Beer taken by northern bird (7)
I believe the answer is:
bittern
'bird' is the definition.
(bittern is a kind of bird)
'beer taken by northern' is the wordplay.
'beer' becomes 'bitter' (bitter is a type of beer).
'taken by' means one lot of letters go next to another.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'bitter'+'n'='BITTERN'
(Other definitions for bittern that I've seen before include "Source of boom" , "Marsh bird of the heron family" , "large wader" , "Aquatic bird" , "Bird with a booming cry" .)