Sunday, 24 September 2017

Two Sand Martins? One Sand Martin? No Sand Martins?

There had been three 'Sand Martins' the previous weekend at San Gu, but this has now fallen to two. Exactly what you're supposed to look for in them I now find myself seriously discombobulated over! I feel to be digging a hole for myself even by acknowledging their presence, but as I did get some nice photos of them this weekend I am somewhat obliged to do so! My working hypothesis over the last few years has been that the birds that turn up in Tainan County early in the autumn (August) are Pale Martins Riparia diluta. This has been based on having seen at least some tarsal feathering on a number of adults in the past. As all other field criteria for separating these two seem to be of no practical use, tarsal feathering really has been all I've had to go on. However, Sand Martins Riparia riparia, too, can have at least some tarsal feathering, and it is precisely where the boundary between the two lies that (for me at least) is the source of all the confusion. What I'm hoping to find at the end of the day is an individual like this one (individual 20-24) which, with its continuous ridge of feathering all the way up its hind tarsus, can only ever be a Pale Martin. However, the birds I find at San Gu invariably look more like the individual here (a bird which is in fact considered to be a Pale Martin), with a thick clump of three/four feathers immediately above the hind toe and bare tarsus beyond that. The rather well-marked stocky individual of last week is a good example of this type. In the strong winds of the previous week, the tuft of feathering was blowing around wildly, at times suggesting that it covered the entire hind tarsus. Although last week I concluded that there were only two tufts of feathers above the hind toe, images (of this individual or, if not, one very similar to it) this week show that there were in fact rather more than that.

I also learnt (much to my surprise) during the week that Sand Martin (sensu lato, as per my rather antiquated pre-split copy of Svensson) has a complete post-juvenile moult, meaning that juveniles (presumably of both Sand and Pale Martin) will replace their primaries during their first winter, so a moult limit now might not necessarily indicate that a bird is adult. Apropos of nothing, I have also been assuming that juveniles might have less well-developed tarsal feathering than adults, which might help explain the second bird that was hanging around San Gu this weekend.

I had assumed from the active moult in the primaries of this bird that it could only ever be an adult. However, there are also quite a lot of nice pale fringes distributed evenly throughout the plumage and a scaly look to the lower back, more suggestive of juvenile. The tail fork is also much shallower on this bird than on the first one, with R6 appearing shorter even than R5, and I would have thought it would have been deeper on an adult bird, with R6 longer and more tapered. Something about the 'browns' of the unmoulted remiges and rectrices also appear juvenile, and these feathers too look similarly-aged and not terribly worn. From the rounded tail and liberal amount of 'pale' through the upperparts of this bird, I was very hopeful (believing it to be an adult) of seeing some very heavily-feathered tarsi when I finally got it perched. I would ultimately be disappointed when I managed to see the legs clearly, as they turned out to be practically bare.

If this bird is in fact juvenile, then bare tarsi would perhaps not count against an identification as Pale Martin, and such an advanced moult (with P5 almost grown and P6-7 already dropped) would count in its favour as the bird would necessarily have had to have 'been around' for a good while to be so advanced (i.e. be from a southerly-distributed population). However, with presumably both species having complete post-juvenile moults and presumed adults elsewhere moulting at seemingly any time they choose between August and March (wherever you find images of Pale or Sand Martins online, invariably at least some individuals will be in primary moult during these months), I'm no longer confident in ageing anything but the very freshest juvenile (which at this time of year would most likely have come from a more northerly population). At least I did manage better shots of this individual than I usually do, just a shame that everything about it is 'inconclusive' (though a rounded tail even when closed would seem to suggest Pale Martin).

As I seem only to encounter unco-operative snipe, head-scratchy stints, and unidentifiable Riparia martins there (not to mention quite distasteful behaviour from the resident Riparia), it will probably do my sanity a lot more good to steer well clear of San Gu for what remains of the autumn migration! Thank heavens it is now rapidly drying out! Above photos taken at San Gu, Tainan County 23-24/9/17.

Sunday, 17 September 2017

A Tale of Two Sand Martins?

When the waders start to get boring, there are of course the hirundines to look through. Typically, this means the one or two Sand Martins Riparia riparia or Pale Martins Riparia diluta that turn up annually in amongst the Grey-throated Sand Martins Riparia chinensis at either Tu Cheng or San Gu, though precisely what they are (perhaps both species) remains unclear. There were three adults to go at on Thursday afternoon, two tidy-looking ones and one that looked a bit scruffy. The scruffy one only landed for a few seconds, leaving me with only one tidy-looking one to play with.

