Abstract
Reports on the diel activity of Microtus are contradictory. In the present study, specimens of the vole, Microtus agrestis, were placed in glass cages, and automatic records were made of their movements. Two series of experiments were made, extending almost without interruption from January 16th to June 28th, 1956 and continuing later in 1956 and in 1957. The diel activity reversed from winter to summer. In winter the peak of activity was the afternoon and the period of least activity was in the early morning. In summer the peak was early morning and the least activity was in the afternoon. In spring and fall there was a transitional condition, with two peaks of activity each day.