Leave high ground for game bird (9)
I believe the answer is:
partridge
'game bird' is the definition.
(partridge is a kind of game bird)
'leave high ground' is the wordplay.
'leave' becomes 'part' (parting is a kind of leaving).
'high ground' becomes 'ridge' (I've seen this before).
'part'+'ridge'='PARTRIDGE'
'for' acts as a link.
(Other definitions for partridge that I've seen before include "Game bird (in a pear tree?)" , "Peculiarly apt girder for the game bird" , "Widespread bird" , "1st" , "Flier" .)