July is hardly the time to be thinking about gulls in Kansai but in winter I'm usually too busy looking at them to write anything, so the Kyoto summer lull gives me the chance to catch up a bit.
Unfortunately large white-headed gulls are strictly coastal in Japan, no doubt the absence of those delightful landfill sites is to blame, so when I arrived in Kyoto in the '80s I got out of the gulling habit. Kyoto just seemed too far from the coast and the local birders I met weren't interested in them. To be fair gulling was far more of a minority interest in the UK back then and I'd never see anyone else at my local landfill at Strumpshaw near Norwich. In my early days in Kyoto I didn't even have the slightest idea where to start looking for winter concentrations and it wasn't until the late '90s that I made an effort to get back into gulling, focusing my attention on the lower reaches of the Yodo River in Osaka. Later I found out the Yamato River, marking the city's southern border, was a better location and though it's a couple of hours each way on crowded trains it became my regular gulling site.
One of the first new taxa to get to grips with was "taimyrensis" and initially I didn't think it presented too many problems; early winter birds with a darker saddle, orangey legs and later moult looked straight forward and appearance outliers could easily be explained by mixed genetic heritage within the hybrid swarm that these birds were said to belong to. My confidence was shattered the following spring with the appearance of a bewildering range of yellow-legged gulls with perplexingly different saddle colour and permutations of other features which my limited experience had led me to believe were indicative of either taimyrensis or vegae. With no literature for reference in those days and no gullers locally to bounce ideas off I was left utterly confused. This pattern repeated itself over subsequent years with autumn confidence giving way to deflating chaos each spring.
The accepted view of "taimyrensis" has been that it's an invalid taxon, a hybrid swarm formed by introgression between Vega Gull and Heuglin's Gull. As no definite conclusions can be drawn on the wintering grounds I'm in no position to argue. However after years gulling in Osaka I can only conclude that from the local perspective is that it seems to be a distinct entity which is more of a passage migrant than winter visitor and that the moult is about seven weeks behind Vega. Taimyr Gull is therefore a necessary label to describe these gulls... whatever their ancestry.
When my gulling season starts at the beginning of November there are parties of gulls (usually up to 30) already present, the adults form homogeneous looking groups and with plumage obviously different to the early Vegas, this sets them apart even without the strikingly different moult timing. It also has a very distinctive juvenile plumage at this time (previously posted here), which is largely retained until mid-winter, however once the juvenile moult gets underway it's more continuous than the stop-start Vega moult with next generation tertials and coverts appearing concurrent with the last scapulars. So while the immature plumage bears little or no resemblance to the corresponding appearance of Vega throughout winter and puts them firmly in the fuscus camp, identification of all adults can become less clear, if not downright confusing, as winter passes.
November 23. Part of a flock of Taimyr Gulls. Unfortunately this is the only group shot I've got and this only because I was more intent in getting the unusually dark kamtschatschensis Common Gull (third from left). Even from this shot it's possible to get a feeling for the lighter head and neck markings as well as much cleaner breast sides compared to Vega.So much for the obvious November birds, below are a couple of shots of an "intermediate" bird taken January 11, the first shows a Vega on the right with the mixed feature bird. This is the kind of gull the casual gull spotter might overlook as a Vega, it certainly isn't Taimyr, but I'd call it a Vega with Taimyr influence, not necessarily an F1 hybrid, one of the stepping-stones that really muddy the water. The legs are fleshy with a distinct yellow element especially about the knees (much more obvious in life), though the yellow isn't clear in these images it will probably become very yellow in spring. The head markings are Taimyr type but become broader and messy on the hind neck, spilling rather too heavily across the breast. The primary moult would be possible but exceptionally late for Vega while slightly early for Taimyr. The saddle colour looks indistingiushable from Vega.
