Ostriches' kin (4)
I believe the answer is:
emus
'ostriches' kin' 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 "laboratory units" , "Large flightless birds of Australia" , "Largest native Australian birds" , "Running birds" , "Aussie birds" .)