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The Okavango Delta, lying between 18°20’S and 20°00’S, and 21°50’E and 23°55’E, is undoubtedly the most important wetland in southern Africa. An extensive wetland system in northern Botswana, in the semi-arid Kalahari sandveld region, it is the largest wetland (and largest Ramsar Site) in southern Africa and has a greater range of habitats than any other wetland in the region. The Okavango river enters Botswana from Namibia as a single meandering channel, following a minor north-west to south-east rift that forms the ‘Panhandle’ of the delta. The delta is formed where a low gradient (1:3,500) and dense vegetation cause the water in the river to fan out, filling an extensive flood-plain and saturating the sandy soils. One fault (Gumare), running north-east to south-west, limits the northern end of the wetland, and two parallel faults (Kunyere and Thamalakane) the southern end. Where the river crosses the Gumare fault, it splits into four channels: the Selinda or Mogwegana, flowing north-east into the Linyanti river, the Ngoqa/Mwanachira (east), the Jao/Boro (south-east) and, in the west, the Thaoge (south). At the northern tip of Chief’s Island, in Moremi Game Reserve, the Ngoqa–Mwanachira splits again into the Kwai system (east) and the Mboroga–Gomoti–Santantadibe system (south-east).The flow patterns of the delta are highly dynamic, due to the build-up of silt in river channels. Currently, due to a series of years with lower-than-average rainfall, flow levels in the delta are very low, but the main flow is in the Ngoqa–Mwanachira–Mogogelo system. When flows are high, water from the delta reaches the Thamalakane river, which flows through Maun and then into the Boteti river, and the Nhabe and Kunyere rivers, which flow south-west into Lake Ngami. (Lake Ngami, whilst an integral part of the Okavango Delta, is treated as a separate IBA, BW004.)The main habitats in the delta are open clear water (rich in aquatic plants), permanent swamp dominated by papyrus Cyperus and Miscanthus, seasonal swamps dominated by reed Phragmites, and river flood-plain dominated by grasses, which grades into areas of dry land with trees, including higher sandveld areas such as the sandveld tongue of Moremi Game Reserve which is dominated by mopane woodland. There is a complex mosaic, within these main habitats, of lagoons, swamp vegetation, channels, islands, seasonally flooded depressions or pans, riparian woodland and drier woodland and grasslands. The delta has a diversity of trees, from semi-aquatic figs Ficus and wild date palms Phoenix, to knobthorn Acacia and fan palms Hyphaene on the marginal flood-plains, to the drier mopane and mixed Acacia woodlands.The main land-uses are tourism, sport- and subsistence hunting, recreational and artisanal fishing, cutting of grass, sedges and reeds and gathering of veld products (plants and insects) for food, arrow poison and basketry; human settlements (some inside the buffalo fence), cattle-grazing outside the buffalo fence and some arable production occur in the north-west and south-west. Under a newly introduced land-use plan, the majority of revenues generated from tourism and hunting are channelled to local authorities and communities.
See Box and Table 2 for key species. The delta is poor in nutrients and, in general, bird densities are not high, but its great size, overall richness of bird species and high numbers of individual birds make it of international significance. A total of 450 species of bird have been recorded in the delta—the avifauna is similar to Kafue Flats in Zambia.Of particular note are breeding and visiting Grus carunculatus and breeding Egretta vinaceigula. The delta is the most important breeding site in the world for the latter, very restricted species: a breeding colony of hundreds has been reported, and there was a colony of 50–60 pairs mixed with Ardeola rufiventris in reedbeds Phragmites north of Xaxaba on the Boro river during the early 1990s.A wide variety of other wetland birds occur in the delta, notably Pelecanus onocrotanus and P. rufescens, 18 species of heron (Ardeidae) and, in the ‘Panhandle’, breeding Rynchops flavirostris. There are significant mixed breeding colonies of commoner species of heron, together with Leptoptilos crumeniferus and Mycteria ibis, at Gcodikwe, Xakanaxa (Cacanika) and Gcobega. Large mixed roosts of herons, egrets, storks and ibis are known at Xakanaxa and Gcodikwe in Ficus trees (up to 1,000 birds) and of herons and egrets at Xaxaba in reeds Phragmites (up to 2,000 birds). Many species occur in numbers exceeding 0.5% of the relevant population. There are good numbers overall, but not exceptionally high densities, of many species of Anatidae, including Anas erythrorhyncha, Dendrocygna viduata, Plectropterus gambensis and Thalassornis leuconotus, but only Nettapus auritus has a major stronghold for southern Africa in the delta. Falco chicquera has an important resident population, whilst F. vespertinus and F. amurensis occur as Palearctic visitors in good numbers. Other notable species include Vanellus crassirostris, Centropus cupreicaudus, Scotopelia peli, more than 3 million summering and roosting Hirundo rustica, Turdoides leucopygius, Phyllastrephus terrestris, Macronyx ameliae and Acrocephalus rubescens (these last two species at their southernmost limit in Africa), Laniarius bicolor and Ploceus xanthopterus.
Non-bird biodiversity: Over 1,000 plant species occur in the delta, one of which, an orchid Habenaria pasmithii, was believed to be endemic to the area, but it has now been found at another site, in Zambia. There is much concern about the decline of many of the delta’s large mammals, although populations of Loxodonta africana (EN) are increasing.
BirdLife International (2019) Important Bird Areas factsheet: Okavango Delta. Downloaded from http://www.birdlife.org on 12/12/2019.