South Australians nick name is "Crow eaters".

My guess is life was tough and hungry in early years of settlement, and that joke was people had to eat crows.

Reading the above, perhaps it wasn't a joke. German-Silesian and Prussian settlers made up a substantial proportion of early settlement. Maybe they did eat the crows. Crows are big and annoying plentiful. Myself I'd prefer a brace of nice lorikeets, or a slow cooked galah.