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 global population is estimated to number 6,500,000-7,000,000 individuals (Wetlands International 2015). This roughly equates to 4,300,000-4,700,000 mature individuals. The European population is estimated at 170,000-233,000 pairs, which equates to 340,000-466,000 mature individuals (BirdLife International 2015).
The overall population trend is decreasing, although some populations may be increasing and others have unknown trends (Wetlands International 2015). In North America, the species has undergone a large, significant increase over the last 40 years (based on Partners in Flight; A. Panjabi in litt. 2017). The European population trend is estimated to be stable (BirdLife International 2015).
Behaviour This species is highly migratory although it may be present all year round in parts of Europe (del Hoyo et al. 1992). It arrives on the breeding grounds from March where it breeds in solitary pairs or loose groups in the northern spring (chiefly from mid-April to June) (Madge and Burn 1988, del Hoyo et al. 1992). Males undergo a post-breeding moult migration from early-May to early-June (females moulting one month later) during which they are flightless for 3-4 weeks (Scott and Rose 1996). The autumn migration chiefly occurs between September and October (western Europe), during which the species is likely to travel on a broad front (e.g. across Arabia and into Africa) (Scott and Rose 1996). The species is usually found in pairs or small parties, although it often congregates when feeding (flocks of 20 or 30 to several hundred individuals occur in favoured areas in Africa and large concentrations form at stop-over sites on migration) (Johnsgard 1978, Brown et al. 1982, Madge and Burn 1988, Kear 2005). The species forages diurnally and roosts communally at night (Brown et al. 1982).
Habitat It inhabits permanent shallow freshwater wetlands from sea level up to 2,900 m (Ethiopia), preferred sites being those surrounded by dense stands of reeds or other emergent vegetation whilst being free of overhanging trees or fringing forest (Brown et al. 1982, del Hoyo et al. 1992, Snow and Perrins 1998). Copious submerged aquatic vegetation sheltering abundant planktonic invertebrates is a valuable habitat characteristic (Johnsgard 1978). Suitable habitats include well-vegetated lakes and marshes and with muddy shores and substrates in open country (e.g. grasslands), as well as oxbow lakes, channels and swamps (former U.S.S.R.) (Johnsgard 1978, Brown et al. 1982, Flint et al. 1984, Madge and Burn 1988, del Hoyo et al. 1992, Kear 2005). It also frequents artificial waters bordered by lush grassland such as sewage farms, rice-fields and fish ponds (Snow and Perrins 1998, Kear 2005, Musil 2006). In the winter it can be found on coastal brackish lagoons, tidal muflats, estuaries, coastal shorelines, fresh and brackish estuarine marshes, inland seas and brackish or saline inland waters, occasionally occurring (briefly) on marine waters during migration (although it generally avoids very saline habitats) (Johnsgard 1978, Madge and Burn 1988, del Hoyo et al. 1992, Snow and Perrins 1998, Kear 2005).
Diet Its diet consists of small aquatic invertebrates such as adult and larval insects (e.g. caddisfly larvae, damselfly and dragonfly nymphs, adult beetles, bugs and flies), molluscs, planktonic crustaceans, the seeds of emergent and aquatic plants (e.g. bulrushes and waterweeds), annelids, amphibian spawn, tadpoles, spiders, fish and the vegetative parts of aquatic plants (e.g. duckweeds) (Johnsgard 1978, Brown et al. 1982, del Hoyo et al. 1992, Snow and Perrins 1998, Kear 2005).
Breeding site The nest is a scrape or depression on the ground in tall grass, among hummocks, in the open or (rarely) in bulrush marshes (Flint et al. 1984, del Hoyo et al. 1992, Kear 2005). Usually the species nests close to water but if grass cover is unavailable in the wetland site it may also nest far away from water under bushes, in hayfields or in meadows (Flint et al. 1984, Kear 2005). Although it is not a colonial species, several pairs may nest in close proximity (Madge and Burn 1988).
Management information A study in the Czech Republic found that fish ponds with a fish stock density of less than 400 kg/ha, water transparency of more than 50 cm, mixed fish stocks (e.g. tench and pike or perch) rather than monospecific stocks (e.g. of carp), and systems that include ponds with fish fry (to provide areas with low fish competition and high invertebrate availability) are more successful in supporting breeding pairs of this species (Musil 2006). The cyclical removal of adult fish from an artificial waterbody (gravel pit) in the UK attracted nesting pairs to the area by causing an increase in invertebrate food availability and an increase in the growth of submerged aquatic macrophytes (Giles 1994). The removed fish (dead or alive) were sold to generate funds (Giles 1994).
The species is threatened by habitat loss in Britain and Ireland (Kear 2005), is occasionally killed by collisions with power transmission lines (Malcolm 1982), and suffers from nest predation by American mink Neovison vison (Opermanis et al. 2001, Nordström et al. 2002, Bartoszewicz and Zalewski 2003). It is susceptible to avian influenza (Melville and Shortridge 2006, Gaidet et al. 2007) and avian botulism (Forrester et al. 1980), so may be threatened by future outbreaks of these diseases. The species may suffer from 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 suffers mortality as a result of lead shot ingestion (Camargue, France and Spain [Mateo et al. 1998, Mondain-Monval et al. 2002]).
Utilisation The species is a favoured quarry species throughout most of the world, but is rarely taken in large numbers (Kear 2005). It is hunted for sport in North America (Baldassarre and Bolen 1994), Denmark (Bregnballe et al. 2006) and the Po delta, Italy (Sorrenti et al. 2006), and is 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).
Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II and III. The following information refers to the species's European range only: Some studies have been done on the requirements of this species. A study in the Czech Republic found that fish ponds with a fish stock density of less than 400 kg/ha, water transparency of more than 50 cm, mixed fish stocks (e.g. tench and pike or perch) rather than monospecific stocks (e.g. of carp), and systems that include ponds with fish fry (to provide areas with low fish competition and high invertebrate availability) are more successful in supporting breeding pairs of this species (Musil 2006). The cyclical removal of adult fish from an artificial waterbody (gravel pit) in the U.K. attracted nesting pairs to the area by causing an increase in invertebrate food availability and an increase in the growth of submerged aquatic macrophytes (Giles 1994). The removed fish (dead or alive) were sold to generate funds (Giles 1994).
Conservation Actions Proposed
The following information refers to the species's European range only: A network of key sites needs to be preserved and low-intensity farmland practices encouraged to help preserve habitat for this species. Power lines should be moved or made more visible and appropriate predator control undertaken in breeding areas. The impact of hunting should be researched and monitored to ensure bag numbers are sustainable.
Text account compilers
Malpas, L., Ekstrom, J., Butchart, S., Ashpole, J, Elliott, N.
Evans, M. & Panjabi, A.
BirdLife International (2021) Species factsheet: Spatula clypeata. Downloaded from http://www.birdlife.org on 21/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/10/2021.