It's highly likely that there will be hybrids here between Taimyr and Vega (and possibly even Taimyr Gull and Heuglin's Gull) to confuse the situation. This applies to elsewhere in the range and surely Taimy x Heuglin's must be causing confusion somewhere. In Osaka it seems there's a higher proportion these more confusing "intermediate" birds from mid-winter after most Taimyr have passed through and larger numbers of Vega have arrived. Having already implied that November birds are straight forward I'd have to set the record straight by saying there are some lighter-saddled early birds too, which aren't so obviously Taimyr, and would be tricky if seen later in winter when moult is no longer an aid to identification. It's fortunate that a few adult Taimyr do remain throughout winter allowing an appreciation of their moult progression.
No matter how confident I feel about these gulls in autumn certainty goes out the window in late winter and I don't seem much further forward than my first spring in Osaka. There is suddenly a large number of yellow-legged gulls displaying a wide variation in size and structure, saddle colour, primary markings, and that gulls are losing tell-tale head markings adds another layer of difficulty. Another obvious yellow-legged contender is Mongolian, there aren't many here in winter but their number could increase a little in spring, at a time their pinkish-grey legs are yellowing and they are no longer so obvious due to other taxa become equally white-headed. Further there are some gulls identical to Vega but for yellow legs and whether birulai exists or not it's possible that some Vega do develop yellow legs in the breeding season without any need to consider past Taimyr influence. Types which might have been sending mixed Taimyr/Vega signals during winter can suddenly develop yellow legs and are more suggestive of direct hybrids or recent back-crossing. On top of this there are a few otherwise typical Taimyr Gulls that are pink-legged in spring and could represent historical Vega influence just as yellow-legged Vegas may. Interestingly there is a very small number of darker-saddled gulls which don't fit comfortably with either Taimyr or anything else that could potentially occur such as heuglini or barabensis.
Ultimately whether Taimyr Gull is a hybrid swarm or a valid taxon, it's likely that ongoing hybridisation with Vega to the east and Heuglin's to the west will result in many confusing birds in the field, whether in Japan or elsewhere. The two images below raise yet another question, regarding saddle colour. In spring there seem to be distinct clusters of light- (the majority) or dark-saddled birds, each with a more or less full suite of Taimyr features, rather than continuous range between light and dark extremes. The plumage, bare parts and structure of the paler gull show no sign of Vega influence (other than the saddle being closer in colour), it looks a standard Taimyr in all respects. Admittedly this shot doesn't show anything beyong fine head streaking, yellow legs, longish wing with small A-spots and fine fingernail separator on p6 while the other individual is darker than most birds occurring in Osaka. Is the paler bird Taimyr Gull, whether that is part of a stable hybrid swarm or not, and could the darker bird be an example of hybridisation between Taimyr and Heuglin's or could it even be Heuglin's Gull?
April 9. Two yellow-legged gulls in spring when significant difference in saddle colour occurs. There seems to be two distinct types, each slightly variable, without a continuous range between the two. The obvious conclusion being one is a Taimyr and the other a hybrid. However the paler-saddled bird averages slightly darker-saddled than Vega but with no other features indicating Vega influence. Could they instead be Heuglin's and Taimyr Gull? The paler of the two is by far the more common here. 
April 9. Another shot of the dark bird above. Compare the small A-spots to the Vega on the left and there's black down to (at least) p4. Black reaches the primary coverts in p7 which also has a very fine but distinct fingernail sepatator. Heuglin's? Heuglin's x Taimyr hybrid?Structurally Taimyr average smaller than Vega though there's a lot of overlap. Many but not all are of slighter build, more attenuated at rest and proportionately longer-winged in flight. Some are quite small-headed, bills vary in size but are often slimmer and normally have a less steeply curved tip to the upper mandible creating a longer more pointed bill compared to the blunter tip of Vega. At the other extreme some birds, presumably males, have disproportionately massive bills looking far more powerful than those of Vega. Under field conditions the irids of both Taimyr and Vega can be so heavily flecked to appear totally dark or seem unmarked pale yellow, even whitish. The latter is more likely in Taimyr but not impossible in Vega.
