Bird seed needs it (5)
I believe the answer is:
pipit
'bird' is the definition.
(I know that Pipit is a type of oscine)
'seed needs it' is the wordplay.
'seed' becomes 'pip' (as in a fruit pip).
'needs' means one lot of letters go next to another.
'pip'+'it'='PIPIT'
(Other definitions for pipit that I've seen before include "Bird related to wagtail" , "Songbird with streaky brown plumage" , "Ground-dwelling songbird" , "Lark-like songbird" , "Singer" .)