Bird down (7)
I believe the answer is:
swallow
This clue is a double definition.
'bird' is the first definition.
(swallow is a kind of bird)
'down' is the second definition.
(both can mean to consume or eat)
(Other definitions for swallow that I've seen before include "Believe gullibly - bird" , "flier" , "Buy < and consume" , "Long-winged, fork-trailed bird" , "Songbird" .)