Tag: Hibernation

Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.

While I’ve mentioned how certain animals are well adapted to being active in winter, some choose to save their energy and sleep the winter away. Maintaining a constant body temperature in winter, when air temperature is relatively low, can require consuming great amounts of energy stores, such as fat. This can be especially difficult during a time of year when food is scarce.

Smaller animals especially struggle with heat loss because, relative to their body size, they have much more surface area from which they can lose heat. Compare a mouse to a bear- the bear will retain heat much better because it has a larger body compared to the area of its outer surface. Not to mention, a bear’s fur is much thicker than that of a mouse!

For certain animals, it makes sense to lower body temperature while being inactive so that they can conserve as much energy stores as possible. This can happen in several different ways. Sleeping for part of a daily cycle can conserve a little energy since body temperatures drop slightly during sleep. If air temperatures are particularly low and food is scarce, some animals will enter torpor, allowing their body temperatures to drop closer to air temperatures in order to save even more energy. An animal can be in torpor for just a night, or perhaps a few days. If it is able to store enough energy reserves and can survive a decrease in body temperature for longer periods, some mammals may enter deep torpor and hibernate for several weeks or months in the winter. During this time, the rate of energy consumption is just a small fraction of what it might normally be when the animal is active.

Body size and energy stores influence just how inactive an animal can be in winter. Some of our smallest mammals, such as shrews and mice, lose heat so readily and can store so little fat that they cannot afford to hibernate. They must always find food in order to survive. Even though some small birds, like the black-capped chickadee, may enter torpor, they use almost all of their energy stores each night. If they fail to replenish their fat reserves each day, they might not survive.

The true hibernators are the mid-sized mammals. While ground squirrels, jumping mice, and bats may hibernate for much of the winter, they occasionally wake up for a day or two of activity. Even larger mammals, including raccoons, skunks, and bears, don’t actually need to hibernate. Their body temperature drops just a little, and they are able to survive on their stored fat simply by sleeping.

So, while I sometimes envy the true hibernators on some of those cold winter days in Utah, I’m still thankful that I can adapt to winter and enjoy our great outdoors year-round.

For Wild About Utah, I’m Mark Larese-Casanova.

Credits:

Images: Courtesy US FWS and Stephen Peterson, Bridgerland Audubon Society

Text:     Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
Additional Reading:

Heinrich, B. (2009). Winter world: The ingenuity of animal survival. Harper Perennial.

Eckert, R., D. Randall, and G. Augustine. Animal physiology: Mechanisms and adaptations. W. H. Freeman and Company.

As Utah’s blanket of snow grows thicker and cold temperatures set in, some of our furred friends quietly retire for the winter. Gone are the marmots that basked on sunny slopes, the bears that browsed in the forests, and the bats that winged silently overhead.

Animals have a number of different strategies to help them survive in winter. Some, such as hummingbirds, migrate to a more temperate climate. Some have special adaptations that allow them to withstand cold temperatures such as mink, which grow wonderfully thick winter coats. And some, such as marmots, bears, and bats, simply find a cozy place to sleep away the winter.

The general term for this period of inactivity is “dormancy,” which includes more specific terms such as “hibernation” and “torpor.” During this time, an animal’s heart rate, breathing rate and metabolism slows down considerably. Contrary to popular belief, most of the mammals that hole up for the winter do not actually hibernate. The term hibernation applies to only a small portion of our Utah mammals – a few species of bats and some rodents like the marmot. True hibernation means that an animal’s metabolism turns off to the point that its body temperature nearly matches that of the environment around it. And in winter, this means that body temperatures can drop to nearly freezing. Hibernating animals become unresponsive to environmental stimuli such as loud noises and being touched, and it takes hours and lots of energy for them to finally awaken.

In contrast, consider the bear, which does not technically hibernate, but instead enters a state called torpor or ‘winter lethargy’. A bear’s body temperature does decrease during this time but never approaches freezing. Bears also remain semi-active occasionally moving about in their dens, or even giving birth and tending to their newborns. Other animals that become largely inactive in winter but do not fully hibernate include skunks, raccoons, and opossums. These animals can respond very well to environmental stimuli and can resume their full abilities in less than a minute if disturbed – something to keep in mind in case you stumble across a bear’s den this winter.

Thanks to the Rocky Mountain Power Foundation for supporting research and development of this Wild About Utah topic. For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

Credits:

Photos: Courtesy Utah Division of Wildlife Resources and Copyright Lynn Chamberlain, photographer

Text: Andrea Liberatore, Stokes Nature Center

Additional Reading:

Encyclopædia Britannica. 2010. “Dormancy.” Encyclopædia Britannica Online. https://www.britannica.com/EBchecked/topic/169514/dormancy (Accessed Nov. 20, 2010)

New Jersey Division of Fish and Wildlife. 2010. Black Bear Biology and Behavior. https://www.state.nj.us/dep/fgw/bearfacts_biology.htm (Accessed Nov. 20, 2010)