Pacific Swift Apus pacificus
Estimated average number of individuals by week based on eBird data, Jul 2012 to Jun 2022
Peak week Oct 29-Nov 04
Early date 22 Jul 2017
Late date 20 May 1989
A fixture at raptor migration hotspots in Oct and Nov. With some effort (and very good photos), you may be able to pick out a Cook's Swift, which has not yet been recorded in Singapore as of Sep 2022.