Green’s Dictionary of Slang

(Aus.) a tramp, a vagrant living in the Great Plains of Western Queensland.

1955		D. Niland Shiralee 27: An old bundle of a man came down the road from the west. Macauley watched him approaching and recognized him at once for what he was, a flat-country bagman, a type on his own [...] In his time he had met plenty of these plain-turkeys, as they were known. [Ibid.] 28: The old turkey looked at him wonderingly.
1965		H.P. Tritton Time Means Tucker (rev. edn) 16: He started off by saying that anything was good enough for ‘bloody plain turkeys’.
1978		T. Davies More Aus. Nicknames 80: Plain Turkey A generic nickname for any swaggie who plodded the Central Queensland plains. Such men were usually loners, like the game bird from which they took their name.