Small nocturnal bird (5)
I believe the answer is:
owlet
'small nocturnal bird' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for owlet that I've seen before include "Baby bird; moth" , "Baby bird of prey" , "Wise young" , "Young hooter" , "Young nocturnal bird of prey" .)