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). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not 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 overall trend is suspected to be increasing (Wetlands International 2006).
Behaviour This species is partially migratory over much of its range with substantial numbers of individuals undertaking seasonal movements related to the availability of water and moulting (Scott and Rose 1996). Between November and December adult birds migrate short distances to congregate in flocks of around 400 (Johnsgard 1978, Madge and Burn 1988, Scott and Rose 1996) to as many as 5,000 (Scott and Rose 1996) on large deep water lakes to undergo a flightless moulting period (Johnsgard 1978, Madge and Burn 1988, Scott and Rose 1996). The species then disperses in single pairs to breed between May and September (Johnsgard 1978, Madge and Burn 1988, Scott and Rose 1996), although large flocks of non-breeding pairs and single females may also occur at this time (Scott and Rose 1996). Outside breeding and moulting seasons the species gathers in smaller flocks of several hundred birds (Johnsgard 1978, Madge and Burn 1988). The species is both a diurnal and nocturnal feeder (Johnsgard 1978). Habitat Breeding During the breeding season this species inhabits small, permanent, shallow freshwater and brackish lakes, pools in river courses, rivers and exposed inland mud flats, in both upland and lowland areas of open country (Johnsgard 1978, Madge and Burn 1988, del Hoyo et al. 1992). Non-breeding In the non-breeding season the species prefers deep freshwater lakes, artificial reservoirs, salt pans, sewage works (Madge and Burn 1988, del Hoyo et al. 1992, Kear 2005a) and shallow brackish pans (Scott and Rose 1996). It may also be found away from water in natural grassland, Karoo veld, fynbos, ploughed land, stubble and fields of crops (Hockey et al. 2005). This species requires large, deep freshwater lakes, reservoirs (Scott and Rose 1996, Hockey et al. 2005) and dense swamps (Hockey et al. 2005) on which to undergo a post-breeding wing-moult (Johnsgard 1978, Geldenhuys 1981, Brown et al. 1982). Diet Breeding During the breeding season in South Africa its diet consists entirely of vegetable matter, such as maize seeds (Geldenhuys 1977) and other ripe kernels and seedlings of grain crops (such as wheat, oats, barley and sorghum), potatoes, peanuts, sunflower seeds, rice and over-ripe figs (Hockey et al. 2005). The species also takes the seeds, leaves and roots of grasses, reeds (e.g. Phragmites and Typha) and pondweed, as well as filamentous algae. Non-breeding During the non-breeding season the species is omnivorous (Geldenhuys 1977), feeding on both animals (mainly crustaceans, brachiopods and insect larvae and pupae) (del Hoyo et al. 1992, Hockey et al. 2005, Kear 2005a) and plants (submerged macrophytes) (Geldenhuys 1977). During the moulting period the diet of this species is predominantly made up of wheat seeds (Geldenhuys 1977). Breeding site It often nests on the slope of a hill at the end of old mammal burrows (typically those of Aardvark or Porcupine) (Kear 2005a) or in other cavities that may be up to 2km from water (Madge and Burn 1988, del Hoyo et al. 1992).
Human recreation (e.g. watersports) poses a threat to this species through disturbance (Kear 2005a). In South Africa, the Aardvark is considered threatened so the species's reliance on this mammal for nest sites is a concern (del Hoyo et al. 1992, Kear 2005a). The species may also come under threat through range shifts or contractions as a result of climate change (van Jaarsveld et al. 2005) and West African populations have already come under threat by the desiccation of the Sahel zone (Scott and Rose 1996). The species is susceptible to avian botulism, so may be threatened by future outbreaks of the disease (Blaker 1967, van Heerden 1974). At the Klingnau Dam in northen Switzerland the species has been known to hybridise with Ruddy Shelduck Tadorna ferruginea from escaped captive populations, which could pose a threat to the integrity of both species (Owen et al. 2006). Utilisation The species is hunted mainly for sport (Little et al. 1995, Hockey et al. 2005, Kear 2005a), but there is no evidence that this currently poses a threat.
Text account compilers
Ekstrom, J., Butchart, S., Malpas, L.
BirdLife International (2022) Species factsheet: Tadorna cana. Downloaded from http://www.birdlife.org on 23/01/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/01/2022.