Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be moderately small to large, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The population is estimated to number 12,000-28,000 individuals, roughly equating to 8,000-19,000 mature individuals.
The overall trend is decreasing, although some populations may be stable (Wetlands International 2006).
Behaviour This species is partially migratory (Scott and Rose 1996) or semi-nomadic (Kear 2005a), making local dispersive movements during the rainy season (Brown et al. 1982, Madge and Burn 1988) to take advantage of temporary wetlands (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 (Kear 2005a) of 20 to 100 individuals (Brown et al. 1982) on more permanent lakes and marshes (Kear 2005a). The species is crepuscular (Kear 2005a) and obtains its food almost solely by diving (Brown et al. 1982). Habitat The species inhabits quiet shallow freshwater lakes, pools, lagoons (del Hoyo et al. 1992), pans, inland deltas (Brown et al. 1982), flood-plains (Madge and Burn 1988), marshes and swamps (del Hoyo et al. 1992) fringed with abundant emergent and floating vegetation (Brown et al. 1982, del Hoyo et al. 1992) (e.g. reeds, papyrus and water-lilies Nymphaea spp.) (Kear 2005a), generally avoiding very open water (del Hoyo et al. 1992). It also often inhabits forested lakes in Madagascar (Kear 2005a) and may frequent farm impoundments or stock-ponds in other areas (Scott and Rose 1996). Diet 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). Breeding site The nest is constructed of vegetation either floating on or up to 45 cm above water (Brown et al. 1982) amongst reedbeds (Brown et al. 1982, del Hoyo et al. 1992) or papyrus beds (Brown et al. 1982), 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 (Kear 2005a), the introduction of exotic plants, deterioration in water quality as a result of deforestation and soil erosion in catchment areas (Scott and Rose 1996), and pollution (Kear 2005a). The species has also declined in Madagascar due to hunting and trapping (Langrand 1990, del Hoyo et al. 1992), and its large eggs are especially prized as food by people living near wetlands (Kear 2005a).
Text account compilers
Ekstrom, J., Malpas, L., Butchart, S.
BirdLife International (2023) Species factsheet: Thalassornis leuconotus. Downloaded from http://www.birdlife.org on 22/03/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/03/2023.