Sunday, 23 September 2018

Not more Riparia martins!

A distant Oriental Plover Charadrius veredus at Tu Cheng last Sunday was a bird I missed off of my last post as it didn't really fit the theme of it. It doesn't really fit this one, either, but it needs to go on somewhere. Much of this week was also spent at Tu Cheng as my woodlot was depressingly quiet (what with the onset now of the dry season). No waders of interest there, really, just the odd Red-necked Phalarope Phalaropus lobatus and a sizeable juvenile Ruff Calidris pugnax.

The presumed Pale Sand Martins Riparia diluta are still at Tu Cheng, of course, and these continue to lead me their merry dance. I thought it might be interesting to compare them with a few Grey-throated Sand Martins Riparia chinensis to see which age class of those they best match (hence the composite below). The top two photos show a fresh juvenile (left) and an adult (right) and were taken in mid-July. Although the pale tips to the coverts have already worn off the juvenile, the primaries show negligible (even) wear and are all of same age as evidenced by the growth bars at their tips. P1-2 have been dropped, indicating that this bird is just commencing its post-juvenile moult. The adult, on the other hand, shows heavily abraded and decidedly ragged-looking P9-8 (both one year old) which contrast with fresh (recently replaced) inner primaries (P1-6). Most of the secondaries are also worn. The bottom two photos show an unknown age class (left) and an adult (right) and were taken in mid-September. The primaries of the left-hand bird are very fresh as this bird has only just completed its moult. Once a first-calendar year bird has completed its post-juvenile moult, there are few clues left in its plumage to help separate it from adult. However, one such clue is present in the right-hand bird, which has traces of wear in its inner primaries but fresher-looking outers. This indicates that the inner primaries are already 'old' and that they were likely replaced earlier in the season, probably as part of the complete moult of adult.

The presumed Pale Sand Martins tend to be quite confiding at Tu Cheng, and with patience can be photographed well. I like it best when they stretch their wings as this lets me see each primary feather in detail. The bird below is rather retarded compared to some, having only replaced P1-2 and a few greater coverts. This would fit adult Collared Sand Martin Riparia riparia (of nominate race; I have no info about ijimae) well, but what about the outer primaries (P9-4)? These show no signs of wear, and even retain the narrow white fringe to the inner webs (best seen on the closed wing in the background) of a fresh feather. They also all appear to be of the same age. As there is no wear to the secondaries, either, this bird is a juvenile.

This attractive juvenile was the most confiding of the birds I found Saturday (so there are more photos of it below), allowing a close approach whilst it sat there preening. It was furthermore 'pale' and had extensive 'silvery-greys' throughout its plumage. A juvenile ijimae here does not show such extensive greys in its plumage. It is also fresh in October and shows no signs anywhere of having yet started its moult. Diffuse ear coverts and black lores which contrast with a paler crown are said to be features of Pale Sand Martin, too (though the bird in the link also shows these).

Here are three more individuals (which have replaced two, three, and four of their inner primaries respectively) taken this weekend which show an identical suite of features to the bird above. I believe them all to be juveniles due to the absence of any wear in the outer primaries.

And here are two birds showing the extent of the tarsal feathering in these juveniles. The first bird is the most typical, with a clump of feathers above the hind toe and just the odd 'spike' between that and the feathering around the intertarsal joint. The second bird may well be reward for all the time I've spent with these things as it shows much more feathering high up on the tarsus. Despite being 'wispy' and containing one or two breaks, it is essentially continuous.

Finally, the bird below was vocalising on Friday and I managed to record it (here). The 'jirr' calls in the foreground are those of Grey-throated Sand Martin; the scratchy burbling in the background is the bird in question. I'm not entirely sure what these sounds represent: It's not much of a song if that's what it is, yet it sounds too complex for a call. I guess the bird was just 'excitable', being sat as it was in amongst other Riparia martins. I wish I knew what to listen for in these vocalisations (though get the impression from the paper here that they are of negligible use anyway).

I have barred myself now from the 'hoops' at Tu Cheng as I don't see what else I can really do with these birds. I do enjoy a good puzzle, but only when there seems to be the possibility of a solution. With these things, a definitive answer as to what they actually are is not at all forthcoming! Above photos taken at Tu Cheng, Tainan County 16-23/9/18.

