Is this a perpallidus Common Kestrel?

 There's pervading view that the perpallidus subspecies of Common Kestrel is a rare winter visitor to Japan. But how rare might it be? It doesn't even occur according to the current edition (published 2012) of the OSJ Japan list! I first heard of 'pale continental birds' about 20 years ago but am still none the wiser as to their occurrence or identification; the vague “it’s paler” is as far as easily accessible information has taken me. But in what respect is it paler? 

Earlier this week I spotted a small bird of prey in flight about 800 metres distant across the fields. When I got the bins on it, it was clearly a Kestrel but a strikingly pale one, looking a rather uniform sandy colour. With the posibility of perpallidus in mind I dog-legged my way along the narrow roads through the patchwork of fields to where the bird had been. It was still present and I rattled off a few record shots from a healthy distance, not wanting to disturb it and have it disappear over the horizon.

I needn't have worried as it stuck to a very limited stretch of fields, either perching on short bamboo polls, bushes or farm outbuildings, when not hovering over the fields. In particular, one small bean field had a magnetic attraction, presumably because the cover looked/was more vole-friendly, and the bird frequently returned to hover persistently over it, as close as 10 metres from where I stood. It proved remarkably tolerant of approach when perched too. 

At one point another Kestrel overflew the bean field resulting in low aerial confrontations, leaving them sitting about 10 metres apart, first on the road then in a bare field, allowing brief but good comparison. Both were first winter birds, the pale individual a male and I suspect the other a female but that’s based purely on its larger size.

I returned two days later and found both birds in their exact same places. However temporary they may be, these areas seemed to be clearly defined territories, boundaries recognizable even to the human eye. Although they could both be on view at the same time, they remained within their respective small areas of what is actually a large expanse of fields, thus direct comparison was never possible except for that one occasion on the first visit.    

I’m not claiming this Kestrel is perpallidus, I don't know anything about their appearance, but if perpallidus is known as a pale version of the usual Kestrels here, then this has to be a bird of interest. It looked eye-catchingly pale at longer distance as no dark markings or areas of contrast could be made out. Looking at it perched in the distance I was reminded of Isabelline Shrike in terms of pale uniformity. At closer range it looked less remarkable as it shares the same basic pattern as intersinctus, however, the blackish markings aren’t heavily saturated, they look more grey than black. Further, the bars on the lower scapulars, tertials, and all wing coverts are noticeably narrower than on the other bird present. Even the flight feathers have a brownish cast compared to the blacker plumage of the larger bird. The upper scapulars are adult-type so not relevant to a direct comparison with the other bird.

One other point of interest, this bird spent as much time hovering to scan as perching to scan and never employed Merlin-like pursuit hunting methods. Rightly or wrongly, I always think this is suggestive of a continental bird where hunting for terrestrial mammals is likely to be more successful. I never saw the larger bird hover at all. 

As I haven’t been able to find any info on how to separate these taxa, or even whether they can be reliably separated; I'm at a loss. That perpallidus is believed to visit Japan in winter implies that it is possible to identify them, I've just yet to meet someone who can tell me more than 'it's paler'.

This is a pale, uniform Kestrel, even the flight feathers don't contrast greatly with the rest of the upperparts. The terminal tail band is the only feature that stands out as blackish and contrasting.  

Compare with this intersinctus present. This is an altogether darker bird and the tail band doesn't look strikingly black in contrast with the rest of the plumage. The coverts, especially towards the bend of the wing, and the whole of the upperparts look blackish with pale markings. Whereas the possible perpallidus is looks pale with dark markings.  

The intersinctus again. The black bars are broader than the paler ground; the wings coverts are particularly blackish. Compare with the possible perpallidus below.

The possible perpallidus. Ignoring the adult-type upper scapulars, the others have dark bars distinctly narrower than the pale ground, additionally the saturation is such that they appear grey not black. This is also true of the wing coverts, most markedly the lesser coverts. The primaries have a brownish cast.  

