Wildlife In Winter & Climate Change

Wildlife In Winter & Climate Change: American Dipper Peter Hart, Photographer Photo credit: PEHart via Visual hunt / CC BY-SA
American Dipper
Peter Hart, Photographer
Photo credit: PEHart via Visual hunt / CC BY-SA
Last Saturday 3 intrepid young families joined us for a morning with the Stokes Nature Center slipping and sliding along a canyon trail to discover animal and plant adaptations to survive the winter. We marveled at the American dipper as it enjoyed plunging in icy water hoping to capture its prey. The dipper remains dry due to a super-sized uropygial gland used for waterproofing its feathers as it preens combined with a thick layer of super isolative fur like feathers. Its temperature actually drops in extreme cold reducing radiated heat loss.

Water reptiles and amphibians were in deep sleep in their mud cocoons. They manage winter through slowing metabolic processes which greatly reduces their need for oxygen, nutrition and waste elimination. What little oxygen needed can be absorbed through their skin without breathing.

Animals such as bears can go into an alternate, light hibernation state called a torpor. Torpor is like hibernation, but in this condition, the bear can be awakened easily. I was reminded of this fact from a friend tagging bear cubs in Book Cliffs of eastern Utah. She would enter the bear din very gingerly trying not to awaken a grumpy mom! Ground squirrels are also among animals who torpor, however they shift between hibernation, torpor, and being awake.

The common poorwill, an uncommon bird in Utah Mountains, is the only bird that goes into true hibernation. It hibernates during extreme temperatures — when it is either too hot or too cold — and at times of food scarcity. The common poorwill can even hibernate while they are incubating eggs, proving to be not only a true survivor, but also a riveting multitasking animal.

Grouse Snow Angel Exiting Subnivean Cave Courtesy US FWS & Wikimedia, Tamarac Refuge, MN
Grouse Snow Angel Exiting Subnivean Cave
Courtesy US FWS & Wikimedia, Tamarac Refuge, MN
Snow is an excellent insulator where many of our more active animals spend most of their winters in subnivean (beneath the snow) environments. Mice, voles, and shrews retreat here for protection from cold temperatures, bitter winds, and hungry predators. Food is right at hand: grass, leaves, bark, seeds, and insects are free and unfrozen. These tiny mammals create long tunnel systems complete with air shafts to the surface above. Perhaps you’ve seen the pocket gopher tunnels revealed as the snow retreats- a snaking ridge of soil creating some interesting, artistic patterns.

Short-tailed weasels, also known in winter as ermine, have a long, slender body shape that allows them to invade subnivean tunnels to prey upon smaller mammals.Photographer: Steven HintCourtesy WikimediaLicensed under Cc-by-sa-3.0
Short-tailed weasels, also known in winter as ermine, have a long, slender body shape that allows them to invade subnivean tunnels to prey upon smaller mammals.
Photographer: Steven Hint
Courtesy Wikimedia
Licensed under Cc-by-sa-3.0
It takes only six inches of snow for mice, voles, and shrews to have a sturdy roof over their heads and roomy living quarters below. Add another two inches and the subnivean zone remains within a degree or two of 32°F, regardless of the temperature and weather conditions in the outside world.

Living under the snow is not without risk. Owls can hear mice and voles running around underground from thirty yards away. With balled-up feet, they crash through the top crust and all the layers of snow to grab their prey. Foxes and coyotes detect by scent. With an acrobatic pounce, these predators will dive right in for their meal. Suffocation is a hazard for those left behind in a collapsed tunnel.

So what happens to these little critters in a low snow-no snow winter becoming more common in a changing climate? I’m guessing a much higher rate of mortality which may not bode well for those bigger critters- hawks, owls, fox, coyote, etc., who munch them.

This is Jack Greene and I’m Wild about Utah!!


Images: Peter Hart, Photographer, Photo credit: PEHart via Visual hunt / CC BY-SA
Courtesy Wikimedia Steve Hint, Photographer, Licensed under Cc-by-sa-3.0
Courtesy US FWS Digital Library
Text:     Jack Greene

Additional Reading:

Larese-Casanova, Mark, The Shape of Wildlife in Winter, Wild About Utah, Jan 26,2012, https://wildaboututah.org/the-shape-of-wildlife-in-winter/

Mackay, Barbara, The Subnivean Zone: Shelter in the Snow, Northern Woodlands, Dec 29, 2014, https://wildaboututah.org/the-shape-of-wildlife-in-winter/

Peering into the secret world of life beneath winter snows, National Science Foundation,

Snow Tracks, National Wildlife Refuge System, https://www.fws.gov/refuges/features/SnowTracks.html

Glacier National Park:
Winter Ecology Teacher’s Guide https://www.nps.gov/glac/learn/education/upload/Winter%20Ecology%20Teacher%20Guide%202010.pdf

Subnivean Samba: https://www.nps.gov/glac/learn/education/subnivean-samba.htm

4-6, Unit Five, Activity 1: “Snug in the Snow” https://www.nps.gov/glac/learn/education/4-6-unit-five-activity-1-snug-in-the-snow.htm

Winter Ecology, Preparing for your Trip, 3rd-5th Grade Field Trip, https://www.nps.gov/glac/learn/education/upload/3rd-5th-winter-field-trip_GNP.pdf

Rocky Mountain National Park:
Winter Ecology Teacher Guide, https://www.nps.gov/romo/learn/education/upload/Winter-Ecology-Teacher-Guide-for-web.pdf

Craters of the Moon National Monument & Preserve:
Lesson Plan, Prepare for Cold Air!, https://www.nps.gov/teachers/classrooms/prepare-for-cold-air.htm

Helping you share Utah’s natural world!, Utah Nature Explorers, Utah Master Naturalist Program, https://extension.usu.edu/utahnatureexplorers/index

Porpora, Alex, Butts, Neicca, Larese-Casanova, Mark, An Introduction to Nature Journals, Utah Master Naturalist Program, https://extension.usu.edu/utahnatureexplorers/pdflessonplans/generalnature/naturejournaling/Nature%20Journaling.pdf

Sleeping the Winter Away

Click to view larger image of male Black Bear, Photo Courtesy US FWS, Mike Bender, Photographer
This Black Bear will retain heat
much better during hibernation
because it has a larger body
compared to the area of its outer
surface and it has thicker fur
compared to smaller animals
Photo Courtesy US FWS
Mike Bender, Photographer

Click to view the Mountain Chickadee, courtesy and copyright Stephen Peterson
Mountain Chickadee
Even though some small birds, like chickadees, may enter torpor,
they use almost all of their
energy stores each night.
Courtesy & Copyright
Photographer: Stephen Peterson

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.


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.



Sleeping Winter Away

Yellow-bellied marmots,
one of Utah’s true hibernators
Photo courtesy Utah Division of Wildlife Resources,
Copyright Lynn Chamberlain

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.

A black bear,
which survives winter
in a state called torpor
Photo courtesy Utah Division of Wildlife Resources,
Copyright Lynn Chamberlain

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.


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)