Bird in another nest (4)
I believe the answer is:
erne
'bird' is the definition.
(erne is a type of bird)
'in another nest' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ERNE' is hidden in the letters of 'another nest'.
(Other definitions for erne that I've seen before include "European sea eagle" , "Marine flyer" , "flyer in the main" , "Island-studded lake in Fermanagh" , "bird of prey" .)