To me it looks like one of the many varieties of cuckoos that arrive in Oz for the summer, like the really annoying koel.
http://t1.gstatic.com/images?q=tbn
aR9yzVq3pA2lM:
With a bit of reasearch, it could actually be the female of the common koel. I've seen a local male, it's a largish bird, black, and its 3am "KOELLLL" cry has earnt it a price on its head.