Structure, Location and Availability of Hibernacula of Columbian Ground Squirrels (Spermophilus columbianus)

Abstract

The hibernacula of 39 Columbian ground squirrels (Spermophilus columbianus) from populations at two elevations in southwestern Alberta were excavated and compared for differences in structure and location between age/sex classes within and between populations. Squirrels at high elevation (HE) used hibernacula that were larger and shallower than those at low elevation (LE). The size of the hibernaculum was proportional to the weight of the occupant except that adult males used hibernacula larger in proportion to their weight than did adult females or juveniles. Adults at LE used deeper hibernacula than did juveniles; the same trend was seen at HE, but some juveniles occupied large and deep hibernacula as well. Juveniles usually hibernated close to their mother and siblings, those that hibernated more than 20 m from relatives being less likely to survive the winter. The data suggest that juveniles use hibernacula within the natal burrow system when available and may not construct their own chambers. The structure of hibernacula in this study is similar to that described by Shaw (1926a) for the same species in Washington. Washington squirrels used hibernacula that were smaller but at similar depths to those observed for both populations in this study.