In order to determine the factors affecting wintering waterfowl populations, the number of wintering swans and ducks, the snow depth, and the minimum temperature during the period from 1984 to 2006 in northern Japan were analyzed. There were increasing trends in both in the swan and duck populations during that period. In the area of heavy snow along the Japan Sea coast, it was determined that the minimum temperature affected the wintering population of swans, and the depth of snow affected the wintering population of ducks. However, in the area of light snowfall along the Pacific Coast, there were few snow and temperature effects on wintering waterfowl. The minimum temperature may affect roost/resting sites through freezing, and the snow depth may affect foraging conditions. These results suggest that roost/resting site conditions may strongly affect wintering swans, and foraging conditions may strongly affect wintering ducks.
2007 by Japan Bird Research Association