As described in the Birds Korea Preliminary Report on the “Anticipated Impacts of the Four Rivers Project on Waterbirds” published in 2010, the Scaly-sided Merganser Mergus squamatus is a globally Endangered and declining species that is ecologically dependent on rivers. Being shy, it is still rather poorly-known. Most of the world population (of less than 5000 individuals) probably breeds in Far East Russia and winters in China. In the ROK, the species is believed to be a rare migrant and winter visitor. There are records of the species from more than 10 rivers during the 2000s. However, the annual Ministry of Environment’s winter bird census found a total of only 14 Scaly-sided Merganser nationwide in early 2010, and the “government says it has no data on the merganser” (Oliver, Sep 21 2009, Financial Times).
As our 2010 report stated, “There has been no coordinated census of the Scaly-sided Merganser in the ROK…the estimate of between 30-50 nationwide most winters is rather conservative”.
Scaly-sided Merganser Mergus squamatus, Nov 2011. Digiscoped photo © Jason Loghry
In the winter of 2010/2011, Birds Korea started regular monitoring of a river in the south-east. We recorded over 50 Scaly-sided Merganser on this one river at peak, and found the species on several other rivers. This monitoring program continues, and includes habitat description and attempts at ageing non-adults. Still, it was clear that we needed to survey more sites if we were to develop a national population estimate and over time to identify population trends.
Therefore, supported by the generous and essential financial support of long-time Birds Korean Mr. Ed Keeble, two Birds Korean teams surveyed more than 10 rivers between February 3rd and February 7th. We recorded a total of between 140 and 149 Scaly-sided Merganser nationwide. Several rivers that hold the species were not surveyed completely, and it seems likely that there will be other rivers that support the species. It therefore seems probable that between 150 and 200 Scaly-sided Merganser are present in the ROK this winter.
In addition to counting this species and other waterbirds, we recorded details of river width, ice-cover and potential disturbance elements. Although detailed analysis will take some weeks, most Scaly-sided Merganser were concentrated in areas with little disturbance. It is clear that some stretches of river which previously held the species have become much degraded due to infrastructure development. In some cases, such river stretches (now flanked by new roads, bicycle and hiking roads) either no longer support the species or supported lower numbers than recorded during previous survey effort.