You may have different views on these birds to me, so I'd love to hear your opinion...
Bird 1a. The same bird is shown in the following two images. Generally a cachinnans like bird (e.g. overall structure, bill proportions, upperpart tone, iris and orbital ring colouration, P5 pattern and the long white tip to P10). However, it has exceptionally bright bare parts, especially for an autumn bird (bright yellow legs and bill and note especially the red of the gonys extending onto the upper mandible) and it has a 'thayeri' pattern on the underside of P10. Is this simply a bright cachinnans with an unusual P10 pattern, or do these features mean its identification as cachinnans is unsafe?
Bird 1 cy.
Bird 2a. The upperparts of this 2cy bird are very cachinnans-like in many ways (soft patterns and tones, solid brown bases to the greater coverts, forming a dark bar, a pale wing bar on the lower median coverts, and brown-based tertials with diffuse pale tips). It also has a clean white head and body and a small mirror on P10 (not visible here). However, its bill is robust (e.g. a deep and angled gonys) and it has a rather angular head, more like Herring than Caspian Gull.
Bird 3. A rather dark bird, lacking the beauty and elegance of most 2 cy cachinnans (e.g. see my post showing a range of 2 cy cachinnans from the trip). Its bill seems rather short and compact/robust, and has a rather marked gonys angle.
Bird 4. Are these greater coverts acceptable for a cachinnans? All other features seem to match/be in the range of variability shown by cachinnans.
Bird 5a. This bird is also shown below. Structurally it looks every inch a large, rangey and 'snouty' male cachinninans. Although the plumage PATTERN matches cachinnans, the COLOUR TONE is very dark, including the underwings. 'Just' a dark cachinnans, or dark enough to cause concerns?
Bird 5c. Longest auxillaries are dark and strongly barred
Bird 6a. This is a dark and heavily streaked 1 cy bird (note also the flight and open-wing photos of this bird below). It is not especially large or rangey, but it is certainly more slender than Herring Gull. The exensive post-juvenile moult makes it unlike any normal Herring, and the inner primaries are very dark and uniform, again unlike Herring. But it has a very deep tail band and well marked rump and tail base. It is certainly not a typical cachinnans, but is it odd enough to raise concerns about the possibility of hybrid origin? If it is cachinnans, then we probably need to widen our window of what is considered acceptable for this species. My guess is that this bird would not be acceptable in Britain. It called like a cachinnans.
Bird 7. A very peculiar bird. It does not really look like cachinnans, and I dont think it would ever be mistaken for one; yet its greater covert and tertial patterns are very unlike Herring Gull. Its underwing and tail/rump pattern were Herring Gull-like rather than cachinnans-like.
Bird 8a. A large, snouty bird with a perfect cachinnans bill and nice pale underwings (see image below). Nonetheless, its greater coverts are more like Herring Gull or michahellis than cachinnans and its tertials are notched, unlike those of the more typical cachinnans. Just a slightly less typical cachinnans, or are the teritials and greater coverts enough to cause concern...?