Where birds are devouring corn seriously (2,7)
I believe the answer is:
in earnest
'seriously' is the definition.
(synonyms)
'where birds are devouring corn' is the wordplay.
'where birds are' becomes 'in nest' (birds live in nests).
'devouring' indicates putting letters inside.
'corn' becomes 'ear' (an ear is a piece of corn).
'innest' placed around 'ear' is 'IN EARNEST'.
(Other definitions for in earnest that I've seen before include "seriously" , "resolutely" , "Sincere and serious" , "with enthusiasm" , "Not joking" .)