Richardson's ground squirrels hibernate alone in a special chamber called a hibernaculum. The hibernaculum chamber is intially constructed as an excavation off the main burrow system, but that connection is plugged off with soil when the animal enters hibernation. The hibernaculum system is a closed system consisting of a hibernaculum chamber, a drain tunnel to carry away moisture, and an exit tunnel that reaches almost to the surface. In spring, the animal emerges above ground by connecting the exit tunnel to the surface.
The hibernaculum is a grass-filled chamber in which the ground squirrel curls into a ball with its nose tucked between the hind legs and enters a state of torpor. (see Burrow Systems and Hibernacula) Adults hibernate for 7-9 months, juvenile females for 6-7 months, and juvenile males for 4-5 months. (see Annual Activity Cycle)
During torpor, a ground squirrel's body temperature drops to that of the surrounding soil. By late winter, body temperature may fall as low at 0°C during torpor bouts. Respiration slows, as does the heartbeat. Torpor is not continuous, as ground squirrels arouse periodically throughout hibernation. (see Hibernation Physiology)
Male ground squirrels tend to cache
food, such as grass seeds, which they carry to the hibernaculum in cheek
pouches. Seeds are cached under the grass bedding in the hibernaculum
chamber. This food store is used at the end of the hibernation season
when male ground squirrels remain in their burrows at normal body temperature
for several days to permit testicular recrudescence. (see Reproductive
Physiology) Males rarely exhaust food caches before emergence,
but they do not return to the hibernaculum to eat remaining seeds after
they have emerged.