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Scaly-sided Merganser Mergus squamatus
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This species has a very small population which is suspected to be undergoing a continuing and rapid decline as a result of habitat loss, illegal hunting and disturbance. It is therefore listed as Endangered.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

52-58 cm. Striking merganser with shaggy crest and scaled flanks. Adult male has black, glossed green head and neck with long crest. Creamy-white lower foreneck, breast and central underparts. Whitish flanks, ventral region, and rump with grey scaling. Blackish mantle, hindneck and scapulars. Mostly white innerwing. Adult female has warm buffish head and neck with dusky lores and wispy crest. Whitish breast and central underparts. Similar spp. Male Red-breasted Merganser M. serrator has white collar and rufous breast and lacks heavy scaling on flanks. Female also lacks scaling.

Distribution and population
Mergus squamatus breeds in Khabarovsk, Amur, the Jewish Autonomous Region and Primorye in south-east Russia, North Korea and Heilongjiang, Jilin and Inner Mongolia in north-east China (BirdLife International 2001). Some birds winter in south-east Russia and North Korea, but most winter in central and southern China (the majority of wintering flocks found on rivers and other water bodies in the Yangtze River catchment (He Fen-qi et al. 2002, Solovyeva et al. in press), with small numbers in Japan, South Korea, Taiwan (China), Myanmar and Thailand. Its population is estimated at fewer than 2,500 mature individuals and declining, although recent estimates suggest that there could be around 10,000 mature individuals or more (D. Solovyeva in litt. 2007, Anon. 2009, B. Hughes per Moores et al. 2010, Cranswick 2011); however, this requires further study and verification. Most breed in Russia where, in the early 1980s, there were c.1,000 pairs in Primorye and c.100 pairs in Khabarovsk but, by 1990, the total number was estimated at c.950 pairs. However, recent survey results revealed that breeding density along rivers in Primorye has more than doubled since the 1960s/1970s (Solovyeva et al. 2006), and a total of 173 individuals were recorded along a 20-km stretch of the Iman River in 2003 (Robson 2003). Where historical data was available for comparison, breeding populations in Russia showed some increases but this trend seems to have stabilised during 2003-2007 (D. Solovyeva in litt. 2007, 2008). The breeding population in China was estimated at 200-250 pairs (now restricted to the Chingbai mountains following extinction in the Xingan Mountains and Wusuli basin) and declining (Peiqi Liu et al. 2010). Recent surveys of the Chingbai mountains suggest that the population there now numbers 150-200 pairs (Peiqi Liu et al. 2010). In 2003, a population of c.40 individuals was found on the lower Chongchon river in central Korea (Duckworth and Chol 2005). A total of 300 individuals (including one flock of 80 birds) were recorded on a stretch of river not more than 3 km long, at Song Jiang He in Jilin Province, China, representing a post-breeding congregation prior to migration (Peiqi Liu in litt. 2007, 2008). Surveys of c.1,000 km of rivers and 11 reservoirs in south-east China in the winters of 2006 and 2008 found a total of 71 individuals (31 and 40 respectively) (Cao and Barter 2008), and wintering birds at four sites in northern Jiangxi during 2002-2007 included a peak of 88 on a 22-km stretch of Xinjiang River (Yu Chang-Hao et al. 2008), but the whereabouts of the majority of the wintering population is still unknown (Cao and Barter 2008, Cranswick 2011). In the winter of 2007/2008, 1-2 birds were reported from Yalujiang River, north-east of Dandong City, Liaoning province (Bai Qing-Quan 2008), indicating that a few birds winter within the species's breeding range in north-eastern China and probably representing some of the most northerly wintering individuals in China.

Population justification
In Russia, c.1,575 pairs nest in Sikhote-Alin (Solovyeva et al. in press). In China, 180-200 pairs breed in the Changbaishan Mountains (Liu et al. 2010) and perhaps 30-40 pairs in Lesser Xingan. In North Korea, probably less than 200 pairs breed, mainly on Mayang Chosuji reservoir (Chong and Morishita 1996). The total world population is therefore likely to consist of less than 3,000 pairs (Solovyeva in litt. 2012), however, there are other estimates of perhaps several thousand pairs (B. Hughes in litt. 2010). In recognition of this uncertainties, the number of mature individuals is estimated at 2,400-4,500, following Peiqi Liu et al. (2010). This is roughly equivalent to 3,600-6,800 individuals in total. Further research is required in order to verify this.

Trend justification
A rapid and on-going population decline is suspected (see BirdLife International 2001). The density of breeding pairs more than doubled since the 1960s/1970s in the species's stronghold in Russia, but has since stabilised (Solovieva et al. 2006). The Changbai (China) breeding population may be increasing, but the western population (found in Xingan, China and Zeya-Bureya, Russia) has declined rapidly.

