Data Zone
Justification of Red List category
This species has an extremely large range in which it occurs at a large number of sites, such that it does not meet or approach threatened thresholds based on range parameters. Despite the fact that the population trend appears to be decreasing and rates of reduction are suspected to increase over the next three generations, the rate of decline is not anticipated to become sufficiently rapid to approach the thresholds for Vulnerable. However, the population size is estimated to be small to moderately small with a minimum bound below population size thresholds: 8,500-20,000 mature individuals. In addition, there is an inferred population decline based on the recorded declines in Uganda, Madagascar and those reported from West Africa. Despite this concerns, the largest subpopulation is not close to thresholds for listing as threatened and rates of population reduction are not sufficiently rapid, as yet, hence the species is assessed as Least Concern.
Improved monitoring of this somewhat enigmatic species is advised, noting on one hand that improved population size estimates may result in an increased population size given the size of the range and the limitations of current monitoring schemes, but on the other that there is now a continuing decline in mature individuals and the specific predictions of an increasing rate of habitat loss due to unmitigated climatic shifts.
Population justification
The species is locally common, but has declined in parts of its range, such as Uganda (Carswell et al. 2005). The West African population was suspected to number less than 1,000 individuals at the start of the century (Kear 2005), and less than 500 individuals in 2006 (Dodman 2007, Wetlands International 2021). The overall population in Eastern and Southern Africa was estimated in 2002 to be between 10,000 and 25,000 individuals (Wetlands International 2021), with censuses of 500 individuals at both Lake Naivasha in Kenya and Kafue Flats in Zambia (Dowsett 2008). Subspecies insularis has historically been widespread across Madagascar, but may now be rarer due to local extinctions, with the most recent estimate of 2,500-5,000 individuals (Dodman 2007, Wetlands International 2021). Based on these estimates, the total population size is suspected to be between 13,000 and 30,000 individuals, which is equal to 8,666-20,000 mature individuals, rounded to 8,500-20,000.
Trend justification
The overall trend is decreasing, although some populations may be stable (Wetlands International 2021). The West African population seems to be decreasing with less than 1,000 individuals at the start of the century (Kear 2005), and less than 500 individuals in 2006 (Dodman 2007, Wetlands International 2021), although coverage is poor is this region. Similarly, local extinctions in Madagascar, such as at Lake Alaotra (Bamford et al. 2015) are likely contributing to a decreasing population size of subspecies insularis. Climate change modelling has projected this species will be likely to suffer a range contraction by 2050, with its current range reduced by up to 30% over approximately 50 years (Nagy et al. 2021), equivalent to 10 to 11 % over three generations. Considering the potential for additional reductions due to localised hunting, and assuming that the rate of habitat loss as measured directly relates to features that limit the species' population, future reductions are suspected to occur at a rate of between 10-19 %.
This species is partially migratory (Scott and Rose 1996) or semi-nomadic (Kear 2005), making local dispersive movements during the rainy season to take advantage of temporary wetlands (Brown et al. 1982, Madge and Burn 1988, del Hoyo et al. 1992). The timing of breeding varies geographically although it generally coincides with periods of higher or more stable water levels (del Hoyo et al. 1992). The species breeds in solitary pairs or loose groups (del Hoyo et al. 1992), dispersing after breeding (as water levels drop) to gather in small flocks of 20 to 100 individuals (Brown et al. 1982) on more permanent lakes and marshes (Kear 2005). The species is crepuscular (Kear 2005) and obtains its food almost solely by diving (Brown et al. 1982). The species inhabits quiet shallow freshwater lakes, pools, lagoons, pans, inland deltas, flood-plains, marshes and swamps fringed with abundant emergent and floating vegetation (e.g. reeds, papyrus and water-lilies Nymphaea spp.) (Brown et al. 1982, Madge and Burn 1988, del Hoyo et al. 1992, Kear 2005), generally avoiding very open water (del Hoyo et al. 1992). It also often inhabits forested lakes in Madagascar (Kear 2005) and may frequent farm impoundments or stock-ponds in other areas (Scott and Rose 1996). Although the species is predominantly herbivorous (taking the seeds and leaves of aquatic plants such as water-lilies Nymphaea spp. and Polygonum spp.) the young may feed on Chironomid insect larvae (del Hoyo et al. 1992). The nest is constructed of vegetation either floating on or up to 45 cm above water amongst reedbeds or papyrus beds, or on the ground in waterside vegetation on small islands (Brown et al. 1982, del Hoyo et al. 1992). The species will occasionally use the abandoned nests of grebes or coots as nest bases (Brown et al. 1982, Madge and Burn 1988).
The species is threatened by the modification of wetlands especially where the native aquatic flora is affected, e.g. through the introduction of herbivorous fish, the introduction of exotic plants, deterioration in water quality as a result of deforestation and soil erosion in catchment areas, and pollution (Scott and Rose 1996, Kear 2005). The species has also declined in Madagascar due to hunting and trapping (Langrand 1990, del Hoyo et al. 1992). Intensive anthropogenic changes at Lake Alaotra, such as marsh clearance, intensive fishing, and the introduction of exotic fish species, have caused the local extinction of this species in the area (Bamford et al. 2015). Its large eggs are especially prized as food by people living near wetlands (Kear 2005). Mass-mortality in gill-nets has also been reported at Lake Naivasha in Kenya (Lewis and Pomeroy 1989). Climate change modelling has projected this species will be likely to suffer a range contraction by 2050, with its current range reduced by up to 30% (Nagy et al. 2021).
Text account compilers
Rotton, H., Martin, R.
Contributors
Butchart, S., Ekstrom, J. & Malpas, L.
Recommended citation
BirdLife International (2024) Species factsheet: White-backed Duck Thalassornis leuconotus. Downloaded from
https://datazone.birdlife.org/species/factsheet/white-backed-duck-thalassornis-leuconotus on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/11/2024.