and Ethiopia drain off from an ironstone plateau that belts the regions of Bahr El Ghazal and Upper Nile. The terrain can be divided into four land classes: Highlands: higher than the surrounding plains by only a few centimeters; are the sites for “permanent settlements”. Vegetation consists of open thorn woodland and/or open mixed woodland with grasses. Intermediate Lands: lie slightly below the highlands, commonly subject to flooding from heavy rainfall in the Ethiopian and East/Central African highlands; Vegetation is mostly open perennial grassland with some acacia woodland and other sparsely distributed trees. Toic: land seasonally inundated or saturated by the main rivers and inland water courses, retaining enough moisture throughout the dry season to support cattle grazing. Sudd: permanent swampland below the level of the ; covers a substantial part of the floodplain in which the Dinka reside; provides good fishing but is not available for livestock; historically it has been a physical barrier to outsiders’ penetration. Ecology of the large basin is unique; until recently, wild animals and birds flourished, hunted rarely by the agro-pastoralists. The Dinka's migrations are determined by the local climate, and their agro-pastoral lifestyle responding to the periodic flooding and dryness of the area in which they live. They begin moving around May–June at the onset of the rainy season to their “permanent settlements” of mud and thatch housing above flood level, where they plant their crops of millet and other grain products. These rainy season settlements usually contain other permanent structures such as cattle byres (luak) and granaries. During the dry season (beginning about December–January), everyone except the aged, ill, and nursing mothers migrates to semi-permanent dwellings in the for cattle grazing. The cultivation of sorghum, millet, and other crops begins in the highlands in the early rainy season and the harvest of crops begins when the rains are heavy in June–August. Cattle are driven to the in September and November when the rainfall drops off and allowed to graze on harvested stalks of the crops. Dinka tribes The number of Dinka sub-divisions is hotly contested as the border or line between group, sub-division, and sections is blurred and often difficult to determine. For example, one can divide the Atuot into Apak and Reel, Bor, Twic, Nyarweng and Ho l and Panaruu into Awet and Kuel and Ciec into Ador and Lou, where Ador and Lou are sub-divided into Ciec Manyiel (Jieng). Rek