Ngorongoro Crater is one of the world’s largest intact volcanic caldera. It is just one part of a much larger area of interrelated ecosystems. Had it not become the world's sixth-largest unbroken caldera, then what is now known as the Ngorongoro crater could have been a towering volcanic mountain, as high as Kilimanjaro. Ngorongoro Crater is an internationally important wildlife site. The crater is the flagship tourism feature for the Ngorongoro Conservation Area. It is a large, unbroken, un-flooded caldera, formed when a giant volcano exploded and collapsed some three million years ago. The Ngorongoro crater sinks to a depth of 610 metres, with a base area covering 260 square kilometres. The height of the original volcano must have ranged between 4,500 to 5,800 metres high. Apart from the main caldera, Ngorongoro also has two other volcanic craters: Olmoti and Empakai, the former famous for its stunning waterfalls, and the latter holding a deep lake and lush, green walls. On the leeward of the Ngorongoro highlands protrudes the iconic Oldonyo Lengai, an active volcano and Tanzania's third highest peak after Kilimanjaro and Meru. Known to local people as the Mountain of God, Mount Lengai's last major eruption occurred in 2007. At the mountain's foot is Lake Natron, East Africa's major breeding ground for flamingoes.
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.
The crater has one of the densest known populations of lions, numbering 60 in 2012. A side effect of the crater being a natural enclosure is that the lion population is significantly inbred. This is due to the very small amount of new bloodlines that enter the local gene pool, as very few migrating male lions enter the crater from the outside. Those who do enter the crater are often prevented from contributing to the gene pool by the crater's male lions, who expel any outside competitors. The lion population is also influenced to some extent by the takeover of prides by incoming males, which typically kill small cubs. The biggest influence, however, appears to be disease, particularly canine distemper.
The Ngorongoro is the best place in Tanzania to see the big five. A healthy population of black rhino and some of the largest tusker elephants left in Africa today are the prize spots, but the Crater is home to strong populations of lion, leopard and hyena along with good herds of wildebeest, buffalo and zebra. Other game in the Ngorongoro includes serval cat, cheetah, jackal, Grant's and Thompson's gazelle, flamingo and bat eared foxes along with approximately 500 species of bird.
The legendary annual wildebeest and zebra migration also passes through Ngorongoro, when the 1.7 million ungulates move south into the area in December then move out heading north in June. The migrants passing through the plains of the reserve include 1.7 million wildebeest, 260,000 zebra, and 470,000 gazelles. The Lake Ndutu area to the West has significant cheetah and lion populations. In summer enormous numbers of Serengeti migrants pass through the plains of the reserve, including 1.7 million wildebeest, 260,000 zebra and 470,000 gazelle. Waterbuck mainly occur mainly near Lerai Forest; serval widely in the crater and on the plains to the west. Common in the reserve are lion, hartebeest, spotted hyena and jackal. Cheetah, classed as vulnerable although common in the reserve, are scarce in the crater itself. The endangered wild dog Lycaon pictus has recently disappeared from the crater and may have declined elsewhere in the Conservation Area as well. The golden cat has recently been seen in the Ngorongoro forest.
The mixture of forest, canyons, grassland plains, Lakes and marshes provide habitats for a wide range of bird life. The wet months see the arrival of the Eurasian migrants at the pools: White storks, yellow wagtails and swallows mingle with the local inhabitants: stilts, saddle-bill storks, ibis, ruff and various species of duck. Over 500 species of birds have been recorded within the NCA. The edges of Lake Magadi within the crater, Lake Ndutu, and the Empakaai Crater Lake look pinkish from a distance due to the large flock of greater and lesser flamingoes. Lesser flamingos fly in to feed from their breeding grounds at Lake Natron. And the pools around Mandusi swamp are rich with water birds such as waders, storks, ducks and herons. Distinctive grassland birds such as ostriches, kori bustards, crowned cranes, rosy-throated longclaws, augur buzzards, crested eagles and the localized egyptian vultures are plenty. The rest of the NCA also has areas which will reward the keen ornithologists.