Attacker beheaded and butchered rare bird (6)
I believe the answer is:
raider
'attacker' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for raider that I've seen before include "Surprise attacker" , "One attacks" , "One making incursion" , "One plundering" , "One who makes surprise attack, perhaps to steal" .)