[Birds Korea] Scaly-sided merganser, shy endangered bird of Korea's rivers

A pair of scaly-sided mergansers, female on the left and male on the right, show off the unique pattern on their flanks that gives this species their name. Courtesy of Birds Korea

By Dr. Nial Moores

Sitting low in the water, close to the river bank, a scaly-sided merganser rests, half-hidden by the shade of an overhanging tree and by a line of jagged black rocks. Waking, the bird moves away from us quietly, and is soon joined by another and then another. Seen well, the details of each of these birds is exquisite: jagged crests, bright fire-red bills and flanks with black and white fish scales that mirror perfectly the ripples and reflections on the water.

The scaly-sided merganser is a species that comes to Korea from the wildest river forests of East Asia, from summers in remote mountain valleys shared with the Siberian tiger. They are shy, doing all they can to keep their distance from that most fearful of predators: people.

Researchers from Birds Korea Yeoncheon search for scaly-sided mergansers along the Namhan River in Yeoju, Feb. 15, 2022. Courtesy of Birds Korea

They need fish to survive, caught in a series of shallow dives, often close to the river bank or in riffles where the flow is fastest. Each autumn, as the rivers further north freeze over, they have no choice but to move south, to spend the winter in landscapes that must now seem almost unrecognizable to them ― curving, gurgling rivers that have been dammed, dredged and straightened; cars and campsites on shingle banks; formerly dark, silent forested banks spotted with private houses, coffee shops and restaurants playing the latest K-pop hits; quiet river bends, once safe refuges, made ever-more accessible to fast-moving packs of cyclists and hikers on paved highways, oblivious to the exceptional biodiversity around them.

Fewer and fewer places remain in Korea for the scaly-sided merganser, and for many of the species that share the same habitat: ground-nesting long-billed plovers and tree-nesting Mandarin ducks, river otters and freshwater turtles and endemic fish species. A whole suite of species confined to ever-smaller spaces; once connected ecosystems now fragmented.

Formerly an important area for the secretive scaly-sided mergansers, this stretch of the Bukhan River below Chuncheon, seen Feb. 18, 2022, is now too exposed and disturbed for them to use because of bike paths and other infrastructure. Courtesy of Birds Korea

What can be done to slow down and then reverse this decline in biodiversity, along Korean rivers and indeed in almost all the habitats on our increasingly degraded planet?

For the scaly-sided merganser, this means first finding where the species can still survive, and then identifying the most efficient ways to reduce disturbance, river stretch by river stretch. In a world where quick economic returns are valued over sustainability, this means identifying ways in which local communities can genuinely benefit from conservation, be it through eco-tourism, local branding or subsidy support, as well as in helping build local pride.

There is, as far as we know, still no fully protected stretch of river anywhere in South Korea that is 100 percent free from the threat of river-works and increasing disturbance. Nonetheless, 2022 has seen substantial progress.

River-works have stripped away the specialized biodiversity of the Nam River in Sancheong County, South Gyeongsang Province, Feb. 21, 2022. Courtesy of Birds Korea

With funding from Yeoncheon County in northern Gyeonggi Provine, Birds Korea has been able to build on research in the Yeoncheon Imjin River Biosphere Reserve ― a core area for the species during migration ― to identify key stretches, propose mitigation measures and raise awareness.

And thanks to a small grant from the East Asian-Australasian Flyway Partnership (EAAFP) and funding from the Hanns Seidel Foundation office in Seoul, Birds Korea was also able to conduct its third national winter survey of the scaly-sided merganser, finding 175 nationwide ― about 4 percent of the estimated world population. This also revealed more about their migration strategy, counting 215 along three rivers in mid-November. The EAAFP's small grant also provided vital support for in-field training in identification and counting, and in the production of an educational pamphlet

This immature scaly-sided merganser, photographed in a "tiger forest" of the Russian Far East, will either spend its winter in Korea, or cross the whole peninsula to migrate to China. Courtesy of Scaly-sided Merganser Task Force

Much remains to be done, of course. But the information gaps are closing, and more and more people now feel their deep connection to this wary, fish-patterned bird, this endangered spirit of the river wild.

Dr. Nial Moores is director of Birds Korea, an NGO dedicated to the conservation of birds and their habitats in Korea and the wider eco-region. Birds Korea is an active member of the EAAFP Scaly-sided Merganser Task Force. Visit birdskoreablog.org or birdskorea.org for more information.