Complex sentence: By contrast, the territory of Norfolk Island, although under Australian sovereignty, is entirely outside the migration zone, as are the uninhabited territories of Heard Island and McDonald Islands (in the South Indian Ocean) and the Australian Antarctic Territory.
Split into simpler sentences: By contrast, the territory of Norfolk Island, although under Australian sovereignty, is entirely outside the migration zone. As are the uninhabited territories of Heard Island and McDonald Islands (in the South Indian Ocean) and the Australian Antarctic Territory.