C.b. australis is a subspecies. You won't find any bibroni around ever and you would be extremely lucky to find any australis.

bibroni has a slightly different morphology than australis, though they are very closely related (if not actually the same species from different locales).

For more info, check Conway's Candoia Bible on this site.
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John R. Stebbins
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1.1 Candoia bibroni australis
0.2 Candoia carinata carinata
1.0 Candoia paulsoni
2.0 elaphe guttata guttata