Recently Leonard and I were walking along the road to Schonchin Springs near Little Medicine Lake (Siskiyou County CA). This golden-mantled ground squirrel (Citellus lateralis) sat watching us and practically begged to be photographed. He (?) was such a cute little fellow. No matter how many pictures of golden-mantled ground squirrels I have, I cannot resist such a cooperative model.
It is late in autumn and although the day was warm, before long the top of the Medicine Lake volcano will be covered in snow. This ground squirrel will need to begin its winter hibernation – and that got me thinking about hibernation.
Hibernation is a physiological state characterized by extreme reduction in bodily functions, such as metabolism and body temperature. Golden-mantled ground squirrels spend the winter in a state of hibernation, from approximately October to April or May, in underground burrows. This ground squirrel species adds layers of fat to prepare for hibernation and, unlike some other mammals that hibernate, does not set up large stores of food. Ground squirrels will cache a little food in their burrows for early spring when they first emerge from hibernation. However, food storage is not their survival strategy.
John A Phillips, writing in the “Canadian Journal of Zoology” (1979), described his research into the zeitgebers (I learned a new word meaning “external stimulus that resets the circadian or circannual clock of animals) for golden-mantled ground squirrel hibernation. These ground squirrels, even if the external conditions such as temperature, photoperiod or food availability signal that it is time to hibernate, cannot do so until their internal signals indicate there is a sufficient amount of fat on their bodies. Once enough body fat has accumulated will the ground squirrel begin its hibernation.
Pengelley and Fisher, writing in the same journal in 1961, found that golden-mantled ground squirrels wake briefly from hibernation about every 16 days. When they wake, the ground squirrels do not eat or drink nor do they defecate. Yet each time their sleep is interrupted the golden-mantled ground squirrels do urinate a little. These authors speculate that metabolic end products accumulate as the animals “sleep”, and once the concentration of the metabolites reaches a certain level provide the arousal stimulus so that the ground squirrels can urinate and remove the excess accumulation.
Golden-mantled ground squirrels are often used as subjects in hibernation experiments and many other scientific papers can be found describing their hibernation.
Golden-mantled ground squirrels have had several genus names over the years. Spermophilus and Callospermophilus, among others, are often seen in the literature as the genus names of golden-mantled ground squirrels.