Utilizing data obtained at 3.5-d intervals for a population of Microtus ochrogaster, we compared efficacy of monthly and semi-monthly trapping of small mammal populations in respect to frequency of change of population density, survival and proportion adult females that were reproductively-active. For all three variables, both monthly and semi-monthly intervals closely tracked the 3.5-d intervals. The main exception was the monthly intervals under-recorded by 20% the peak density of one of four population fluctuations during the study; the semi-monthly intervals under-recorded the highest peak density by 4%. Overall, efficacy of a monthly monitoring protocol appeared adequate to describe the three demographic variables and differed little from that of a semi-monthly protocol. Consequently, the additional time and resources required for a semi-monthly trapping protocol do not appear warranted.