Appropriate, as birds turning up from the south (6)
I believe the answer is:
assume
'appropriate' is the definition.
(assume can mean to take or appropriate)
'as birds turning up from the south' is the wordplay.
'birds' becomes 'emus' (emu is a kind of bird).
'turning up from the south' says the letters should be written backwards (in a down clue, letters go up or head \'north\').
'emus' reversed gives 'sume'.
'as'+'sume'='ASSUME'
(Other definitions for assume that I've seen before include "Take on, affect" , "Dark brown fur" , "Be arrogant" , "Take as read" , "Wrongly take" .)