Taimyrensis seems widely viewed as a hybrid swarm resulting from introgression between western Vega and eastern Heuglin's and received scant coverage in Olsen's "Gulls". So perhaps it's hardly surprising that many visiting birders don't pay much attention to it, preferring to get Black-tailed and Slaty-backed out of the way, before moving on to 'more important' Japanese birds. Nevertheless, for the last 15 years 'taimyrensis' has been an indispensable label to describe the large number of distinctive gulls I see passing through Kansai in autumn and spring. Which is incidentally also a less popular time with visiting birders, who probably never get to see flocks of these gulls.
Having already said that they're distinctive, and many if not most are easily separable from Vega, I must say I've struggled year after year to reconcile the very distinctive individuals I was seeing that bore little or no resemblance to Vega on one hand while on the other the there are less clear cut birds that are at first sight much more Vega-like due to paler saddle (equal to mid-range Vega grey) and pink legs. Plus the variable iris colour (from whitish to wholly dark under field conditions) can also give pause for thought. It's easy to understand how any taimyrensis with dark eyes plus pale-end saddle and pink legs could suggest a hybrid or even go unnoticed altogether. I have wondered whether this variance could be due to ongoing hybridisation occurring in areas of sympatry between Vega and the presumed stable intergrade swarm.
Part of my problem has probably been I've been hoping all individuals to fall within a narrow range of both readily recognisable and consistent features rather than allowing for the wide range of variation typical of all accepted taxa. In other words it's as if I've been attempting to apply the stringent identification criteria that would be required of a vagrant to a whole population.
However, over the years I began to realise I wasn't seeing any more variation in size or saddle and bare parts colouration than I'd expect to see in Vega, European Herring Gull or any other large white-headed taxon, indeed there was actually far less variation than I see in Vega. As far as saddle colouration is concerned there is undoubtedly a lot of overlap with Vega. Olsen's "Gulls" gives the Kodak Grey Scale as 6-8 for taimyrensis and (5)6-7(8) for Vega. That said I've never seen any Vega approach the darkest taimyrensis, nor any taimyrensis as light as pale-end Vega.
Darker taimyrensis are very easy to pick out amongst Vega, even in these sunny conditions when contrast would ordinarily be less obvious (March 22). Photographic images never seem to do the contrast justice but whether in bright sunshine or in the dullest conditions, as can be seen in the final shots of this post, the difference can be obvious.
Another gull in bright sunlight, this an excellent example; smaller and slimmer than Vega, longer-winged with a clearly darker saddle and bright yellow legs (March 26).
The van Djik et al paper in Dutch Birding (Taimyr Gulls: evidence for Pacific winter range, with notes on morphology and breeding) states (citing Leibers 2000, Leibers et al 2001, Leibers and Helbig 2002, Leibers et al 2004) "Genetic analysis has shown that they represent a distinct population, ie, with a measurable degree of genetic differentiation and without obvious introgression". I haven't read these papers and the citation doesn't make clear how this was measured, but it is interesting that Olsen also citing Leibers et al 2001, amongst others, states that barabensis and heuglini are not genetically different at an MtDNA level. Perhaps more interesting the van Djik paper goes on to say that they not only found no evidence of assortative breeding on the Taimyr Peninsular but that Taimyr Gull is the only taxon breeding in this region. According to Olsen, who treats taimyrensis as a hybrid population, it is sympatric with Vega across the western half of the 400,000km2 Taimyr Peninsular.
This more recent work suggests a situation very far removed from the hybrid swarm theory, perhaps more birders will be paying more attention to taimyrensis in the future.
APPEARANCE
I always think of taimyrensis as averaging slightly smaller than Vega but with much overlap. Longer wings in flight frequently translate into a more attenuated appearance at rest, though this isn't always the case and I sometimes think the typically smaller apical spots play a significant role in enhancing this feature in some individuals, as do the overall slimmer lines of some birds.
Head and bill shape are somewhat variable (Vega even more so), the head can be gently rounded to angular with a distinctly long sloping forehead which when combined with an often slim bill lacking strongly pronounced gonys, the head can look very long. At the other extreme some male-type birds' bills can be quite deep at the gonys and combined with a blunt tip can look rather stout and stubby.
As far as bare parts are concerned, the bill and more particularly the orbital ring colouration seem reasonably consistent. The legs less so. The orbital ring is normally a conspicuous reddish that can lean towards a more orange shade whereas Vega tends to show a wider range from flesh through orange- (even yellowish-) pink to darker, through taimyrensis red to an even dark colour which to me looks purplish under field conditions.
The gonys tend to show more extensive red than Vega, often extending from near the tip to the proximal edge of the gonydeal expansion while abutting the cutting edge for much of the upper edge. Sometimes red spills onto the upper mandible but this is not the norm. A greater number of birds show a slight amount of dusky to blackish in the lower mandible than might be expected from just the young adult population but there's no way to know if this is an age related feature. A smaller number also have dusky/blackish in the upper mandible but this is often combined with restricted red on the lower indicating these individuals are younger birds, often further borne out by other signs of immaturity such as the presence of dark streaks in the greater primary coverts.
