Bird in danger, nesting (4)
I believe the answer is:
erne
'bird' is the definition.
(erne is a kind of bird)
'in danger nesting' is the wordplay.
'in' says the answer is hidden in the clue.
'ERNE' is hidden within 'danger nesting'.
(Other definitions for erne that I've seen before include "Eagle, river and lough" , "European sea eagle" , "Marine flyer" , "flyer in the main" , "Great lake in Fermanagh with lots of islands" .)