As already mentioned saddle colour is variable but on average slightly darker than Vega, though some are indistinguishable, while others are as dark as Slaty-backed. Vega can have quite fine head streaking in winter, Taimyr invariably does and this develops into well defined lines on the hind neck with at most only a little blotching at the very base and usually clean white breast sides whereas Vega markings tend to coalesce into a muddy grey shawl around the base of the hind neck frequently spilling onto the breast sides and meeting across the centre on heavier marked birds. Taimyr primaries normally have smaller A-spots than Vega, the number of primaries with black sub-terminal markings overlaps but on average Taimyr has more and also averages blacker towards the primary coverts.
The following images attempt to convey the appearance of typical Taimyr and how confusing some other birds can be.
October 12. I never start gulling in Osaka until the beginning of November so am unsure when the first Taimyr arrive but this is an early bird on Hegurajima nicely compared to two Vegas. The smaller size and slimmer build are obvious, as are the still bright yellow legs and the later moult. The head is still completely white while the Vegas are already looking smudgy, all the visible primaries are retained with small worn apical spots whereas the Vegas both have new p6-7 beyond the tertials and one has dropped all the old feathers. The neutral light here gives a good indication of the difference in saddle colour.November birds
November 5. Taimyr on the left with a Vega on the right. Like this bird, some still have a clean white head and neck but others are developing fine streaks and some even limited Vega-like grey at the base of the hind neck. The gonys spot is often far more prominent than that of Vega even when distant. All five visible primaries are retained with very worn apical spots while the Vega has new p8 in place. Many missing coverts "stretch" the tertial fan giving an elongated appearance, nevertheless it is a longer, slimmer bird. The usual strong light in Osaka renders any difference in saddle colour much harder to detect. 
November 5 (as above). A view of the underside of the five retained outer primaries. The p10 tongue is variable, often it is more restricted than this with just a short wedge but it can be slightly longer and square.
November 5 (as above). Two shots showing the upperside of the retained primaries and the extent of coverts moult revealing white bases. The legs are fairly washed but there's still a distinct yellow cast which was more obvious in life and even in the original images. The black on p9 falls short of the primary coverts on this bird but it isn't unusual to have black to the base of p9 and even p8.
November 12. A typical individual; fine streaking on the crown, cheeks and hind neck. In this case markings extend onto the breast but are clearly defined, not blotchy as in Vega. It has a slim, pointed bill with a significant length of the prominent gonys spot abutting the cutting edge (unlike non-breeding Vega), dropped greater coverts and retained outer primaries.
November 19. A typical individual on the right and though by comparison the other may suggest Vega it is in fact Taimyr. The dark hooded effect is created by fine streaking densest on the lores as is often the case, though it's dangerous to generalise about head markings as they are very variable in both Taimyr and Vega. Some Taimyrs show this surprisingly short but still pointed bill. 
November 19 (as above). The less obvious Taimyr on the left has three retained primaries with no sign of new feathers beyond the tertials and the degree of coverts moult is typical for November. The head streaking is fine even though dense enough to create a dark-headed appearance. The occurrence of pink legs often combines with a paler yellow bill whereas the other bird with yellower legs also still has an intensely yellow bill. Having said that, most winter birds have more orange element to the legs than this bird and later in the winter this gull may be ignored as just a 'funny' Vega.
November 19 (as above). The lowest hind neck streaking remains fine lacking any Vega-like grey smudging.
November 22. Another dark-headed bird but this still with intensely yellow bare parts.December birds
December 4. A typical bird with small oval p9 mirror. Moult is advanced on this bird.
December 4. Two shots of a bird that hasn't dropped p8 yet, p10 is displaced revealing a small split mirror on p9. Typical large greater coverts gap for this time of year.
