Many voles shifted their home range and a few did so abruptly. The large range of a female vole, described above and plotted in Fig. 6, indicated an abrupt shift from one home range to another. More common is a gradual shift as indicated by the range of the male shown in Fig. 7. Large parts of each monthly range of this vole overlapped the area used in other months but his center of activity shifted from month to month. [Illustration: FIG. 6. Map with cross-hatched areas showing the range of vole #20 (female). Dots show actual points of capture at permanent trap stations 30 feet apart. Vertical lines mark area in which vole was taken 17 times in October and November, 1950. Horizontal lines mark area in which vole was taken five times in March and April, 1951. This vole was not captured in December and January.] [Illustration: FIG. 7. Map showing range of vole #52 (male) with seeming shifts in its center of activity. Dots show actual points of capture at permanent trap stations 30 feet apart. Solid line encloses points of six captures in October and November, 1950. Broken line encloses points of five captures in February and March, 1951. Dotted line encloses points of nine captures in April, May and June, 1951.] That home ranges overlapped was demonstrated by frequent capture of two or more individuals together in the same trap. No territoriality has been reported in any species of _Microtus_, to my knowledge, and my voles showed no objection to sharing their range. Voles taken from the field into the laboratory lived together in pairs or larger groups without much friction. Definable systems of runways and home ranges were not coextensive. Runway systems tended to merge, as described later in this report, and relationships between them and home range were not apparent. Home ranges had no characteristic shape. LIFE HISTORY Reproduction