The Effect of Abiotic Factors on the Overwintering Success in the Meadow Vole, Microtus Pennsylvanicus: Winter Redefined^*

* A version of this paper was presented at the Circumpolar Ecosystems in Winter Symposium, 16-21 February 1990, Churchill, Manitoba, Canada.

Abstract

Meadow vole mortality, nest construction, nest temperature, and environmental conditions were studied prior to and during the season of permanent snow at Sudbury, Ontario. Prior to snow the animals burrowed into the soil, and mortality was high owing to heavy rains followed by subfreezing temperatures. Grass nests were built beneath the snow with vole mortality being high under conditions of shallow or icy snow and saturation of nests during the thaw period.

Nest temperatures prior to the thaw varied on a diel basis between 6 and 19°C with ambient subnivean temperature at 0°C. Barely detectable penetration of shortwave solar radiation was observed under a 60-cm thickness of winter snow, but increased rapidly during the thaw period owing to freeze-thaw metamorphism.

The results support the redefinition of winter into four distinct periods, each with its own characteristic environmental conditions, namely, Pre-Nival, Nival, Thaw, and Post-Nival.