It's after seed, this bird (5)
I believe the answer is:
pipit
'bird' is the definition.
(pipit is a kind of bird)
'it's after seed' is the wordplay.
'it's' becomes 'it' (I can't explain this - if you can you should give a lot more credence to this answer).
'after' says to put letters next to each other.
'seed' becomes 'pip' (as in a fruit pip).
'it' after 'pip' is 'PIPIT'.
'this' acts as a link.
Can you help me to learn more?
(Other definitions for pipit that I've seen before include "Singer" , "Ground-dwelling songbird" , "Lark-like bird" , "Lark-like songbird" , "Meadowland bird" .)