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 extremely 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 population is estimated to number 7,100,000-7,200,000 individuals (Wetlands International 2015). This roughly equates to 4,700,000-4,800,000 mature individuals. The European population is estimated at 210,000-269,000 pairs, which equates to 419,000-539,000 mature individuals (BirdLife International 2015).
The overall population trend is decreasing, although some populations may be stable and others have unknown trends (Wetlands International 2006). In North America, the species has undergone a large and statistically significant decrease over the last 40 years (77.3% decline over 40 years, equating to a 31% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count [Butcher and Niven 2007]), and in 2015 the population was estimated to be 24% below the 1955-2014 long-term average (Zimpfer et al. 2015). In Europe, the population size is estimated to be decreasing by less than 25% in 20.4 years (three generations) (BirdLife International 2015).
Behaviour This species is strongly migratory throughout its northern range, although some populations in the Southern Hemisphere are sedentary (del Hoyo et al. 1992, Kear 2005). It breeds in solitary pairs or loose groups from April to June, with males leaving the breeding areas first from May to early-June to undertake extensive moult migrations (females following later) (Madge and Burn 1988, del Hoyo et al. 1992, Scott and Rose 1996). During moult, large sexually segregated flocks gather in moulting areas (e.g. in the Netherlands and Russia), although small gatherings are also possible (Madge and Burn 1988, Scott and Rose 1996, Kear 2005). The flightless moult period lasts for around 4 weeks between July and August, after which flocks move southwards to winter quarters from mid-August onwards (Johnsgard 1978, Madge and Burn 1988, Scott and Rose 1996). The species is highly gregarious in winter and on passage, often forming enormous concentrations (although the size of flock depends on the size of the wetland) (Madge and Burn 1988, Scott and Rose 1996, Snow and Perrins 1998). It feeds nocturnally; flocks are roosting by day on open water (Brown et al. 1982, Hockey et al. 2005).
Habitat The species shows a preference for open lowland grassland, prairie or tundra habitats containing freshwater, brackish and saline wetlands with shallow water (10-30 cm deep) to facilitate dabbling (Johnsgard 1978, Snow and Perrins 1998, Kear 2005). Wetland habitats include shallow freshwater marshes, small marshy lakes, slow-flowing rivers, wet meadows, flood-plains and sewage ponds (southern Africa), especially favouring ponds with low, dense marginal vegetation and wetlands interspersed with brushy thickets or copses (Johnsgard 1978, Madge and Burn 1988, del Hoyo et al. 1992, Hockey et al. 2005). During the winter, it also frequents large inland lakes, brackish coastal lagoons, brackish and saline marshes, shallow fresh or brackish estuaries, tidal flats and river deltas with adjacent agricultural land (e.g. stubble fields) and scattered impoundments (Johnsgard 1978, Brown et al. 1982, Madge and Burn 1988, del Hoyo et al. 1992, Scott and Rose 1996, Steele et al. 1997, Snow and Perrins 1998).
Diet This species is omnivorous and opportunistic, its diet consisting of algae, seeds (e.g. cereals and rice), tubers (e.g. potatoes), and the vegetative parts of aquatic plants, sedges and grasses, as well as aquatic invertebrates (e.g. insects, molluscs and crustaceans), amphibians and small fish (Johnsgard 1978, Brown et al. 1982, del Hoyo et al. 1992, Hockey et al. 2005).
Breeding site The nest is a slight hollow on the ground amongst vegetation (e.g. rushes, grass or low scrub) and can be close to or more than 1 km away from water (del Hoyo et al. 1992, Snow and Perrins 1998, Kear 2005). The species is not normally colonial, but neighbours may nest as close as 2-3 m apart (Kear 2005).
The species is threatened by wetland habitat loss on its breeding and wintering grounds (Scott and Rose 1996). Reclamation of coastal areas for industrial development poses a threat in Europe, and major river diversion and irrigation schemes threaten wintering areas in Niger and Nigeria (Scott and Rose 1996). The species is also threatened by petroleum pollution, wetland drainage, peat-extraction, changing wetland management practices (decreased grazing and mowing in meadows leading to scrub over-growth) and the burning and mowing of reeds in Russia (Grishanov 2006). Over-exploitation is a concern in Europe (Kear 2005). It also suffers poisoning from lead shot ingestion in North America (Baldassarre and Bolen 1994), poisoning from white phosphorous (from firearms) ingestion in Alaska (Steele et al. 1997), and reproductive impairment as a result of selenium accumulation in liver tissues (selenium contained in sub-surface agricultural drain-water used for wetland management in California led to bioaccumulation of the element in the food chain (Paveglio et al. 1997). The species is predated by feral cats Felis catus and rats Rattus norvegicus on islands (del Hoyo et al. 1992), and it is susceptible to avian botulism and avian influenza (Melville and Shortridge 2006, Rocke 2006, Gaidet et al. 2007), so may be threatened by future outbreaks of these diseases.
Utilisation The species is hunted for sport widely across its range; for example in North America (Baldassarre and Bolen 1994, Schmidt 2006), Denmark (Bregnballe et al. 2006) and the Po delta, Italy (Sorrenti et al. 2006), and it is also hunted commercially and recreationally in Iran (Balmaki and Barati 2006). The eggs of this species used to be (and possibly still are) harvested in Iceland (Gudmundsson 1979). The species is also traded at traditional medicine markets in Nigeria (Nikolaus 2001).
Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II and III. The following information refers to the European range of this species only: An EU management plan for the species was published in 2007. Important sites for the species are protected in Belgium, Denmark, Estonia, France, Germany, Ireland, Netherlands, Sweden, U.K., Spain, Portugal and Greece (Jensen 2007).
Conservation Actions Proposed
The following information refers to the European range of this species only: Hunting of this species should be banned during migration and at the end of the breeding season and annual data on bag numbers should be collected for all countries where the species is hunted. Breeding sites should be identified, preserved and managed to increase reproductive success and colonising ability and all internationally important staging and wintering sites should be designated as SPAs and managed favourably. Censusing of winter populations and breeding populations, to provide an assessment of breeding productivity, should be carried out annually. Ringing on breeding and wintering sites should also be carried out and existing ringing data analysed to identify population units and provide annual estimates of mortality (Jensen 2007).
Text account compilers
Everest, J., Ashpole, J, Ekstrom, J., Butchart, S., Malpas, L., Elliott, N.
Dowsett, R.J. & Evans, M.
BirdLife International (2020) Species factsheet: Anas acuta. Downloaded from http://www.birdlife.org on 09/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 09/08/2020.