A bird in the wilderness (4)
I believe the answer is:
erne
'a bird' is the definition.
(erne is a type of bird)
'in the wilderness' is the wordplay.
'in' says the answer is hidden in the clue.
'ERNE' is hidden in the letters of 'wilderness'.
(Other definitions for erne that I've seen before include "Irish lough" , "Irish river - sea eagle" , "Sea bird: lough in Ulster" , "Eagle, river and lough" , "flyer in the main" .)