Bird in the other nest (4)
I believe the answer is:
erne
'bird' is the definition.
(erne is a kind of bird)
'in the other nest' is the wordplay.
'in' says the answer is hidden in the clue.
'ERNE' can be found hidden inside 'other nest'.
(Other definitions for erne that I've seen before include "Sea-eagle in an Irish lake" , "River and lake of the North" , "Sea eagle and Northern loch" , "Flier" , "flyer in the main" .)