Big bird in Australia (3)
I believe the answer is:
emu
'big bird in australia' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for emu that I've seen before include "Aussie runner" , "Australian bird related to the ostrich" , "Ostrich-like bird" , "Fast runner in Oz" , "Native Australian bird" .)