Three fixed, 200-foot transects were used to study the dispersal and increase of voles from the time of their invasion of a 47-acre island in the summer of 1958 until May 1960. Voles populated the entire island during the first winter and spring but did not exploit it fully until the summer of 1959. In the 2nd season rates of increase were highest in the habitat which had the lowest initial density of voles, and lowest in the habitat with the highest initial density. Runways were used for 4-100 weeks. Many short-lived runways were built in relatively poor areas during population peaks. Runways in use for 36 weeks or more tended to be clumped in good habitats. Voles arriving 1st in an uninhabited area built runways at random; a more stable pattern of runway distribution reflecting improved microhabitat develop later as the voles continued to exploit the habitat.