Birds Greek character captured in French art (4)
I believe the answer is:
emus
'birds' is the definition.
(emu is a kind of bird)
'greek character captured in french art' is the wordplay.
'greek character' becomes 'mu' (letter from the Greek alphabet).
'captured in' is an insertion indicator.
'french art' becomes 'es' ('is' in French - 'art' can mean 'is' eg 'thou art').
'mu' inserted within 'es' is 'EMUS'.
(Other definitions for emus that I've seen before include "Aussie birds" , "Running birds" , "Fast, but not high-fliers" , "Largest native Australian birds" , "laboratory units" .)