Abstract
Seasonal changes in paddy field and river foraging habitats used by herons and egrets were examined to determine the relative value of the two foraging habitats at the reintroduction site of the oriental white stork in Toyooka basin, Hyogo Prefecture, Japan. Herons and egrets gathered at the site to breed. Population size fluctuations were driven by changes in the paddy field; three times as many herons and egrets occurred in the paddy field than at the river. Therefore, it would seem that the herons and egrets depended on the paddy field for food during the breeding season, when the largest amount of food is required. During the non-breeding season, however, the majority of the herons and egrets did not forage in the paddy field, and particularly not in the rice ground. This suggests that the quality of the paddy field as a foraging habitat decreased during the non-breeding season, probably because the area had become dry. In contrast, the river provided a constant supply of food to the herons and egrets throughout the year. The river habitat may have been saturated with foraging herons and egrets, because their numbers did not increase during the non-breeding season, when they did not forage in the paddy field. It is necessary to increase the aquatic fauna of the paddy field during the non-breeding season for the success of this reintroduction.
