Bird unsettling a pig in Maine (6)
I believe the answer is:
magpie
'bird' is the definition.
(magpie is a kind of bird)
'unsettling a pig in maine' is the wordplay.
'unsettling' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'maine' becomes 'me'.
'a'+'pig'='apig'
'apig' with letters rearranged gives 'agpi'.
'agpi' inserted within 'me' is 'MAGPIE'.
(Other definitions for magpie that I've seen before include "chatty bird" , "'One is for sorrow, two for joy (6)'" , "Long-tailed crow" , "said to bring sorrow" , "Bird - obsessive collector" .)