It breeds below c.900 m in mountainous areas, along rivers with tall riverine forest, mainly within the temperate conifer-broadleaf forest zone. It is largely confined to primary forests, with an abundance of potential nest-holes. During a study on the Russian breeding grounds, river size, mountain slope, human population, estimated forest cover and water clarity all failed to explain the observed distribution, but the species showed a marked preference for the middle reaches of rivers (Solovieva et al. 2006). It prefers freshwater habitats in winter, only c.10% are known to winter on coastal waters (Solovyeva et al. in press). On passage and in winter it feeds along large rivers. Flocks of up to 20 individuals have been noted on passage or in winter (Duckworth and Chol 2005). In Russia, they moult on a range of water bodies within the breeding range and north and east of breeding range, including rivers, estuaries and the sea (Solovyeva et al. in press).

In the 1960s and 1970s, its decline in Russia coincided with economic development of the taiga. Primary forests in the valleys of all large rivers were greatly altered, but large-scale deforestation in river valleys is now prohibited; however, the new Russian Forest Codex (2007) requires a water protection zone (no deforestation) of only 100 m for large rivers (50 m on each side), and 50 m (25 m each side) for rivers shorter that 100 km, which is likely to significantly reduce suitable breeding habitat for this species, which nests up to 150 m from rivers (D. Solovieva in litt. 2007, 2008). Logging of river sources and adjacent slopes has led to reduced spring water levels and changes in fish abundance; since logging began on the Avvakumovka River in 2004, spring water levels and merganser populations have undergone continuous declines (D. Solovieva in litt. 2007, 2008). Other major threats within the breeding range include illegal hunting, drowning in fishing nets (a major cause of mortality at Russian breeding sites in 2003-2007 [D. Solovieva in litt. 2007, 2008]), disturbance from motor boats during the breeding season, river pollution and natural predators. Increased hunting of waterfowl for sport together with poor regulation of the spring hunting season (which is intended to coincide with passage migration and avoid targeting locally breeding birds) is a significant and increasing threat; large numbers were reportedly shot in the Kievka River basin, southern Primorye, in spring 2008 (D. Solovieva in litt. 2007, 2008). Threats in its breeding range in China include dam construction, deforestation, illegal hunting, human disturbance and the use of poisons and/or explosives for fishing (Peiqi Liu in litt. 2007, 2008). Fine-meshed nets were a significant threat to the post-breeding congregations at Song Jiang He in Jilin Province, China, but illegal fishing at the site has been reduced and only large-meshed nets are used in legal fish-farming (Peiqi Liu in litt. 2007, 2008). The site remains threatened by industrial pollution (Peiqi Liu in litt. 2007, 2008). The proposed Korean Grand Canal project, which aimed to canalise 3,134 km of the Korean peninsula's rivers and radically alter the Han and Nakdong rivers (which currently support an estimated 30-50 birds in winter), was suspended in June 2008 (Moores 2008), and an alternative scheme, the Four Rivers Project, was proposed in December of that year, with an environmental impact assessment and launch of construction in 2009 (Moores et al. 2010). In South Korea, the species is impacted by increased river turbidity due to construction and dredging, bridge-building activities, river-bank strengthening and road-widening schemes (Moores et al. 2010). Some of these activities are associated with the Four Rivers Project on several stretches of river used regularly or irregularly by the species. Other significant aspects of habitat modification will include the deepening of rivers and the removal of boulders and islands, which are used for roosting. Many stretches of river are expected to be rendered unusable for the species owing to habitat degradation and disturbance (Moores et al. 2010). The species has low genetic diversity (Solovyeva and Pearce 2011). High levels of heavy metals, especially As and Hg, were reported in females and their eggs after wintering in the Yangtze catchment (Solovyeva in litt. 2012). Poor egg hatchability recorded within Sikhote-Alin population could be a result of pollution on the wintering grounds.

