Madagascar, the fourth-largest island in the world, lies in the Indian Ocean off the coast of Mozambique. It includes several much smaller islands. A central chain of high mountains, the Hauts Plateaux, occupies more than half of the main island and is responsible for the marked differences - ethnically, climatically and scenically - between the east and west coasts. The narrow strip of lowlands on the east coast, settled from the sixth century by Polynesian seafarers, is largely covered by dense rainforests, whereas the broader west-coast landscape, once covered by dry deciduous forests, is now mostly savannah. The east coast receives the monsoon and, on both coasts, the climate is wetter towards the north. The southern tip of the island is semi-desert, with great forests of cactus-like plants. The capital, Antananarivo, is high up in the Hauts Plateaux near the island's centre. Much of Madagascar's flora and fauna is unique to the island. There are 3000 endemic species of butterfly; the many endemic species of lemurs fill the niches occupied elsewhere by animals as varied as raccoons, monkeys, marmots, bushbabies, sloths and even (though this variant is now extinct) bears. There is a similar diversity of reptiles, amphibians and birds (especially ducks), and also at all levels of plant life.