The Hadejia-Nguru wetlands (HNW) lie on the southern edge of the Sahel savanna in north-eastern Nigeria. The area is a flood-plain complex, comprised of a mixture of seasonally flooded lands and dry uplands. Prior to the droughts of the 1970s, the wetlands covered an area of about 4,125 km², but are now reduced to c.3,500 km². The wetland is supplied by the Hadejia and Jama’are rivers. The Jama’are rises in the Jos Plateau, the Hadejia in the hills around Kano; they join within the HNW to form the Yobe river, which discharges into Lake Chad. River flow is highly seasonal and varies considerably depending upon rainfall and run-off. Peak flow occurs in August and September when banks overflow and the area is inundated. Three broad vegetation-types are identifiable. One of these is scrub savanna, which includes the upland farmland areas and Acacia woodlands. The second grows on the ‘tudu’ lands, sandy ridges which, with the exception of scattered, ephemeral ponds, are never inundated. Characteristic tree species here include Acacia spp. (especially A. albida), Ziziphus spp., Balanites aegyptiaca, Tamarindus indica and Adansonia digitata, while common grasses are Cenchrus biflorus, Andropogon spp. and Vetiveria nigritana. There are also pockets of riparian forests, known as ‘kurmi’. Common trees of the kurmi forests, at about the northern limit of their distributions, are Khaya senegalensis, Mitragyna inermis and Diospyros mespiliformis. In some parts, kurmi has been replaced with orchards of mango Mangifera indica and guava Psidium guajava. The third main vegetation-type includes the seasonally flooded marshes and ‘fadama’, in which the tree Acacia nilotica is common while Dum palms Hyphaene thebaica grow on small raised islands. Aquatic grasses such as Echinochloa and Oryza spp. are common in the marshes, while in drier parts Dactyloctenium aegyptium, Setaria spp.and Cyperus spp. occur. There are also extensive beds of Typha australis while Mimosa pigra thickets are common on edges of the lakes. Large parts of the fadama are under rice cultivation during the rainy season and, during the dry season, are usually utilized for growing other crops as water-levels drop. Uncultivated areas are grazed by livestock. Annual rainfall ranges between 200–600 mm, confined to the period late May–September.
See Box and Table 3 for key species. A total of 377 bird species have been recorded. A few individuals of two species of global conservation concern, Circus macrourus and Galinago media, winter occasionally. Numbers of overwintering Aythya nyroca have declined considerably in recent years. The wetlands are extremely important for waterbirds, both for breeding species and for wintering and passage Palearctic waterbirds, while the surrounding areas hold significant numbers of species of the Sahel biome and Sudan–Guinea Savanna biome. Total numbers of waterbirds recorded during the January African Waterbird Census counts were 259,767 in 1995, 201,133 in 1996 and 324,510 in 1997.
Non-bird biodiversity: The mammal Gazella rufifrons (VU) occurs, but is scarce. At least 89 species of freshwater fish are reported to occur.
Pressure/threats to key biodiversity
Parts of the wetlands are protected by five Forest Reserves, a Wildlife Sanctuary and a Ramsar Site. Two of the Forest Reserves, Zurgun Baderi and Gorgoram, as well as Dagona Wildlife Sanctuary form part of the Chad Basin National Park, while Nguru Lake and the Marma Channel complex (58,100 ha) are designated a Ramsar Site. Several consecutive years of drought in the 1970s reduced the extent of the wetlands. In the last two decades, several dams (including two large ones at Tiga and Challawa) and other hydro-agricultural projects with intensive water demand have been commissioned at locations upstream. These have interrupted the natural flood regime, diverting flood water in the wet season and releasing damaging flood surges during the dry. Fish migration, groundwater recharge, grazing and farming are disrupted as a result. In addition, pastures are overgrazed, soils compacted and tree regeneration is hampered by pastoralists who migrate into the area during the dry season. Depredation of crops by Quelea quelea and other avian pests hardens farmers attitudes against bird conservation. Chemical control of Quelea quelea often kills non-target species. Increasing human population and the rising demand for land is resulting in cultivation of land previously considered marginal. Finally, the fuelwood demand from the surrounding urban settlements is depleting the tree-cover of Forest Reserves in the wetland complex. The area has been the subject of a collaborative project between State Government, NCF, RSPB and IUCN. The project has succeeded in demonstrating the value of natural and traditional uses of the wetland and has been able to agree on dam releases that mimic natural flood patterns.