Temperatures of Hibernacula and Changes in Body Composition of Arctic Ground Squirrels over Winter

Soil temperatures near hibernacula of free-living arctic ground squirrels (Spermophilus parryii) were recorded over 3 winters (October-April 1993-1996) at Toolik Lake, Alaska. Means and minima of soil temperature at 20 burrows averaged -8.9 and -18.8°C, respectively. Soil temperatures were 5 months, which represented the duration of winter that hibernating arctic ground squirrels were actively thermogenic. Individual burrows did not differ significantly in mean soil temperature over 3 years, but significant differences in mean and minimum soil temperatures were observed among burrows. Sites of burrows with shrubby vegetation accumulated more snow and had significantly higher soil temperatures over winter than windswept sites in non-shrubby vegetation. Female ground squirrels hibernated in burrows that had significantly higher mean and minimum soil temperatures than burrows of males, and adults hibernated in burrows with significantly higher soil temperatures than burrows of juveniles. Although ground squirrels occupying colder burrows were predicted to lose more body mass during hibernation than those in warmer burrows, changes in body, fat, and lean masses over winter were not correlated with soil temperature for any sex or age. Relationships between change in body composition of hibernating arctic ground squirrels and temperatures of their hibernacula may be confounded by use of food caches, differing thermal conductance of nests, or differences in individual's energetics of hibernating not related to the gradient between body and soil temperatures.