The Crater Highlands were created from a series of eight volcanoes that dominated the landscape between 3.6 and 2.5 million years ago when the caldera of Ngorongoro itself was formed. To the north-east, Mount Kerimasi developed and, as it died, Mount Lengai was created. Today, after many centuries of weathering, these mountains sit above the Eastern Rift. There are four peaks above 3,000 m, dominated by open moorland habitat at high altitude. The eastern flanks of the highland block are cloaked in montane forest with Croton spp. dominating the lower areas, Acacia lahai and Albizia gummifera the higher ridges and Cassipourea malosana in the steep valleys. At lower elevations there are dry acacia woodlands and open grass plains in the rain-shadow of the mountains. Several important wetlands lie within the site, including Lake Makat on the floor of Ngorongoro Crater, at an altitude of 1,700 m. It is shallow and saline and only dries out occasionally.
See Box and Tables 2 and 3 for key species. Over 500 species are known from the site. Falco naumanni is a passage migrant and Circus macrourus occurs on passage and in winter. Acacia woodland holds the largest known population of Agapornis fischeri, Parus fringillinus is resident and there have been recent records of Apalis karamojae from Acacia drepanolobium woodland in the south-west of the site. Although there are no recent records of Prionops poliolophus it may well occur near Maswa Game Reserve. Gallinago media occurs infrequently on passage. Several wetlands hold important numbers of waterbirds, including Lakes Lagaja (also known as Ndutu) and Masek at the western end of Olduvai Gorge and a lake in the Empakai Crater which seasonally holds huge numbers of Phoenicopterus minor. This lake is also an important site for both Anas capensis and Oxyura maccoa both of which are now rare in East Africa. Lake Makat is important for Phoenicopterus minor and Phoenicopterus ruber, although there have been no regular counts. Gorigor, a freshwater swamp on the eastern side of the crater floor, holds a heronry (at least Threskiornis aethiopicus and Ardeola ralloides) and several uncommon wetland species including Rallus caerulescens and Chlidonias hybridus, both of which probably breed. During years of exceptional rainfall both the Olbulbul depression and the Malange basin hold temporary wetlands that support large numbers of breeding birds. A roost of 7,000 Bubulcus ibis was located on the edge of the Olbalbal depression in December 1997.The highland grassland and crater floor support resident populations of Euplectes jacksoni and are seasonally important for large numbers of Ciconia ciconia and Ciconia abdimii. The only Tanzanian population of Corvus capensis is centred on the Crater Highlands, as is Picoides obsoletus crateri. The short-grass plains that support such an abundance of ungulates are important habitat for all seven species of vulture that occur in East Africa. The population of Gyps rueppellii within the Serengeti–Ngorongoro–Loliondo ecosystem is approximately 3,000 pairs.
Non-bird biodiversity: The only remaining viable population of Diceros bicornis (CR) in Tanzania is in the IBA. The crater floor is reputed to hold the highest density of mammalian predators in Africa. Panthera leo (VU) are numerous for such a small area and Acinonyx jubatus (VU) frequent visitors. There are few Loxodonta africana (EN), but considerable numbers of Syncerus caffer (LR/cd).
Pressure/threats to key biodiversity
The Ngorongoro experiment of allowing pastoralists and tourists use of the land while striving to protect the habitat and wildlife has led to some conflict, but the plan has been largely successful. There is a growing problem of agriculture within the Conservation Area especially on the western flanks of the crater, where a whole altitudinal belt of natural vegetation is being destroyed. Attempts should be made to prevent agriculture from destroying the short-grass plains within the Loliondo Game Controlled Area, especially in the vicinity of the Sanjan river. There is also a need to increase fire control along the edges of the remaining montane forest, especially on Lemagrut.