I decided to follow up a tip from Hor Kee, who wrote that Brown-backed Needletails were coming down to drink in the evening at Air Itam Reservoir.
The needletails did eventually arrive - but when it was already far too dark for photography. However, this was made up for by the presence of 10-20 Grey-rumped Treeswifts flying low to and fro along the dam, which gave me a good opportunity to try and capture some flight shots.
This seems to be the inter-breeding period. Most birds were in wing and tail moult, with some having lost their longer outer tail feathers altogether, which made them look quite odd in flight!
Toward dusk they went to roost in some small trees near the guard house. This was a challenge photographically, as they were against a colourless sky, and I was very limited in my viewpoint options (mostly directly below!). Hope to go back and improve these shots on a better day.
A Brahminy Kite provided a considerably simpler challenge!