Common Swift
Apus apus
Common swifts are 16–17 cm (6.3–6.7 in) long with a wingspan of 38–40 cm (15–16 in) and entirely blackish-brown except for a small white or pale grey patch on their chins which is not visible from a distance. They have a short forked tail and very long swept-back wings that resemble a crescent or a boomerang. Their call is a loud scream in two different tone pitches, the higher of which issues from the female. They often form "screaming parties" during summer evenings, when 10–20 swifts will gather in flight around their nesting area, calling out and being answered by nesting swifts.
ID text from Wikipedia, CC BY-SA 4.0
House Swift
Apus nipalensis
The house swift looks quite similar to the little swift. It is a small bird, but a medium-sized swift, with a wingspan of 12.5-14.5 cm. Its body size ranges from 14 to 16 cm and weighs approximately 20-35 g. This species has a dark, slightly forked tail. Other than the white rump band and white throat-patch, the house swift has a black plumage, darker than the little swift. Voice: House swifts make a ti-ti-ti-tititrrrrrr sound, among many others, as part of their vocal catalogues.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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