Wednesday, 28 January 2015

Lake Wollumboola Sand Plovers

Following my previous post about my White-rumped Sandpiper twitch to Lake Wollumboola on 13 January, I received an email from Chris Brandis about the sand plovers that have been being reported from Lake Wollumboola. In my original post I included in the list of birds seen a single Lesser Sand Plover (Charadrius mongolus). This identification was no doubt influenced partly by the fact that that is what other people had been reporting from the site, but probably also partly because Lesser Sand Plovers are generally more common on the NSW coast than Greater Sand Plovers (Charadrius lechenaultii), though neither is seen there either particularly regularly or in great numbers. In so doing I committed one of the birdwatcher's cardinal sins!

Lesser and Greater Sand Plovers are notoriously difficult to tell apart at times, especially when the two are not present together for comparison. The National Photographic Index of The Shorebirds of Australia has this to say: 
In a mixed flock of waders, the Large Sand Plover (sic - an alternative name for the Greater Sand Plover) may be distinguished from other small plovers by its slightly larger size, longer legs and bigger, heavier bill. But when seen alone in its eclipse plumage, as is generally the case in Australia, it resembles the Mongolian plover (sic - an alternative name for the Lesser Sand Plover) and the Double-banded Plover. Considerable experience and expertise is required to distinguish with confidence between the Mongolian and the Large Sand Plover, and there are few features which are infallibly diagnostic.  Much reliance must be placed on subjective impressions, and these have been perhaps most succinctly summarised by M. J. Rogers, who said that, to him, the Mongolian Plover is quite a pleasing little bird, while the Large Sand Plover is "an ugly brute, with a body too small for its legs, a head too large for its body and a bill too large for its head"!

So Chris's comments, that he thought he had seen four Greater Sand Plovers, not Lessers, made me go back and look at my photos, none of which I had really paid a great deal of attention to, either in the taking or the subsequent assessment.

But looking at them now, it seems likely that the two birds for which I have reasonable photos are both Greater Sand Plovers. A third bird was seen but only shows up as a blurred bird in the distance in my photos, but even it I assume was also a Greater Sand Plover.
[But it seems I was quite wrong in this conclusion - see Postscript at end of this post...]

The first two photos in the following sequence are of the same bird, and the other seven photos are of another bird (and the final two photos are from Northwest Island in the Great Barrier Reef for comparison). 

The stance, long-legged appearance, and long bill of the first bird seems to me to be fairly characteristic for a Greater Sand Plover. 

Wollumboola bird #1

Wollumboola bird #1

The perspective of the second bird as it walks away from me makes the distinguishing features less obvious, but its size compared to the Red-necked Stint in the  photos is also supportive of a Greater Sand Plover ID.

Wollumboola bird #2

Wollumboola bird #2

Wollumboola bird #2

The size and shape of the bill in the second bird is more equivocal.

Wollumboola bird #2

Wollumboola bird #2

But the largely whitish rump and tail edges of the bird in blurred flight is more suggestive of a Greater Sand Plover - a Lesser Sand Plover would show only narrow white edges. What these photos unfortunately don't show is any evidence of toe extension beyond the tail.

Wollumboola bird #2 in flight

Wollumboola bird #2 in flight

For comparison, the next photo is of a Lesser Sand Plover taken in January 2014 on Northwest Island in the Capricornia Cays of the Great Barrier Reef (see earlier post from March 2014 ). The bird is much "tidier-looking" and has a distinctively smaller bill.

Northwest Island Lesser Sand Plover

And the next photo, also from the earlier Northwest Island post, includes both several Lesser (lower left) and a Greater (upper right) Sand Plovers together - the difference becomes fairly clear-cut.

Northwest Island waders, including Lesser and Greater Sand Plovers

So on balance, I'm concluding that the three sand plovers I saw at Lake Wollumboola that day were all Greater Sand Plovers (I've updated my earlier post to this effect). I'd like to hear from anyone who thinks I might have it wrong.

There may well have been Lesser Sand Plovers at Lake Wollumboola as well, but if so, I don't think I saw them.

Postscript  (31 January 2015)

Well, after quite a bit of email traffic on Birding-aus over the past couple of days, both public and private, the consensus is very clearly that the two birds I photographed at Lake Wollumboola are both Lesser Sand Plovers. Bird #1 came “close” but was still universally considered a Lesser. I asked some of the respondents for additional tips as to why and can summarise as follows.

To a large degree it is the “jizz” of the bird, particularly around the overall proportions and shape of the head, legs and body, but especially, the bill length seems to be key. None of this was new to me, and these are all features identified in the field guides to look for, but clearly I just don’t have the experience with these birds to ‘get it’ just yet.

Some of the comments included:

“I find it's immediately a 'jizz' thing. Greaters just look so long-legged they look awkward. The tibia is very long which elevates the body way up off the knees. They look as if they're about to topple forwards. The bill is important too. A Greater has a bill that is much longer and thicker than a Lesser and if stuck onto the side of the head of the bird (ouch) would probably reach behind the eye.”

“The bills of your birds look very much on the short side for Greater, and also relatively bulbous- and blunt-tipped which is better for Lesser. Similarly, the overall shape and proportions are much 'nicer', whereas Greaters tend to look more gangly with oversized heads and bills. That said, there is significant variation in both species, and birds with more intermediate features can be extremely challenging to assign to species”

So it seems there will be some individuals, at either end of a scale, that will fit neatly into clear-cut ‘identifiability’ as one or the other. My photo above of the Lesser Sand Plover from Northwest Island is one of these. But I suspect a large number of birds, if not the majority, will fall instead within the range of ‘confusability’ for a large number, if not the majority, of people. I take some comfort from the statement in the NPIAW – The Shorebirds of Australia which states that, “Identification is therefore far from easy, even for experts, especially as individual birds may be at different stages of their moult”.

It’s probably worth keeping in mind the maxim that: “if there’s any doubt, then it’s a Lesser”.

So, as foreshadowed in my initial email to Birding-aus, I have ended up slightly embarrassed (and my credibility as a wader watcher and birdwatcher more generally must be well and truly shot!), but it has been worth it for the feedback it triggered and the better understanding I now have. Thanks to all. 

PS: It seems there have also been Greater Sand Plovers at Lake Wollumboola, but I didn't see them!

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