Bird jaw (4)
I believe the answer is:
chat
This clue is a double definition.
'bird' is the first definition.
(chat is a kind of bird)
'jaw' is the second definition.
('chat' can be a synonym of 'jaw')
(Other definitions for chat that I've seen before include "Inconsequential conversation" , "Talk easily; songbird" , "Chinwag" , "waffle?" , "tittle-tattle" .)