Lake Chilwa is a shallow lake (1.5–3 m, maximum 5 m) that drains an area of c.8,000 km² of hills and mountains; it is bordered on all sides by swamps and seasonally flooded grassland, especially extensive on the flat western and northern shores. The lake itself is c.700 km² in size (or more at maximum extent), but dries up occasionally after a series of dry years (as in 1968, 1973 and 1995). It is very rich in fish and supports a population of c.60,000 people. The swamp vegetation consists mainly of Typha (c.650 km²) and Phragmites reedbeds (150–300 km²), with extensive patches of Scirpus in the open lake, whereas flood-plain grassland covers c.400 km². Several large rice-growing areas have been developed in the swamp, and the edges are cultivated (under maize) in the dry season, covering an estimated 10% of the surface overall.
See Box for key species. There has been no systematic survey of the avifauna, but over 160 species of birds associated with the Chilwa wetlands have been identified so far. In periods of flood the area supports very high numbers of waterfowl, but the flat terrain, the enormous size of the swamp and the nature of the vegetation all make counting of even the larger waterbirds a nearly impossible task. Preliminary studies carried out in 1996 have shown that numbers of at least nine species of waterfowl exceed the 1% thresholds; for the four main species snared by trappers (Dendrocygna bicolor, Gallinula angulata, Porphyrula alleni and Amaurornis flavirostris) the latest survey of commercial hunting in 1998–1999 has revealed that over one million birds were taken in a few months. It is likely other species exceed thresholds, e.g. a combined total of 41,500 Anas hottentota and A. erythrorhyncha were snared and shot in 1998–1999, but the proportion of each is unknown. Of species of global conservation concern, Falco naumanni winters in some numbers (flocks of 25–30 at any one spot are not unusual) and the Chilwa flood-plain is certainly the most important site for this species in Malawi. Circus macrourus and Gallinago media both winter annually is small numbers while Phoenicopterus minor is only an occasional visitor. In general, much more fieldwork is needed, especially in seasonally flooded grassland, in order the verify the very high figures of crakes and other species reported by trappers. A ringing scheme aimed particularly at the migratory duck species would be useful in determining the origin of these seasonal populations.
Non-bird biodiversity: None known today; large mammals have been exterminated.
Pressure/threats to key biodiversity
Lake Chilwa was designated a Ramsar Site on 1 November 1997. Snaring and shooting of birds have been practised for a long time, but commercial exploitation of waterfowl started on a large scale in 1996, following the drying up of the lake and collapse of the fishery in 1995. It was estimated then that over 356,000 waterfowl were trapped on the western shores. Despite the recovery of the fishery industry, commercial waterfowl trapping has remained at a very high level, and a more detailed survey in the rains of 1998–1999 showed that over 450 villagers were involved in the activity on a full- or part-time basis. It is estimated that over a million waterfowl were snared between December and April, and over 70,000 birds shot, all of this taking place in the main breeding season. Birds shot include several legally protected species such as pelicans, flamingoes, spoonbills, ibises and storks. Several large waterbirds have already been eliminated through hunting (e.g. both species of cranes and Ephippiorhynchus senegalensis) and others are clearly decreasing. A Danish-funded project is currently under way which aims at involving the local communities in managing their waterfowl resources, by setting up some areas as breeding refugia where snaring should be abandoned, and by restricting access for bird-shooters in various ways. This latter idea clearly appeals to the local villagers as most bird hunters come from outside and cause a lot of disturbance to ‘their’ birds. If some form of control is not set up in time and the present scale of trapping is allowed to continue, one can expect a population crash in several key species, both resident and migratory.
BirdLife International (2019) Important Bird Areas factsheet: Lake Chilwa and flood-plain. Downloaded from
http://www.birdlife.org on 12/12/2019.