Enclosures for female swans (4)
I believe the answer is:
pens
I believe this is a double definition.
'enclosures' is the first definition.
(pen is a kind of enclosure)
'female swans' is the second definition.
(a female swan is a pen)
'for' is the link.
(Other definitions for pens that I've seen before include "birds" , "Female swans" , "Literary thought or reflection" , "writers" , "Writing implements" .)