Fleeces black birds (5)
I believe the answer is:
rooks
I believe this is a double definition.
'fleeces' is the first definition.
(I've seen this in another clue)
'black birds' is the second definition.
(I've seen this before)
(Other definitions for rooks that I've seen before include "Chess castles and birds" , "Castles, also, in chess" , "Cheats" , "Chess pieces or black birds" , "Large, crow-like birds" .)