Bird seed extremely important (5)
I believe the answer is:
pipit
'bird' is the definition.
(I know that Pipit is a type of oscine)
'seed extremely important' is the wordplay.
'seed' becomes 'pip' (as in a fruit pip).
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'important' with its middle taken out is 'it'.
'pip'+'it'='PIPIT'
(Other definitions for pipit that I've seen before include "Bird related to wagtail" , "Meadowland bird" , "Songbird of open country" , "Small bird of rock or meadow" , "Titlark" .)