December 24. New p6 beyond the tertials. The lower hind neck is dark, heavily marked but this is clearly the result of dense distinct lines unlike the more usual uniform grey wash of Vega.
December 24 (as above). With Vega for comparison. About 70% of Vega look full-winged by the end of December, if p10 isn't in place its not far behind the fully grown p9. Most of the rest have p9 longest but not fully grown or like this bird with p8 as the longest feather. The greater coverts are always complete. I'd consider this Vega a laggard in moult terms but not exceptional, while gulls with p7 as the longest are very uncommon by this time. 
December 24 (as above). Taking off with Vegas, the latter are full- or nearly full-winged as I'd expect at this time. Though the non-breeding leg colour is obviously far less intense than when breeding these shots show the typical orange-pink quite different to those of Vega. 
December 24 (as above). Greater coverts on the underwing are at a similar stage of moult as the corresponding upperwing tract.
December 24. Two shots of another bird, on the same date, this with p7 in place which is definitely advanced by Taimyr standards and could be matched by very late moulting Vega. Note the full-winged (or nearly so) Vegas behind it.February birds
After some of those December birds suggesting moult timing might not be so very different, even if only in a few cases, we can fast forward to February and see how typical gulls are progressing.
February 6. The typical Vega primary moult would look something like this about seven weeks earlier in mid-December.
February 12. Another example with p8 the longest primary. Though the hind neck is heavily spotted the markings remain largely distinct and don't coalesce into a muddy shawl.
February 20. A powerful looking male type having p7 as the longest new primary, p10 retained. The combination of relatively white head but prominent darker loral feathering is a feature quite often seen on Taimyr but not Vega. 
February 20 (as above). Broken band on p4, loral markings darker than those on crown.
February 20 (as above). P10 tongue can be longer and squared off but is usually short and angled like this.
February 20. A more gentle-headed female type on the same date. Again p7 is the longest primary and loral markings the darkest on the head. 
February 20 (as above). A good view of non-breeding leg colour, yellowish blending to pinker feet producing an overall orangey effect.March birds
After only a small number of Taimyr being present through winter larger numbers start to re-appear on the Yamatogawa in March.
March 13. A party of three birds, two adults and a young adult with black on both mandibles. Some birds have proportionately massive bills, the bird on the left is large-billed but by no means as large as they get, it contrasts astonishingly with the very stubby-billed examples. Of course all large white-headed gulls can show enormous variation between the largest- and smallest-billed but dramatic differences are relatively frequent with these gulls.
March 28. A powerful male type gull with an eye at the light end of the scale. As some of the previous images show the degree of flecking is so variable that in field conditions eye colour varies from all dark to white; much as Vega.
March 12. This bird shows very mixed features between Vega and Taimyr. The massive rather pointed bill, largely white head with darker feathering along the bill are clear Taimyr features however the hind neck markings are indistinct and continue across the breast in true vega fashion. The extensive black in the outer primaries look good for Taimyr but the very large A-spots lean strongly towards Vega. The legs lack any yellow element, which would be odd for Taimyr in March. I've no idea how to read this gull but it's a good example of a real muddy-the-waters Japan "intermediate". April birds
If anything late March and into April is the most confusing time to identify adult Taimyr in Osaka. I'd expect birds to be yellow-legged by this time yet some are quite pink, Vega are losing heavy winter foreparts markings and are closer in appearance, worst of all is the large range of saddle colour amongst otherwise typical looking Taimyr.
April 3. Two shots of the same bird with intensifying colour on the bare parts. Winter head markings are much weaker but hind neck spots are sharp and loral markings are again more prominent than other head streaks. Like all gulls the head shape can change dramatically. Saddle colour is the lighter type.
April 3. Three birds together with varying head markings. These are also at the more usual light type saddle colour, much lighter than the Slaty-backed. By contrast the following gull on the same date is much darker-saddled than the Vegas and a good match for the Slaty-backed present.
