Hunting dog decapitated bird (5)
I believe the answer is:
eagle
'bird' is the definition.
(eagle is a kind of bird)
'hunting dog decapitated' is the wordplay.
'hunting dog' becomes 'beagle' (beagle is a kind of hunting dog).
'decapitated' means to remove the first letter.
'beagle' with its first letter taken off is 'EAGLE'.
(Other definitions for eagle that I've seen before include "Bald, golden, bird" , "Valuable piece" , "high-flier" , "two strokes fewer?" , "experts are putting more than albatross?" .)