Crazy night fliers (4)
I believe the answer is:
bats
This clue is a double definition.
'crazy' is the first definition.
(bats can informally mean crazy)
'night fliers' is the second definition.
(I've seen this in another clue)
(Other definitions for bats that I've seen before include "Cuckoo" , "Those striking" , "Night-flying creatures" , "Loopy; mammals" , "cracked" .)