Black bird of prey hunting dog (6)
I believe the answer is:
beagle
'hunting dog' is the definition.
(beagle is a kind of hunting dog)
'black bird of prey' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'bird of prey' becomes 'eagle' (eagle is a kind of bird of prey).
'b'+'eagle'='BEAGLE'
(Other definitions for beagle that I've seen before include "5 [MANS BEST FRIEND]" , "hunting animal with smooth coat" , "Small hunting dog" , "Darwin voyaged in this ship" , "Breed of dog in a glebe" .)