Mammals in temperate and cold climates develop several physiological
and behavioural adaptations to increase heat production
or reduce heat loss during winter. However, it is still generally
observed that this is the time period when small mammals experience
their greatest mortality. Large population declines during
the winter have been noted in bank voles Clethrionomys glareolus
(Gipps et al. 1985; Pucek et al. 1993), short-tailed field voles
Microtus agrestis (Bradshaw 1992), tundra voles Microtus oeconomus
(Aars and Ims 2002) yellow-necked mice Apodemus flavicollis
(Pucek et al. 1993) and house mice Mus musculus (Berry et al. 1973).
Hence, traits that help survival in harsh winter conditions are of
special importance.
Burrowing and nest-building along with huddling are widespread
behavioural adaptation that may be responsible for
increased tolerance of low temperatures (Reichman and Smith
1990). Most burrows contain nest chambers lined with plant
material or fur. In general, their main role is to insulate animals
from ambient temperatures (Casey 1981) and may also serve as