There isn't much that can be said really about this Sand Martin, other than 'it looks like a lot like one'; the caveat here of course being that so do the fohkiensis Pale Martins that pass through Hong Kong (and should be breeding across the water in Fujian). It can at least be aged as adult due to the lack of broad pale fringes and a moult limit in the inner primaries. Although difficult to see in the photos, it does have tarsal feathering, and the shape and extent of this might be of some use. Each leg has two tight clumps of long 'spur-like' feathers on it, and these 'spurs' are located immediately above the hind toe. There is no feathering higher up on the tarsi than this which (given how well-developed the two clumps of 'spurs' are) one would expect on an adult Pale Martin. From what reading I have been able to access, this is actually the kind of distribution of tarsal feathering I would be expecting to see on a Sand Martin, hence that is what I presume this first bird to be. It (or another near-identical individual) was also present in the same spot at San Gu on Friday.

Once more there isn't much that can be said about this bird, but I think it could be described as rather dumpy/stocky. It's difficult to say precisely whereabouts the primaries fall, but I would estimate that it is about level with the tail tip. In addition to lots of dark steely-greys in the plumage, there are also plenty of dark tans, all of which suggest Sand Martin. The scruffy bird also returned on Friday and hung around for longer, and this bird proved to be much more interesting indeed!

There are so many differences between this individual and the other two that it's hard to know where to start. First of all, it is obviously paler and greyer than the other birds above, with a much stronger contrast between the greyish back and wing and far less between the face and throat. It also differs in structure, being slenderer and lacking the 'chunky' look of the Sand Martins (especially at the neck and shoulders); indeed, it looks variably 'scrawny' or 'emaciated'. It is even smaller and slenderer than Grey-throated Sand Martin, with a much smaller bill (and seems to have a thinner/less deep lower mandible than the Sand Martins, giving a finer bill). It also has a face pattern more akin to Grey-throated Sand Martin given the absence of a white half-collar on the neck, a quick way of picking out 'side on' Sand Martins in amongst flocks of Grey-throated Sand Martins. The throat patch is therefore much smaller than on Sand Martin, and the border between it and the ear coverts more diffuse. It also adopted a different posture to any of the other (hundreds of) martins around it, permanently crouched and almost lying flat on the ground.

Although various factors might have resulted in a Sand Martin coming to have such an appearance (it could be a runt, actually be emaciated, be individual variation, etc.), what I find interesting about this bird is that, although it might not be one, it is the first individual to turn up here that actually looks like a (textbook) Pale Martin! Most texts I have found on the subject deal exclusively with Pale Martins in western parts of its range (desert areas), where such birds are reportedly small, pale, and greyish, not at all unexpected given the habitat. However, small, pale, and greyish seems to be a very good description of this bird! As there are no texts describing eastern race fohkiensis and any of the morphological differences it might have from ijimae Sand Martin, it's hard to be certain even what the 'control group' of Sand Martins are (i.e. the first bird(s) above), but from the shape of the tarsal feathering, they are likely Sand Martins. Unfortunately, I have no images sharp enough to determine the shape and extent of tarsal feathering in this individual, so a question mark continues to hang over its identity. However, I can't help but feel that it probably is a Pale Martin, and perhaps even one from a population other than fohkiensis.

My customary default at San Gu at this time of year is to go and find some Little Stints Calidris minuta. There are literally dozens around at the moment (ranging all the way from orange-rufous to almost sepia-toned), and they come in all shapes and sizes!

It's all very repetitive stuff year in year out, but at least I did manage some sharper shots of one or two birds over the weekend (which makes for a pleasant change from recent form). The martins only land on the road when the wind is very strong, and with these now easing after the passing of a nearby typhoon, it's unlikely I'll manage any better shots of these birds than those I already have above! Above photos taken at San Gu, Tainan County 14-17/9/17.

Sunday, 10 September 2017

'Spectacled Sandpiper'

The OCD-like spell of stint-watching resumed today, after a day spent at home in restraints which I hoped might result in a cure. Everything has now moved to San Gu, and all of the usual suspects can be readily found there. Things can often be a bit harder to photograph at San Gu than at Tu Cheng (which is now virtually dry), and I came away with little on my camera this afternoon save for a few more Red-necked Stints Calidris ruficollis and a juvenile Temminck's Stint Calidris temminckii (a plumage which I perhaps have not photographed before).

The most interesting bird of the day was an adult winter 'Spectacled Sandpiper' (!), a bird which (if memory serves) I have come across at least once before in Taiwan (in winter). I cannot recall whether the white spectacles on that individual were quite as striking as they were on this one, and I was very disappointed that I couldn't manage to get closer to this wonderful thing than I did.

The bird is of course a Long-toed Stint Calidris subminuta, just a surprisingly-patterned one. I'm guessing it was probably female as it was both small and repeatedly being chased off its preferred feeding patch by juveniles (which no self-respecting male would put up with).

