Characteristic of bird captivates artist (5)
I believe the answer is:
trait
'characteristic' is the definition.
(I've seen this before)
'bird captivates artist' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'captivates' means one lot of letters goes inside another.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'tit' going around 'ra' is 'TRAIT'.
'of' is the link.
(Other definitions for trait that I've seen before include "Decorative band" , "Habit" , "A characteristic of straitened kind" , "Characteristic or distinguishing quality" , "Quirk" .)