Barrier between swine and birds (8)
I believe the answer is:
swallows
'birds' is the definition.
(swallow is a kind of bird)
'barrier between swine' is the wordplay.
'barrier' becomes 'wall' (a wall acts as a barrier).
'between' indicates putting letters inside.
'swine' becomes 'sows' (I can't justify this - if you can you should believe this answer much more).
'wall' put inside 'sows' is 'SWALLOWS'.
'and' is the link.
Can you help me to learn more?
(Other definitions for swallows that I've seen before include "Accepts" , "Birds with forked tails" , "Small migratory birds" , "Seasonal visitors" , "Knocks back" .)