Rook? It's a bird (4)
I believe the answer is:
gull
I believe this clue is a double definition.
'rook?' is the first definition.
(both can mean to trick)
'a bird' is the second definition.
(gull is a kind of bird)
'it's' is the link.
(Other definitions for gull that I've seen before include "Dupe - aquatic bird" , "Fool - bird" , "Seabird with a raucous call" , "Common seabird" , "Aquatic bird with long pointed wings" .)