Green’s Dictionary of Slang

(Aus.) a sparrow, esp. the (introduced) House Sparrow, Passer domesticus.

[1815		Scott Guy Mannering xi: John Wilson was a blustering kind of chield, without the heart of a sprug.
1861		Age (Melbourne) 11 Feb. 6/6: [T]he priests pointed out to a pert little ‘sprug’ perched on the shoulder of one of the chief josses, for one of the foreigners to have a shot at it.
1869		Argus (Melbourne) 27 Dec. 5/4: [A]although we do not look on ‘Jack Sprug’ as such an immaculate friend of the gardener and farmer [...] we feel it our duty to do him the justice of putting forward a theory in his favour.
1908		Queenslander (Brisbane) 8 Aug. 46/2: He and his school companions [...] saved up their pennies and bought a pistol and shot, and many a poor little ‘sprug,’ or sparrow, they shot without any feelings of compunction.
1918		Maryborough Chron. (Qld) 10 Apr. 4/4: ‘[S]prig’ is the wrong name for the sparrow, but ‘sprag’ or ‘sprug’ is correct.
1953		Record (Emerald Hill, Vic) 31 Oct. 1/5: An old Scottish name for them, I believe, is ‘sprug,’ and a good name, too.