Abstract
Distribution, composition of the species of small rodents and utilization of the forest island habitat (isolated patches of forest) were surveyed in the farmland area near Asahikawa, Hokkaido, Japan. Twelve trapping stations using the capture-recapture method were established in the forest area (Byobu-yama), three forest islands (Oya-yama: 5.1ha, Ko-yama: 4.1ha and Kubo-yama: 0.3ha) and farmlands (rice fields, sugar beet fields, wheat fields, grassy strips along railroads and farm roads, barns and green houses). Dominance and relative density of eight species of small rodents were determined at each station every month from June 1986 to November 1988 except during the snow season (from December to April). Three species: Clethrionomys rufocanus bedfordiae, Apodemus argenteus and A. speciosus ainu were confirmed as the principal constituents of the fauna in the forest area and the forest island. In the farmland, four species—C. r. bedfordiae, A. peninsulae, Rattus norvegicus and Mus musculus—were confirmed as the principal constituents of the fauna here. Three types of habitat utilization by small rodents were recognized as follows: a) C. r. bedfordiae used both the forest island and the farmland as main habitats, and migrations between the forest island and the farmland were observed all year round. b) A. argenteus and A. s. ainu utilized the forest island as a habitat and the farmland were utilized as a dispersal corridor in the autumn. If habitat area in the island was small, they would use the forest islands as a temporary winter habitat. c) A. peninsulae, R. norvegicus and M. musculus utilized the farmland as its main habitat and also invaded the forest island from September to November to utilize it as a temporary habitat.