April 3. Though this gull is much darker-saddled than the previous birds on the same date all the other expected Taimyr features are the same. 
April 3 (as above). A good comparison with Slaty-backed.
April 9. A typical bird.
April 9. This bird on the same date is slightly paler-saddled, the bill is rather long and typical Taimyr. 
April 9. Another on the same date, this slightly darker-saddled but with unusually pink legs for this time.Does heuglini occur?
Unlikely as it may seem there's always a possibility that Heuglin's Gull occurs in Japan. Certainly there are gulls that wouldn't raise to many eyebrows if Geography weren't an issue. The following gull was in with a flock of Vega and instantly stood out as a Taimyr but on closer inspection it differed subtly in several respects. However if it's difficult to be sure about taimyrensis in Japan, confirming heuglini is even more problematic.
February 5. Amongst the Vegas its white head with smudged mascara before the eye really made it stand out. The legs look slightly pink in this image but were more flesh in life.
At first glance it looked a classic Taimyr but in retrospect even in a shot like this there's nothing that looks out of place for Heuglin's. 
P10 is almost fully grown making this a fairly advanced individual compared to several of the February birds above. There's a small p9 mirror on the left wing but not the right. Unusually for Taimyr the far wing lacks a fingernail white separator between the grey and black on p7 and there are dark streaks in the greater primary coverts. It's often said that eastern birds more often have dark streaks in the greater primary coverts but this should never be construed as often having streaks. In fact this is the only such bird I've seen that doesn't have other signs of what would normally be considered indicators of immaturity.
The black in the wing tips is more extensive than the average Taimyr Gull, it has the squared-off look of Mongolian Gull. Equally intriguing is the narrow, even-width trailing edge along the secondaries which becomes exceptionally narrow along the inner primaries.
From below the inner primaries look very dark because of the minimal white at the tips. Sub-adults are a consideration but most (all?) show signs of immaturity such as the two birds below on the same date. Both look very similar to adults but show dark markings on the bill. One has large areas of sub-terminal black on the outer webs of the primaries down to p2, the other only to p4 but it also has black streaks in the greater primary coverts and a black base to single secondary.
February 14. Poorly defined black markings on both mandibles.
February 14 (as above). Extensive black in outer primaries. 
February 14 (as above). Large black notches on the outerwebs of the primaries down to p2. 
February 14. Slightly heavier bill markings and pinker legs than the previous individual.
February 14 (as above). Black streaks in outer greater primary coverts and a single black-marked secondary. Mystery gull
It goes without saying that unusual gulls aren't very unusual but it's less common that striking birds looking as though they should be easy to put a name to come along. The following adult or sub-adult accompanied by an equally odd 2CY first winter is such a bird. When I first saw it I wondered if it could be barabensis because of the gleaming white head in the middle of winter (Feb 1) however the extremely pale eye and dark saddle made this unlikely so thoughts turned to heuglini. However the white head seems wrong, the p10 tongue too long and if the the first winter that seemed inspearable from it is the same taxon, then its exceptional degree of wear and fading of some second generation feathers suggests a far more southerly natal area.
February 1. The combination of gleaming white head and dark saddle was quite remarkable and demanded attention. Unfortunately so much so that I never noticed the 2CY gull next to it until going through the images. 
P4 has a complete subterminal band, black very nearly reaches the coverts on p7. 
The p10 mirror is relatively small and round, and the slightly concave tongue is well over 50% of the feather length. Black seems restricted on all the inner webs creating a surprisingly pale underside to the outer primaries. The first winter is very faded, the coverts and primaries are quite a light brown, quite unlike Taimyr Gull.
Hind neck distinctly marked, probably more so than any barabensis and also the is eye very pale. The head looks cleaner than heuglini as well as p10 looking wrong. The first winter gull already has a surprisingly pale eye.
Compared to Vega the terial crescent is narrower and the wing extension longer. The Vega p7 tip typically reaches just beyond the tail, very different to this long-winged gull.