Population ecology of Sorex shrews in North-East Siberia

The ecology of Sorex shrews was studied in two localities of North-East Siberia with continental and maritime climates (Kolyma river and the coast of the Sea of Okhotsk). During 1972—1988, 4608 shrews of 8 species were caught. Sorex caecutiens was the dominant species, accounting for 79% of all individuals. The dominant and sub-dominant species tended to be spatially segregated. An important feature of food selection is frequent consumption of larch seeds (when the harvest is abundant). The litter size of S. caecutiens was 8.6±0.3 in the Kolyma river basin and 7.5±0.3 on the north coast of the Sea of Okhotsk. Females may give birth to up to four litters during the breeding season. In the years of low spring density, young females of the first litters take part in reproduction, greatly contributing to the rapid recovery of populations after low density. Winter mortality was generally higher in the continental than in the maritime region, but between-year variation in winter mortality mostly depends on food availability.