A quiet bird due to change disposition (8)
I believe the answer is:
aptitude
'disposition' is the definition.
(thesaurus)
'a quiet bird due to change' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'bird' becomes 'tit' (tit is a kind of bird).
'to change' is an anagram indicator.
'due' with letters rearranged gives 'ude'.
'a'+'p'+'tit'+'ude'='APTITUDE'
(Other definitions for aptitude that I've seen before include "Update it, having natural skill" , "Inherent ability, natural talent" , "A natural talent or skill, for which there may be a test" , "Bent" , "capacity" .)