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
Little Swift
Apus affinis
Little swifts are readily identified by their small size. Their wingspan is only 33 cm compared to 42 cm in the case of common swift. Their plumage is black except for a white throat and rump, the white rump patch extending onto the flanks. They have a short square tail, with all rectrices round-tipped. The flight is fluttering like that of a house martin, and the call is a high twittering. Like other swifts they are very short-legged. The legs are used for clinging to vertical surfaces only.
ID text from Wikipedia, CC BY-SA 4.0
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