Flightless Australian birds (4)
I believe the answer is:
emus
'flightless australian birds' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for emus that I've seen before include "Largest native Australian birds" , "Aussie birds" , "Muse about flightless Australian birds" , "Large flightless birds of Australia" , "Fast, but not high-fliers" .)