As the days grow shorter and temperatures drop in Grand Teton National Park, many species begin their preparations for the harsh winter months ahead. Average winter temps in the park are in the 20’s during the day and close to zero at night, while average snowfall near the south entrance of the park is around 277” (according to a 2021 count by Buckrail). So how do bears, moose, and elk prepare to survive these cold and snowy conditions and emerge in the Spring? Through some remarkable and varying ways:
Bears: Fattening Up & Finding a Den
Bears are perhaps the most well-known winter preparers. As summer wanes, they spend their time gorging on a variety of foods, including berries, nuts, fish, and even carrion (animal carcasses), to build up a substantial layer of fat. This rapid consumption of calories is called hyperphagia. This stored energy will sustain them throughout their long hibernation period.
Fun Fact: Technically bears enter torpor (a “lighter sleep state”) rather than true hibernation. You can learn more from the National Forest Foundation.
Once they’ve accumulated enough fat, bears seek out suitable den sites (and sometimes re-use a den), in holes in the ground, in caves, hollow logs, or under fallen trees. They then curl up and enter a deep sleep, significantly slowing their metabolism to conserve energy. During hibernation (or torpor), heart rate and respiratory rate slows, while body temperature decreases by around 10 degrees F (from 98 degrees to 90 degrees). In contrast some of the rodent hibernators may lower their body temperature into the high 30 degrees.
Most bears enter their den by mid-November; although, some males remain active through December.
From the National Park Service:
Bears sometimes awaken and leave their dens during the winter, but they generally do not eat, drink, defecate, or urinate during hibernation. They live off a layer of fat built up prior to hibernation. The urea produced from fat metabolism (which is fatal at high levels) is broken down, and the resulting nitrogen is used by the bear to build protein that allows it to maintain muscle mass and organ tissues. Bears may lose 15–30% of their body weight but increase lean body mass during hibernation.
Moose: Adapting To the Cold
Although they are better adapted to survival in deep snow than other ungulates, moose also have to make preparations for winter. While they don’t hibernate, they do alter their behavior and diet to cope with the colder temperatures and reduced food availability. As the leaves fall and vegetation senesces, moose shift almost entirely to woody browse, such as twigs, bark, and buds that stick up above the snow. Like most Grand Teton mammals, moose can stock up on nutrients and rely on their fat storage in the coldest months.
To stay warm, moose grow a thick, winter coat that can withstand even the harshest conditions. “Their chocolate moose color helps them absorb every ray of sunshine and their nasal passages are even designed to heat air when it’s inhaled which warms their lungs.” (Buckrail) Their long legs also help them to wade through deep snow in search of food.
Some moose that summer in the park migrate in winter to lower elevations west and south of Yellowstone, and into Grand Teton National Park where willow shrub branches remain exposed above the snow. But many some moose move to higher elevations (as high as 8,500 feet) to winter in mature stands of subalpine fir and Douglas-fir.
Elk: Herding & Migration
With their mating season mostly behind them, elk in the Greater Yellowstone Ecosystem are moving into herds which will provide them with warmth and protection in the winter. Furthermore, the advantage of migrating in larger group provides extra sets of eyes, noses, and ears to detect predators while traveling and then a significant part of large groups on winter habitat is that winter habitat is very limited compared to tons and tons of summer habitat across the ecosystem. They also start migrating to lower elevations where food is more available. Unlike moose, who are able to reach twigs and woody plants all winter long, elk eat grasses and leaves. Elk are generalists. They will do a good bit browsing like moose, but elk will scrape down through the snow with their front hooves to get to grass below.
The National Elk Refuge shares that from October through December, deepening snow will push the elk down from the high elevation summer ranges to seek food and shelter at lower elevations in Jackson Hole.
“Roughly 8,000 elk will spend winter on the Refuge, in search of food, water, shelter, and space. During this time, visitors are able to see large numbers of elk gathering in open fields on the Refuge.”
For the chance to observe these animals (and more) and their incredible adaptations, book a trip with Wildlife Expeditions of Teton Science Schools. There really is no more beautiful backdrop to witness resilience in action than Grand Teton National Park.
As you are out recreating this fall, please be sure to give these animals distance as they are working hard to prepare for winter just like us.
Sources-
AllTrips, Grand Teton National Park
https://www.gtnpf.org/wildlife-whereabouts-hibernation-and-migration/
https://www.nps.gov/yell/learn/nature/bear.htm
https://www.nps.gov/yell/learn/nature/moose.htm
https://buckrail.com/explainer-how-do-moose-survive-the-winter/