Conservation Actions Underway
CMS Appendix II. Primary forest is protected at some breeding localities in China and at the most important breeding site in North Korea. Small proportions of its breeding and non-breeding populations occur inside protected areas, notably Sikhote-Alin' State Biosphere Reserve, Lazovskiy State Reserve and Botchinskiy State Reserve (Russia) (D. Solovyeva in litt. 2007, 2008), and Changbai Shan Nature Reserve (China). An artificial nest programme in Russia, involving the provision of at least 180 nest boxes (Cranswick 2010), has shown positive results, increasing habitat capacity along rivers with logged flood-plains (D. Solovieva in litt. 2007, 2008; Anon. 2009). The programme involves the continued maintenance of artificial nests, liaison with hunters and fishers and collaboration with local communities, including information and education activities and the construction of a research and visitor centre (D. Solovyeva in litt. 2007, 2008; Anon. 2009). This has already resulted in a change in fishing practices by local people. It has also facilitated the capture of females for tagging with geolocators, allowing the identification of staging and wintering sites (Cranswick 2010, Solovyeva et al. in press).
Conservation Actions Proposed
Delineate the breeding range in Russia. Survey breeding populations and locate rivers with a high density of breeding pairs within the main breeding range (Primorye and Khabarovsk Region). Continue to monitor population trends. Carry out research into the impacts of human activities. Identify and protect key wintering areas in China and the Korean peninsula. Establish new protected areas at important breeding localities, notably the Bikin and Iman river basins (Russia). Establish seasonal protected area at moulting sites. Promote forestry management that maintains primary forest along rivers. Implement an artificial nest programme on key rivers. Initiate education programmes to raise public awareness and reduce levels of illegal hunting.

Anon. 2009. Large-scale plans. Waterlife: 38-39.

BirdLife International. 2001. Threatened birds of Asia: the BirdLife International Red Data Book. BirdLife International, Cambridge, U.K.

Brazil, M. 2009. Birds of East Asia: eastern China, Taiwan, Korea, Japan, eastern Russia. Christopher Helm, London.

Cao, L. and Barter, M. 2008. Non-breeding season survey for Scaly-sided Mergansers in Fujian, Guangdong and Jiangxi Provinces. University of Science and Technology of China, Hefei.

Cranswick, P. 2010. Conservation of the Scaly-sided Merganser in Far East Russia. WWT Conservation Report 2008-2009: 33.

Cranswick, P. 2011. Earning our stripes. Waterlife: 38-41.

Duckworth, J.W.; Kim Chol. 2005. Scaly-sided Mergansers Mergus squamatus on the lower Chongchon River, central Korea. Wildfowl 55: 133-141.

He Fen-Qi.; Melville, D.; Gui Xau-Jie.; Hong Yuan-Hua.; Liu, Zhi-Yong. 2002. Status of the Scaly-sided Merganser wintering in mainland China in the 1990s. Waterbirds 25: 462-464.

Moores, N. 2008. The Korean Grand Canal: another huge threat to the region's wetlands and waterbirds. BirdingASIA: 48-53.

Moores, N.; Kim, A.; Park, M.-N.; Kim, S.-A. 2010. The anticipated impacts of thre Four Rivers Project (ROK) on waterbirds: Birds Korea preliminary report.

Peiqi Liu; Feng Li; Huidong Song; Qiang Wang; Yuwen Song; Yusen Liu; Zhengji Piao. 2010. A survey to the distribution of the Scaly-sided Merganser (Mergus squamatus) in Changbai Mountain range (China side). Chinese Birds 1(2): 148-155.

Solovyeva, D. V. and Pearce, J. M. 2011. Comparative mitochondrial genetics of North American and Eurasian mergansers with an emphasis on the endangered scaly-sided merganser (Mergus squamatus). Conservation Genetics 12: 839-844.

Solovyeva, D. V., Afanasiev, V., Fox, J. W., Shokhrin, V. and Fox, A. D. In press. Previously unknown Chinese and Korean scaly-sided merganser wintering sites revealed by geolocators.

Solovyeva, D.; Shokhrin, V.; Vartanyan, S.; Dondua, A.; Vartanyan, N. 2006. Scaly-sided Merganser surveys in Primorye, Russia, 2003-05. TWSG News: 60-69.

Yu Chang-Hao; Sun Zhi-Yong; Wang Zhi-Ru. 2008. Winter distribution of Chinese Merganser in Jiangxi. China Crane News 12(1): 35-36.

Further web sources of information
Detailed species accounts from the Threatened birds of Asia: the BirdLife International Red Data Book (BirdLife International 2001).

Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Benstead, P., Bird, J., Chan, S., Crosby, M., Peet, N., Symes, A., Taylor, J., Allinson, T

Barter, M., Cao, L., He, F., Hughes, B., Peiqi, L., Solovyeva, D.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2016) Species factsheet: Mergus squamatus. Downloaded from on 21/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 21/10/2016.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Scaly-sided merganser (Mergus squamatus) 0

Key facts
Current IUCN Red List category Endangered
Family Anatidae (Ducks, Geese, Swans)
Species name author Gould, 1864
Population size 2400-4500 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 862,000 km2
Country endemic? No
Links to further information
- Additional Information on this species