| Citation |
BirdLife International. 2019. Aythya ferina (amended version of 2017 assessment). The IUCN Red List of Threatened Species 2019: e.T22680358A155473754. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T22680358A155473754.en. Downloaded on 20 June 2020. |
Description |
JUSTIFICATION
This species has an extremely large range in both the breeding season and in winter, and an extremely large population. New information suggests the population has declined rapidly across the majority of the range, and it has therefore been uplisted to Vulnerable. Although the species might be expected to benefit from a reduction in eutrophication, this does not appear to have been the case.
DESCRIPTION
The global population is estimated to number c. 1,950,000-2,250,000 individuals (Wetlands International 2012).
Trend Justification: The overall population trend is decreasing, although some populations may be stable and others have unknown trends (Wetlands International 2006). In Europe the population size is estimated to be decreasing by 30-49% in 22.8 years (three generations) (BirdLife International 2015). In winter, the population size in Europe is estimated to be decreasing at the same rate. Europe holds between 35% (breeding) and 40% (wintering) of the global population, so these declines are significant. The flyway population breeding in western Siberia and wintering in south-west Asia also appears to be declining, although this may at least partly reflect recent variation in monitoring effort (Nagy et al. 2014). No recent information is available about the sizes or trends of the two other flyway populations, which breed in central Asia and winter in south and east Asia, respectively (Wetlands International 2012), and which together are thought to comprise around one third of the global population. Populations in Bangladesh (S. Chowdhury in litt. 2015), Japan (K. Ushiyama in litt. 2015) and South Korea (N. Moores in litt. 2015) are reported to be decreasing. Population declines have not been observed in China (M. Ming in litt. 2015) or Mongolia (S. Gombobaatar in litt. 2015).
HABITAT AND ECOLOGY
This species requires well-vegetated eutrophic to neutral swamps, marshes, lakes and slow-flowing rivers with areas of open water and abundant emergent fringing vegetation. It also breeds on saline, brackish and soda lakes and occasionally even in sheltered coastal bays (Kear 2005). The breeding grounds are reoccupied from early March (in the south) to early May (in Siberia) (Scott and Rose 1996) with breeding starting from April-May. During the winter the species frequents similar habitats to those it breeds in, including large lakes, slow-flowing rivers, reservoirs, brackish waters, marshes, weirs (Africa) and flooded gravel pits (Brown et al. 1982, Madge and Burn 1988, del Hoyo et al. 1992, Fox et al. 1994, Scott and Rose 1996). The nest is a depression or shallow cup in a thick heap of vegetation positioned on the ground in shallow water (Johnsgard 1978, Madge and Burn 1988, del Hoyo et al. 1992, Snow and Perrins 1998, Kear 2005b). As in the breeding season, the species will shift to coastal habitats such as brackish lagoons, tidal estuaries and inshore waters (where it may associate with sewage outfalls [Kear 2005b]) when driven by frost or other compelling factors (Madge and Burn 1988, del Hoyo et al. 1992, Scott and Rose 1996, Snow and Perrins 1998).
The species is omnivorous, its diet consisting of seeds, roots, rhizomes, the vegetative parts of grasses, sedges and aquatic plants as well as aquatic insects and larvae, molluscs, crustaceans, worms, amphibians and small fish (Johnsgard 1978, Brown et al. 1982, del Hoyo et al. 1992, Marsden and Bellamy 2000, Kear 2005b).
Northern populations of this species are highly migratory (Scott and Rose 1996, Snow and Perrins 1998). Those breeding in the milder parts of western or southern Europe are sedentary or only make short-distance movements, often in response to harsh weather conditions (del Hoyo et al. 1992, Scott and Rose 1996, Snow and Perrins 1998), although individuals from some areas, such as France may utilise mulitple localities up to 200 km apart in one winter (Keller et al. 2009, Gourlay-Larour et al. 2012).
THREATS
It is thought that the primary factors that have led to the decline in this species are most likely to be a combination of: (i) loss of breeding habitat in eastern Europe, and (ii) changes in water chemistry (especially from hyper-eutrophication caused by agricultural runoff). The loss of habitat is thought to primarily result from changes in land management; either the abandonment or intensification of management of lowland marshes and fish ponds (Fox et al. 2016). The abandonment of traditional lowland grazing marshes results in succession to scrub and other unsuitable habitats, whilst greater agricultural intensification leads to marshes being drained. Negative changes to fish pond management also arise from either a reduction in fish production or an intensification that leads to greater use of fish food and medication treatments, and an increase in nutrient inputs. (Fox et al. 2016).
The species suffers from predation and nest predation by several introduced and native mammals including American Mink Neovison vison (Bartoszewicz and Zalewski 2003), Raccoon Dog Nyctereutes procyonoides, Raccoon Procyon lotor, Red Fox Vulpes vulpes and Wild Boar Sus scrofa. Increased predation levels may be partly related to declines in Black-headed Gull Chroicocephalus ridibundus colonies, with which Pochard often associate for the benefits of predator deterrence (Fox et al. 2016). Invasive carp may also provide competition for resources with this species (see Fox et al. 2016).
The species may also be threatened by disturbance from hunting (del Hoyo et al. 1992, Evans and Day 2002, Kear 2005b), water-based recreation (Fox et al. 1994, Kear 2005b) and from machinery noise from urban development (Marsden 2000), as well as by habitat destruction (del Hoyo et al. 1992) on its wintering grounds due to eutrophication (partially as a result of nutrient run-off from agricultural land) (Kear 2005b, L. Raudonikis in litt. 2015). Adults are poisoned by ingesting lead shot (Spain) (Mateo et al. 1998) and drowned in freshwater fishing nets with mesh sizes greater than 5 cm (China) (Quan et al. 2002). The species is also susceptible to avian influenza, so may be threatened by future outbreaks of the disease (Melville and Shortridge 2006). It is also hunted in numerous countries across its range (e.g. Mateo et al. 1998, Evans and Day 2002, Balmaki and Barati 2006, Sorrenti et al. 2006, H. Ibrahim in litt. 2016).
CONSERVATION ACTIONS
Conservation and Research Actions Underway
EU Birds Directive Annex II. CMS Appendix II. Listed as part of AEWA, for which Waterbird Harvest Specialist Group of Wetlands International (WHSG) (2015) published Guidelines on Sustainable Harvest of Migratory Waterbirds. 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. The removed fish (dead or alive) were sold to generate funds (Giles 1994). In the Trebon Basin Biosphere Reserve, Czech Republic, it was found that artificial islands and wide strips of littoral vegetation are the most secure breeding habitats that can be created for the species (nest survival in littoral habitats was improved by reduced nest visibility, increased water depth, and increased distance from the nest to the habitat edge, and nest survival on islands was improved with increased distance to open water) (Albrecht et al. 2006). The use of lead shot in Europe is being phased out, and there is now a CMS resolution for global action (R. Hearn in litt. 2016).
Conservation and Research Actions Proposed
This species would benefit from the protection and maintenance of wetland habitat. Lead shot use should continue to be prohibited and legislation properly enforced. Accurate monitoring of bag numbers in countries where this species is hunted should be implemented and maintained, and these data used to manage harvests sustainably (R. Hearn in litt. 2016). Reduce nutrient run-off from agricultural land. If feasible, local control of non-native mammals should be implemented (R. Hearn in litt. 2016). |
