The bird in the nest (3)
I believe the answer is:
hen
'the bird' is the definition.
(hen is a kind of bird)
'in the nest' is the wordplay.
'in' indicates the answer is hidden within the clue.
'HEN' is hidden within 'the nest'.
(Other definitions for hen that I've seen before include "Laying bird" , "Female bird" , "Insufficient in amount" , "Farm bird" , "Coop resident" .)