As I write this, it is July 8th. It is not uncommon to hear feeding parties of swifts. Look up and there they are. Tonight there was a party on the wing of about 20 birds.
Suddenly they will all be gone. They fly south to central Africa, where insects are more plentiful. It beats me why they migrate as I would have thought there would be a plentiful supply of flying insects there all year around. The journey is a hazardous one crossing deserts and much of Europe.
Numbers seem to be holding up here. There is a concern about losing nest sites on old buildings and barns. I can't say numbers appear lower here. Indeed I have also seen more swallows than last year.
Once they have gone it takes a few weeks to realise they are not here. In this part of the UK most are back by mid May. When they are here they are one of the most common birds seen. They feed and sleep on the wing. It gladdens my heart when they return. They have been making his journey for thousands or even millions of years completely oblivious of wars that trouble humans.
See https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/swift/ .