The winter of 2024 will be remembered as one of the driest winters on record for Montana. According to the Natural Resource Conservation Service (NRCS), the average statewide snow water equivalent (a measure of how much water is in our snowpack) was only about an inch above the 30-year-average record low in March. In the Mission Mountains of the upper Swan River watershed, the snow water equivalent was 36% below average. These conditions aren't a complete surprise, as forecasters predicted that El Niño climate patterns would impact our winter weather. El Niño is a term used to describe the weakening of trade winds that normally move warm air across the Pacific Ocean. Without those powerful trade winds, the warm air moves east, leading to warmer and drier weather across the northern U.S and Canada. While El Niño is a natural, temporary phenomenon, climate change has increased the frequency of these weather patterns.
The Montana Climate Assessment (MCA) found that between 1950 and 2015 winter temperatures increased by 3.9°F (2.2°C) and winter precipitation decreased by 0.9 inches (2.3 cm), partially due to an increase in El Niño events. Looking ahead, the authors of the MCA predict that "the state of Montana is projected to continue to warm in all geographic locations, seasons, and under all emission scenarios throughout the 21st century."
As I look out across the bare forest floor, I can't help but wonder, how does this declining snowpack impact our winter-adapted wildlife? This question is largely unanswered for snow-dependent species such as Canada lynx and wolverines, but researchers can shed light on one specific adaptation for living in snow environments: the ability to turn white in the winter.
Montana is home to six species that molt seasonally to match their environment: white-tailed ptarmigan, white-tailed jack rabbits, snowshoe hares, and long-tailed, short-tailed, and least weasels. (Fun fact: wolverine kits are born white, but their coats start to darken at six weeks.) In the Swan watershed, snowshoe hare and the three weasel species are the most prominent. You've likely encountered the tracks of snowshoe hares, aptly named for their enormous hind feet that enable them to easily bound on top of deep snow. Even though they are abundant throughout western Montana, their excellent camouflage makes them difficult to see unless they are moving.
This year, however, you may have observed a white hare glowing like a neon sign in a dark room against the brown, snowless ground. We often refer to them as the "Snickers bars of the forest," because of all the other animals that prey upon them. To avoid all of these predators, snowshoe hares freeze when they encounter a possible threat and rely on their camouflage to hide, rather than retreat to a burrow like most other lagomorph (rabbit and hare) species. The shift of their fur color from brown to white is linked to the photoperiod, or change in daylight. As the climate and snowpack changes, but the photoperiod remains the same, snowshoe hares and other animals that seasonally change color are stuck in a "phenological mismatch." This leaves researchers asking, can the snowshoe hare adapt to a changing environment?
Dr. Scott Mills, a wildlife biologist at the University of Montana, has studied snowshoe hares for over a decade. Mills found that hares did not behave differently when mismatched in dangerous situations, suggesting that they will not adapt their predator avoidance strategy. As you can imagine, this drastically changes the likelihood of a snowshoe hare being caught by a predator. In fact, researchers found that hares have a 7% higher chance of being killed for every week that they are mismatched with their surroundings. If they are unlikely to change their behavior, can they change their coats? Maybe, say researchers.
There are populations of snowshoe hares where some individuals molt to winter coats and some stay brown. These "polymorphic" populations have the greatest opportunity for snowshoe hares to adapt; individuals who mismatch their environment will likely be eaten, and those who match will more likely survive and pass on their genes to the next generation. Hares also may have some flexibility in changing the timing of their color transition, also known as "phenotypic plasticity." However, they will probably not be able to change at the same rate that the climate is changing.
All in all, there might be hope for hares and other seasonally molting animals. This is tentatively good news, as in the areas Dr. Mills has studied, snowshoe hare molting is only mismatched by a week or two. Predictions indicate this mismatch could be off by as much as eight weeks by 2050, which could lead to rapid population decline, based on the increased predation statistics mentioned above. A steep decline in snowshoe hares would ripple across the forest, as so many other animals depend on them for food. The relationships between seasonal color-changing animals and the other species they impact has not yet been studied, but is an important next phase of this research.
In our small part, Swan Valley Connections continues to work with partners to monitor and study Canada lynx, a threatened species, whose fate is closely tied to climate change and snowshoe hare. In fact, a study in northwest Montana found that snowshoe hares made up 96% of a lynx's diet. In comparison, the second most common prey species of lynx was red squirrels, but they only made up 2% of the lynx's total diet. Ongoing research around lynx and hares will be key in identifying conservation strategies to ensure these Snickers bars, and those who eat them, are here to stay.
Visit https://www.umt.edu/mills-lab/ to learn more about Dr. Scott Mills' work.
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