The Oriental Dollarbird is the only member of the Roller family to be found in Australia. In Australia it is a breeding migrant arriving from Papua New Guinea and eastern Indonesia in September and leaving in April. It is also distributed in much of south-east Asia and China. See the distribution map at Birdlife International.

Apparently it gets its English name from the blue-white wing spot which you can see in photo 4. Doesn't look much like a silver dollar to me.