Nocturnal predators (4)
I believe the answer is:
owls
'nocturnal predators' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for owls that I've seen before include "Members of Parliament" , "Avian symbols of wisdom" , "Slow kind of birds" , "Slow (anag) -- birds of prey" , "Wise old birds - quite slow" .)