Scaly-sided Merganser Mergus squamatus


Justification of Red List Category
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. This species may warrant a downlisting in the future but this will depend on a robust understanding of the threats on the status of the breeding population.

Population justification
In Russia, c.1,643 pairs nest in Sikhote-Alin (Solovyeva et al. 2014), with just 11 pairs estimated to nest north of the Amur river. In China, 155 pairs breed in the Changbai Mountains  and 11 pairs in Lesser Xingan (Solovyeva et al. 2014). In North Korea, breeding occurs at Mayang Chosuji reservoir and 116 pairs are estimated to breed in the Changbai Mountains (Chong and Morishita 1996, Solovyeva et al. 2014). Pair densities were found to be highest on the Fuerhe River in the Chinese Changbai Mountains (0.918 pairs/km) and on the Pavlovka River in Sikhote-Alin (0.63 pairs/km) (Solovyeva et al. 2014). The total world population is therefore estimated at 1,936 pairs (Solovyeva et al. 2014). There are, however, other estimates of perhaps several thousand pairs (B. Hughes in litt. 2010). In recognition of these 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.

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 estimates of 3,561 ± 478 individuals over wintering in China in total (Zeng et al. 2015). Small numbers winter in Japan, South Korea (150-200 individuals estimated for South Korea in 2012 [Partnership for the East Asian-Australasian flyway 2008]) Taiwan (China), Myanmar and Thailand. It had been suggested that there could be around 10,000 mature individuals or more globally (D. Solovyeva in litt. 2007, Anon. 2009, B. Hughes per Moores et al. 2010, Cranswick 2011); though more recent estimates suggest 1,936 breeding pairs (Solovyeva et al. 2014).

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 2012, the total number in these areas was estimated at c.448 pairs (Solovyeva et al. 2014), with 1,654 pairs in Russia in total (Solovyeva et al. 2014). 

The breeding population in China was estimated at 150-200 pairs from 2008 and 2009 surveys (Peiqi Liu et al. 2010) and 166 pairs in 2012 (the majority of which are found in the Chingbai mountains [155 pairs], with a small number of breeding pairs in the lesser Xingan Mountains [11 pairs]) (Solovyeva et al. 2014), with a declining trend (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). Seventy one over wintering individuals were found in eastern Jiangxi (Cao & Barter 2013) 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 represent some of the most northerly wintering individuals in China. In 2012 a new wintering site was discovered in Chongqing, a municipality in southwest China (W. Qian in litt. 2013) and in 2013 a ringed bird was identified in Taoyuan county, southern China (Zeng et al. 2013).


It breeds below c.900 m in mountainous areas, along clear flowing 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). On passage and in winter it feeds along large rivers and tracking of several birds over multiple years suggests winter site fidelity (Barter et al. 2015). 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 but the stable isotope analysis confirmed that the species is predominately confined to freshwater habitat (Solovyeva et al. 2014b). A satellite tracking study of individuals breeding in the Lesser Xingan Mountains found migration to last on average 42 days, stopping at several sites on route. This study was however based on a very small sample size and so may not necessarily be representative of the population as a whole (Dong-Ping et al. 2014).  


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 (Solovyera 2013), 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), despite environmental arguments against the project. 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

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 over 200 nest boxes (Partnership for the east Asian-Australasian flyway 2008), has shown positive results, increasing habitat capacity along rivers with logged flood-plains (D. Solovieva in litt. 2007, 2008; Anon. 2009, Solovyeva et al. 2013). 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). Collaboration with General Motors has resulted in the re-use of Chevrolet Volt battery covers as successful nesting boxes in the Changbai Mountain National Nature Reserve in China (General Motors Green 2015). In 2015, 11 ducklings hatched from the chinese nest box programme (Cranswick in litt. 2015). The Scaly-sided Merganser project has been running in Primorye since 2000 and has collated information on the threats facing the species (Solovyera 2013). In 2010 a task force was formed to develop a species action plan (East Asian-Australasian flyway partnership 2016). 

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.


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.


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

Fen-qi, H., Peiqi, L., Solovyeva, D., Hughes, B., He, F., Barter, M., Cao, L.

Recommended citation
BirdLife International (2022) Species factsheet: Mergus squamatus. Downloaded from http://www.birdlife.org on 17/08/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/08/2022.