Winter is hard, and for wildlife in Colorado, it’s even harder. To survive, many species have developed adaptations over hundreds of thousands of years that allow them to weather the storms, including hibernation, thicker coats, food storage and migration. Some of the most interesting – and leas t understood – adaptations, though, are by the animals that change color seasonally, from their summer coats or plumage of brown or gray to snow white, something that helps them match the environment around them. An ermine looks out from a burrow under the roots of a spruce tree in Sax Zim Bog, Minnesota. (Photo courtesy of Dawn Wilson Photography) Only 21 species worldwide are known to do this, almost all in northern climates, according to an article in the journal Science. Four of them live in Colorado: snowshoe hares, white-tailed ptarmigan, short-tailed weasels and long-tailed weasels (the latter two are often referred to collectively as “ermine”). “It’s kind of a rare adaptation,” said Hannah Rumble, the Community Programs Director for the Walking Mountains Science Center, an Eagle County nonprofit that offers education and activities relating to nature and the environment. “So, it’s really uncommon.” The reasons why these animals change color are probably twofold, she explained. The primary purpose is camouflage, whether it’s to hide from predators or, in the case of the ermine, to disguise itself from its prey. But scientists believe that a secondary advantage is warmth; after the animals molt in the fall, their fur and feathers grow back without the melanin that creates color, meaning they are hollow. The air in the hollow areas provides more insulation. Why some cold-weather animals developed this adaptation and others didn’t is less well understood, but the change appears to be set off by the changing number of sunlight hours in the day as winter approaches (called a photoperiod), Rumble said. Bridget O’Rourke, a public information officer for the Colorado Parks Wildlife, pointed out that pikas use rock piles as a defense against predation, while black-tailed jackrabbits (relatives of the snowshoe hare) don’t change color because they live in the prairie or demi-desert environments where there is much less snow. One modern-day problem with this adaptation is that, as the climate warms, there is less snow in their habitats. So, while the animals still turn white, they may not be camouflaged. This situation, when the environment changes faster than a plant or animal can adapt to it, is called a phenotypic mismatch. “There is a lot of concern for alpine species,” Rumble said. So, where are you most likely to see Colorado’s color-shifting species? Here’s a general guide. Ermine Two kinds of weasels live in Colorado: the long-tailed weasel, which is fairly common on public lands throughout the state, and the smaller short-tailed weasel, which primarily makes its home in forested mountains. Both are brown in the summer and “a brilliant white” in the winter (aside from their black-tipped tails), according to Colorado Parks Wildlife (CPW). Colloquially grouped as ermine, weasels are sometimes seen from chairlifts by skiers at Vail and other resorts, as well as in Rocky Mountain National Park. But the best place to search for them in winter is from snowshoe or cross-country ski trails during the daytime when “they are more active, especially in the winter, to stay warm,” Rumble explained. At night, they go to their dens. Walking Mountains Science Center offers nature walks and backcountry hikes, both on snowshoes, at some of its four locations in Eagle County during the winter, including one at the top of the Eagle Bahn Gondola at Vail Mountain, and Rumble said she has seen both mammals on those walks. (The walks are free, but Vail charges $50 or more to ride the gondola.) On the nonprofit’s Sweetwater Campus, she once saw a long-tailed weasel carrying away a cottontail rabbit (which is smaller than a snowshoe hare) that it had hunted and killed. “It was amazing to witness because there are not a lot of predators that go after something larger than them. A rabbit is three to five times heavier than a weasel,” she said. Snowshoe hares Snowshoe hare tracks seen en route to Castle Creek Valley in Pitkin County. While it may not be easy to spot a snowshoe hare in the wild when they are camouflaged against the snow, their tracks are another matter. Almost comically obvious, the prints are made by their oversized, snowshoe-like hind feet, which help keep them buoyant in deep powder. “Compared to a cottontail rabbit, their legs are huge… a lot bigger than you might expect,” Rumble said. She suggested looking first for the tracks and then using a pair of binoculars to follow them with your eyes. Snowshoe hares can be found “across most of Colorado’s mountains, except for the southeastern Front Range (Pikes Peak area) and Sangre de Cristo mountains,” CPW said. Like ermine, the hares are more commonly seen during the day when they are staying active. Cross-country skiing and snowshoe trails are good places to look. White-tailed ptarmigan While ptarmigan are difficult enough to find during the summer, where they live above 9,500 feet in elevation and blend in so perfectly that they seem to melt into the rocky slopes, they’re even more elusive in the winter, Rumble said, for the simple reason that very little of Colorado’s high alpine tundra is accessible to people at that time. “Alpine species stay there year-round, but most of us can’t get that high in winter.” Related Articles Where Colorado’s gray wolves traveled in December, including the mountains west of metro Denver Some Boulder foothills open spaces closed until August to protect golden eagles Study finds manmade whitewater parks in Colorado may inhibit fish migration Colorado winter bird migration carries increased risk of avian flu exposure to wildlife, domestic animals Colorado wolf re-released in Grand County after crossing into New Mexico A member of the grouse family, ptarmigan are about the size of a pigeon, and they match the mottled color of rocks and scrub at high altitudes during the summer and the snow during the winter. Before winter, they can be seen (by sharp-eyed viewers with binoculars) near high-alpine lakes in the backcountry, as well as along Trail Ridge Road in Rocky Mountain National Park, above timberline on peaks like Mount Blue Sky and Pikes Peak (both of which can be accessed by vehicles) and from high passes like Loveland Pass. Trail Ridge Road and Mount Blue Sky are closed in the winter, but Loveland Pass and Pikes Peak are open. It takes a great deal of patience and luck to spot one, she pointed out, even when you are looking right at it. Subscribe to our weekly newsletter, The Adventurist, to get outdoors news sent straight to your inbox. ...read more read less