Bird in better nest (4)
I believe the answer is:
tern
'bird' is the definition.
(tern is a kind of bird)
'in better nest' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TERN' can be found hidden inside 'better nest'.
(Other definitions for tern that I've seen before include "Fork-tailed relative of the gull" , "Small slender gull" , "Sea bird, a small gull" , "Small gull with forked tail" , "Gull-like sea bird" .)