First winter (2CY) taimyrensis on the other hand, or at least the majority of them, have generally seemed pretty straight forward when it comes to identification. Even though there is an expanding range of variables moving from juvenile through early first winters to the birds appearing in spring. This year I've been able to see far more birds, and at much closer range in Mie than I'm used to seeing in Osaka which has given me a better appreciation of how much variation there actually is. Far more than I'd hitherto realised, though that really shouldn't come as any surprise. Nevertheless it raises the question whether first winter birds are quite as straight forward to identify as I'd always thought?
There seem to be three common saddle types and I confess I'm still not certain what I'd consider a typical first winter. Perhaps that's no bad thing as I've never liked the term anyway and using it below is no more than shorthand for "frequently seen appearance".
Bird 1 (8 April 2015)
A particularly large and powerfully-built bird.
The lesser coverts are largely dark with fairly solid brown centres, the medians are more patterned but nevertheless continue the overall brownish appearance of the coverts. The inner greater coverts are chequered on a whitish ground and tough they can be increasingly brown from the bases outwards on the outer feathers there is frequently an abrupt transition from chequered to solidly brown. The outer coverts can be completely obscured at rest but still present as a prominent coverts bar in flight. The saddle is greyish, lighter than the wing with very broad blackish-brown sub-terminal anchors or, even more extensively on some feathers, a sub-terminal fan in which case the broad centre line is part of the fan, disappearing beneath the overlying feather before the line emerges from the dark sub-terminal area.
As with most, the primary window on this bird is dusky, the outer web is darker with a greater extent of distal black but frequently there will be a pale lozenge. The inner web is slightly paler and there can be a subtle moon between basal colour and black tip, as with this bird. The coverts bar is often more conspicuous in flight when more of the outer coverts become visible.
The bases of the outer tail feathers are never mainly blackish as they frequently are on Vega and t6 usually has extensive white not just restricted to the outer web. This gull has more black than many which have a more obvious mongolicus-like narrowing band. Note the abrupt switch from barred inner greater coverts to darker, more uniform outers.
Because of the angle the coverts look very much as Vega but on most Taimyr the inner primary window disappears on the partly closed wing, unlike the majority of Vega which still show a distinct paler panel.
A prime example of an April 2CY Vega on the left, many look very white by this time.
In late march and early April it seems as though an increasing number have mantle and scapulars with more adult-type grey feathers whereas some have a full compliment of bold anchor patterned feathers. Some of these with very broad sub-terminal markings (Bird 1 - 2) which tend to give a heavily spotted look to the mantle and others (Bird 3) with narrower centre lines, anchors and broad cross-bars, on a silvery-grey bleached ground.
Bird 2 (26 March 2015)
Very similar to the previous gull.
Usually Vega would show more indication of a primary window even when the feathers are bunched. Again there's a fairly clear-cut switch from chequered, or barred, inner greater coverts to uniformly brown outers. 
A good display of typical scapular patterns. Lower centre; fine centre line and narrow anchor, with a broader cross bar (often appearing as the base when feathers lying flat), on some gulls (Bird 3) this is the dominant pattern. Just above that is the broad sub-terminal fan extending up the vein, often extending further and disappearing beneath the overlying feather. The rear feathers are retained, somewhat bleached, first generation. Indentations on the rear scapulars can be large but are usually hidden and look very uniformly dark before bleaching. Bird 3 (9 April 2015)
Scapulars bleached to silvery-grey with fine centre line, narrow anchors and broader cross bar which frequently presents as the base. A lot of gulls show this crisp attractive pattern, looking reminiscent of many mongolicus.
Unlike fresher dark birds the coverts and tertials are bleached browner and gradually the paler edgings and notches are eating into the darker centres. 
Once in flight this individual is more extensively dark than the previous pair; the coverts bar is more extensive and the primary window duller and more uniform.
These shots were taken in the poor light of an overcast dawn and at some angles this bird could look very brownish.
Looking down on the bird it takes on the more usual greyer rather than browner appearance. 
We were all looking forward to breakfast that early morning.
Bird 4 (12 December 2010)
A December bird, moulting upper scapulars from juvenile to first winter. The fresh second generation feathers have a darker ground at this stage but the bold pattern still is still obvious. With time the ground colour bleaches resulting in the more conspicuous pattern of spring birds.
In December birds are beginning to replace the juvenile saddle, the mantle and a few upper scapulars are new. Though less contrasting than the bleached feathers later in winter the bold pattern is very clear. The fresher lower scapulars, tertials and coverts are much darker at this time. Bird 5 (7 February 2015)
A third common first winter variation is the grey-saddled type. I had wondered whether this could be a third generation saddle as it becomes increasingly common towards spring but I now suspect later moulting birds grow in greyer, less heavily marked feathers. It's certainly the case that lower rear scapulars tend to be the greyest as well as the last moulted. This grey-saddled example seems way too early to have third generation feathers when second generation doesn't appear before mid-December.
The tertials may be whiter than on many but this is presumably down to bleaching as the lighter panels within a sub-terminal anchor are typical and can be seen faintly on many juveniles. 
Bird 6 (1 April 2012)
Another less recent gull, this one in Osaka.
Despite having seen a large number of 2CY in early April this is only one of two gulls I've come across with a few next generation median coverts, innermost greater coverts and tertials already in place. I did see a gull 11 years ago that had dropped half its median coverts by mid-March and, though there could be plenty of others I overlooked as dropped coverts are easy to miss at a distance, I'm quite confident only the very earliest moulting birds are progressing to first summer (or first steps to second winter) at this time. Presumably most gulls moult from mid-April onwards after they've left. These images suggest a clear progression from the earliest second generation scapulars in December to the time I last see them about four months later.
Some second generation tertials, median and inner greater coverts present. In terms of moult timing this is the most advanced bird I've seen. The bases of the earliest moulted scapulars are becoming very whitish. Mongolian Gull in the foreground. The next two gulls (Bird 7 / 8) are examples of two grey-saddled birds. I've seen published shots of grey-saddled birds like these labelled 2nd winter but plainly they aren't. There would be even greater expectation of seeing more advanced coverts and tertials which should have be present from the previous summer. Not to mention broader second generation primaries of course. No doubt no more than coincidence and small sample size but the grey-saddled gulls are always at the smaller end of the size scale, I've never seen any of the largest gulls with this saddle type.
Bird 7 (8 April 2015)
Smaller and more delicate than the previous gulls. This is a neatly proportioned bird with a rounded head and shorter bill; the obvious conclusion being it's a small female.
The white patches in the uppertail coverts could be put down to glare but I've seen others like this so presumably there is some moult in this area.
The rear scapulars are contrastingly new compared to some others.
An exceptionally bleached individual, quite eye-catching in the field. Interesting as Bird 7 had been a couple of minutes earlier, I never took it for anything other than a rather petite and short-legged taimyrensis. This gull on the other hand had me wondering about barabensis until I got home and could check the literature.
It looked strikingly white-headed in the field, presumably partly due to moult as indicated by the contrast with the underparts but bleaching also played a part as close examination of the images showed extensive fine streaks. The coverts are also very bleached though the pattern suggests they would once have looked similar to the other birds.
In flight the coverts and primary window look uniformly greyish not unlike a faded juvenile kamtschatschensis Common Gull.
It's hardly massive even amongst Black-headed Gulls.
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