Flightless bird, male, captured by painter (4)
I believe the answer is:
rhea
'flightless bird' is the definition.
(I know that rhea is a type of flightless bird)
'male captured by painter' is the wordplay.
'male' becomes 'he' (he refers to a man).
'captured by' is an insertion indicator.
'painter' becomes 'RA' (member of the Royal Academy of Arts).
'he' put within 'ra' is 'RHEA'.
(Other definitions for rhea that I've seen before include "South American flightless bird - mother of Zeus" , "Ostrich-like bird - satellite of Saturn" , "New World ostrich" , "Grounded bird" , "S. Amer. flightless bird" .)