Abstract
Population changes of small rodents in relation to predation by foxes were studied in eastern Hokkaido, Japan. In this report, seasonal changes in predation pressure, prey preference and predation effect are particularly described. By taking the average of two estimates, it was determined that the foxes consumed about 4, 000 to 10, 000 rodents per year within the study area of 415 hectares. Predation pressure against rodents was high in spring but low in winter, and these seasonal changes might be caused by the changes in ground cover. Prey preference for the genus Clethrionomys was assessed by making a comparison between the number of rodents consumed and the number living in the study area. Although a weak positive correlation was detected between the annual average number of rodents consumed per day and the annual total number available for foxes, seasonal fluctuation of the rodent population seemed to be independent of fox predation. There were no significant correlations between the annual predation pressure in the spring and the increase rate in the number of rodents from spring to summer, or between the annual consumption rate by foxes in winter and over-wintering rate of the rodents.
