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' indicates a hidden word (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" .)