This ready acceptance on short acquaintance of strange voles into the family or social group suggests that lack of territoriality extends even to the use of the nest burrows, and that groups of voles may share the same nest, huddling together and deriving mutual benefit from the association, such as warmth in cold weather. Schmidt (1931: 113), studying this vole in Clark County, Wisconsin, noted its colonial habits. He found isolated small mounds that were riddled with burrows, and little sign in intervening areas. At one mound he trapped two adult males, one adult female, and two young; at another mound, two adult males, two adult females, and four young were trapped. My individuals that were released from live-traps were on many occasions trailed by means of a stiff wire collar with spool of thread attached, to holes that presumably were their home burrows. Data obtained in this manner indicated that ordinarily several or many individuals use the same burrow system. The histories of individual voles on the study area at the Reservation indicate shift of home base from time to time, usually for short distances within the area already included in the home range, but occasionally to new areas relatively remote from the original home range. Severe fighting between adult prairie voles occurs at times. Occasionally, sharp squeaks accompanied by brisk rustling in the grass suggesting pursuit or conflict, are heard in their habitat. An unusually large adult male, long resident on a study area, suddenly lost weight and deteriorated in condition over a period of several days, then was found dead in a nest-box attached to a trap. Dissection revealed numerous punctures in the skin and flesh of the neck and back, probably made by the incisors of another vole. Extensive hemorrhage and swelling had occurred, and obviously these injuries were the cause of death. Although it was not feasible to study the home life of the voles underground, clues were gained from those uncovered in runways and nests beneath large boards and strips of tarpaper, previously distributed for this purpose. Nests were constructed by the voles beneath several such pieces of tarpaper and runways appeared beneath all the pieces that were placed in habitat favorable to the voles. In summer, however, the high daytime temperatures beneath these shelters made them uninhabitable to the voles, and they were used mainly in spring. From February 15 to May 1, 1953, 14 voles were caught 19 times beneath five of the tarpaper strips, and many other voles that were seen beneath them escaped. Upon turning one of the strips I often discovered voles in close proximity. Sometimes two or more darted from the same nest. The disturbance of repeatedly raising the strips and exposing the voles' shelters soon caused them to desert the sites; consequently the information obtained by this means was limited. SEXUAL BEHAVIOR