Further Discussion of Identification of claimed Spoon-billed Sandpiper in China:
Nial Moores, December 27th 2011
Yes, despite all the necessary caveats that come with trying to identify a bird from images (especially poor images) I do also have an opinion on the Guangdong shorebirds photographed by Jonathan Martinez (JM) on December 17th 2011 (see previous post). Considering the extreme rarity of Spoon-billed Sandpiper Eurynorhynchus pygmeus and the paucity of information on their identification at long-range, this opinion is detailed below. As always, comments are welcome!
Seen close to in good light, Spoon-billed Sandpipers (SBS) are remarkably distinctive: often active, stint-sized, rotund, with a heavy bill, deep and wide at the base, widening further into that remarkable spoon. Here in the ROK, the usual challenge of picking one out at longer range comes from needing to rule out a Red-necked Stint Calidris ruficollis with a muddied bill, or during southward migration, from the slightly larger Broad-billed Sandpiper Limicola falcinellus which shares a heavy bill, rather pale appearance, and strong supercilium and eye-patch.
How about at long range among Dunlin Calidris alpina in December, from low resolution video and heavily-cropped stills?
Looking first at the two cropped stills sent by JM, I thought the birds looked remarkably Sanderling-like, but that there might be a suggestion of a hind toe shown by one of them (which would rule out Sanderling Calidris alba and help support the ID as SBS). Looking at the first few seconds of 12-second video, before it zooms in, however, I did not even known what birds to look at. I could not see any stint-sized shorebirds. Here in the ROK, SBS are often found with Dunlin (now our most numerous shorebird), and they look obviously small in direct comparison. Looking again at the stills, the hint of hind toe appeared rather more only to be shadow or reflection of the foot in the water, and in neither stills nor video did I get the impression that the bill was especially wide at the base. I was therefore genuinely puzzled by the short statements sent to JM confidently supporting the ID as SBS, and I have tried to look for the features that they could see (including the “Very characteristic profile of head and base of bill” and “The thickly-based bill and the pale face, the contrastingly brown neck and white underparts [which] all seem to fit non-breeding plumage”). However, despite best efforts, I have been unable to find anything that rules out Sanderling. Perhaps others can?
My reasons for default ID as Sanderling were then outlined in a couple of mails to JM (who appeared increasingly persuaded by others’ comments that these were indeed SBS) and then finally to the fuller email group (sent on December 22nd). This mail, which aims to be constructive and helpful, is pasted in below with additional comments and images:
I still do not agree with the identification as SBS…in the absence of being able to see any definitive SBS features I would simply identify the birds (seen poorly at very long range) as Sanderling…again in the belief that SBS are best not claimed unless something diagnostic is seen), some of the reasons for my ID as Sanderling include:
1) Size. The birds appear to me (and to others I have shared the video clips with) to be as large as Dunlin in direct comparison. SBS are stint-sized. SBS therefore look very small in direct comparison with either Dunlin or Sanderling, and only slightly larger than Red-necked Stint. Is this how these birds look to anybody else? JM’s first thought was that these were probably Sanderling: sadly, I can only agree.
One respondent on the list replied to my email that he could indeed see a “quite marked” size difference in the video clip, while JM attributed the apparent larger-than-expected size of the birds to optical illusion, as he correctly stated that birds focused on in the foreground can often look rather smaller than birds in the background even when similarly sized. With respect to them both, however, I see no evidence of either a quite marked size difference or of optical illusion. The birds appear to me to be at the same distance from the observer as several Dunlin and are more or less the same size.
Measurements given in leading shorebird guides (including Richard Chandler’s 2009 “Shorebirds of the Northern Hemisphere”) suggest Sanderling (at 20cm) should have a total length marginally longer than Dunlin (at 19cm, though size “variable”). However, while Dunlin generally do look smaller than Sanderling, the subspecies in East Asia are articola and sakhalina. These are very long-billed, and rather large. Sanderling in Far East Asia therefore can often appear a little smaller than Dunlin in direct comparison. SBS at 15cm on the other hand are much smaller than either and are instead close to Red-necked Stint in size (14.5cm). Some disgiscoped images from the ROK (Fig. 1-3), show how similar SBS are in size to Red-necked Stint; how obviously smaller they are than Dunlin and Sanderling; and how a Sanderling to the rear in Figure 2, which should perhaps look larger than it is due to optical illusion, still appears smaller than some of the Dunlin).
