Runway systems and burrows are used by groups of voles rather than by individuals. Most of the activity of voles is confined to these runways and an exposed individual is seldom seen. A home range may include several runway systems, and the ranges of individuals overlap extensively. Both home ranges and patterns of runway systems change constantly. Runways seem to be primarily feeding trails, and are extended or abandoned as the voles change their feeding habits. Groups of adult voles using a system of runways seem to have no special relationship. Juveniles tend to stay near their mothers, but as they mature, they shift their ranges and are replaced by other individuals. Males wander more than females, and shift their ranges more often. No intolerance of other voles exists and, in laboratory cages, groups of voles lived together peaceably from the time they are placed together. Crowding does not seem to be harmful directly, therefore, and high densities will develop if food and cover resources permit. As a prey item, the prairie vole proved to be an important part of the biota of the Reservation. It was eaten frequently by almost all of the larger vertebrate predators on the Reservation and was, seemingly, the most important food item of the long-eared owl. The ability of the prairie vole to maintain high levels of population over relatively broad areas enhances its value as a prey species. LITERATURE CITED ALBERTSON, F. W. 1937. Ecology of a mixed prairie in west-central Kansas. Ecol. Monog., 7:481-547. BAILEY, V. 1902. Synopsis of the North American species of _Sigmodon_. Proc. Biol. Soc. Washington, 15:101-116. 1924. Breeding, feeding and other life habits of meadow mice. Jour. Agric. Res., 27:523-536. BAKER, J. R., and R. M. RANSOM. 1932a. Factors affecting the breeding of the field mouse (_Microtus agrestis_). Part I. Light. Proc. Roy. Soc. London, Series B, 110:313-322. 1932b. Factors affecting the breeding of the field mouse (_Microtus agrestis_). Part II. Temperature. Proc. Roy. Soc. London, Series B, 112:39-46. BLACK, T. D. 1937. Mammals of Kansas. Kansas State Board Agric., 13th Biennial Rep., 1935-36:116-217. BLAIR, W. F. 1939. Some observed effects of stream valley flooding on small mammal populations in eastern Oklahoma. Jour. Mamm., 20:304-306. 1940. Home ranges and populations of the meadow vole in southern Michigan. Jour. Wildlife Mgmt., 4:149-161. 1941. Techniques for the study of small mammal populations. Jour. Mamm., 22:148-157. 1948. Population density, life span and mortality rates of small mammals in the bluegrass meadow and bluegrass field associations of southern Michigan. Amer. Midland Nat., 40:395-419. BODENHEIMER, F. S., and F. SULMAN. 1946. The estrous cycle of _Microtus guentheri_ D. and A. and its ecological implications. Ecol., 27:255-256. BOLE, B. P., JR.