Australian birds in the museum (4)
I believe the answer is:
emus
'australian birds' is the definition.
(I've seen this before)
'in the museum' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EMUS' is hidden within 'the museum'.
(Other definitions for emus that I've seen before include "Running birds" , "Largest native Australian birds" , "Fast, but not high-fliers" , "Large flightless birds of Australia" , "Aussie birds" .)