Fig 1. Two Spoon-billed Sandpiper with Red-necked Stint and Dunlin, Geum Estuary, October 2008.
Nial Moores/Birds Korea.
2) Structure. SBS are longish-billed and long-legged, with longish tibia, and can almost look cross-legged when running (Fig 4). These birds look like Sanderling. I do not see anything definitive in the bill length or shape to suggest SBS either. Like Sanderling, SBS has a deep-based bill. However, seen from the front, the rear or from near-the-rear, the bill of SBS is also very broad at the base, before widening into the spoon (Fig 5 & 6). I would expect to see some hint of this. I cannot see it in the video or stills, nor apparently could JM in field views. Can anyone else?
Fig. 4 Spoon-billed Sandpiper with Dunlin showing relative size and hint of “cross-leggedness” in SBS, Nakdong Estuary, August 2005. Christian Artuso.
3) Plumage. Typically, SBS in non-breeding plumage (including the apparently rather similar First-winter and adult non-breeding plumages) look capped, with a strong supercilium and often a hint of a paler collar. To me, they appear grey-tinged-brown (rather than silvery grey like non-breeding Sanderling) on the upperparts. The birds in JM’s video look more silvery grey, and lack an obvious cap, collar or supercilium. While non-breeding SBS can/do show a dark forewing (when not covered by breast feathering), they also show wing coverts that are darker than the mantle (Fig. 7 & Fig. 8).
Fig. 7 Non-breeding (presumed Juvenile -> First-winter) Spoon-billed Sandpiper, Geum Estuary,
October 2008. Kjetil Scholberg.
One or more of these birds, however, show a very Sanderling-like dark spot on/near the carpals and paler (not darker) wing coverts. On neither of these birds do I sense that the wing coverts are darker than the mantle. Does anyone else?
The final main plumage-based reason JM gave for the ID as SBS and not as non-breeding Sanderling is that when one of the birds took flight it did not seem to show as much white in the upperwing as a Sanderling should. Although a low-res video of a bird taking off at 200m range, the video clip seems to show a bird with very extensive white on the upperwing – especially on the inner wing apparently extending to the outer primaries (Fig. 9). Isn’t this about as much white as would be expected in a Sanderling?
Fig 9. Still image from JM’s video clip, showing one of birds in question in flight (at second 05). There appears to be much white on the upperwing, especially on the innerwing. Guangdong, December 2011. Jonathan Martinez.
All the same, this feature does not seem enough to claim or rule out either species, as SBS also show quite a lot of white on the upperwing (Figs. 10 & 11). Blurring of a poorly-pixelated image makes definitive interpretation of such a short flight-sequence too difficult. All the same, perhaps SBS might be expected to show rather less white on the innerwing and more on the outerwing than is suggested in Fig.9?
Fig.10. Spoon-billed Sandpiper (juvenile) showing spread upperwing. Nakdong Estuary, September 2007. Jan van de Kam/Birds Korea.
4) Feeding behaviour. JM described that the birds “were foraging in a curious way…they didn’t pick up prey by up and down movement but held their bill in the shallow water and moved it a bit horizontally for a short period (it was a bit similar to what spoonbill ‘platalea’) can do”.
The behaviour recorded in the video clip appears to be of one or more birds walking rapidly, changing direction frequently, while holding the bill down (furrowing through the shallow water or surface of the mud). There does not appear to be much (if any) strong sideways movement of the head and bill. While distinctive, this behaviour is not at all typical feeding behaviour for SBS (with this observation based on several hundred SBS over the years). Foraging SBS typically feed with a rapid walk, followed by a rapid peck and search action, and then, once potential prey is located, either by a quick sideways swish or more often by a rapid pummelling motion, followed by bill lifting, followed again by quick walking (see http://www.birdskoreablog.org/?p=1613). Personally, I have only seen SBS feed platalea-like a few times, and I cannot remember ever seeing them furrow through water or wet sand like the birds in JM’s video. The behaviour is, however, similar to behaviour I have seen in Sanderling several times (see http://youtu.be/7gwHJcuJp_8?t=20s, disgiscoped by Jason Loghry at the Nakdong Estuary in October 2011).
Your comments are welcomed (SBS or Sanderling?) and will be forwarded to JM (who much to his credit accepts that the record is not confirmed, and has thus returned to the site to re-find the birds). Along with everyone else, here’s hoping that his search turns up some SBS at this excellent-looking site!