Barrier; bird (4)
I believe the answer is:
rail
This clue is a double definition.
'barrier' is the first definition.
(rail is a kind of barrier)
'bird' is the second definition.
(a wading bird)
(Other definitions for rail that I've seen before include "Part of train track" , "Waterside bird; part of track" , "Rant" , "Water bird; bar" , "Complain about - marsh bird" .)