Slow-flying birds (4)
I believe the answer is:
owls
'birds' is the definition.
(owl is a kind of bird)
'slow-flying' is the wordplay.
'flying' is an anagram indicator (letters fly around into new positions).
'slow' anagrammed gives 'OWLS'.
(Other definitions for owls that I've seen before include "Members of Parliament" , "Avian symbols of wisdom" , "Nocturnal birds" , "Types incredibly wise" , "Wise old birds - quite slow" .)