Green’s Dictionary of Slang

kelly n.²

a crow.

1936		Grenfell Record (NSW) 30 Nov. 1/6: ‘Kelly’ Outwitted. Crows [...] are responsible for heavy losses of ewes, and lambs on many properties in the Dunedoo district. A novel method of getting rid of these destructive birds has been evolved by Mr. James Yeo.
1941		Baker Popular Dict. Aus. Sl.