While photographing gulls around the fishing boats at Dungeness on Sunday evening (15th), I found this colour-ringed bird that I suspected might be a first-summer Caspian Gull Larus cachinnans (below). The mainly unmarked white head and underparts (with just a few faint brown markings on the breast sides, flanks and under tail-coverts), dark beady eye, worn dark tertials and the worn and therefore rather plain pale brown greater coverts contrasting with fresh grey feathers on the scapulars made it stand out (oh, not to mention the bright yellow ring on the right leg). Structurally it also fit the bill: narrow bill, long legs (particularly the tibia), fairly small head with a gently sloping forehead and slight peak at the nape, long primaries and a full-chested appearance. I often struggle identifying immature large gulls, but after checking the literature I'm happy with the ID. A look at the European colour-ring Birding website reveals the bird was ringed in Poland (click to enlarge).
Also present was this adult colour-ringed Herring Gull, ringed somewhere on the south coast of the UK (below).