I am nowhere near an expert, and have no field experience with Western Sandpiper and haven't seen a stint in far too long, but to me this bird looks like a Red-Necked Stint.
We can sit here till the cows come home saying the bill is long and downcurved in a way you wouldn't expect in a RN, but by the same reasoning it is short and straight for a Western. In all honesty, I wouldn't even go as far as to say it is completely left-field for a Red-Necked, and while we are used to being told their bills are straight, Michael Morcombe's Field Guide to Australian Birds
states [Red-Necked Stint] "Bill short, thick-based, almost straight except very slightly downcurved and bulbous tip"
. To me, that's a pretty good description for what we have here.
I think that Steve is correct in saying:
Steve Wood wrote:Even the posture of Imogen bird says to me RN stint.( no neck)
The bird has that stereotypical hunchback pose classic of the Red-Necked Stint, with the head held just lower than the shoulder in most of the photos. While Western Sandpiper can look hunchbacked while foraging, they seem to stand a bit taller in most photos, field guide illustrations and texts, with the head held just above the shoulder.
A clinching detail for me is the tail. Once again turning to Michael Morcombe, Red-Necked Stint have "long wings that extend beyond tail tip, giving the bird a slender, attenuated rear end,"
while the Western Sandpiper has short wings that end level with the tail tip. All the photos posted of this bird in the field, including Grahame's original, Jochen's resighting and Imogen's latest photos, show tail feathers protruding well beyond the tail.
Looking then to the plumage of the bird, and the breastband too has strong evidence of a Red-Necked. It is smudgy and brown all over, perhaps lightly streaked but not in a way that is particularly note-worthy. In Morcombe, this is called "a dark smudge"
, which I think is pretty apt in relation to this bird. In a Western Sandpiper, we would expect this to be more distinctly striated (Simpson and Day, Morcombe, Robertson and Heather). In most images on the internet, even in non-breeding attire these streaking patterns tend to have some scatterings of the distinctive "arrowheads" of a Western's breeding plumage, but Imogen's photos don't show any sign of such markings.
Hope this helps