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 Nettapusauritus 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.
Pressure/threats to key biodiversity
The site is partly protected by Moremi Game Reserve, which covers 4,871 km² in the east, and by Wildlife Management Areas. About 75% of the area outside Moremi Game Reserve is designated as multiple-use Controlled Hunting Areas, where traditional rights to hunt, fish and collect veld products exist alongside commercial safari/tourism use. The delta was designated a Ramsar Site in 1996.A buffalo fence restricts movement of game to the north, west and south, but also keeps cattle out of much of the delta to prevent their coming into contact with Syncerus caffer under the Diseases of Animals Act. Cattle occur to the north-west of the delta in the ‘Panhandle’. An extension in 1997 of the northern buffalo fence to the Namibian border severely restricts migratory game, as too does a new double fence constructed in 1997 along the Namibian border to stop cattle movements to or from Namibia. Serious local overgrazing by cattle and goats occurs in some of the communal planning areas with wind erosion recorded in the west. Overgrazing by cattle and donkeys along the Thamalakane and Boro rivers has caused deterioration in riverine and flood-plain plant communities. Tsetse-fly control measures (destruction of wildlife, bush-clearing, ground-spraying with dieldrin and DDT in the early years, aerial spraying with endosulphan and other chemicals between the 1960s and 1980s and, more recently, the use of insecticide-treated, odour-baited targets to which the flies are attracted) have been operational in parts of the delta since the 1920s. Aerial spraying with Deltamethrin, a pyrethroid insecticide, is due to take place over extensive areas of the delta in May 2001.The two main issues in the Okavango Delta, other than veterinary fences, are future land-use and water needs.Whether the delta continues to be used primarily for wildlife-based industries or for agriculture and livestock is the crucial question. Expansion of the agriculture and livestock industry into the delta would cause ecological degradation. The livestock industry outside the main delta is ecologically non-sustainable and is generating pressure on the delta. Immediate issues include an increasing human population and settlements within and on the periphery of the delta; burning and cultivating of areas formerly dominated by papyrus Cyperus in the west of the delta; burning and cutting of mature reedbeds, which deplete nesting habitat for the near-endemic Egretta vinaceigula, and roost- and nest-sites for other species; overgrazing by cattle; veterinary cordon fences which prevent movements of game and thereby affect the vegetation; the increase in elephants which may be adversely affecting vegetation and other species of game; disturbance to vulnerable species such as Rynchops flavirostris and to heronries from motorized tourist craft and planes, as well as from humans, cattle and mokoro (canoes); wash from boats destroying nests; conflicts between traditional use of natural resources and commercial use for tourism and related activities; and over-hunting and over-use of natural resources (for example, the high bag-limits and lack of close season during the breeding period may have caused a large decline in sandgrouse Pterocles numbers; large-scale fishing with monofilament gill-nets may be reducing fish populations). The blockage of channels, following the over-hunting of Hippopotamus amphibius which formerly kept areas of water clear of vegetation, is sometimes perceived as an issue. Whilst there is little evidence for this, Hippopotamus has been severely reduced in the western delta.The need for more water in Botswana led to a proposal in the late 1980s for the Boro river to be dredged and canalized and water transferred to a reservoir near Maun. This Southern Okavango Integrated Water Development Project was at an advanced stage, contracts already having been awarded, before it was dropped by the government following strong local opposition and at the recommendation of the IUCN in 1992. Botswana has continually increasing water requirements, which will create increasing demands on the Okavango’s waters. The same is true for Namibia and Angola, whose governments have current schemes to take water from the Okavango river before it reaches Botswana. During a drought, the problem is exacerbated both by increased demands and reduced flows. Water extraction must be kept below levels that will cause irreversible changes to the ecology of the delta and physical interventions such as dredging of channels should be avoided so that the delta flow system remains dynamic and flexible. A tripartite water commission, OKACOM, exists between Botswana, Namibia and Angola. OKACOM, in 1997, began a broad environmental assessment of the river and delta as a basis for water abstraction. Drought in Namibia prior to 1996/97 led the Namibian government to put forward an emergency pipeline scheme to transfer water from the Okavango river to Windhoek, in advance of the findings by OKACOM. Good rains in the 1996/97 summer caused a deferment of the scheme. An environmental assessment of that scheme has been produced, but will be incorporated into the OKACOM study.
BirdLife International (2022) Important Bird Areas factsheet: Okavango Delta. Downloaded from
http://www.birdlife.org on 30/06/2022.