Old jailers ignoring last of warden's failures (7)
I believe the answer is:
'failures' is the definition.
(turkey is a kind of failure)
I cannot understand how the rest of the clue works.
(Other definitions for turkeys that I've seen before include "Birds with fan-shaped tails", "The birds for cranberry sauce, or theatre flops", "Movie flops", "Theatre flops or Christmas birds".)