Saturday, 10 June 2017

Two-barred Greenish Warbler? How about Arctic (borealis ssp)?

Last Sunday (June 4) was the first chance for the ferry to get out Hegurajima after a productive-looking low pressure system over the Sea of Japan had created a strong three-day airstream from the continent. There were no photographers with bazooka lenses staking out likely spots, just seven or eight birders scouring the place actually looking for stuff, which probably indicates a perception amongst some that spring migration is over. Well, it ain't.

My first and lasting impression out there was that island was alive with Kamchatka Leaf Warblers. A week earlier there had been a huge number on a wet morning in Kanazawa, harder to see but calling and singing constantly, this time round they were far more visible in the sun but less vocal; you can't have it all I suppose. Because the birds quieter could mean that even more went unnoticed and it would be interesting to know how many were on the island; hundreds I have no doubt. Just to be clear, all the birds I did hear were Kamchatka Leaf.

With about an hour and a half left till the return ferry departure time I learnt that a 'Tickell's' Leaf Warbler had been heard in the morning and I made my way in that direction without much hope of finding it, largely because of the general lack of vocalisation. So of course it came as no surprise that I couldn't find it. But... I did come across a couple of interesting, stubbornly silent, phylloscs in with a crowd of Kamchatka Leaf in a loosely isolated clump of trees. Both seemed smaller and more active than the many Kamtchatka Leaf present and were easily picked up each time they ventured into the open. Not to mention separable from each other, as one had two prominent wing bars and the other didn't. However all warblers collectively were only visible sporadically as they moved above or below a dense foliage line across the copse, about five metres up. The lower trees were impossibly leafy but protruding pines offered a clearer view when warblers 'surfaced', though it was a lottery where and when a given bird would next flit into view. Because of this it was frustrating trying to get or confirm details on these two birds when, as often as not, the 'other' bird would appear.

Once back on the ferry I told someone that I'd had a possible Two-barred Greenish and their unexpected reply was that they had heard a Two-barred about 300 metres from the spot I'd seen this bird!

Though I considered it a good contender for Two-barred Greenish in the field, I've since had doubts after reviewing the images but it's an interesting bird nevertheless and worth posting I think. It was clearly smaller and less heavily-built than the Kamchatkas, cleaner below and more active. So it drew attention to itself from the outset and was easily picked up every time it appeared above the dense foliage line. It was generally faster moving, less deliberate and more likely to hover than Kamchatka; it would suddenly emerge from the dense foliage into the pines flit quickly through the branches or simply hover briefly before dropping directly back into the thick stuff below.

The light was bright and in such conditions care is needed judging colouration, particularly differing greens or subtle shades on the underparts which are easily 'lost' in direct sun, this is even truer where images are concerned. However I did get a small number of reasonable shots of this bird out of the direct sun. Kamchatka Leaf was never a cause of identification concern as this bird stood out so clearly from them. The other common spring warblers here are Eastern Crowned and Sakhalin Leaf. The former is a relatively substantial and deliberate warbler to my eye, mostly bright greens and yellows and it shouldn't ever be suggestive of the Greenish complex given a reasonable view, however brief. With the views I had eliminating it was straight forward and in any case the bulk of them come through a month earlier. So that leaves Sakhalin Leaf Warbler, a separation which doesn't sound too difficult on the face of it, however Sakhalin does bear some similarity and looking at the images I wondered whether this bird may have been no more than a unusually bright, fresh-looking individual at a time most are worn and dull in appearance. Though I'd also expect Sakhalin Leaf to be on the breeding grounds by now and haven't seen one since mid-May when they were still reasonably common passing through.

The two most obvious plumage features when I first saw this bird, even more than the generally pale underparts, were two prominent wing bars and strikingly plain, hollowed-out white ear coverts, the latter outstanding viewed from any angle. On closer inspection the long supercillium was just as broad over and behind the eye as across the lores and the eye-stripe was distinctly narrow across the lores, giving a totally different impression to spring (worn) Kamchatka. The lower mandible looked entirely yellow in the field but the images consistently show a slightly dusky 'keel' so possibly this isn't an artifact and I simply missed it while watching the bird.

I've dismissed Kamchatka Leaf but why? At this time of year Kamchatka invariably lacks a median coverts bar (even fresh birds tend to have a relatively inconspicuous bar), though the lower bar is frequently broad. The ear coverts are more evenly mottled lacking a bold whitish crescent below the eye and therefore duller and less contrasting with the eye-stripe, the ear coverts often (not always) look open without a distinct border with the throat. The supercillium is prominent and usually blunt-ended mid-lores but becoming narrower over the eye and extending well back on the head without expansion, effectively a long slash from eye to nape side. Sometimes it will look broader and looser but this is probably temporary and dependant on feather position. More importantly perhaps the eye-stripe is of more or less even depth before and behind the eye and doesn't narrow markedly across the lores. On this bird it was narrow on the central lore and further pinched before the eye and base of the bill.

