In contrast to the Namib, the Kalahari is no true but a fossil desert - encompassing a range of vegetations types from dornbush savannah in the south to open woodland in the north. Surface water is rare for most of the year, but only the southwest with annual rainfall of less than 175 mm is really dry. The characteristic 5 to 25 m high red dunes are covered with a stabilizing cover of drought resistent grasses and low shrubs; other adapted species include the Tsamma melon. National parks host a variety of wildlife, including hyena, lion, meerkat, giraffe, warthog, jackal, various antelope and many species of birds and reptiles. The huge nests of weaver bird colonies are a frequent sight, and seasonal wetlands like the Makgadikgadi Pans of Botswana, are visited by tens of thousands of flamingos during the rainy season. Humans - as represented by the San people - have lived in this harsh environment for some 20000 years as hunter-gatherers, frequently recording their everyday life in the form of rock paintings or engravings.