One of the great spectacles at Khao Yai is to watch the Needletails as they come in to drink in the late afternoon after a day of feeding over the forest canopy.
The birds fly in squadrons, much like jet planes. They approach the water at high speed and go back up to continue their circular flights.
These Swifts are very robust, look like 'flying cigars with wings' or boomerangs, to me. The most common one is Brown-backed which has a rather brownish pale back. The white lore is always present and distinct with these birds, atleast at Khao Yai.
The slightly smaller Silver-backed has a more white colored back with a pale throat.
This species is a lot more uncommon.