Dog and black bird (6)
I believe the answer is:
beagle
'dog' is the definition.
(beagle is a kind of dog)
'black bird' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'bird' becomes 'eagle' (eagle is a type of bird).
'b'+'eagle'='BEAGLE'
'and' acts as a link.
(Other definitions for beagle that I've seen before include "Hound dog" , "Darwin voyaged in this ship" , "5 [MANS BEST FRIEND]" , "Short-haired dog" , "Type of hound" .)