Although about 90% of Botswana is covered by some kind of savanna, even the Kalahari Desert contains adequate vegetation to support tens of thousands of wild animals. Common trees are the mopane, camel-thorn, motopi (shepherd's tree), and baobab. Botswana is a natural game reserve for most animals found in southern Africa, including lions, leopards, cheetahs, elephants, giraffes, zebras, hippopotamuses, rhinoceroses, African buffalo, hyenas, and 22 species of antelope. The duiker (a small, horned antelope), wildebeest (gnu), and springbok (gazelle) are familiar. Five of the country's 164 species of mammals were threatened as of 2000. Also indigenous to Botswana are an estimated 386 bird species, seven of which were threatened as of 2000.