Quite unconcerned by my presence, sheltering from the slanting, sleety rain in the lee of a farm outbuilding.

Heuglin's Gull: Do they occur in Japan, and have I seen one?

Across twenty-odd years of gulling here, I've seen a very small number of gulls which looked good contenders for Heuglin's Gull L. (fuscus) heuglini. However, can we ever be a hundred percent sure about this identification in Japan? Might not a Taimyr Gull L. (f) taimyrensis with a 'perfect storm' of heuglini-like features be impossible to eliminate without DNA confirmation? This has been a perennial frustration, a question to be pushed to one side for however many winters before another suspect re-centres it. This winter has seen another.   

It isn't even possible to ascertain how often Heuglin's Gull is claimed in Japan, let alone their true status if they do occur. Images of some claims inevitably come to attention online, some look good, others are less convincing. Although judging online images adds another layer of incertitude. 

If it seems surprising that Heuglin's could turn up with any regularity at all, given their expected wintering range, no more so than Iceland Gull L. glaucoides kumlini (also?) being a somewhat regular vagrant. And unlike the distinctive and eye-catching kumlini, Heuglin's runs the risk of being either over-recorded on one hand, because of optimism and/or confusion over taxonomy, or under-recorded on the other due to the ease with which this taxon could slip under the radar. The latter not least because of the relative paucity of gullers in Japan; you're far more likely to see non-birders taking pictures of 'seagulls' on the beach than find a birder going scrutinizing a flock. 

On 22 November, an adult gull knocking on the dark-end door of the Taimyr grey-scale range stood out amongst a flock of about 80 gulls, numerically, Vega just edged a near 50/50 split with Taimyr. After securing a couple of distant record shots, I approached to scope it from about 50 metres. 

Possible adult Heuglin's Gull

The first thing to catch the eye was the dark grey saddle (Fig 1). Once focused on the gull, the combination of long, sloping forehead and long bill, the slim build and flat back seemed to justify the attention, definitely suggesting this had the potential to be something other than the usual Taimyr. Additionally, the rather aggressive facial expression struck a jarring note with the gender expectation normally associated with small size and slim build. The saddle colour was also of interest as wear on the scapulars and coverts created a variably brownish, grey-brown or even silvery wash depending on the angle of view and lighting, but basically giving a 'dirty' appearance. This is something which is never obvious on Taimyr. Yes, worn Taimyr do share this same effect produced by wear, but there's far less contrast against the paler ground colour, making it apparent only when looked for. The brown wash was immediately noticeable on this dark-saddled gull.

Size and structure

The bird was small compared to most gulls present, but more striking was the slim build, accentuating the attenuated appearance. It also gave the impression of being long-legged compared to Taimyr, which tends to be a short-legged taxon. Indeed, some Taimyr look remarkably short-legged but this isn't always the case so I wouldn't put too much emphasis on this point. The slim appearance was in part due to its flat back and absence of tertial bulge, but it must be pointed out the upper tertials had been dropped which may have enhanced this impression. When the bird adopted an upright stance, the angle from hindneck to scapular crescent was very steep, and then, with no tertial bulge, there seemed a gentle concave sweep through to the primaries tips (Fig 4). The forehead was long and sloping, peaking behind the eye, the long bill with shallow gonydeal expansion added to a long-headed look (Fig 2); Taimyr is typically short-billed and rounded-headed, especially the smaller individuals, while large individuals often have more angular heads and strong bills with a deep gonydeal expansion.

