Scaly-sided Merganser Mergus squamatus, ROK, © Robin Newlin / Birds Korea

The Scaly-sided Merganser Mergus squamatus was described as a rare and little known species in the first major review of the Korean avifauna, with the earliest record for the ROK being one collected near Seoul in November 1927 (Austin 1948). Subsequently, there was only a single published record until the mid-1990s when survey effort of suitable habitat increased. Park (2002) listed observations in four provinces between 1995 and 2001. Records were spread between October 28^th and March 15^th, and included 12 in the eastern province of Gyeongsangbuk in late January (reported by Kim Su-Kyung) and 30 in November and December 2000 in the south-eastern province of Gyeongsangnam (reported by Park Jin-Young and Jeong Ok-Sik). These records confirmed the presence of the Scaly-sided Merganser as a regular winter visitor to the Republic of Korea (ROK) and formed the basis of a minimum national population estimate of probably 30-50 most winters (Moores 2002).

Despite its national and global rarity, count effort remained somewhat opportunistic through the first decade of the present century. There was no coordinated national survey focused on the Scaly-sided Merganser of which we are aware and the Ministry of Environment’s annual national winter bird census (conducted on one or two dates in January or February) recorded a mean of only13 Scaly-sided Merganser between 2000 and 2009 (range 0-51) (MOE 2000-2012). In addition, several of the sites known to support the species in the ROK had already been or were threatened either directly or indirectly by infrastructural development (Moores 2002, Duckworth & Kim 2005). Further degradation of several stretches of river used by the species were also anticipated with the Four Rivers project, which entailed deep-dredging of seasonally shallow rivers; the building of additional dams and the construction of new boardwalks and cycle-ways along hundreds of km of previously relatively undisturbed rivers (Moores et al. 2010).

Scaly-sided Merganser habitat, ROK, January 2012, © Birds Korea

In order to improve understanding of Scaly-sided Merganser distribution and wintering ecology, survey of birds and habitat was conducted by Birds Korea on nine dates between December 5^th 2010 and April 10th 2011 along approximately 15km of river in the south-east. This was the same river that supported 30 birds in November and December 2000 (Park 2002). Scaly-sided Merganser were found on eight dates (last on March 23^rd). A mean of 30 were recorded through the winter, with a maximum of 56 on February 6^th. Although there is no robust methodology available with which to interpret counts, we assume that the majority of birds counted during this survey effort over-wintered either on this or on adjacent rivers, perhaps undertaking local movements as local rivers freeze or thaw.

In 2012, from February 3^rd-7th, two Birds Korean teams then surveyed more than ten rivers, including the south-eastern river and almost all other sites where the species had been recorded since 2000. In addition to recording habitat and disturbance elements we counted between 140 and 149 Scaly-sided Merganser in total (Birds Korea 2012). Several rivers that held the species were not surveyed completely, and it seems likely that there will be other rivers that support the species that still remain to be surveyed. We therefore estimate that probably between 150 and 200 Scaly-sided Merganser over-wintered in the ROK in February 2012. This number is substantially higher than the 30 recorded nationwide by the MOE census in 2012, and does not include an unknown number suspected to migrate through the ROK between Russian breeding and Chinese wintering areas.

Habitat degradation at one of the nation's most important sites for Scaly-sided Merganser, January 2012, © Birds Korea

While our analysis of habitat preference and disturbance elements is still ongoing, we believe that optimal conditions for Scaly-sided Merganser remain in only a few areas in the ROK. The species appears to be effectively confined to stretches of river that contain both fast-flowing shallow water for feeding and slower-moving stretches with boulders and sandbanks used for loafing. This is habitat broadly similar to that used by the species in DPR Korea (Duckworth & Kim 2005). Typically too, the species is shy, easily flushed (occasionally by people >250m from the birds) and at least during the day avoids heavily-disturbed stretches of river. While some birds appear able to habituate to increased disturbance, declines are evident in formerly-important stretches of river that have become most disturbed.

An increase in survey and monitoring effort is urgently required to identify further sites and to improve the presently poor understanding of winter distribution and ecology at a range of scales (along single river-stretches; within river-basins; and nationally).  As disturbance along rivers continues to increase, we suspect that the species will decline – at least at the local and national level However, we also believe that an improvement in disturbance-management (by e.g. screening some stretches of river and by restricting access to others) would likely provide a quick and cost-effective method with which to enhance several stretches of river used by this and several other river species. Over the longer term, in line with the Task Force’s goal of improving the conservation status of the species, a more comprehensive national action plan will also be required. Such a plan will need to address larger issues of river management and riverine biodiversity and will also need to involve a broad range of stakeholders if it is to improve conservation opportunities for this beautiful flagship species of East Asian rivers.

Acknowledgements

Birds Korea would like to thank participating surveyors and Ed Keeble for financial support of the February 2012 survey.

References

• Austin, O. L., Jr 1948. The birds of Korea. Bulletin of the Museum of Comparative Zoology, Harvard University 101: 1-301.
• Birds Korea. 2012. Birds Korea Survey: 140+ Scaly-sided Merganser nationwide! http://www.birdskoreablog.org/?p=3110
• Duckworth, J. & Kim C. Scaly-sided Mergansers Mergus squamatus on the lower Chongchon River, central Korea. Wildfowl (2005) 55: 135-144.
• Ministry of Environment. 2000-2012. Annual Reports of the Winter Bird Census (in Korean).
• Moores, N. 2002. Wetlands: Korea’s most threatened habitat. Oriental Bird Club Bulletin 36: 54-60.
• Moores, N., Kim, A., Park M-N., & Kim S-N. 2010. The Anticipated Impacts of the Four Rivers Project (Republic of Korea) on Waterbirds. Birds Korea Preliminary Report, published by Birds Korea. March 2010.
• Park, J-Y. 2002. Current status and distribution of birds in Korea. Department of Biology, Kyung Hee University, Seoul (unpublished thesis, in Korean).