Hogwarts messengers (4)
I believe the answer is:
owls
'hogwarts messengers' 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 "Slow kind of birds" , "Types incredibly wise" , "Slow (anag) -- birds of prey" , "Night birds" , "Avian symbols of wisdom" .)