Hibernation & Spring Emergence

Columbian ground squirrels hibernate for a majority of the year. The typical length of hibernation lasts 8 months (Murie, 1984). In most cases, S. columbianus goes into hibernation in early August and emerges in mid to late April. Thus, the average active season is about 90-100 days long (Elliott 1991).  Unlike some species that will hibernate in groups to help reduce heat loss and maintain fat stores such as the alpine marmot, Columbian ground squirrels hibernate individually (Neuhaus 2000).  Thus, with such a long hibernation, a great demand is put on the squirrels to eat an appropriate diet, and gain enough mass and fat stores to survive the hibernation season.

Female squirrels are under a great deal of pressure to be prepared for hibernation if they are to successfully wean a litter of offspring. Adult females, on average, emerge from hibernation, a few weeks after their male counterparts; which on average is around the end of April (Harris, 1982). Females mate within the first few days of emerging from hibernation (Neuhaus 2000). If they are not successful initially, they will continue to mate for up to six more weeks (Elliott 1991). Depending on whether or not they are successful during mating will greatly affect the females’ activity during the active period.

Male squirrels are the first to emerge from their hibernacula, typically in mid-April. They will mate with the females within a few days of their emergence, and then return to their own activity shortly thereafter. After mating season, the males focus particularly on gaining fat stores for their upcoming hibernation. Adult males typically enter hibernation in the first week of August (Neuhaus 2000).

Females who successfully get pregnant will see their energy demands dramatically increase. As is the case with all pregnancies in the animal world, the pregnant female’s energy demands go up significantly while she is gestating. Upon giving birth, the female will need to care for her young for up to a month (Elliott 1991). After successfully weaning them, the female then needs to recover and replace any lost fat stores (Neuhaus 2000). Due to weight loss, and delayed weight gain and fat storage, females that successfully weaned a litter of offspring tend to enter hibernation more than a week later than their unsuccessful counterparts (Neuhaus 2000).

Unsuccessful females will not have the added stress of having to wean a litter of offspring, and will focus on putting on enough weight to survive their hibernation. Unsuccessful females typically enter hibernation earlier than their successful counterparts (Neuhaus 2000). It has been postulated that the unsuccessful females will enter into hibernation in late July because food is becoming scarcer, and the risk of predation is increasing (Neuhaus 2000).

Juveniles typically emerge from their nests in the first weeks of June (Harris 1982). This gives them a very limited amount of time to accumulate the necessary body fat reserves to survive their first hibernation. This type of time constraint impacts the rate of survival for juveniles (Harris 1982). Juveniles that are lighter than normal from lack of fat storage tend to have a significantly lower survival rate than those that are at the average, or above it (Murie 1984). Thus, juveniles are at a distinct disadvantage when compared to adults in preparing for hibernation.

This website was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2008.

Please send any comments, questions or suggestions regarding this website to Kevin Cook or Professor Verna Case.