Population estimates and geographical distributions of swans and geese in East Asia based on counts during the non-breeding season

Abstract

SummaryFor the first time, we estimated the population sizes of two swan species and four goose species from observations during the non-breeding period in East Asia. Based on combined counts from South Korea, Japan and China, we estimated the total abundance of these species as follows: 42,000–47,000 Whooper SwansCygnus cygnus; 99,000–141,000 Tundra SwansC. columbianus bewickii; 56,000–98,000 Swan GeeseAnser cygnoides; 157,000–194,000 Bean GeeseA. fabalis; 231,000–283,000 Greater White-fronted GeeseA. albifrons; and 14,000–19,000 Lesser White-fronted GeeseA. erythropus.While the count data from Korea and Japan provide a good reflection of numbers present, there remain gaps in the coverage in China, which particularly affect the precision of the estimates for Bean, Greater and Lesser White-fronted Geese as well as Tundra Swans. Lack of subspecies distinction of Bean Geese in China until recently also limits our ability to determine the true status ofA. f. middendorffiithere, but all indications suggest this population numbers around 18,000 individuals and is in need of urgent attention. The small, highly concentrated and declining numbers of Lesser White-fronted Geese give concern for this species, as do the major declines in Greater White-fronted Geese in China (in contrast to numbers in Japan and Korea, considered to be a separate flyway). In the absence of any demographic data, it is impossible to interpret the causes of these changes in abundance. Improved monitoring, including demographic and tracking studies are required to provide the necessary information to retain populations in favourable conservation status.