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