In the mixed areas of grassland and clover that were described above, the cotton rat (_Sigmodon hispidus_), the deer mouse (_Peromyscus maniculatus_), and the little short-tailed shrew (_Cryptotis parva_) were commonly caught in the runways of the prairie vole. Less frequently trapped were the common mole (_Scalopus aquaticus_), the large short-tailed shrew (_Blarina brevicauda_), the Cooper lemming mouse (_Synaptomys cooperi_), the pine mouse (_Pitymys nemoralis_), and the harvest mouse (_Reithrodontomys megalotis_). In the dense growth of Japanese honeysuckle, the prairie vole shared runways with the white-footed mouse (_Peromyscus leucopus_), the large short-tailed shrew, and the pine mouse. NEST AND BURROWS The prairie vole makes a tortuous network of paths through the grass and honeycombs the topsoil with its tunnels. The underground passages lead to nests or to chambers where food is sometimes stored. The runways through the grass are 40 to 50 mm. wide, and usually lie slightly below the surface of the ground. By using the same path repeatedly, the voles create little ruts in which they run. The bottom of the runways are bare soil or are covered with only a thin layer of trampled grass. Cotton rats, on the other hand, apparently do not use their runs over long periods, for they are not well-beaten runways, but are made merely by parting the grass and not by trampling it down or cutting it off. Voles were trapped in runways of the cotton rats, but no cotton rat was caught in a typical runway of a vole. The burrows of the prairie vole are 40 to 50 mm. in diameter, and the shallowest part is usually 50 to 100 mm. below the surface of the ground. Burrows leading to nests or food chambers may descend deeper than the others. Some prairie voles were trapped in tunnels of the common mole (_Scalopus aquaticus_). The voles make their own burrows, and are especially active at this task when a hard rain has loosened the previously hard, dry soil. The rain in the first two weeks of October, 1945, made the soil much more friable than it had been at the beginning of the month, and the voles took advantage of the favorable opportunity to construct many new burrows. In October, particles of soil were packed beneath the toenails of many specimens. In this time fifteen nests were found. They were 6 to 18 inches below the surface of the ground, and two tunnels led from each nest to the surface runway. The nest cavities were spheroidal, and measured 150 to 200 mm. horizontally, and 80 to 100 mm. vertically. The floors were slightly concave and were covered with loose dirt and a mixture of dried grass and one or two leaves. The remainder of the cavity was filled with the dry grass of which the nest was composed. Criddle (1926) stated that at Treesbank, Manitoba, this vole makes its nests in the burrow systems of the pocket gopher (_Thomomys talpoides_); and Kennicott (1857:98) found nests of the prairie vole in old ant hills.