As yet another autumn passage period passes rapidly by without me having found anything of note amongst the waders, I'll gladly take this 'curiosity' as reward for putting in the effort (in place of the alternative, which would have been nowt). Above photos taken at San Gu, Tainan County 10/9/17.

Friday, 8 September 2017

More head-scratching!

I'm spending way too much time looking at these troublesome stints! I only do it because (with a bit of patience) they will typically come close enough to point a camera at and photograph. Whether I'm learning anything or not (or, indeed, whether or not this constitutes a productive use of time) remains a moot point! With adult Red-necked Stints Calidris ruficollis now in a baffling array of 'states', I've been waiting for juveniles (which, you would think, as they are fresh, ought to be more 'consistent' in appearance). Interestingly, juveniles of Red-necked Stint are the last of the stints to arrive in Taiwan (a few juvenile Little Stints Calidris minuta have been present for a while now), but the first few (two) did show up today. With a nice juvenile Little Stint in the same group, the small flock I was watching today contained a total of three juvenile stints, all of which I was able to photograph. What was 'head-scratching' about them was that each one of the three looked about as different from the next one as did the other (though the third (left unstated but much-looked for) species was certainly not present). Of the three, the Little Stint perhaps stood out the most, with its leggy appearance, fine bill, and high rear end when feeding. Other features of this bird which were noticeable were dark-centred lower scapulars (though these were certainly not solidly black) and the obvious extension of the primaries beyond the tail, regardless of posture.

There is always a caveat that needs throwing in with these things, though, as the dark centres to the scapulars and wing coverts (a strong pointer towards Little Stint) had the magical property of being able to disappear almost completely in stronger sunlight!

The Little Stint was the second juvenile I found today, with the third juvenile being a 'good' Red-necked Stint. Although the bill of this individual is on the long side, its evenly-patterned head, subtle greyish-pinkish breast band (hard to make out due to the light being strong), and longish rear end all fit Red-necked Stint perfectly. The primaries fall about equal in length with the tail tip, perhaps a factor in making the rear end typically appear 'fuller' than in Little Stint, and just look at those lower scapulars! These are pale grey-centred, with even white tips ('perfectly manicured nails' as I have read somewhere), and nobbut a narrow black shaft streak at their centres.

Even though the lower scapulars in the Little Stint did manage to turn greyish-looking in strong sunlight, they never approached the obviously very pale grey centres of this bird. The pattern at the centre also differs markedly: a large, dark blob distally in the Little Stint and a fine shaft streak in the Red-necked Stint (with virtually no lateral expansion towards the tip of this streak).

Two straightforward birds today, then, a prototypical Little Stint and a prototypical Red-necked Stint, but these two did not start the day. Actually, the third juvenile was the one I found first, and it got me very excited for several reasons. Firstly, it had an obvious cap (unlike the other juvenile Red-necked Stint above) and (depending on the angle) the ear coverts often appeared dark. Secondly, it looked decidedly pot-bellied and dumpy, an impression exaggerated by the short-looking primaries which consistently fell well short of the tail tip, regardless of posture. Finally, it looked small-headed, and lacked the 'full' nape of most of the Red-necked Stints I have looked at recently.

It did have plenty of features of Red-necked Stint (and none at all of Little), including a breast band (which was strongly pinkish in the centre) and pale greyish lower scapulars with dark shaft streaks. However, unlike the Red-necked Stint above, most of the shaft streaks broadened distally into blob-shaped marks, some of which I think could perhaps be referred to as 'anchor-shaped'.

Although I never really thought that the bill looked sufficiently 'blob-tipped' to suggest the third (left unstated, but much-looked for) Calidris species, I became rooted to the spot after finding the second Red-necked Stint and seeing just how much this individual differed from that one. In fact, the second juvenile Red-necked Stint appeared so sleek in its proportions by comparison that it even managed to have a look of Ruff Calidris pugnax about it, and the 'mystery stint' looked about as different from that Red-necked Stint as it did from the nearby Little Stint.

It would be nice to be able to write that 'it didn't take long' for the party to be spoilt when I eventually managed to get shots of the spread toes. Unfortunately, however, that was not the case at all: it took several hours. The bird was forever in either water or in mud, and only on very rare occasions ventured onto 'higher ground' when its toes could be clearly seen. 

The lack of any webbing between the middle and outer toes means that this bird can only be a Red-necked or a Little Stint, despite its cap, potbelly, and short wings. As this bird has no real features of Little Stint and plenty of Red-necked Stint, it is therefore (unsurprisingly) the latter. It is perhaps just my luck that the first two juveniles I would run into this autumn would exhibit pretty much the maximum range of variation acceptable within the species. A learning curve, perhaps, but then why does the experience leave me walking away scratching my head wondering why I bothered to look at them in the first place? Above photos taken at Tu Cheng, Tainan City 8/9/17.