New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island), and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. New Zealand is notable for its geographic isolation, situated about 2000 km (1250 miles) southeast of Australia across the Tasman Sea, and its closest neighbours to the north are New Caledonia, Fiji and Tonga. During its long isolation New Zealand developed a distinctive fauna dominated by birds, a number of which became extinct after the arrival of humans and the mammals they introduced.