Black bird; boast (4)
I believe the answer is:
crow
I believe this clue is a double definition.
'black bird' is the first definition.
(I've seen this before)
'boast' is the second definition.
(to crow about something is to boast about it)
(Other definitions for crow that I've seen before include "Large black bird" , "Brag; carrion bird" , "shout in triumph" , "Bird in 1's poems" , "Express triumph; bird" .)