Mustela erminea
Fast, fearless, and remarkably adaptable, the ermine, also known as the short-tailed weasel or stoat, is one of the most captivating small mammals in the Greater Yellowstone Ecosystem. Despite its small size, this sleek predator plays an outsized role in maintaining balance among the valley’s rodents and small birds.
Often glimpsed darting across snowy meadows or vanishing between rocks along the Snake River, the ermine embodies the wild, unpredictable spirit of the Tetons. For visitors on a Jackson Hole Wildlife Safari, spotting one is a rare treat—a flash of motion that reveals a world of quiet drama just beneath the surface of the snow.
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About
A Predator in Miniature Size
Ermines belong to the weasel family, a group of agile carnivores that includes mink, martens, and otters. Measuring just 7–13 inches long and weighing only a few ounces, ermines are built for life on the hunt. Their long, slender bodies allow them to slip into burrows and chase down prey in spaces most predators couldn’t reach.
They primarily feed on small mammals like voles and mice but will also take birds, insects, and even young rabbits when available. Constantly on the move and with a metabolism that demands frequent meals, ermines are efficient hunters that help keep rodent populations in check—playing an important role in the health of the local ecosystem.
A Master of Disguise
One of the ermine’s most remarkable traits is its seasonal transformation. In summer, its coat is reddish-brown with a pale underbelly, blending seamlessly with the forest floor and sagebrush-covered hillsides. But as the snow arrives, the ermine turns pure white, except for the black tip on its tail, a distinguishing mark that remains year-round.
This winter camouflage helps it evade predators like owls and foxes while allowing it to stalk prey undetected. The white winter form is what most visitors associate with the name “ermine.” This transformation is triggered not by temperature but by the length of daylight, a finely tuned adaptation to life in the mountains.
Life in the Jackson Hole Valley
Ermines are found throughout the Greater Yellowstone Ecosystem, from the meadows and cottonwood forests of Jackson Hole to the alpine slopes of the Tetons. They favor areas with a mix of vegetation and cover—fallen logs, rock piles, and riverbanks that offer both shelter and hunting opportunities.
In winter, ermines travel through a hidden network of subnivean tunnels—the open spaces beneath the snow created by small mammals. There, they continue their endless pursuit of prey, unseen by most park visitors. For guides and naturalists, spotting the tiny tracks of an ermine crossing the snow is a clue to the intricate web of life operating just below the surface.
Behavior and Adaptations
Despite their small stature, ermines are formidable. They are active year-round, never hibernating, and use abandoned rodent burrows for nesting and food storage. Their dens are lined with fur and grass for warmth, and they often cache extra prey to survive harsh conditions.
They are primarily crepuscular—most active at dawn and dusk—but may be seen at any hour, particularly in the low light of winter. Visitors lucky enough to catch a glimpse of an ermine standing upright on its hind legs, surveying the snowy landscape, will never forget the sight.
Best Times to See Ermine in Jackson Hole
Ermines are present year-round in Grand Teton National Park and the surrounding valley, but they are easiest to spot in winter, when their white coats stand out against the snow. Look for them near the Snake River, Antelope Flats, or forested areas around Mormon Row and Moose Junction.
During spring and summer, their brown coats help them blend into the landscape, making sightings rarer. However, with patience, and a keen-eyed guide, these agile predators occasionally reveal themselves along shaded streambanks or meadows.
FAQs
What is an ermine, and how is it different from a weasel?
An ermine is a short-tailed weasel. The term “ermine” refers to its white winter phase, while “weasel” is used for the same animal in its brown summer coat.
Where can I see ermines in Jackson Hole?
Ermines are found throughout the region, particularly near the Snake River and forest edges in Grand Teton National Park. Winter safaris often offer the best chance of spotting one.
Why does an ermine change color?
Ermines molt twice a year. The change from brown to white is triggered by shorter daylight hours, allowing them to blend with snow and avoid predators.
What do ermines eat?
They are carnivores that hunt small mammals, birds, and insects. Their high metabolism means they must eat frequently, often several times a day.
Are ermines common in the Tetons?
Yes, but they are elusive. Their small size and quick movements make them easy to overlook. Winter offers the best visibility when their white fur contrasts with snow.
Further Reading
Jackson Hole Wildlife
Jul 12, 2024
Thanks to the range of different habitats that scatter across the sprawling valley, there is a plethora of wildlife to be found. The forests house woodland creatures like foxes, mule deer, black bears, pine martens, and elk.
A Month by Month Guide to Grand Teton National Park
Jun 21, 2024
Each and every month has something special to note, meaning that no matter what season you visit will be a special time. Use this guide to determine what time of year aligns best with what your interests and goals are.