Masai mara is found in the Rift Valley covering an Area of 664,000 ha with an altitude of 1,500 - 2,170 meters. This area includes the Masai Mara National Reserve (181,200 hactares) and the surrounding wildlife dispersal areas (482,800 hactares) in southwestern Kenya. Collectively, the reserve and its surroundings are often called the Greater Mara here, Masai Mara refers to the entire Important Bird Area. The site adjoins the Serengeti National Park along the Kenya/ Tanzania border, and is considered part of the same ecosystem. The National Reserve is Kenya's most-visited protected area, world famous for its high density of herbivores and predators, and the annual migrations of wildebeest Connochaetes taurinus.

In 1996, it was nominated for designation as a World Heritage Site. To the north, east and west are large parcels of land demarcated as group ranches owned and inhabited by the semi-nomadic pastoral Maasai people. This communal land forms an extensive wildlife dispersal area for the reserve, comprising the group ranches of Siana (152,000 hactares), Koiyaki (94,000 hactares), Olkinyei (80,000 hactares), Lemek (66,000 hactares), Kimindet (37,000 hactares), Olorien (26,000 hactares), Olchorro Ouirwa (11,800 hactares), Kerinkani (8,100 hactares) and Angata Baragoi (7,900 hactares).

Habitats in the Masai Mara are varied, including open rolling grassland, riverine forest, Acacia woodland, swamps, non-deciduous thickets, boulder-strewn escarpments, and Acacia, Croton and Tarchonanthus scrub. The permanent Mara and Talek rivers, and their tributaries, flow through the reserve and approximately trisect it. There is a pronounced rainfall gradient from the drier east (with c.800 milimeters rain per year) to the wetter west (with 1, 200 milimeters per year).

The Mara's extensive grasslands are a stronghold for the threatened, migratory Crex crex and the near threatened, restricted-range Euplectes jacksoni. The woodlands around the reserve are probably the centre of abundance for the threatened, restricted-range Prionops poliolophus. The restricted-range Histurgops ruficauda has recently been sighted within the reserve, near the southern border, and may be expanding its range northwards. More than 500 other bird species are known to occur, including 12 species of Cisticola and 53 birds of prey. Grassland birds are especially well represented.

Large numbers of Palearctic migrants winter in the area, including Charadrius asiaticus and Ciconia ciconia. The Oloololo or Siria Escarpment is one of the few Kenyan sites for Cisticola aberrans. Other local and unusual birds in the Masai Mara include Ardeola rufiventris, Neotis denhami, Centropus grillii, Cercomela familiaris, Calamonastes undosus, Cisticola angusticauda, Hippolais icterinia (in the northern winter), Hyliota flavigaster, Eremomela scotopus and Corvinella melanoleucus. There is a single record of Balaeniceps rex, from the Musiara swamp. Regionally threatened species include Anhinga rufa (occasional visitor), Casmerodius albus, Ephippiorhynchus senegalensis (several pairs nest), Trigonoceps occipitalis (regularly nests), Circaetus cinerascens (small numbers), Hieraaetus ayresii (occasional visitor), Polemaetus bellicosus (resident), Stephanoaetus coronatus, Coturnix adansonii (rare intra-African migrant), Porzana pusilla (occasional visitor), Podica senegalensis (resident), Neotis denhami (possibly only 2 - 3 individuals), Scotopelia peli (resident) and Buphagus africanus (common resident).