|I was looking for the Red-billed Starling that Martin Kennewell found earlier in the day and bumped into Low Choon How and his spouse, who were also searching for the bird. We stood around at Neo Tiew Lane 3 chatting when I heard three to four unfamiliar, rather rail-like "kek" call in succession (repeated short bursts of a nasal sound). As I turned to find the sound source I saw a rail-like bird ("confirming" my initial guess, which to my chagrin caused my in-view identification to suffer) flying eastwards above the grassfields adjacent to the road. It was about 30 metres from us and flying less than 10 metres above the ground.
The bird was medium sized; it gave an impression of being bigger than a White-breasted Waterhen, but smaller than a Watercock. It had narrow and pointed wings with rather shallow flapping. The carpals were constantly bent when the bird flapped. The bird also had 1) slightly elongated, but not a slim neck (no where as long as an egret nor a heron. It was, if I may use a comparison again, less than twice more jutted out from the body than a flying Pink-necked Green Pigeon); 2) long drooping legs with tarsus and tibia of roughly equal length (reminiscent of - and I am getting repetitive here but - a darn rail). As it was 1820 and the sky was cloudy, I was unable to make out any colours with my naked eye with the exception of some white flash on the wings when the bird flapped down.
By the time I was able to get my binoculars on the bird it was already past my perpendicular. For the next 10 seconds or so I had views of the bird flying away at a (seemingly) constant speed. Through my binoculars, I was again unable to make out any colour on the bird with the exception of the white flash visible when the bird flapped down, which through my binoculars I could tell were restricted to the secondaries. The primaries and rest of the wings were not white, but of colour I could not tell; everything was just dark due to the bad lighting condition. The bird's long legs were also drooping down throughout view, a strange observation I could not reconcile. Choon How only managed to get his binoculars on the bird after me and likewise only saw the bird flying away.
After the bird disappeared, we confirmed our observation with each other: that the white on the bird's wings were restricted to the secondaries, and that the drooping legs were odd, as if the bird was trying to come to a stop (which it did not). It took me about five seconds of mental gymnastics to figure out what the heck I was looking at, but after eliminating all rails I knew it occurred to me that the Grey-headed Lapwing was a prime candidate. The long legs narrowed down the choice of possible birds in Singapore, and the size and white secondaries ruled out all rails After reaching this conclusion I played two recordings of the Grey-headed Lapwing from xeno-canto labelled "flight call" on the spot. https://xeno-canto.org/414502 seemed too dragged out and strong, but Choon How and I agreed that what we heard was superficially similar to https://xeno-canto.org/657678. We drove and searched the NSRCC and nearby grass patches together but to no avail. I later spent about 10 minutes driving around Harvest Link but could not find the bird either.
I am now at home writing this report with the luxury of browsing through more recordings, and https://xeno-canto.org/534379, frustratingly labelled just "call" but noted in the comments that the bird was in flight, is a good fit for what we heard. Flipping through Robson's fieldguide to check other options, the bird surely can't be a Pheasant-tailed Jacana (too much white on wings), River or Yellow-wattled Lapwing (not enough white on wings), the default Red-wattled Lapwing (again not enough white on wings), any heron or other shorebird (shape too different).