Believe a bird (7)
I believe the answer is:
swallow
This clue is a double definition.
'believe' is the first definition.
(to swallow something is to accept or believe it)
'a bird' is the second definition.
(swallow is a kind of bird)
(Other definitions for swallow that I've seen before include "Get down" , "Believe gullibly - bird" , "Songbird" , "put up with" , "Small migratory bird with forked tail" .)