Birds on display in the museum (4)
I believe the answer is:
emus
'birds' is the definition.
(emu is a kind of bird)
'display in the museum' is the wordplay.
'display in' says the answer is hidden in the clue (I've seen 'displayed in' mean this).
'EMUS' is hidden within 'the museum'.
'on' acts as a link.
(Other definitions for emus that I've seen before include "Muse about flightless Australian birds" , "laboratory units" , "Large flightless birds of Australia" , "Running birds" , "Largest native Australian birds" .)