Birds chatter about new bag (7)
I believe the answer is:
gannets
'birds' is the definition.
(gannet is a kind of bird)
'chatter about new bag' is the wordplay.
'chatter' becomes 'gas' (I've seen this before).
'about' means one lot of letters goes inside another.
'new' becomes 'n'.
'bag' becomes 'net' (I've seen this in other clues).
'n'+'net'='nnet'
'gas' enclosing 'nnet' is 'GANNETS'.
(Other definitions for gannets that I've seen before include "Birds" , "people grabbing grub" .)