This seasonally inundated flood-plain lies to the north of the Chimala Escarpment along the northern edge of the Kipengire mountains. To the west the Mbeya mountains extend north beyond Chunya and to the north and east lie gently rising hills cloaked in miombo woodland. Several major rivers flow from these highland areas to form the Ruaha river that meanders north-eastwards through the flood-plain before becoming the southern border of Ruaha National Park (TZ007). The natural vegetation of the Usangu varies from small areas of permanent swamp and waterside vegetation in numerous oxbow lakes, through open grassland (much of this is now permanent bare ground due to overgrazing) and thickets of Acacia seyal and Acacia kirkii thorn-bush. On slightly higher ground Commiphora and Combretum woodlands dominate (depending on soil characteristics) and these mix with miombo woodland towards the hills. In the more open, rocky areas baobabs are characteristic.The Great North Road runs along the base of the Chimala Escarpment and from this access point two commercial rice-schemes penetrate into the Usangu. These rice-schemes hold permanent water and are an important habitat for many birds, especially during the dry season (June–October). A new rice-scheme at Madibira will also become important to wetland birds, especially when permanent vegetation develops.
See Box and Table 3 for key species. Some 418 species have been recorded from the site. Most records of waterbirds are from a tiny area around the Mbarali and Kapunga rice-schemes and numbers of waterbirds in the whole site are likely to be larger than given. Most information is qualitative; ‘acres’ of Dendrocygna bicolor, for example. Balearica regulorum certainly occurred until recently in thousands and the population of Plectropterus gambensis may number tens of thousands. Among species likely to meet 1% thresholds are Egretta garzetta, Ardeola ralloides, Ardeola rufiventris, Mycteria ibis, Anastomus lamelligerus, Plegadis falcinellus, Dendrocygna bicolor, Plectropterus gambensis, Himantopus himantopus, Charadrius asiaticus and Vanellus albiceps. This is the only regular site known in East Africa for significant numbers of Glareola nordmanni. Grus carunculatus occurs at the Mbarali rice-scheme; 12 in January 1995. Acrocephalus griseldis is only known from a single record in 1995, but it may winter in reasonable numbers. Falco naumanni (passage) and Gallinago media (winter visitor) have been recorded in small numbers and there are several recent records of Circus macrourus.The Usangu is the only known locality in Tanzania that holds populations of four species of coucal; Centropus cupreicaudus, C. superciliosus, C. senegalensis and C. grillii all breed at Mbarali and the first three are likely to be resident there. Burned grassland is utilized by a small population of Ardeotis denhami that are probably cold-season altitudinal migrants from the nearby Kitulo plateau (TZ073). The Usangu basin represents the southernmost extension of the Somali–Masai arid corridor. This is reflected in the avifauna which includes two Tanzanian endemics, Cosmopsarus unicolor and Agapornis personatus.
Non-bird biodiversity: Large mammals listed for the site include Loxodonta africana (EN) and Panthera leo (VU). Lycaon pictus (EN) are likely to occur, but Diceros bicornis (CR) were extirpated during the late 1970s. There is a large selection of antelope including Hippotragus equinus (LR/cd) and H. niger (LR/cd).
Pressure/threats to key biodiversity
There is extensive degradation of the woodland and grassland habitat as a result of massive overgrazing. The type and quantity of chemicals applied at the three commercial rice-schemes are a concern and there is anecdotal evidence of large-scale bird-kills. Many large waterbirds are shot for food; duck hunting is regular and birds such as Haliaeetus vocifer have been accidentally shot in the past. The Usangu Game Reserve covers part of the IBA, although the adjacent permanent Lyanyoni swamps are excluded.
BirdLife International (2022) Important Bird Areas factsheet: Usangu flats. Downloaded from
http://www.birdlife.org on 17/01/2022.