Almost 50% treasure birds (9)
I believe the answer is:
ostriches
'birds' is the definition.
(ostrich is a kind of bird)
'almost 50 treasure' is the wordplay.
'50' suggests halving the letters.
'treasure' becomes 'riches'.
'almost' halved is 'ost'.
'ost'+'riches'='OSTRICHES'
(Other definitions for ostriches that I've seen before include "Fast-running flightless birds" , "People not facing the reality" , "Largest living birds" .)