Water, Wetlands and Wattled Cranes
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|Water, Wetlands and Wattled Cranes
The endangered Wattled Crane is endemic to Africa and ranges across eleven countries from Ethiopia to South Africa. Wattled Cranes are the most wetland-dependent of Africa's cranes. The majority of Wattled Cranes occur in the extensive floodplain systems of southern Africa's large river basins (especially the Zambezi and Okavango); they also use smaller upland wetlands (dambos) throughout their range especially in South Africa and Zimbabwe.
Loss and degradation of wetland habitats constitute the most significant threat to the species. Intensified agriculture, overgrazing, industrialization, and other pressures on dambos have contributed to the decline of Wattled Cranes, especially in South Africa and Zimbabwe. In the large floodplain systems of southern Africa, the breeding and feeding cycles of Wattled Cranes are linked to natural flood cycles of rivers. Wattled Crane pairs are "triggered" to nest as floodwaters begin receding after peak flooding. Nesting in shallow open water after the major flood rise and crest ensures that nests will be protected from predators and wildfires but will not be drowned by further rising floodwaters. As floodwaters slowly recede, Wattled Cranes raise their single chick on the pulse of exposed plant and insect life. The natural cycle of flooding and drying also stimulates the production of underground tubers of the spike rush (Eleocharis) and water lily (Nymphaea). These tubers support vast numbers of feeding Wattled Cranes, ducks, and many other waterbirds.
When the ancient flood cycles of river floodplains are altered by dams, diversions, and other water development projects, Wattled Cranes may be particularly vulnerable. Large dams on the Zambezi River, for example, have resulted in a vast reduction in suitable breeding and feeding grounds in the Zambezi Delta. Wattled Cranes breed only in the far-western portion of the delta that is fed by perennial runoff from the adjacent Cheringoma escarpment. This narrow fringe of wetlands receives floodwaters during the rainy season, and maintains high water table conditions during the dry season. Such conditions support large expanses of Eleocharis angulata, a sedge species that produces underground tubers that are the major food source of Wattled Cranes. Across most of the delta, where hydrological conditions are unsuitable for tuber production due to the lack of regular Zambezi flooding over the past forty years, Wattled Cranes and many other waterbird species are absent (see also: The sustainable management of the lower Zambezi Valley and Delta, Mozambique). Since the construction of Itezhitezhi Dam in Zambia, there has been a dramatic restriction in Wattled Crane nesting sites and feeding areas in the Kafue Flats as well. In a year of normal flooding conditions on the Kafue Flats, about 40% of Wattled Crane pairs attempt to breed, but when floods fail only about 3% of all pairs breed. When floods are absent, tuber productivity decreases, floodplain soils become impenetrable, and the feeding grounds are abandoned by Wattled Cranes and other species. If conditions do not improve, the population of Wattled Cranes in the Kafue Flats may soon disappear as it has over most of the Zambezi Delta.
As Wattled Cranes are affected by river regulation, so too are the farmers and fishermen who depend on the natural hydrological fluctuations in river-floodplains for their livelihoods. In the Zambezi River Valley, large dams have caused great hardship for hundreds of thousands of Mozambican villagers whose livelihoods depend on the ebb and flow of the Zambezi River. Subsistence fishing, farming, and livestock grazing activities have collapsed with the loss of the annual flood. The productivity of the prawn fishery has declined by more than $10 million per year. Changes in the flooding regime have affected the availability of water supplies, fuel wood, building materials, and medicinal plants, as well as general public health and the cultural relationship between local people and the river. Similar declines are also reported for the subsistence fishery of the Kafue Flats following river regulation. Because of these links between Wattled Cranes, water, wetlands, and human welfare, the Wattled Crane is an excellent flagship species for wetland conservation in southern Africa. Large, conspicuous, and well-known among local villagers and resource managers, Wattled Cranes may well serve as a focal point for the wetland management programs and, through these efforts, indirectly benefit many of the lesser-known species that are similarly dependent on natural hydrological conditions. In certain locations, Wattled Cranes may also be an important indicator species for assessing deleterious changes in wetland hydrological conditions, and evaluating the impact of such changes on wetland biodiversity and subsistence production systems.
Recent surveys in countries that were long-thought to be strongholds for Wattled Cranes – Botswana, Mozambique, Tanzania, and especially Zambia – indicate that the global population of Wattled Cranes may be only half of what has been reported in recent years (see Table below).
|Wattled Crane Population Table (.pdf 11KB)