Friday 20 January 2017

Eastern Yellow Wagtails in winter

I dug out an old copy of 'British Birds' with a short paper on the occurrence of Eastern Yellow Wagtail in Britain recently. Eastern was added to the British list on the strength of two first-winter specimens collected on Fair Isle in 1909 and 1912. Genetic analysis of the two specimens showed the earlier bird was indeed of eastern origin but that the 1912 bird was not. While classification of the many subspecies(/species) of Yellow Wagtail has seen significant changes over the last 100 years, field identification is still fraught with difficulty. Even aging the things in the field can be difficult.

Alstrom and Mild's 'Pipits and Wagtails of Europe, Asia and North America' (which sadly I don't own) would be the best ready reference and starting point to attempt to sort out any yellow wagtails in the field. Oh to find a Western in Japan! But as I struggle to identify the eastern taxa in all but spring breeding plumage, I'm not holding my breath. That last sentence may suggest spring birds are easy... well, up to a point. There's always the question as what is acceptable variation and what might suggest hybridization.

One of the highlights of a winter Kyushu trip is seeing a few non-breeding Eastern Yellow Wagtails. I see plenty of taivana and tschutschensis in spring on Japan Sea islands (the further west the better) and a single putative macronyx. However non-breeding plumages are more of a challenge to say the least. Starting from scratch I had no idea what I was looking at and though I wish I could say I've made progress over the last three winters I can't. Nevertheless patterns are emerging. Not that emerging patterns mean I know what the race/gender/age individuals are with any certainty, just that there are... patterns. And because of this repetition it's safe to say they're Eastern... hardly a revelation.

I'm uncertain about the status of Eastern Yellow in Kyushu in winter, obviously they winter there but I don't know how widespread they are. They have been easy to find each year on the fields at Isahaya but I've only seen one in about six days birding at Arasaki. I didn't see any at Tamana over two days spent there despite it being very good for pipits with three species present on the fields, or on the much smaller area of fields at Yatsushiro despite four visits during the three winters. Not exactly a comprehensive study! Nevertheless Isahaya stands head and shoulders above any other sites I've visited and I wonder what suitable areas along the north coast might be like.

The images below were all taken during the last week of December or first week of January since the end of 2014. All look good for taivana though one bird does stand out as being a little odd.

Bird 1. Anything with yellow in the supercillium surely has to be taivana. With extensive yellow on the underparts, greenish upperparts plus those evenly worn and narrowly tipped greater coverts I might push the boat out and boldly claim an adult male. I'm uncertain whether there's any significance in the all dark bill, at one time I had thought a pale base to the lower mandible might indicate a young bird but there appears to be huge variation, from all-dark to dark-tipped. Note the longest tertial looks fresh while the upper two are worn.

Bird 1. On the left side the middle tertial has also been replaced and two or three median coverts have been dropped.

Bird 1. A view from the rear clearly shows the difference between the old and replaced central tertial.

Bird 1. The cleaner white throat contrasting with brownish-grey breast and flanks seems typical.

Bird 1

I think that bird is about as straight forward as it gets, beyond this it's not exactly a quagmire but the ground gets progressively less firm under foot.

Bird 2. It's got to be another taivana due to the yellow supercillium and another adult I'd guess because of that yellow and the narrowly tipped, even greater coverts. Does the lack of yellow below (it's restricted to small areas on the lower throat, centre breast and vent sides) indicate female or is there too much individual variation to read anything into the duller underparts? This bird has a pale base to the lower mandible and cutting edge so if it is an adult then pale or lack thereof of the lower mandible isn't any indication of age. This bird has a very dark forehead and fore-crown to go with the lore and cheeks.

Bird 2

Bird 2

Bird 2. Little more than a hint of yellow on the underparts.

Bird 2. Asymmetric tertial moult again, the longest feather on the left side has been replaced.

Bird 3. Another adult taivana, like the first bird, it has extensive yellow on the underparts but the non-yellow areas are cleaner and less grey similar to the previous bird. Also the centre of the ear coverts is paler, slightly hollowed out as with Citrine, and the lores are less dark with just a darker spot before the eye. This bird has a whitest supercillium with just a slight greenish-yellow tint. Again the upperparts are greenish and the greater coverts narrowly fringed and tipped. The lower mandible is more extensively pale with just a dark tip. 

Bird 3

Bird 3

Bird 4. Yet another with extensive yellow on the underparts, it looks similar to the first bird.

Bird 4. Distinct yellow in the supercillium and narrowly tipped greater coverts. Is there a moult contrast visible in the greater coverts? It's difficult to tell in this poor image and the one below but as far as I'm aware this shouldn't be the case in adult birds.

Bird 4. The upperparts look greyer but the rump and uppertail coverts are distinctly green.

The next bird is the only bird I've seen a little further south at Arasaki. It was more distant, across a river, and because I didn't have my scope at hand to check details I felt this was a strikingly grey and white bird compared to the Isahaya birds. However after checking the images it clearly has distinct greenish tints across the crown and upperparts, even the extensively yellow throat didn't stand out in the field.

Bird 5. This bird had a strikingly grey and white appearance in the field, even the yellow throat didn't stand out, though the light was already going very quickly when I found it.

Bird 5

Bird 5

There are some constants here, such as the greenish upperparts and the narrowly tipped greater coverts whereas the extent of yellow below and on the supercillium is highly variable, as is the extent or even presence of pale on the lower mandible. However if my estimation that these are adults is correct, where are the first winter birds? Am I mistaken or are there fewer young birds wintering in Kyushu? None of these birds match the grey and white first-winters that catch the eye as potential Eastern Yellow in a European context.

The next three birds seem a far better fit for first winters; paler grey and white overall, each with a bold greater coverts bar due to prominent white tips. The first of the two seems an obvious example to my untrained eye, I didn't get good views of the second and the third bird is a little odd in that it shows more green on the upperparts than I'd expect and it's the only bird I've seen which is either actively moulting its tail or has suspended moult leaving an untidy state of re-growth.

Bird 6. A cleaner, colder individual with the merest hint of yellow below the throat and on the vent sides.

Bird 6. Very grey and white, there's just a hint of yellowish at the side of the vent and a bold greater coverts bar.

Bird 6. Very clean underparts, no yellow in the supercillium.

Bird 7. I don't think I should even try to age this bird with the little I know about the subject.

Bird 7. The central tail feathers are very worn, the outers look less so but the quality of the images isn't good enough to be sure of anything.

Bird 7. The upperparts looked greenish at times but grey at others, blowing the image up there seems to be a mix of grey and greener-tinted feathers on the mantle, the uppertail coverts don't seem uniformly grey either. There's a green tint supralorally and clearer green in the ear coverts. I don't have any suitable images which could show whether there's a moult contrast in the greater coverts.

Bird 8. Very broad tips to the greater coverts here and basically a plain grey and white bird. There is a definite green cast on parts of the head and mantle, as well as greater covert and tertial fringes. It gives the impression of being a tips/surface feature which could wear off leaving the bird greyer and whiter however as a juvenile shouldn't show any green (too my knowledge) that doesn't seem a plausible explanation.  

Bird 8
Bird 8. The tail is at a strange and untidy stage of growth.

Finally a couple of very poor images of a bird which doesn't quite sit comfortably within this series but as it also appears to have some yellow in the supercillium when the images are blown up I presume it must also be taivana.

Bird 9. This bird stood out because of its very dark mask and contrasting supercillium as well as having the greyest and most thrush-like breast of any of the birds I've seen to date.

Bird 9. Unfortunately because of distance and angle to the light it isn't possible to be sure of details and it may simply be this that enhances a somewhat different impression.  

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