Winter Wildlife AdaptationsMigrate, Hibernate or Adapt
By Hannah Holcomb | Naturalist & Snowshoe Guide
Winters in Jackson Hole can be among the longest and coldest of anywhere in the United States.
Temperatures can dip as low as -50F and snowfall in the mountains often exceeds 400 inches. Unlike humans, local wildlife doesn’t have the luxury of heated homes and technical warm layers to stay comfortable. Animals must migrate, hibernate, or adapt in order to cope with these harsh conditions.
Some of Jackson Hole’s wildlife leaves the area for the winter. For example, sandhill cranes spend summers, about April to September, in Jackson Hole and marshy meadows of the Yellowstone region where they feed on insects, amphibians, and rodents and raise their young. In the fall, Sandhill Crane families seek staging habitat, a place with ample food and predator protection to prepare for migration. Teton Valley hosts about 2,000 birds, the largest population of staging cranes in the Greater Yellowstone Ecosystem. When they leave the area in the fall, the birds congregate in flocks of about 200 individuals, traveling together to reach the southern United States.
Ungulates like elk, moose, and deer, don’t leave the Greater Yellowstone Ecosystem, but migrate to lower elevations to avoid the mountains’ deep snowpack and colder temperatures. Elk spend summers around 10,000 feet, but when fall snowstorms bury the foods they graze on, they’ll begin migrating to lower elevations where food is more abundant. Elk herds journey 30-90 miles to their winter habitat, with the large, strong bulls leading the herd and packing down the snow.
Animals hibernate through the winter to conserve energy during a period of bad weather and sparse food. Though we often think of hibernation as a long nap, hibernators aren’t just sleeping. They lower their heart rate and metabolism significantly. Bears might be the most famous hibernators, but chipmunks, Uinta ground squirrels, and bats all undergo some state of dormancy during winter months.
Bears hibernate for about 5 months, though the length of hibernation varies by species and den location. During hibernation, a bear’s heart rate gets as low as 8 beats per minute, they take one breath every 45 seconds and their body temperature falls by about 12 degrees. While hibernating, bears often don’t eat, drink, urinate, or defecate. Instead, they burn the body fat they packed on in the fall during hyperphagia, a period of excessive eating. Bears aren’t asleep during the entire hibernation period. They often move around and mothers wake up to give birth to cubs. When bears emerge from their den in the spring they’re lethargic and look for easy food sources like the carcass of an animal that died during the winter.
While we refer to bears as hibernators in the context of this article, bears are actually not true hibernators. What bears undergo is a similar process called torpor which is essentially a less extreme version of hibernation. For example; while a true hibernator like a ground squirrel will hibernate continuously through the winter, bears will often wake in their dens prior to spring, to feed, give birth, or perhaps just to get comfortable!
Jackson Hole wildlife that don’t migrate or hibernate have special adaptations that allow them to survive the winter. Snowshoe hares frequent Yellowstone and the western slope of the Teton Range. Hares’ coats change color from brown in the summer to white in the winter, which keeps them camouflaged from predators, and they have large feet relative to their body size to help them stay on top of the snow. Further, because nutritious grasses are buried by snow through the winter, snowshoe hares eat woody stems, conifer needles, and sometimes bark. The hare’s digestive system can process this woody material and they excrete a pellet to eat. Though we might squirm at ingesting feces, passing food through their digestive tract a second time helps to glean more nutrients and protein.
Pikas also adapt their behavior to survive in the winter. During the summer, in a process called “haying,” pika leave their dens to cut vegetation with their teeth. They bring the vegetation back to a “haystack” and save it to eat during winter. They’ll pick poisonous plants that they can’t eat immediately, but adding them to their haystack helps prevent mold from growing on the vegetation, and once broken down, the plants aren’t toxic to eat.
Hannah Holcomb is a former Americorps Intern of Teton Science Schools and the Jackson Hole Wildlife Foundation. She helps guide naturalist showshoe tours in Driggs, Idaho for Grand Targhee Resort.