Birds Korea National 호사비오리 Scaly-sided Merganser and River Habitat Survey: Part 1

Dr Nial Moores, Birds Korea, March 2nd 2022

Funded by the Hanns Seidel Foundation (Korea office), “Team Hosa” (comprised of Dr Bernhard Seliger, Ms Lee Su-Young, Mr Baek-Seung-Kwang and myself) surveyed several major rivers and their tributaries largely in the northwest of the ROK. Our survey was focused on counting globally Endangered Scaly-sided Merganser Mergus squamatus 호사비오리 and additional globally threatened species, and was conducted on February 8th, February 11th and between February 15th-18th 2022. Additional survey (which will be covered on the blog in Part 2) was conducted between February 8th and 21st by multiple observers (our thanks to them!) throughout much of the south of the ROK .

Part 1 of the survey covered ~160km of largely unfrozen river, including several stretches which we had not surveyed before, and an additional ~50km of frozen water bodies viewed only briefly from a passing car.

We found a total of 82 Scaly-sided Merganser.

Of concern, only 59 of these were counted along the same stretches of two main rivers where we counted 113 Scaly-sided Merganser in 2014. This suggests either a decline in the species – or a change in their distribution since that year.

One of the 82 Scaly-sided Mergansers found by our survey of rivers toward the northwest of the ROK © Nial Moores

Including Scalies, we found a total of 90 bird species during this part of the survey. Rarest species in the Korean context was a taverneri Cackling Goose (images here). Additional observations of note not already posted on the blog included:

  • Greater White-fronted Goose Anser albifrons  쇠기러기. LC.

Wetlands International (2022) sets the 1% threshold for the Korean non-breeding population very low at 840 individuals. Using this threshold, we observed Ramsar-defined internationally important concentrations in Imjingak (1,200+= >1%) and Yeoncheon (3,800 in one area of fields = >4%) on 8th; and in Chungju on 17th (1,200 or >1%  were seen west of the city, sitting in fields, and in flight).

  • Mandarin Duck Aix galericulata 원앙. LC.

A total of 222 were observed, with the largest concentration 132 along the Gyeongangcheon in Gwangju, Gyeonggi Province.

Mandarins and Eastern Spot-billed Ducks 흰뺨검둥오리© Nial Moores
  • Hybrid Mallard Anas platyrhynchos 청둥오리 x Eastern Spot-billed Duck Anas zonorhyncha 흰뺨검둥오리

Either the most numerous or second most numerous hybrid duck in the ROK (after those Aythya with a rich ancestry that includes Common Pochard, Ferruginous and / or Baer’s!). One was seen (together with Mandarins, Eastern Spot-billeds and a Scaly-sided Merganser!) on 16th.

Hybrid towards centre © Nial Moores. Note green head, grey flanks and russet brown breast of Mallard; and bill pattern and upperparts of Eastern Spot-billed.
  • Hybrid Common Goldeneye Bucephala clangula 흰뺨오리 X Smew Mergellus albellus 흰비오리

One was identified during the preparation of this blog post, while reviewing images taken by Mr Baek Seung-Kwang of a flock of Common Goldeneye on 11th. I am not aware of any records of this hybrid combination in Korea (are there any?), though there are records from much further west, one of which (the mounted specimen from 1825 shown here) looks rather similar to this bird.

Hybrid Common Goldeneye 흰뺨오리 x Smew 흰비오리 with Common Goldeneye © Baek Seung-Kwang. Hybrid is toward the front in the centre. Note the head shape (with small “smew tuft”), the white lines near the bill base and toward the rear of the head, and the dark eye.
  • Common Pochard Aythya ferina 흰죽지. VU.

Wetlands International in 2021 set the 1% threshold for the non-breeding population of this species as 3,000. We recorded a total of 2,645 during the survey, with the largest concentration 1,990 at Paldang on the Han River.

Common Pochard © Nial Moores
  • Long-billed Plover Charadrius placidus 흰목물떼새. LC.

A total of (only) 19 were logged, with 12 of these (an exceptional concentration) found in a single group.

  • Common Sandpiper Actitis hypoleucos 깝작도요. LC.

This species is effectively absent in winter from inland areas of the ROK, with only small numbers wintering along the coast in the southwest. One was heard and seen very briefly inland on 16th in Yeoju.

  • Steller’s Sea Eagle Haliaeetus pelagicus 참수리. VU.

“The” adult was at Paldang – a regular wintering site for the species (with up to five there some winters).

Steller’s Sea Eagle © Nial Moores
  • Japanese Wagtail Motacilla grandis 검은등할미새. LC.

A total of 78 were logged, with birds present along all larger rivers, and a remarkable concentration of 30+ near Yeoju.

  • Rustic Bunting Emberiza rustica 쑥새. VU.

The most numerous bunting and predictably widespread, but only c. 160 were logged in total, with the largest flock c. 40.

Rustic Bunting © Bernhard Seliger

In addition to bird counts, our surveys aimed to gather data on the landscape to enable, if possible, analysis of changes in habitat and distribution of Scaly-sided Merganser between 2012 / 2014 and 2022. If funding and / or technical support can be found, these kind of data can then be used to identify and in the best case provide possible solutions to conservation issues along major rivers, including in areas affected by various phases of the national Four Rivers Project. More on this in Part 2 and especially in the full report which we hope to produce this spring.

The most likely cause of the decline between years of the Scaly-sided Merganser in the northwest of the country appears to be the massive increase in infrastructure along and within the rivers. In addition to the proliferation of weirs and dams these include wide bicycle roads (some already constructed in 2014; some new), now often on both sides of the river; new concrete hiking trails; lots of new housing, some within 100m of the rivers, and camp sites, removal of riverside vegetation; construction of new “parks”; and even the use of land within the river banks as grass runways for recreational aircraft at two sites.

A few examples of river “improvements” © Nial Moores
“Team Hosa”: Dr Bernhard Seliger (HSF and Birds Korea member) and Ms Lee Su-Young and Mr Baek Seung-Kwang (Birds Korea Yeoncheon © Nial Moores

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