Хороший вопрос Посмотрел внимательно все фотографии этой птицы и думаю тоже, что толстоклювый молодой
По мне все же толстоклювый. На Каспии они такие короткоклювые летят... Сам однажды едва не спутал...
Ну по пропорциям вполне монгол. Но с этой парой видов надо оч. внимательно.
this is a most interesting bird, once again the complex LSP/GSP teatch us how variable are the birds....
the flanks are pale and clean with no visible even hint of dark smudges or markings as in Mongolian Plove in any adult plumage ....
therefore this should be a LSP or Tibetan Sp (atrifrons - group)
1) AGEING first as usual: our birds seems to me to be an abraded juvenile... this is for me visible by the rounded and short middle tertials typical in juv shorebirds, by the wing coverts pattern, shape and colour, by the breast band pattern and markings, by the secondaries and primaries shape and pattern (enlargin the imagines, i could detect narrow and pointed primaries, broad secondaries with a sharp clear tip as a little "tooth" at the very tip, typical of juv shorebirds, terns and gulls, raptors etc )
1) Primary Projection appear long and well visible as should be in mongolian -group
2) the tail appear very dark, almost blackish, strongly contrasting with rump and upperparts as in Mongolian
3) the bill appear short and very bulbous tipped as in Mongolina SP
4) the bird appear a very black&white looking shorebird, as it fits better Mongolian
5) supercilium is very well marked and strikingly contrasting as it should be in juv Mongolian
6) breast is very smudgy, very dirty and appear as an almost complete breast band as fit better Mongolian
7) in the fligth shot but also on perched bird, it seems scapular show a frosty white fringing, better fititng Mongolian rather than the warm brownish-buff og Tibetan
the tibia:tarus ratio seems more likely as in mongolian, with the tibia (exposed and feathered too) almost as long as tarsus, while in atrifron tibia is shorter and than the ratio is not 1:1 or 0.9:1 but 0.5:1 or 0.7:1 when feathering abraded off.
1bis) Tail pattern itself is more like Tibetan (atrifrons) for what concern the very striking white tail side and tip
2bis) rump show almost no dark markings that is very rarely if ever the case for Mongolina and fit better atrifrons
3) pale nape and an hint of Kentish-Plover like pale collar fit better tibetan SP (but could it be due to abrasion and sun-bleaching ???)
I would have been happy to see much betetr photos of open tail, and call sound recordings. I do not know how much the bigger and darker "chaeferi" could appear similar to mongolus/stegmanni and I sdo not studied in details variability of juv Mongolian...I only studied variability in juv atrifrons yet !!!
For example, do a very bleached/abraded juv Mongolian may lacks any dark patterning on flanks? I believe the answer is YES !!
So, even if I woudl tend to believe that is one of the Mongolian Sp and therefore a 1st for OSME area, I would suggest people to go there and try to get open tail shots and sound recordings and other closer and cleaner photos.
I am out of my home so my books are there, i could not report for any other hint of variability within the complex or other ID tips, hope that's help though and sorry for the many typos as I am going fast (tomorrow I am elading a birding trip with Brian J Small around Sicily