Partition between pigs and birds (8)
I believe the answer is:
swallows
'birds' is the definition.
(swallow is a kind of bird)
'partition between pigs' is the wordplay.
'partition' becomes 'wall' (wall is a kind of partition).
'between' means one lot of letters goes inside another.
'pigs' becomes 'sows' (I've seen this before).
'wall' placed into 'sows' is 'SWALLOWS'.
'and' is the link.
(Other definitions for swallows that I've seen before include "Birds with forked tails" , "Small swift birds" , "Strange slow laws apply to birds" , "Small migratory birds" , "Book by Arthur Ransome" .)