JACKSON, Wyo. — The recent snowfall is critical for local weasels, whose camouflage defense in the winter is dependent on a white, snowy landscape.
While many animals in the area, from grizzly bears to ground squirrels, hibernate throughout the winter, weasels remain active in the Greater Yellowstone Ecosystem (GYE). According to John Stephenson, wildlife biologist for Grand Teton National Park (GTNP), the weasel’s transition from brown to white fur during the changing of seasons allows them to camouflage against the snow.
Stephenson tells Buckrail that studies indicate it takes about three weeks, roughly 17 to 21 days, for weasels to change color completely. He notes that this transition occurs as a response to shortened daylight and not a change in temperature. Hormones trigger weasel bodies to shed brown summer fur and regrow white fur, a special genetic adaptation for northern species.
“The snowshoe hare and the weasel are the only two mammals whose coats turn white in preparation for winter,” Stephenson says of the GYE.
Long- and short-tailed weasels do retain a black tip on their tail despite their coat transformation, another advantage against predators. Stephenson says the black tip draws a predator’s attention to the weasel’s tail, so that coyotes, owls, hawks, eagles, wolves, bears or foxes will miss the weasel’s body in an attack and allow it to escape.
Least weasels, which are the smallest carnivore in North America and classified as “very rare” in the state by the Wyoming Game and Fish Department, don’t have this black-tipped trait in either summer or winter.
Because the long- and short-tailed weasels, and hares, undergo their physiological change in response to the amount of daylight, they’re unable to adapt to years like this with historically low snowfall. Stephenson calls this a “camouflage mismatch,” where weasels become easier to spot by predators in a low-snow season when their stark white bodies are active against a brown landscape.
This year, though, the lack of snow has been accompanied by an increased vole population. Voles are small rodents that serve as a food source for weasels, and a larger “bumper crop” has helped offset some of the impact of the low snow.
“Having an increased population of voles might possibly mean that the weasels don’t have to travel as far to hunt for food, making them less vulnerable to predators,” Stephenson says.
The less time a weasel spends active across the landscape, the less available they are for predation.
But even hunting closer to home might not be enough to offset the impact of warmer temperatures and lower snow years. A study published in Scientific Reports by a team from the Polish Academy of Sciences confirms the hypothesis that, because of their genetic adaptation, weasels will likely be unable to adjust to climate change and increasing warmer weather conditions in winter.
“Climate change will strongly influence the mortality of the [weasel] due to prolonged camouflage mismatch, which will directly affect the abundance and geographical distribution of this subspecies,” the study says.
The study suggests that global warming will create strong selection pressures that may lead to a change in weasel molting patterns adapted to new environmental conditions.
