Green’s Dictionary of Slang

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

1903		Sydney Mail 6 May 1118/1: The dickey-birds and the cockyolly-birds and the other little birds all over the world wer simply heartbroken.From Jenny Wren to Willie Wagtail and from Cocky Spag to Jacky Winter they all went about with tears in their eyes.
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.
1921		Sun (Sydney) 28 Aug. 2/4: Hanging outside the bathroom in a cage is a canary, and a few days after the ‘spag’s’ first visit he made a pal of the prisoner, and perched on its cage.
1934		Bulletin (Sydney) 8 Aug. 21/2: At Bombala (N.S.W.) two parrots always fly about with a flock of sparrows. They eat the same food and even mimic the spags [...] No matter in which direction the parrots fly the sparrows follow.
1946		Sydney Morn. Herald 7 Dec. 4/5: Wally, her 11-year-old son, arrived, [...] from a bird-nesting expedition. He showed his mother his find. ‘Two beaut spag’s eggs, mum,’ he said.
1951		Bulletin (Sydney) 17 Jan. 12/2: The spag makes no attempt to attack, but waltzes round in a shocked upright posture [...] Soon a regular chorus of chirrups is in full swing as the junior members of the speckled tribe add their bit of cheek, and the sparrows retire beaten.
1960		Bulletin (Sydney) 9 Sept. 19/1: I had found a spag’s nest in the letterbox.
1971		D. Ireland Unknown Industrial Prisoner 130: ‘Those little birds in the yard?’ ‘Spags. Little brown sparrows.’.