Green’s Dictionary of Slang

(Aus.) a ‘double-barrelled’ surname; often as start a fowl-roost, to take on such a name.

1941		Baker Popular Dict. Aus. Sl.
1948		R. Raven-Hart Canoe in Aus. 127: I was written to as Raven Hart [...] avoiding what Australian picturesquely calls the ‘Fowl-roost’.
1993		P.R. Wilkinson Thes. Trad. Eng. Metaphors 177: Start a fowl-roost [Aus] Adopt a surname with two elements and a hyphen between them (- for the hens to roost on!).