Bird in painting, on top of grass amidst lions (9)
I believe the answer is:
partridge
'bird' is the definition.
(partridge is a kind of bird)
'painting on top of grass amidst lions' is the wordplay.
'painting' becomes 'art' (I've seen this before).
'on' indicates putting letters inside.
'top of' says to take the initial letters.
'amidst' is an insertion indicator.
'lions' becomes 'pride' (pride is the collective noun for a group of lions).
The first letter of 'grass' is 'g'.
'g' put inside 'pride' is 'pridge'.
'art' inserted inside 'pridge' is 'PARTRIDGE'.
'in' acts as a link.
(Other definitions for partridge that I've seen before include "early Christmas present" , "Game bird (in a pear tree?)" , "Widespread bird" , "sort of quail" , "Animal" .)