Sunday, 15 May 2016

Sakhalin Grasshopper Warbler?

Just thinking about Sakhalin Grasshopper Warbler Locustella amnicola is akin to picking the scab off an almost healed wound! Basically, this is one bird that I used to count on the strength of what I thought were consistent morphological differences evident between individuals passing through Qi Gu, but later had to admit defeat and removed the lot when the structural differences (apparent mostly in photos, but also in the field) consistently did nothing to back this up. Talk of Locustella obviously means that I spent the weekend in Qi Gu (and, coincidentally, also have plenty of wounds to show for it), and that there was something of a fall of these birds, but this did not happen until Saturday. Friday in Area A did move my year list along, though, with a distant but always obscured Ruddy Kingfisher Halcyon coromanda, my first for several years, but that would be all I would get 'year-wise' from the woodlots for the day.

Moving from Area A to my reserve woodlot brought my first set of wounds for the weekend when I came off my bike on a pile of sand that had been dumped on the road by trucks that have started working in that area. A bruised ankle and (more than anything) a bruised ego were all I came away with from the incident as, fortunately, I had managed to cushion all my optics as I headed towards the ground (admittedly at very slow speed). My subsequent 'hobble' into my reserve woodlot produced a spectacularly late Eurasian Hoopoe Upupa epops and a male Asian Koel Eudynamys scolopaceus, neither of which helped my year list along any. It was, in fact, more exciting to find a Taiwan Scimitar Babbler Pomatorhinus musicus in there than these two, as this is a very scarce visitor to this coast (only my second ever in Qi Gu).

Saturday was the day of the big fall, though I chose to start it by seawatching (and got very little for my efforts). I flushed two Gray's Grasshopper Warblers Locustella fasciolata on entering my reserve woodlot, which suggested that they had arrived overnight, together with a female Asian Koel. Area A was where all the prizes were to be had, though, as approaching a dozen Middendorff's Grasshopper Warblers Locustella ochotensis and a similar number of Gray's Grasshopper Warblers were scurrying around all over the place in this tiny woodlot. I'll post some straightforward Middendorff's photos first before I get into the more thorny issue of the Gray's!

It has been my assumption for some time now that the majority of the Gray's Grasshopper Warblers sensu lato that pass through Qi Gu have to be of the 'nominate' form fasciolata. Although I have seen quite some variety in terms of plumage, all consistently show a very long P9, which ought structurally to make them this form. The white-edged P9 is usually very close to P8 in length, and it also occasionally appears to exceed it in length (albeit marginally) in the field. It is invariably much longer than P7, which, although not ruling out amnicola on its own, would make amnicola difficult to claim (being a form which reportedly has a short P9). Below is a bird I consider to be a 'typical' fasciolata in spring, which was taken in the fall of this Saturday.

It is evident on this one bird alone just how big a difference light makes to apparent plumage tone. In the top photo, due to sunlight, the bird has pale 'golden' tones on its upper mantle and looks uniform pale off-white/greyish below, becoming warmer and more rufescent towards its rear end (characteristics of fasciolata). In the lower photo, in shade, it looks much more 'sullied' altogether, with a redder back and more 'sulphur-stained' underparts (suggesting more amnicola). It does, however, have a contrastingly greyer crown under both light conditions, and the edges of the flight feathers do contrast with the remainder of the upperparts in both (giving a brighter 'rear end', a feature of fasciolata). All this aside, the P9 (as it is on most of the birds in Qi Gu) is very long (=P8), and it is this that has prompted me to give up trying to identify amnicola on plumage (although many resemble what is described for amnicola, all have P9 much too long for that form), leastways absent some kind of supporting structural difference. It is no wonder, then, that I paid little attention to the very first 'Gray's' I saw on Saturday (with others more 'gettable' nearby), and it wasn't until I got home that I noticed that it appeared to have quite a short P9!

Although it is difficult to judge precisely where the P9 ends, it certainly ends a good way short of P8, and appears to be closer in length to (or even shorter than) P7. With almost all birds in Qi Gu having a wing P9=P8 (P8-7), this would make this bird a 'strong candidate' amnicola (it is the first 'Gray's' I have noticed in Qi Gu with such an apparently short P9). Although perhaps unreliable, certain plumage features do also point in the direction of amnicola, including uniform brown upperparts (crown, eye stripe, mantle), lack of contrast between the mantle and the flight feather fringes, pink lower mandible, and sullied buff underparts. Although Kennerley & Pearson (2010) states that few amnicola can be identified on wing structure alone, given the variation in plumage shown by fasciolata (and the quite extraordinary effect that light has on these birds), a short P9 would seem to be a vital component in identifying one away from its breeding grounds!

For my lack of wit in missing this putative amnicola in the field, I was stung by a bee just above my eye on the way home and had to spend much of Saturday evening in hospital (with a swollen face and only half of one eye open and anything like operational), fearful that I would end up missing Sunday. A pile of injections saw to it that that would not be the case, and I was free to hobble around Qi Gu on battered legs Sunday, with a very sore arm and a boxer's mien, getting nothing for my troubles save for a Pacific Swift Apus pacificus (above, together with a House Swift Apus nipalensis for good measure), and a Brown Noddy Anous stolidus offshore Area A. There were a few more 'Gray's' in Area A late morning, but none that would sit still for long enough to be examined as closely as the ones of the previous afternoon. In truth, who knows just exctly what they all are?! Above photos taken in Qi Gu, Tainan County 13-15/5/16.

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