Birds' duet rudely interrupted (9)
I believe the answer is:
disturbed
'interrupted' is the definition.
('disturb' can be a synonym of 'interrupt')
'birds' duet rudely' is the wordplay.
'rudely' indicates anagramming the letters (rude can mean rough or unrefined).
'birds'+'duet'='birdsduet'
'birdsduet' with letters rearranged gives 'DISTURBED'.
(Other definitions for disturbed that I've seen before include "Interrupted" , "Changed the set arrangement or made uneasy" , "Emotionally upset -- worried" , "Intruded on" , "Agitated" .)