Harteman Wildfowl Aviaries
Scaly-sided merganser
Mergus squamatus
Above: Male scaly-sided merganser, also known as Chinese merganser. Photos by Jan Harteman.
The Scaly-sided merganser, Mergus squamatus, is also known as the Chinese merganser. It is a globally threatened species, classified as endangered on the IUCN Red List since 2002. This is justified on the basis that it 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.
The International Action Plan for the Conservation of the Scaly-sided Merganser Mergus squamatus was first published in 2017 and involves actions, both in-situ and ex-situ, to deliver ten different conservation results.
The captive population was established by the European private sector, not via zoo imports, from the Avvakumovka River in Far East Russia. Imports were possibly made on two or three separate occasions. These were also imported from the East Primorye. Birds were bred in aviculture for the first time in 2002 and the captive population has increased significantly since then.
Introduction to Scaly-sided merganser or Chinese merganser (in-situ)
The Scaly-sided Merganser is an endangered, specialized sea duck native to East Asia, known for the unique, dark, scale-like markings on its flanks. Endemic to the region, this piscivorous diving duck thrives on clear, fast-flowing rivers in, primarily breeding in Russia and wintering in China. Due to habitat loss and deforestation, it is protected across its range.
Both sexes feature a long, shaggy, wispy crest and a slender, bright red bill with a hooked tip. The male displays a glossy green head and black-and-white plumage, while the female has a rusty brown head and grey back. Both sexes have dark-edged white feathers on their flanks and rump, creating a distinctive scaled pattern.
They are large sea ducks, generally measuring 50–62 cm in length, with weights ranging from 900–1300 grams.
They require clear, fast-flowing mountain rivers within primary forests, primarily in southeastern Russia, northeastern China, and parts of North Korea. They migrate south to central and southern China, particularly in the middle and lower Yangtze River basin.
They are opportunistic piscivores, relying heavily on fish and aquatic insects, which they catch by diving or dipping their heads in water.
Nesting: These birds are cavity nesters, relying on old, mature trees along rivers, though they also use artificial nest boxes, which are crucial for conservation efforts.
Listed as Endangered by the IUCN, their population is threatened by habitat degradation, pollution, deforestation, mining, and fishing.
Status: While they have shown slight signs of recovery, the population remains small, estimated around 2,000 - 3,500 mature individuals in 2025, and highly vulnerable. Back in 2007 the population was estimated around 8,000 - 10,000 adult birds.
Scaly-sided merganser, adult female, in a Dutch private collection (2025).
Scaly-sided merganser, adult male, in a Dutch private collection (2025).
Above: adult male Scaly-sided merganser and a male Baer's pochard, in a German private collection (2019).
Above: adult female, in a Dutch private collection (2024)
Scaly-sided mergansers in aviculture
The European captive population was established by the private sector, not via zoo imports, from the Avvakumovka River in Far East Russia, via Erwin Maes, of Belgium*. It is possible that further imports were made on two or three separate occasions. These were also imported from the East Primorye. Birds were bred in captivity from the first time in 2002. Since then the first public organisations to have bred them successfully were Pensthorpe, Blackbrook & Berlin Tierpark.
Captive breeding reports from private aviculturists have been documented in Aviornis International magazines in 2006 (Gino van Ronsele), 2010 (Peter Smeyers), 2011 (Hans Bögels) and 2021 (Harry Peeters).
The EAZA Zoo population has been monitored since 2011 and was upgraded to a European Studbook (EEP) on 12 March 2013. There were five EAZA zoos holding Scaly-sided Mergansers in 2014 (Augsburg, Berlin Tierpark, Blackpool, Prague and Wuppertal) plus three other non-EAZA zoos (Pensthorpe, WWT Arundel and Cottbus), which has increased significantly since then.
In European private aviculture the species is sustained in good numbers by numerous private breeders. The North American captive population were imported from Europe in 2007: the International World Waterfowl Association imported birds from the Netherlands to Sylvan Heights Bird Park and Dry Creek Waterfowl Sanctuary. And the Wildlife Conservation Society imported birds to Central Park Zoo. Shortly after, private breeders and public collections have been successful at breeding Scaly-sided mergansers in the USA - at Livingston Ripley, Sylvan Heights, Pinola Conservancy and Dry Creek Waterfowl.
Successfully keeping and breeding the endangered Scaly-sided merganser in aviculture requires specialized, high-investment, and low-disturbance environments. Key needs include well vegetated enclosures with clean, running water, specialized (artificial) nesting cavities, and a high-protein diet (floating pellets), which may be supplemented with fish/ intvertebrates.
Historical notes on captive Scaly-sided mergansers
Not much has been written about Scaly-sided Mergansers in aviculture until the year 2000. Below are some notes from sources before the new millennium.
Frank Finn (The waterfowl of India and Asia, 1909) states: "For many years this merganser, which is found in China, was only known by a young male procured in 1864, but in 1898 an adult pair were procured by Capting Wingate, and figured the "Ibis" for 1900. These came from South-West Hunan and since then the species has been found in Yunnan and Western Szechuen, so that it may be expected sooner or later to turn up within Indian limits.
But no information about any captive propagation.
John C. Phillips (A Natural History of the Ducks, Volume IV, 1926): no information about captive propagation of the Chinese merganser.
Frank S. Todd (Waterfowl: Ducks, geese and swans of the World, 1979) states: "These distinctive mergansers have never been maintained in captivity outside of China, and unless drastic political changes occur they will remain virtually unknown to anyone outside of that country. Hopefully, the recent opening of diplomatic relations with the United States may facilitate study by western biologists. As of 1978, there were two specimens at the Shanghai Zoo".
Frank S. Todd (Natural History of the Waterfowl, 1996): "A few have been held in Chinese zoos, but as far a I am aware, the unusual mergansers have never been maintained outside China".
Above: adult male Scaly-sided merganser, in a Dutch private collection (2024).
Above: juvenile male at the age of 5 months old, in a Dutch private collection (2019)
Above: Adult pair of scaly-sided mergansers, in Dutch private collection (2024).
Above: Adult female in a Dutch private collection (2025).
Above: pink-eared duck and its nestbox. Private collection (2019)
Above: Adult pair of scaly-sided mergansers at Aeres Barneveld (2021)
Above: feeding Scaly-sided mergansers, white-headed ducks, lesser whistling ducks and Baer's pochards at Aeres Barneveld (2021).
Above: A juvenile male scaly-sided merganser (6 months old) in a Dutch private collection (2019).