Monday, 17 September 2018

The path to discombobulation

The paper here greatly changes the landscape in respect of Riparia martins in the region. (Although the paper itself is not accessible via the link, the range maps of the relevant taxa are, and these make for interesting viewing.) In it, we learn that the form occurring in Hong Kong is ijimae Collared Sand Martin Riparia riparia after all, and not fohkienensis Pale Sand Martin Riparia diluta as had been previously assumed. As a result of this, some questions at least can now be given definitive answers. Foremost amongst these would seem to be: 'If ijimae does not migrate through Hong Kong, then where exactly does it go?'. The answer to this (possible this week, but not last) is: 'It goes through Hong Kong!'. The corollary of importance here is that, given its breeding distribution, ijimae Collared Sand Martin must also pass through Taiwan. It is furthermore reasonable to assume that it does so in decent numbers and that any migrant Riparia martin seen here during a passage period will most likely be an ijimae Collared Sand Martin.

Such a thesis is not at odds with my own observations. On Dongyin, I have noted good numbers of Riparia martins moving northwards in late April and early May and, on the return, have picked up small flocks passing Qi Gu (and also leaving from Heng Chwun) in October and November. These dates fit a 'northern' migrant and (given the developments above) these birds can now safely be called ijimae. This would not have been possible just a month ago, as then (with all Hong Kong migrants being Pale Sand Martin, hence this being the one 'on the move' in southern China at passage times) it did not seem possible to assign any migrant an identity with any certainty.

In addition to 'regular' passage birds, though, there are also those that appear in August and September and conform to a pattern all of their own. The 'conventional wisdom' is that adults migrate before juveniles, yet these very earliest of birds are invariably juveniles (by my reckoning, which I may have wrong as I am not a ringer). They are not always fresh-looking and may be worn on the body, with pale tips all worn off (suggesting adults). They have also all commenced moult of the inner primaries (typically with P1-3 replaced), again suggesting adult (which will suspend moult for migration, whereas juvenile will not). (In the image below, the outermost primaries (P9-6) appear dark (not faded) and show no signs of abrasion or wear at the tips. The secondaries are similarly fresh, with their narrow white fringes pristine and exhibiting no signs of wear. These do not look like the flight feathers of a bird that has had to endure the rigours of two migrations and a breeding season!) Despite the fact that some appear 'a bit dark', the early onset of post-juvenile moult suggests that these birds have not originated from within the range of ijimae and have come from somewhere further south (with 'within the range of fohkienensis' a preferred explanation).

The proverbial 'turd in the punchbowl' lurks, though, and is outlined here. We learn from Spurn that there are two waves of Collared Sand Martin migration in autumn due to the fact that sand martins raise two broods per year. The first wave occurs in July and August and (I infer) is comprised entirely of juveniles from the first brood. If such a phenomenon also occurs in ijimae, then both the early arrival dates of these birds and the fact that they are all juveniles can be explained. However, the UK is warmer than East Asia, and Collared Sand Martins are able to arrive there in March. Presumably, the ability to double brood is a product of the extended breeding season afforded by the favourable conditions, and this option might not actually be available to ijimae(?).

There are some great resources now (here, here, here) with multiple images of Pale Sand Martin (just none yet of fohkienensis). From these, one or two things (which contradict earlier descriptions) become apparent: (i) some birds appear quite dark; (ii) some have well-developed breast bands; (iii) some show little in the way of tarsal feathering. No such resources exist for ijimae. The only statement I can find relating to this race anywhere is one that describes it simply as 'dark'. If 'being pale' is sufficient grounds on its own to claim fohkienensis, then the diminutive pale juvenile of last week must make for a good candidate. This bird reappeared briefly at Tu Cheng on Friday, but upsettingly never came very close. It is certainly the most striking of this year's arrivals, with pale silvery-grey throughout its upperparts and primaries renewed right the way up to P5. 

A second pale juvenile was also present on Friday afternoon, a slightly larger individual which had almost completed P4. Although the sun was fierce on Friday (causing birds to appear bleached), both of these individuals were markedly paler than any nearby Grey-throated Sand Martin Riparia chinensis and the upperparts appeared silvery and pinkish rather than brown.


Would that things were all that simple, though! (And as the extensive overlap in morphological features between these two has had regional identification experts fooled for the last decade or so, it is not unreasonably defeatist to wonder what hope there might be for the rest of us!) I only found one distant bird on Saturday, but lucked in on Sunday with three close ones sat on the hoops. The first of these was a very 'typical' individual, being a juvenile in active moult with P3, most greater coverts, and the central tail feathers growing. In overcast conditions Sunday, birds looked much darker, but still this one had a new silvery-grey tertail and extensive grey tones to its nape.

A second juvenile on Sunday was much like the first, but browner, subtly more worn above, and slightly more advanced in its greater coverts. The length of the wings was furthermore 'typical' in both of these birds; exceeding the tail by some distance when folded. This is stated to be a feature of Pale Sand Martin, though is likely no longer valid as Hong Kong birds exhibit this feature.