Sakhalin Leaf might seem a surprising contender for confusion however, like this bird, has a smaller feel and also tends to be quite active. Sakhalin has a greyish head and neck contrasting with brighter upperparts, this is quite distinct, by contrast this bird had only a slight suggestion of a greyish cast so the comparison doesn't hold too well on that point. Sakhalin's head pattern is basically similar to this bird, it has a greyish centre crown and is greener laterally, the supercillium is equally broad behind the eye where it is also whiter than before the eye. However the cheeks are usually mottled, looking duller and more uniform overall, thus the lower portion of the eye-ring is normally readily apparent. Sakhalin's bill is rather fine, though to be honest I'd have expected the Two-barred bill to be no different, yet this bird frequently gave the impression of being rather large-billed. Sakhalin's lower mandible seems remarkably variable, ranging from almost unmarked yellowish to almost completely dark; a match for anything it would seem. The tarsus can be very pale especially at the rear, almost whitish in some cases, but it is often similar to this bird, a purplish- to pinkish-brown at the front and only pale at the rear. However in my experience the feet are much paler and, if seen well, the claws invariably look whitish. Though it wouldn't surprise me if this feature weren't a constant either. Can Sakhalin can still have two prominent wing bars at this time of year? I'd guess this would be quite exceptional however I remember seeing two birds on Mishima one year, the first I actually identified as Two-barred at first but then changed my mind finding another double wing-barred bird the following day. Both were in early May when Sakhalin are passing through in large numbers and I assumed I had misidentified the first and put them both down as Sakhalin. Because the Sakhalin passage is largely over by now (at least I haven't seen one since mid-May) and as they don't breed in my area I don't really know first hand whether worn Sakhalin can still have two distinct wing bars by June.

Kamchatka Leaf is the only member of the Arctic Warbler complex I've heard in Ishikawa Prefecture this spring and as I mentioned there were huge numbers both calling and singing a week earlier, as well as quite a few calling birds on this visit too. As Arctic Warbler and Japanese Leaf Warbler are said to be inseparable from Kamchatka Leaf other than by voice I've discounted them as possibilities for the moment. Arctic Warbler, both borealis and kennicotti could possibly, or are even likely, to occur in Japan during migration. Perhaps wholly or in part at different times due to their respective breeding ranges. I have to say I'm not entirely happy to blithely rule these taxa out because they're said to be morphologically inseparable from Kamchatka Leaf Warbler in the field.

I'll briefly describe this bird then show the images.
A comparatively small warbler, rather plump and dumpy-bodied. Unfortunately I couldn't judge primary projection because of the viewing angle.
Crown, nape and hind neck green with a slight greyish cast only lacking on the greener sides of the crown. Eye-stripe darker green, broad behind eye but narrow across the lores. Supercillium long, reaching the nape, and arching prominently over the eye. Equally broad before and behind the eye where somewhat untidy. Slightly yellowish-white before and over the eye becoming clean white behind. Ear coverts with a conspicuous whitish crescent below the eye, rather extensive and high on face before eye because of narrow eye-stripe. Greenish, fairly uniform lower ear coverts forming a second and larger crescent. Coverts partly enclosed by a narrow darker green border, very conspicuous along the leading edge from the base of the bill, cutting through an area of white. Side neck pale greyish-green behind the ear coverts.
Upperparts green from base of neck to tail but with slight greyish cast on mantle. Wings brighter green lacking the greyish cast. Median coverts with fairly broad yellowish-white tips, duller than greater coverts bar. Greater covert tips whitish forming a bold oblong across the wing. Tertials dark brown with pale green fringes, flight feathers slightly darker. Secondaries and inner primaries fringed bright green. Tail dark brown with broad and rather diffuse bright green edges on proximal half of outer feathers (number unknown).
Upper throat white below eye-stripe and bill with a yellow suffusion from mid-throat, quite a clean break between the two. Breast whitish with faint yellowish tint, delicate pale grey wash at sides around bend of wing. Lower fore-flanks with with subtle greyish cast but faint yellowish cast bordering folded wing. Belly whitish with faint yellow suffusion similar to upper flanks. Vent and undertail coverts white. Undertail feathers with pale fringes (how many unknown).
Bill dark horn upper mandible with paler cutting edge, lower mandible yellow. Front of tarsus pinkish- to purplish-brown darkest towards knee. Feet paler and pinker, claws dark.

A striking head pattern; the combination of broad supercillium behind the eye, narrow eye-stripe before the eye and plain whitish ear coverts extending high in front of the eye is strange for an Arctic complex warbler. Hind neck and crown greyish-green, greener on sides of crown. Wings also brighter green. Underparts clean whitish in this shot with just a little grey around the bend of the wing, though yellowish suffusion just visible on upper flanks and belly. Yellow lower mandible looks slightly darker here due to shadow, both Kamchatka Leaf and Sakhalin Leaf can also lack any trace of dark colouration on the lower mandible. Feet pinkish, tarsus darker.

