关键词: 东方田鼠, 迁移, 种群密度, 性比, 年龄

Abstract: 　M icrotus fortis lives on the beach of Dongting Lake from autumn to spring when the
water level of the lake is low. As the rising of the water level of the lake in spring or in
early summer, and the area of the lake beach becoming narrow , M. fortis crosses the
dike and migrates to the farmland under the pressu re of overcrowd or being forced by
the f lood directly. When M. fortis started to migrate depended on the water level of the
lake and the population density. M. fortis often causes serious damages on crops when
it moves to the farmland. When M. fortis crossed the dike, it distributed on the farm-
land and the uncultivated land. The adults moved longer distance than the youngs did.
There were no differences between sexes on the dispersal distances.
　　The voles were mainly distributed within the area of the farmland or uncultivated
land 5 km from the dike during summer. The rate of capture declined as the distance
from the dike increased. The rate of captu re on uncult ivated land was higher than that
on farmland.
　　When the lake beach emerged in autumn, the volesmoved back. The ratio of males
among the dispersals was high when the voles started to move back in autumn.

Key words: Microtus fortis, Migration, Population density, Sex ratio, Age