It could have something to do with snow, I read this
Once the snowcover has reached approximately 15cm it acts as an insulative blanket for the voles, mice, lemmings and shrews residing in this 'sub-nivian' (beneath the snow) environment.
On this site
http://www.sundogs.sk.ca/borealecology.htm
also see
http://www.brandchannel.com/features_webwatch.asp?ww_id=219Where it says of the brandname Nivea
Nivea" derives from the Latin word "nivius," meaning "snow-white