IMPORTANT BIRD AREAS

Z001 Middle Zambezi River

SITE DESCRIPTION

The Zambezi River, one of Africa’s great rivers, is 2 700 km long and it drains a huge basin of 1.4 million km2. For most of its length along Zimbabwe’s northern border it lies in a rift that forms the southern limit of Africa’s Great Rift Valley. The rift is called the Gwembe Trough at Lake Kariba and its name changes to the Zambezi Valley downstream of the Kariba Gorge. From the northern outlet of Kariba Gorge, at Nyamuomba Island (16°22’S; 28°51’E), to the western entrance of the Mupata Gorge (15°38’S; 30°02’E), the river flows east, through flat plains country. Here it forms the international border between Zimbabwe and Zambia. The rift valley is evidenced by the flat plain (350-600 m a.s.l.) and the nearby rugged escarpments running parallel to the river in Zambia (max height 1 286 m a.s.l.) and Zimbabwe (max height 1 288 m a.s.l.). In Zimbabwe, where the valley bottom is considerably broader, it covers an area of c. 6 825 km2.

The heat and humidity of the Zambezi Valley are extreme, and it is classified as ‘excessively hot’. Temperatures can soar to 44°C in November prior to the rains, and fall to 2°C in July; frost is unknown. Rainfall in the valley varies locally, depending on topography. The annual average at Nyamepi Camp (centre of the IBA) is 826 mm p.a., but in the west at Chirundu it drops to 628 mm p.a. The valley can also be windy, with easterlies and north-easterlies being funnelled through the rift at speeds up to 45 knots.

In some places the Zambezi River is 2 km or more wide, and the wide braided channels flow around many sandy islands, lined with Phragmites and other reedbed vegetation. The distance from Kariba to Mupata is c. 178 km, and the river flows mostly through its own alluvial deposits, laid on Karoo sediments. The river itself is considered to be very clean water, even rather sterile.
There are three main terrestrial vegetation types in the valley. Most of the valley comprises sodic soils which predominantly support Mopane Colophospermum mopane woodland, which in places can reach impressive proportions (tall and straight) and structure, and is called ‘cathedral’ mopane. The river’s alluvial deposits support riparian woodland dominated by the winterthorn Faidherbia (Acacia) albida, but include many other species such as Kigelia africana, Lonchocarpus capassa and Trichilia emetica. Elephants Loxodonta africana and other animals are drawn here when the fruit ripens on the winterthorn trees in the hot dry season. The third vegetation type is colloquially known as ‘jesse’ bush, but is correctly labelled as mixed-species layered dry forest. This is deciduous, and has a thicket-like understorey which can become impenetrable. It is rich in both tree and shrub species, including Pterocarpus lucens, Xeroderris stuhlmannii, Commiphora karibensis, Berchemia discolor, Combretum elaeagnoides and Acacia ataxacantha among others.

BIRDS

Zoo-geographically, the Zambezi Valley presents an anomaly within the region. Several large terrestrial birds are absent or rare, including Ostrich Struthio camelus, Secretarybird Sagittarius serpentarius, the cranes and Kori Bustard Ardeotis kori. Yellow-billed Oxpecker Buphagus africanus is also unexpectedly absent, although it suddenly reappears upstream in the Luangwa and Zambezi valleys.

Cape Vulture Gyps coprotheres is rarely recorded in the valley, as is Malagasy Pond-heron Ardeola idae, Greater Flamingo Phoenicopterus ruber and Lesser Flamingo Phoeniconaias minor. Several Zambezian biome birds are found in the valley (although ‘miombo’ woodland as such does not occur on the valley floor). The area is a major sub-regional stronghold for Dickinson’s Kestrel Falco dickinsoni, Racquet-tailed Roller Coracias spatulata and is particularly important for several thousand Lilian’s Lovebird Agapornis lilianae (an important proportion of the global population). Other species include White-bellied Sunbird Nectarinia talatala, Broad-tailed Paradise-whydah Vidua obtusa and Meves’s Starling Lamprotornis mevesii. The valley is home to more than 400 species of birds, and it is one of the few localities in the Sub-region for Shelley’s Sunbird Nectarinia shelleyi and Livingstone’s Flycatcher Erythrocercus livingstonei.

At least 52 species of raptor (including owls) have been recorded in the valley. The river itself is home to many African Fish-eagle Haliaeetus vocifer (about 1 pr/3 km of frontage) and an unknown number of Pel’s Fishing-owl Scotopelia peli. Being such a huge wildlife area, there is a good representation of vultures (6 species) and eagles (12 species). It is also extremely important for large terrestrial species that are being persecuted outside large reserves and parks. Southern Ground-hornbill Bucorvus leadbeateri, in particular, occur at very high densities.

The banks of the Zambezi River provide habitat for an estimated 10,500 Southern Carmine Bee-eater Merops nubicoides, with unknown extra numbers in tributaries. The sandbanks and sandy islands form essential habitat for African Skimmer Rynchops flavirostris, and in 1986 a survey estimated 136 birds in the IBA. The valley probably holds over half of the southern African population of this species. In the same year, about 320 Rock Pratincole Glareola nuchalis were counted in the Kariba and Mupata gorges (strictly, outside of the presently defined area). The diversity, though not usually the numbers, of waterbirds occurring in the valley is astonishing, comprising some 90 species. Of special interest at a Sub-regional level are large numbers of Rufous-bellied Heron Ardeola rufiventris, Woolly-necked Stork Ciconia episcopus, White-crowned Lapwing Vanellus albiceps and African Pygmy-goose Nettapus auritus.

OTHER THREATENED/ENDEMIC WILDLIFE

A small amount of poaching continues, for Elephant and various antelope; it is thought that there is considerable fish poaching from the Zambian side. The valley supports a full range of predators, including the Wild Dog Lycaon pictus. The river is famous for its huge numbers of Hippopotamus Hippopotamus amphibius (several thousands) and Nile Crocodile Crocodylus niloticus.

CONSERVATION ISSUES

The entire IBA falls under the control of the Parks and Wild Life Estate: the central valley includes Mana Pools National Park, flanked on its west by the Hurungwe Safari Area, and on its east by the Sapi and Chewore Safari Areas. Controlled hunting on quota is permitted in the safari areas. The valley, particularly the Zambezi River, is fully patrolled. It has been protected for a long time, not only by legislation but also by inaccessibility and the tsetse fly, which was eradicated a few years ago. There are two main threats to the ecological integrity of the area. (1) The Zambezi River no longer floods; its original flow regime has been dramatically altered by upstream impoundments, primarily Kariba Dam, and to a lesser extent Kafue Dam. Indeed, the last time that Kariba’s floodgates were opened was in 1981. As a result, the river’s sandy islands are being consolidated and grown over by invasive Acacia albida because they are no longer scoured by floods. Furthermore, the river is cutting down into its bed. (2) The protection of the valley has resulted in population explosions of Elephant and Impala Aepyceros melampus, particularly in the Mana Pools National Park. Undergrowth and grass cover are removed, regeneration is inhibited, and trees are damaged, resulting in the creation of open areas and greatly increased water run-off, leading to flash floods and banks collapsing. Wild fires also occur annually in the dry season.