Australian birds (4)
I believe the answer is:
emus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">australian birds</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for emus that I've seen before include "Large flightless birds of Australia" , "Running birds" , "laboratory units" , "Largest native Australian birds" , "Aussie birds" .)