Maybe cherry's sour for bird (8)
I believe the answer is:
redstart
'bird' is the definition.
(redstart is a kind of bird)
'maybe cherry's sour' is the wordplay.
'maybe cherry' becomes 'reds' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sour' becomes 'tart' (similar in meaning).
'reds'+'tart'='REDSTART'
'for' is the link.
Can you help me to learn more?
(Other definitions for redstart that I've seen before include "bird from Europe" , "Singer" , "One sings" , "Songbird" , "Bird (coloured opening!)" .)