It's after seed, this bird (5)
I believe the answer is:
'this bird' is the definition.
(pipit is a kind of bird)
'it's after seed' is the wordplay.
'it's' becomes 'it' (I've seen this in other clues**).
'after' says to put letters next to each other.
'seed' becomes 'pip' (I've seen this before).
'it' put after 'pip' is 'PIPIT'.
(Other definitions for pipit that I've seen before include "Singer" , "Ground-dwelling songbird" , "Lark-like bird" , "Lark-like songbird" , "Meadowland bird" .)