Game birds snatching feed in river (5,4)
I believe the answer is:
great ouse
'river' is the definition.
(I've seen this before)
'game birds snatching feed' is the wordplay.
'game birds' becomes 'grouse' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'snatching' means one lot of letters goes inside another.
'feed' becomes 'eat' (I've seen this before).
'grouse' going around 'eat' is 'GREAT OUSE'.
'in' is the link.
Can you help me to learn more?
(Other definitions for great ouse that I've seen before include "Fens river" , "Flower" .)