Two prominent wing bars, the upper less white. The face is strikingly white because of the crescent under the eye and the white upper throat forcefully interrupted by the narrow leading border of the ear coverts which stands out as a prominent dark line. In fact when I first saw the bird I was struck by a distinct spectacled effect because of this. At this angle a better appreciation of the underparts is possible; the upper throat and vent are white the lower throat is suffused yellow as are the remainder of the underparts to a lesser extent however there is a soft, uniform greyish area around the bend of the wing which dissipates across the fore-flanks. To me this shot conveys a sense of the bird's small size and dumpy body but that may be purely subjective because I actually  watched the bird in the field.

In this image the hollowed-out ear coverts given an indication of how conspicuous the white crescent looked in the field. Also the white band below the lores/bill contrasting with the yellowish throat is again prominent in this image.

Finally a heavy crop of the first image giving a clear view of the head with the whitish crescent below the eye and a pale greenish or yellowish-green crescent below that. The bi-coloured supercillium, yellowish-white in front and over the eye becoming clean white to the rear.

Below are some comparative spring shots of Sakhalin Leaf taken on May 16th and 5th respectively.

A worn Sakhalin Leaf with little remaining of the wing bars. The cheeks are pale but more evenly mottled and open compared to last Sunday's bird, the lower eye-ring stands out. The bi-coloured supercillium is very similar, and the eye-stripe only slightly thicker before the eye. Flanks greyish without yellow suffusion. The bill looks proportionately smaller and note the almost completely dark lower mandible as well as very pale claws. 

A fresher-looking bird but still primarily greyish and white below without yellowish suffusion. Narrow eye-stripe across the lores (like the recent bird) but again the cheeks are very open and more uniformly mottled contrasting with the eye-ring. The lower wing bar is very distinct with the feathers tight together at this angle. The feet and claws are whitish. As all these birds are adept at hiding their median coverts I've added another image of this bird below, the greater coverts bar is more broken up here and the median bar, though present, is very indistinct. I suspect it can be more conspicuous than this even at this time of year, but quite how much more I don't know. The lower mandible is more visible in this second image and seems to lack any dark colouration, very unlike the previous Sakhalin. Perhaps the bill gives the impression of being slightly larger in this image compared to the previous bird (to me at least) but it still looks more delicate than Sunday's bird.    

I've never seen Two-barred Greenish however I do have a fair amount of experience with the phylloscs occurring regularly in Japan and I find it difficult to reconcile this bird's appearance, the combination of size, behaviour and plumage, with any species I'm familiar with. So though I said at the outset this bird may be no more than an exceptionally fresh-looking Sakhalin Leaf (for want of any other plausible possibility), I doubt it. Indeed I'd find it far more difficult to support a claim of Sakhalin Leaf if it were the rarity in Japan. The big problem was not being able to get enough on this bird, neither call or wing structure to confirm or disproved a claim of Two-barred.

At the risk of making this identification more difficult than it already is, there is another potential piece in this puzzle; the other small warbler in the same group of trees. This other bird was every bit as lively as the other as well as being a compulsive wing-flicker as it moved quickly through the trees. In fact it was so mobile I wasn't able to get a single clear shot. Apart from size and behaviour it also shared the rather uniformly pale underparts with the above bird but the similarities stopped there.

In the field I had the clear impression this was an Arctic complex warbler, structure and plumage patterns were straight off the Arctic production line. The question I faced then hasn't changed; if the Arctic complex warblers aren't identifiable in the field why does this bird stand out so markedly in a group of Kamchatka Leaf Warblers? I couldn't help but wonder about Arctic Warbler. I'll post the best of the images I was able to get, most are heavily sharpened.

Most images of it are in strong light and subtle details are difficult to see, this one is slightly better to assess plumage. The head is Arctic complex to a tee; uniform green crown, broad pre-ocular supercillium stopping well short of the bill and becoming a long thin slash behind the eye, evenly broad eye-stripe not contrasting too strongly with the mottled ear coverts. The underparts however were strikingly paler and more uniform compared to the Kamchatka Warblers under the same conditions in the same trees. Unfortunately a direct comparison, like size and gestalt, is impossible to convey in images. In the next image it almost gives me the impression of a Barred Warbler Sylvia nisoria it looks so large and static!

Upperparts uniformly green, long thin supercillium, narrow greater coverts bar and primary projection midway between tertial tip and tail tip. Everything looks Arctic here. It also has a deeper, less spiky bill in this shot.

In summary, both these warblers stood out from the crowd as lively smaller-looking birds sharing overall paleness. However that one looked a classic Arctic complex bird only serves to emphasise that the other did not. So ultimately the question is whether my impressions in field were correct or not.

No comments:

Post a Comment