Decrease in population of swans (Cygnus spp.) due to the development of areas adjacent to the wintering site

Abstract

The aim of the present study was to investigate the relationship between Cygnus spp. population trends and land-use change and artificial development activities in Nakdonggang estuary. Analysis of the 15-year-long population change revealed a sharp decline of Cygnus columbianus population in winter, which could be attributed to the Nakdonggang estuary becoming unfeasible as their wintering site. In contrast, there was no sharp decline in the Cygnus cygnus population, although a moderate decline was identified. Over the past 30 years, farmland activities decreased by approximately 10% in the areas adjacent to the protected area, resulted from the growth of the urbanized area. The rate of decrease of water body area was evident, identified by the urban development through reclamation. Although the abundance of food resources for Cygnus spp. can only be understood indirectly, changes in land use around the wintering site, where the Cygnus spp. can acquire food, are expected to be decisive in their choice of habitat. C. cygnus and C. columbianus, whose individual characteristics have not been specifically investigated, are generally known to share the same habitat; we could identify a distinct difference in terms of habitat sensitivity. With urban development occurring around the wintering site, C. columbianus was confirmed to be more sensitive to urbanization compared to C. cygnus in Nakdonggang estuary.