The third individual (a Grey-streaked Flycatcher lookalike) was much more interesting, as almost immediately it looked somehow different on account of its tail length. This is the first individual I have found in autumn in which the tail has exceeded the folded wings in length; reportedly a characteristic of Collared Sand Martin. A closer look at the wing also revealed traces of wear in the primary tips and what looked like buffy rather than white tips to the secondaries. I would therefore guess that this is an adult bird, and from its proportions that it is an ijimae Collared Sand Martin.

There are other differences, too, between this individual (on the right below) and the Riparia SP (left) I have been seeing for most of the autumn. The former has a deeper-based and stubbier bill than the latter (in which the lower mandible can barely be discerned). It also looks subtly more robust, sleeker, more 'bullet-shaped' and aerodynamic than the latter (which in turn looks more delicate, with a smaller ('fluffed up') head on a slender body). The tail fork is also very deep on the presumed Collared Sand Martin. There's no serious suggestion here that these differences make the latter a Pale Sand Martin as they may reflect structural differences between adult and juvenile or simply be individual variation. However, they are certainly there and are hence 'of interest'!

Fortunately, perhaps, this weekend likely offered the final opportunity to take a close look at these Riparia martins this autumn as the Tu Cheng area is now starting to dry out. Once the area is dry, all the Riparia martins (including all the Grey-throated Sand Martins) will leave and head off to more inaccessible sites for the winter. Although this is now my millionth year of looking at them, I remain unable to say precisely what all these early birds are (though strongly fancy Pale Sand Martin). Some hope seems to be offered by the early onset of the post-juvenile moult, but if ijimae double broods and migrates early, then first-brood juveniles might also start this early. Sadly, this challenging species pair is one which engenders no interest whatsoever here, and an answer as to what these birds are seems as far away as ever (blundering through them as I am on my own). The best policy in the interests of sanity may well be to kick them all back into the long grass from whence they came, but I worry about just where I would look then. I tried this for five minutes on Saturday at Tu Cheng, looking up instead of down, and only succeeded in quickly coming across four of these (an even deeper and muddier quagmire than even the Riparia martins):

Woodlots and pretty-looking flycatchers from here on in now, please! And how about something a bit lost for a change? Above photos taken at Tu Cheng, Tainan County 14-16/9/18.

Sunday, 9 September 2018

Stints and Swiftlets

An acceptable weekend all told, with a bit of vis mig in evidence and plenty of birds to keep me occupied. There was nothing whatsoever in woodlots Friday and Saturday, but passage over them including, surprisingly, daily Himalayan Swiftlets Aerodramus brevirostris (two on Friday and one each on Saturday and Sunday). Although small-looking in the field, in photos they are actually quite stocky/dumpy, a subtle difference from the more 'pencil-thin' Germain's I think.

With woodlots empty, I spent yet more time with waders. I found yet more Lesser Sand Plovers Charadrius mongolus to play with, which I was more than happy about. The first individual below (five photos) is likely an atrifrons on account of its dark forehead and lack of border between the pale peach breast and white throat. Not sure about the second individual, though this does bear a stronger resemblance to the 'white-fronted' mongolus-type photographed earlier in the week (here). Both races are common enough on passage, though mongolus-types predominate.

The Calidris are a bit overwhelming at the moment, with some peculiar individuals popping up in their midst. Every year, I always want a photo of typical juvenile Red-necked Stint Calidris ruficollis when they start coming through, but am finding mostly oddballs this time out! The first bird below is quite typical, with its white-tipped scapulars, greyish coverts, and peachy wash to its breast. The second bird is brighter, suggesting Little Stint Calidris minuta, but has only a dark shaft through its coverts (rather than a dark centre), together with the structure of Red-necked Stint. I'm not sure what to make of the third individual. Just what kind of bill is that supposed to be?

Although I now have more photos of Little Stint than I know what to do with, I'll happily shoot another one if it's walking around in front of me. I'll also have a Temminck's Stint Calidris temminckii if there's one going, and even a Wood Sandpiper Tringa glareola if it's fresh enough!

There were a few Eastern Yellow Wagtails Motacilla tschutschensis on the mud that I wanted Sunday. These, however, were spectacularly shy, and flushed at considerable range, even though none of the waders were at all bothered by my sitting there in the grass!

Sunday was the pick of the days in the woodlots, too, with an early cold front dropping a couple of decent migrants. Unfortunately, neither the Amur Paradise Flycatcher Terpsiphone incei nor the Forest Wagtail Dendronanthus indicus were willing to pose full bird, and hard-earned record shots were all that was possible. The Grey-cheeked Fulvetta Alcippe morrisonia continues to linger in the woodlot, though is more often heard than seen. 

A solid weekend, then, with the first (very weak) cold front of the autumn providing a nice taster of all that is to come! Above photos taken in Qi Gu and Tu Cheng, Tainan County 7-9/9/18.