Bird heading off from stream (4)
I believe the answer is:
rook
'bird' is the definition.
(rook is a kind of bird)
'heading off from stream' is the wordplay.
'heading off from' means to remove the first letter.
'stream' becomes 'brook' (I've seen this before).
'brook' with its initial letter taken off is 'ROOK'.
(Other definitions for rook that I've seen before include "Gregarious crow" , "Swindle; castle" , "Defraud -- crow" , "Rank - and - file man" , "journalist Jean" .)