Only mammal capable of true flight (3)
I believe the answer is:
bat
'only mammal capable of true flight' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bat that I've seen before include "Small winged mammal, may be vampire" , "Nocturnal flier" , "Club used in cricket" , "The cricketer wields it" , "Creature" .)