Winter breeding of the root vole, Microtus oeconomus, in 1972/1973 at Kilpisjärvi, Finnish Lapland

In January 1973, a parous female and at least four winter-born young root voles belonging to three age categories (age maxima 30, 40, and 50 days) were trapped at Kilpisjärvi Biological Station, Finnish Lapland. This is the first observation of winter breeding in the species. The main food plant of the root vole at Kilpisjärvi is Eriophorum angustifolium. The main winter food seems to be the succulent subterranean parts, chiefly first-year rhizomes. These nutrient-rich rhizomes usually produce a new sterile shoot the following spring, but in 1972, after an unusually long and warm summer, new shoots were formed in the autumn. It is suggested that the breeding of root voles that winter was due to the peculiar autumn food conditions of 1972.