Bird new to this chorus (4)
I believe the answer is:
dawn
'this chorus' is the definition.
(dawn chorus is a type of chorus)
'bird new' is the wordplay.
'bird' becomes 'daw' (daw is a kind of bird**).
'new' becomes 'n'.
'daw'+'n'='DAWN'
'to' acts as a link.
(Other definitions for dawn that I've seen before include "beginning" , "Cockcrow" , "Threshold" , "Begin to appear" , "Sunrise" .)