This post is mainly about one bird - a martin that I spent about one and a half hours watching and trying to photograph this morning. The bird was hawking insects over some uncut padi with a few hundred Red-rumped and Barn Swallows.
The bird was obviously Sand Martin-like, quite warm-brown above (in morning sunlight), but several features made me wonder if it could be a Pale Martin. I am 90% sure only one bird was present, though some of my photos do make me wonder if there were actually two.
According to Robson's Birds of South-east Asia, Pale Martin can be distinguished from Sand Martin as follows: "slightly smaller and smaller-billed with slightly shallower tail fork, upperparts slightly paler and greyer, underparts less clean white, with creamy wash on belly and undertail coverts, breast band paler but neater, lacks dark smudging on centre of breast/upper belly."
Photos on the web show that Pale Martins can show some central breast smudging, especially the race fohkiensis (see here)
What initially drew my attention to the bird was the apparent absence of a central breast smudge. This was not visible at all through binoculars, though is apparent on some photos as a faint greyish wash. The tail looked quite squarish, though it was evident that the bird was in some stage of moult.
The vent and undertail coverts seem to be creamy or buffish on this photo.
I don't have enough recent experience of Sand Martins, nor any of Pale Martin to be able to make a certain identification of this bird. Hopefully, there are others who do who can help out!
Several hours later: Well, I've learned a lot about Pale Martins in a short time! It seems that the best way to separate them from Sand Martins is, when perched, their wings extend well beyond the tail tip. Other than that, they are markedly grey-brown, which my bird clearly was not, so on that basis, it was a Sand Martin! For pics of what a Pale Martin looks like, see here