2013 年 14 巻 1-2 号 p. 15-29
We studied the impacts of human disturbances by boats on wintering waterbirds at 2 sites, in the North and South of Lake Biwa, a Ramsar wetland in Shiga Prefecture, Japan. Most land-feeding ducks (Anas platyrhynchos, An. poecilorhyncha, An. crecca, and An. formosd) slept offshore during the daytime. Herbivorous ducks (An. penelope, An. strepera, and An, falcata) foraged on the water surface. Diving herbivorous waterbirds (Fulica atra) foraged by diving offshore in the North, and by surface-feeding over a wide area of the water surface in the South. Most diving ducks (Ayihya ferina, Ay. fuligula, Ay. marila, and Bucephala clangula) slept on the water surface near the shoreline during the daytime, and some individuals started diving to forage in the afternoon. At both sites, waterbirds were often disturbed by fishing boats. Some birds flew away from the disturbance, but the species foraging in the daytime tended to come back to the same area and resume foraging promptly, whereas the species sleeping in the daytime tended not to come back.