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 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 population trend is decreasing, although some populations have unknown trends (Wetlands International 2006).
Behaviour This species is somewhat nomadic (Madge and Burn 1988) or partially migratory (Hockey et al. 2005), making local dry-season movements dictated by habitat and water availability (Madge and Burn 1988, del Hoyo et al. 1992) or dispersing to favoured moulting areas (Brown et al. 1982). The timing of the breeding season varies geographically (del Hoyo et al. 1992) but may be triggered by the rains (Kear 2005b). The species usually nests in solitary pairs (del Hoyo et al. 1992, Hockey et al. 2005) but is commonly found in small family groups outside of the breeding season (Madge and Burn 1988, Hockey et al. 2005), large concentrations of 10 to 200 individuals (Brown et al. 1982) also forming during the dry season or at moulting sites (Madge and Burn 1988). Habitat The species inhabits permanent or temporary (Madge and Burn 1988) swamps, marshes, inland deltas (e.g. the Okavango), shallow lakes (del Hoyo et al. 1992), pools (Madge and Burn 1988), farm impoundments, flood-plains (Hockey et al. 2005), slow-flowing rivers (del Hoyo et al. 1992) and occasionally coastal lagoons (Madge and Burn 1988). It shows a preference for deep (del Hoyo et al. 1992) clear waters (Brown et al. 1982) with abundant emergent and aquatic vegetation (Madge and Burn 1988), especially water-lilies (Nymphaea spp.) (del Hoyo et al. 1992). Diet Its diet consists predominantly of the seeds of water-lilies (Nymphaea spp.) (del Hoyo et al. 1992), although the seeds and vegetative parts of other aquatic plants (del Hoyo et al. 1992) (e.g. pondweeds Potamogeton spp.) (Hockey et al. 2005), aquatic insects and small fish may also be taken (del Hoyo et al. 1992). Breeding site The species nests in natural hollows or the disused holes of barbets Megalima spp. and woodpeckers in trees (Kear 2005b), preferably those standing in or close to water (Kear 2005b). It may also nest in other cavities (del Hoyo et al. 1992) such as holes in cliffs or termites mounds (Madge and Burn 1988), in the disused nests of Hamerkop Scopus umbretta (Kear 2005b), or in ground sites such as papyrus stands (Kear 2005b) or grass clumps (Brown et al. 1982). Elevated nests are usually up to 10 m (Brown et al. 1982) (occasionally 20 m) above the ground (Johnsgard 1978). The species will also nest in artificially erected nest boxes (Hockey et al. 2005). Management information In South Africa a breeding pair successfully nested in an artificial nest-log (a stem of Euphorbia ingens) measuring 60 x 21 cm with a horizontal oval entrance-hole measuring 7 x 8 cm and an internal cavity diameter of 12 cm that was fixed to a tree 4.2 m above the ground at the edge of water (Brown et al. 1982).
The species has declined is Madagascar as a result of hunting (del Hoyo et al. 1992). It is also threatened by habitat degradation such as the destruction of aquatic plant communities through the introduction of exotic fish (e.g. cichlids Tilapia spp.), siltation, pollution (e.g. herbicides), drainage and tourist water-sports (which destroy lily beds) (Kear 2005b).
Text account compilers
Ekstrom, J., Butchart, S., Malpas, L.
BirdLife International (2019) Species factsheet: Nettapus auritus. Downloaded from http://www.birdlife.org on 19/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/10/2019.