Train a bird (4)
I believe the answer is:
rail
I believe this clue is a double definition.
'train' is the first definition.
(I know that train can be written as rail)
'a bird' is the second definition.
(a wading bird)
(Other definitions for rail that I've seen before include "Barrier around lair" , "Supported bar - inveigh" , "Fulminate - wading bird" , "Rant" , "Complain vehemently" .)