Like many, I keep my eyes open for the first swallows (birds) returning from Africa. Usually I see my first ones in early April. Although I have seen some, I am sure there are fewer. This may be because more perish on the journey due to lack of food.
We still see swifts, although these are later to arrive. To me they make a late spring or early summer evening. Usually you hear their screaming, look up and see them overhead hunting. Swifts are about, although I have seen and heard none yet.
Cuckoos used to be commonly heard, although I heard none last year. They tend to lay their eggs in the nests of willow warblers. Just occasionally they can be heard. More rarely, they can be seen on wires overhead.
See https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/swallow/ .