Plumage

Head white. Fine, pale grey flecks across the forehead and lore coalescing in a dark smudge before eye. Flecks becoming fine dashes around eye highlighting a white upper 'eye crescent'. Crown and hind neck finely streaked pale grey. Base of hind neck more heavily marked with grey, creating collared effect. Conspicuous grey spots spilled onto sides of breast and smaller spots across centre of breast. Saddle grey (I'd judged similar to graellsii albeit without a graellsii for comparison). Wear on scapulars and coverts producing brownish, grey-brown or silvery wash to these tracts (Figs 6-7). P10 mirror restricted to the inner web on left wing, extending onto outer web on right wing (Figs 8-9). Upperside p9-10 black to the coverts (no mirror p9), p8 black to coverts on outer web, grey tongue (probably) extending for just over half the feather length (how much of the worn tip is missing would affect this slightly), p7 black almost to the coverts. P7-8 both with very narrow 'fingernail' white separators between grey tongue and black tip (Fig 9). P5 with complete broad sub-terminal band extending up leading edge. Still growing, it was slightly shorter than p4. P4 with prominent black notch on outer web. P10 underside tongue about a third length of feather, angled diagonally across, p7-9 tongues 'U'-shaped (Fig 8). Underparts white. 

Bareparts

Bill yellow, not washed out but becoming white at the tip. Red gonys spot extensive, covering over a third of lower mandible (Fig 5). Legs orange-pink to pale yellow or straw, depending on light and angle. Eye very pale yellow with limited speckling. Orbital ring deep red.

Moult

Slightly late for the typical Taimyr, but not significantly. Primaries slightly behind average but within expected variation, and coverts a little further behind. The inner four primaries are new, p5 is almost in place. Only a 5-6 dropped greater coverts on the right wing, even fewer on the left, plus a few primary coverts are the only obvious signs of moult, Taimyr normally looks obviously 'patchy' at this time of year, with exposed white feather bases dotted around the wing; very often the white trailing edge of the secondaries is exposed at rest due to missing greater coverts. The uppermost tertails have also been dropped. 

While none of these features are diagnostic of heuglini, nor are any contrary to what might be expected either; collectively they make a good case for this bird being a Heuglin's Gull. I believe this bird would not suggest anything other than Heuglin's within the taxon's normal range and would not stand out within a flock, whereas it certainly does stand out within a flock of Taimyr Gulls.  

Fig 1: The bird at the rear right. Even viewed at a distance the slim, flat-backed appearance is different to all the other gulls present. The difference in head shape can also be guessed at even in this view. The dark gull on front right is Black-tailed.  

Fig 2: Though the foreground Taimyr is out of focus, this shot nevertheless shows the difference in head and bill shape, the slimmer, leggier look and the steeper-angled, flat back to good effect. A grey-brown wash can be seen on the scapulars and coverts. Though mostly obscured, there is more black abutting the coverts at the base of the primaries compared with the Taimyr. A large stretch of the white secondary trailing edge is exposed by missing greater coverts on the front bird, this is typical of Taimyr at present. The bird in question, with very few missing greater coverts, does not expose the secondaries to the same extent and looks much neater. 

Fig 3: Slim, elegant gull compared to bulky Vegas.

Fig 4: Very straight upper bodyline. Long, sloping forehead peaking behind the eye. Bill long, without prominent gonydeal expansion.

Fig 5: Bill yellow with white tip. Gonys not deep but with extensive red. Eye very pale yellow.

Fig 6: The 'dirty' wash across scapulars and coverts (except fresher looking medians...) quite obvious.

Fig 7: Scapulars and coverts variably washed brownish or grey-brown creating 'dirty' appearance.

Fig 8: P10 tongue about a third length of feather, diagonal across inner web. Single mirror restricted to inner web on left wing, extends to outer web on right wing. 

Fig 9: Black of outer webs extends to coverts p8-10. P6-7 are missing, p5 is almost as long as p4; note extent of black up leading edge of what appears to be p4 actually belongs to the growing p5, nevertheless p4 has a substantial black notch.

Fig 10: This image conveys something of the overall appearance of the bird, the slim and attenuated shape and the long head with relatively long bill lacking a prominent gonydeal expansion.   

Fig 11: A long-winged gull. The extent of missing greater coverts on the right wing is easily seen here, the left wing has dropped fewer, and there are no other areas of white exposing feather bases in any of the other covert tracts.

This is point I normally push the record aside. I've got a better set of images of this gull than any previous individuals that caught my attention but I'm still no closer to answering the question posed in the title of this post.