What Causes a Ground Squirrel to Enter and to Exit Hibernation?
What causes a ground squirrel to enter and to exit hibernation? Several factors are known to affect the timing of these events. These include: the slope of the hibernaculum, the cover over the hibernaculum, temperature, and body condition. Learn how to determine when a ground squirrel is hibernating to protect itself from predators. And, as a bonus, you can even find out what factors affect the process!
The northern Idaho ground squirrel is a federally threatened species that hibernates for eight months of the year. Recent population declines are thought to be due to habitat loss. Years of fire suppression have allowed conifer trees to invade ground squirrel habitat, reducing their food sources. The ground squirrels’ diets are thought to have changed because of changes in canopy cover, making them more vulnerable to disease. A detailed baseline of these changes is needed to determine whether management treatments are effective.
A ground squirrel’s diet depends on the availability of certain seeds prior to hibernation. The availability of these seeds is reduced or non-existent in areas with heavy cattle grazing. Land managers can restore vegetation to attract ground squirrels. To encourage these animals, they should provide the necessary habitat for these species to survive. Alternatively, they can plant native trees and shrubs that are suitable for ground squirrels.
The 13-lined ground squirrel’s torpor patterns converge toward increasing time in torpor, minimizing time in euthermia between bouts of torpor, and readjusting biochemical status to optimize torpor. These patterns are similar in other species but have varying rates of torpor persistence. This variation can be attributed to the varying torpor depths of ground squirrels.
Laboratory-based studies of hibernation typically use standard housing. When animals were moved into a dark, cold room, they expressed torpor during fall. Age, body weight, and environmental cues did not predict torpor, and the occurrence of torpor was sporadic before the animals were exposed to cold. Regardless of the causes, the researchers believe this occurrence to be indicative of a ground squirrel’s adaptation to climate change.
In order to maintain their metabolic rate at low temperatures, small mammals must turn off their brains to survive. The brain of a squirrel is able to conserve most of its energy by lowering its metabolic rate by 90 percent. The reduced metabolic rate allows small mammals to survive without a significant amount of food, making the process of rewarming necessary for survival. Hence, the ground squirrel can continue to enter and exit hibernation year after year without any negative consequences.
The results of the present study suggest that the 13-lined ground squirrel experiences transcriptional induction in its skeletal muscle. This transcriptional change facilitates the induction of translation in muscle during interbout arousals. This study identifies the functional gene sets associated with these changes. Ground squirrels exhibit the same changes in gene expression throughout the course of hibernation as the torpid squirrel.
The polar bear and other mammals can survive for years without eating or drinking, but a ground squirrel’s body shuts down most of its functions during hibernation. Cells in its brain shrink and the connecting parts of its body begin to retract. The body gets 90 percent less blood flow, depriving the animal of oxygen. A human would die within minutes of being without oxygen for this long. A ground squirrel can enter and exit hibernation year after year.
When entering and exiting hibernation, ground squirrels make changes in their body temperature. During hibernation, ground squirrels usually prefer warm platforms and don’t show any sensitivity to cold temperatures. Their body temperature drops by almost half during the period, causing them to become torpid, but they can recover and resume activity after a day. However, ground squirrels should not be left unattended in their burrows for long.
Scientists have discovered that a specific chemical messenger in the brain is responsible for causing ground squirrels to enter and exit hibernation. These mice and a chemical messenger in the body are linked to reproductive success, and the chemicals may have an impact on other species. Researchers have been studying the ground squirrel for over two decades and found that these mice have a high sperm count. While the mechanism behind this is still unclear, the researchers believe that this chemical messenger is crucial in ground squirrel reproduction.
When a squirrel goes into hibernation, most of its bodily functions stop. They stop eating, peeing, drinking, and moving. The brain cells begin to retract from each other, depriving their bodies of oxygen. If this happened to a human, the person would die within minutes. Unlike humans, squirrels can continue to enter and exit hibernation year after year.
Seasonal changes in body mass
A ground squirrel’s torpor timing is influenced by changes in its yearly body mass and is governed by its age, photoperiod, and ambient temperature. Its seasonal movements are controlled by an endogenous circannual clock and are influenced by genetic and environmental variations. The arrows point to the first day of torpor.
In late winter, the ground squirrel starts salvaging nitrogen. The nitrogen in the urea pulls nutrients that help build muscles. This process is similar to the process astronauts undergo during space travel. Ground squirrels with depleted gut microbiomes didn’t break down urea and didn’t build muscles. The researchers also found that the ground squirrel’s metabolism is slowed during hibernation and its body mass stays relatively stable.
Jessica Watson is a PHD holder from the University of Washington. She studied behavior and interaction between squirrels and has presented her research in several wildlife conferences including TWS Annual Conference in Winnipeg.