Flying pig? (6)
I believe the answer is:
gannet
'flying pig?' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Perhaps there's an association between them I don't understand?
This is the entire clue.
(Other definitions for gannet that I've seen before include "Large diving fish" , "Large diving sea bird" , "Large fish-eating bird" , "greedy type" , "Large seabird, white with dark markings" .)