Church on island visited by a very loud bird (9)
I believe the answer is:
Here is my best explanation:
'bird' is the definition.
(chaffinch is a kind of bird)
'church on island visited by a very loud' is the wordplay.
'church on' becomes 'ch' (common abbreviation. I am not sure about the 'on' bit.**).
'island' becomes 'inch' (I've seen this before).
'visited by' is an insertion indicator.
'very loud' becomes 'ff' (musical abbreviation).
'chinch' enclosing 'aff' is 'CHAFFINCH'.
(Other definitions for chaffinch that I've seen before include "Common bird", "European bird with black and white wings", "singer", "Singer", "Bird", "Small European songbird", "flier" and "Garden bird".)