The legs can be yellow or pink coming into breeding condition. Post-breeding and winter birds can have orange-flesh, presumably a toned down version of yellow-legged breeding birds, but many are pink-legged which isn't surprising given that many breeding birds are too. The van Djik paper icludes an image of a flock on the breeding grounds in which many of the gulls have pink legs.
Definitely a young adult with very limited red in the bill as well as additional black in the wing. Nevertheless the orbital ring is a very typical bright red. 
Another gull with significant blackish in the bill but no other features that might suggest immaturity. This gull with its longer sloping forehead looks quite different to the following bird.
Yet another with blackish markings but still extensive red. This gull with a gentle, rounded head compared to the previous gull.
More smudged, Vega-like, hind neck markings on these two but both have extensively red gonys. 
Another with heavy hind neck markings, extensive red on the bill and bright orbital ring. This gull with a clean eye. 
A heavily flecked eye that looked completely dark in the field, see a less heavily cropped version below following two Vega images for comparison. The red in the gonys is weaker than on many.
A nearby Vega for comparison; the orbital ring is pinky-flesh and the red in the gonys is more of an isolated spot with very little reaching the cutting edge and falling short of the proximal edge of the gonydeal angle.
Another Vega, this with slightly redder-pink orbital ring and clear yellow between the cutting edge and gonydeal red.
A less heavily cropped version of the last Taimyr image, the eye looks solidly dark here. Though often hidden the extensive black towards the bases of the primaries often creates a uniform block of colour whereas the visible greyer bases of Vega create a narrower black strip with grey between the leading edge and tertial fan. 
The first of the two earlier examples of Vega repeated to show grey bases to mid-primaries. Of course not all Vegas are as pale-winged as this.
A Vega behind two Taimyr, the difference in saddle shade here is a good representation of how typical birds compare in the field in bright conditions. Often Taimyr will show smaller apical spots than those of Vega but not in this case. The two first winters are also Taimyr. At the time I was puzzled why there were more first winter Taimyr than Vega but subsequently realising these sightings are coming on the back of a lemming year it's possible 2014 was a bumper breeding year, experience over the next few spring migration periods may reveal whether there's anything in the theory. 
While being shaded from the strong sunlight there's still no doubt that these are very different looking gulls.
White breaking through to the tip on p10 is very unusual in my experience but this useful image shows it happens.
I didn't notice in the field but either the primaries aren't quiet fully grown yet (this would be very late even for Taimyr) or the feather lengths are unusual giving this odd appearance with p9 just beyond p8.
In the other direction, though p10 is often the longest visible feather it isn't always as far beyond p9 as seen here. This individual lacks any white in the tip of p10. 
P10 with just a tiny white apical spot on this individual.Just a few Vega Gulls on the same dates for comparison.
By late March / early April few Vegas retain heavy winter head, neck or breast markings and don't look any different to Taimyr in that respect. 
Grey mid-primary bases are often visible on standing birds.
This Vega does have a deep reddish orbital ring but nothing else about it suggests Taimyr. From the heavy bill with limited red in the gonys, grey in the primary bases along with much white in the outer primaries and pink legs, it's very much a Vega.
Even more obvious grey tongues on this Vega, not to mention deep purplish-pink legs and small red gonys spot.
The aim of this shot was the hulking first winter Taimyr so the Vega is out of focus but it's an example of a thayeri-type wing pattern. Limited black in the underwing and blackish-grey bleeding towards the coverts on the upper side. Such birds are very uncommon but not rare and seem to genuinely be thayeri-type rather than hybrids or leucistic individuals. By 19 April Vega Vega numbers were getting far lower, because of which Taimyr were again becoming the more numerous of the two, as they are in late autumn. Whether these were lingering birds or part of an ongoing movement I don't know for sure. However the large number of first winters that had been present seemed to have moved on despite common sense dictating they'd have less urgency. So I suspect the adults present on this date were newly arrived, part of a continuing northerly drift from more southerly wintering grounds.
At dawn on an overcast morning Taimyr Gulls were strung out along the beach punctuated by a few stand-out paler Vegas. As light broadened they flew onto the water and drifted out beyond camera range. 
Sub-adult Vega with Taimyrs. 
I'm already looking forward to getting my improved photographic gear onto these birds when they return in late October.
We get a few of them every year outside the breeding season too.
ReplyDeleteVega Gulls seem to vary enormously from individual to individual anyway, now we have to worry about intergrades too. Whoever started spliiting all these species have given a lot of birders a lot of ID headaches.
It's an interesting headache though. I don't really mind if they're split every which way or lumped into just a couple of species (ok, I'd prefer the former) but as long as the various taxa are diagnosable in the field, they provide hours of "fun".
DeleteHope you enjoyed your UK trip.