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

Abstract

This study aimed to analyze the relationship between Cygnus spp. population trends and land-use changes and artificial development activities in the Nakdonggang Estuary for the necessity of management to the buffer area outside the protected area boundary in Korea. Analysis of the 15-year population change revealed a sharp decline in the Cygnus columbianus population in the 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 resulting from the expansion of the urbanized area. The rate of decrease in the water body area was high, attributed to urban development through reclamation. The correlation analysis between the area (ha) of paddy fields and the monthly (Nov.–Feb.) population of C. columbianus indicated that the populations in December (R2 = 0.768) and January (R2 = 0.743) were more correlated with the change in paddy field areas than those in the early winter (November: R2 = 0.457) and at the end of winter (February: R2 = 0.582). In the case of C. cygnus, the population tended to increase with increases in the areas of paddy fields, but the statistical explanatory power was low. We identified a distinct difference in that C. columbianus was more sensitive to urbanization than C. cygnus in the Nakdonggang Estuary.