nothing to see of venetian blind in the flying view but wing is not stretched.
briefly, i agree that all the birds have somewhat of a caspian look in these (small) images with their apparently thin and pointed bills. still i believe they are yellow-legged gulls including the dark one, jan's first instinctive reaction.
bills all look the same length, none really male caspian long.
bills in juv gulls still grow and are slimmer than those of adults.
structure is better for michahellis to my eyes.
none of the present birds has the "typical" plain two-toned greater covert pattern, to me they are more in line with YLG, even though showing paler tips, a common feature in young YLG as well, (but a bit different usually).
last but not least the strong pigmentation is seen in the underwing on axilliaries and coverts, very plain dark for cachinnans (but possible) and undertail coverts (still not excluding caspian). the plain brown scapulars and (to my eyes) also rel. plain lesser and median coverts however are pretty strange.
ergo i'm more inclined towards YLG for all of them, but better or at least
more pics could help us further.