To the population ecology of the birch mouse (Sicista betulina Pall.) at the northern limit of the range. Report I. Abundance, biotopic disposal, daily activity, nutrition

The results of long-term stationary and field research (1958-2019) of the population ecology of the birch mouse related to its habitat on the northern periphery of the range are summarized. In the study region (Eastern Fennoscandia), this species is distributed only in its southern half, and is not numerous in most places. In the collections of small mammals, it accounts for 5.9 % (the sixth largest number). The average long-term accounting index was 0.02 ind. per 100 trap-days (the share in catches 0.07 %) and 0.72 per 10 ditch-days (1.3 %). It lives in different biotopes, but tends to deciduous stands, adhering to sparse areas with a rich grass layer and a sufficient number of shelters in the form of old stumps, piles of dead wood, fallen trunks, etc. Winter hibernation lasts from late September to early May. The activity is polyphasic, with a shift to daylight, typical for the northern limits of the range. The basis of the food of the birch mouse is forest insects (on average 94.3 % of the cases), arachnids (65.2 %) are in second place, and plant food (31.2 %) is in third place.