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We analyzed long-term (1958–2017) data on variations in the numbers of the bank vole (Myodes glareolus Schr.) in Eastern Fennoscandia, which is the northern periphery of the species distribution range. The species abundance under these conditions is relatively low compared to the optimum range (1.9 voles per 100 trap-days or 1.7 voles per 10 pitfall-days), but the species remains a leader in the total small mammal population, accounting for 50.5 % of catches by trap lines and for about 10 % of catches by pitfalls, where it is second in abundance only to common shrews. Pronounced long-term changes in abundance have been revealed, with a significant amplitude of fluctuations and an irregular alternation of short-term and quite high rises and prolonged and deep lows. Itwas found that in contrast to the optimum range, where a major regulator is intrapopulation compensatory mechanisms, this function in the northern periphery is performed byexternal, mainly weather-phenological factors, which in the North are extreme in scope and irregular in manifestation. It can be concluded from the analysis of the materials that among all the versatile factors determining the environmental situation of the year, the key spring onset, temperature and the amount of precipitation in late spring-early summer, and the yield of coniferous seeds (largely responsible for the foraging conditions in winter).

We review the long-standing (1958-2014) materials on the extending, number, reproduction, spatial and environmental structure of the grey red-backed vole (Myodes rufocanus Sund., 1846) population of the Eastern Fennoscandia, that represents the south-west area periphery. It was found that the species is spread in the northern part of the region only, and it is characterized by tiling and unsustainable and low population. The average long-term population of the species for the entire territory of Karelia was 0.005 specimens per 100 trap-days (0.04% of the total catch of small mammals) and 0.005 per 10 specimens of the groove-days (0.04 %), and for the Northern half of this territory — 0.08 specimens per 100 trap-days (1.9%). The overwintered females produce two or three litters and the new adult female voles bear up to two for a season of reproduction. The population comprises several seasonal generations of the young, differing in the rates of growth and development, and the scope of participation in breeding. Juveniles from early litters of the year are known for the rapid growth and development, and almost all of them breed in the year of birth. The young born in the second half of July or later mainly mature only after a winter. Litter size is from 2-3 up to 11-13 with an average of 6.5 fetal for a female, which is obviously lower than the values in the optimum area. The intensity and timing of breeding vary among years depending on the environmental conditions and the consolidated population abundances.