LC
Yellow-billed Duck Anas undulata



Justification

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 stable, 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.

Trend justification
The overall population trend is stable, although some populations have unknown trends (Wetlands International 2006).

Ecology

Behaviour This species is mainly sedentary, although the southern African population is more nomadic, undertaking considerable local movements (up to 50 km (Brown, et al. 1982)) with the availability of seasonal wetlands (Brown, et al. 1982, Scott and Rose 1996). It forms huge colonies in the non-breeding season, but disperses to breed at the onset of the rainy season (Brown, et al. 1982). Adults undergo a post-nuptial wing moult three or four months after the peak of the breeding season, rendering them flightless for a period of about four weeks (Johnsgard 1978, Kear 2005b). The species is mainly nocturnal: typically foraging at dusk and after dark whilst remaining sedentary throughout the day (Johnsgard 1978). Habitat This species frequents slow-flowing rivers with pools and adjacent flooded grasslands, permanent and seasonal lakes, streams, marshes, brackish coastal lagoons, artificial reservoirs associated with mining, dams, salt pans, sewage works and the open water of estuaries (del Hoyo, et al. 1992, Hockey, et al. 2005, Kear 2005b). It cannot tolerate highly acidic habitats or those where sodium chloride concentrations are very high, but can tolerate high concentrations of other salts around pH 10 or more (Brown, et al. 1982). It also avoids fast-flowing water (Hockey, et al. 2005). Diet It is omnivorous, with a diet consisting of the fruits, seeds, roots, leaves and stems of aquatic and terrestrial plants, aquatic insects and their larvae (including mayflies, water beetles and grasshoppers) (Hockey, et al. 2005), crustaceans, molluscs and agricultural grains such as maize and sunflower seeds (Brown, et al. 1982, del Hoyo, et al. 1992). Breeding site The nest of this species is situated on the ground and is made of grass, rushes and reed stems (Brown, et al. 1982, del Hoyo, et al. 1992). It is usually protected and screened from above by dense, overhanging vegetation (del Hoyo, et al. 1992) and some nests may have tunnel access through the surrounding grass (Brown, et al. 1982).

Threats

Pollution is a threat that still needs to be controlled within the species's range to keep the current population stable (Kear 2005b). Hybridisation of the species with the Northern Mallard Anas platyrhynchos represents a threat to the integrity of the species (Hockey, et al. 2005, Kear 2005b, Owen, et al. 2006) because the two species hybridise easily and produce fertile progeny (Owen, et al. 2006). Northern Mallard Anas platyrhynchos was introduced both deliberately and accidentally into the Cape Provinces of South Africa and has since become naturalised (Owen, et al. 2006). Other exotic ducks may associate with the species (e.g. Laysan Teal at Gauteng Province) and these species pose a further potential threat (Owen, et al. 2006). The species is also susceptible to avian botulism, so may be threatened by future outbreaks of the disease (Blaker 1967). Utilisation The species is hunted (Dean and Skead 1989, Little, et al. 1995, Kear 2005b), and although there is no current evidence that such activities pose a threat to the species (Dean and Skead 1989), hunting levels may still need to be controlled in order to maintain current population levels (Kear 2005b). The species is also traded at traditional medicine markets in Nigeria (Nikolaus 2001).

Acknowledgements

Text account compilers
Ekstrom, J., Butchart, S., Malpas, L.


Recommended citation
BirdLife International (2020) Species factsheet: Anas undulata. Downloaded from http://www.birdlife.org on 13/07/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 13/07/2020.