Green’s Dictionary of Slang

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

1876		Punch (Melbourne) 27 July 3/1: Pat had dug it all up, put the seed in [...] put lots of strings across [...] with little bits of red rag to frighten the ‘spaggers’ away.
1915		Argus (Melbourne) 13 Feb. 7/2: ‘What are you doing with road metal in your pockets. Drain?’ ‘To chuck at the birds, sir, when they come at me. I’m awful afraid of birds, sir, especially spaggers’.
2008		Birding-Aus 22 July 🌐 [W]edgies, woodies, reddies, bloods, diamys, spagga, spoggies, poms etc. Please! Some of that sounds a lot like cage bird industry jargon to me .