The concentration of animals in Ngorongoro Conservation Area cannot be over emphasized. The crater offers a haven for animal enthusiasts. Approximately 25,000 large animals, mostly ungulates, live in the crater. Large animals in the crater include the black rhinoceros (Diceros bicornis), the local population of which declined from about 108 in 1964-66 to between 30 and 40 in 2012 and the hippopotamus (Hippopotamus amphibius). There also are many other ungulates: the wildebeest (Connochaetes taurinus), Burchell's zebra (Equus burchelli), the common eland (Taurotragus oryx), and Grant's (Nanger granti) and Thomson's gazelles (Eudorcas thomsonii). Waterbuck (Kobus ellipsiprymnus) occur mainly near Lerai Forest. There are no topis (Damaliscus lunatus), oribis (Ourebia oribi), or crocodiles (Crocodylus niloticus). Impala (Aepyceros melampus) are absent because the open woodland they prefer does not exist. Giraffe also are absent, possibly because of a lack of browse species. Cheetah (Acinonyx jubatus), African wild dog (Lycaon pictus), and leopard (Panthera pardus) are rarely seen. Although thought of as "a natural enclosure" for a very wide variety of wildlife, 20 percent or more of the wildebeest and half the zebra populations vacate the crater in the wet season. Buffalo (Syncerus caffer) and eland do the opposite. Their highest numbers are during the rains. Servals (Leptailurus serval) occur widely in the crater. Lake Magadi, a large lake in the southwest of the crater, is often inhabited by thousands of mainly Lesser Flamingoes.