Snowshoe hares avoid predation by blending into their surroundings — which historically has meant a brownish-gray coat in summer that starts to turn white in the fall, in preparation for winter’s snow. But warmer winters and later snowfalls are causing hares’ coats to reach their pure white state when there’s still no snow on the ground, making them easy targets for owls, foxes and other predators.
Researchers in Montana are studying how this mismatch is affecting snowshoe hare populations in the western region of the state. The hares change color in response to light — not temperature — so they change about the same time each year, regardless of the weather. The researchers are starting to find that mismatched hares die at higher rates than those who manage to blend in to their surroundings — a problem that’s likely to get worse as winters continue to warm.
“If the hares are consistently molting at the same time, year after year, and the snowfall comes later and melts earlier, there’s going to be more and more times when hares are mismatched,” researcher Alex Kumar told NPR.
The research, led by Scott Mills of North Carolina State University, follows a previous study led by Mills that was published this April. In that study, Mills and his team kept track of snowshoe hares for three winters, noting the number of hares that were considered mismatched — those hares whose coat colors were at least 60 percent different than their surrounding areas. That study found that, though the hares had some ability to speed up or slow down their coat change in colder or warmer winters, it probably wouldn’t be enough to keep up with climate change. The study analyzed climate models for the area of the Rocky Mountains where the research was conducted, and found that by 2050, the snow season could be up to a month shorter, and by 2100 it could be up to 2 months shorter — changes that could result in white hares living in snow-less regions for up to 36 days by 2050.
Mills says that though the team’s most recent findings are troubling, there is some hope: some hares in Washington State don’t turn white in winter at all. But Mills isn’t sure whether hares in other areas can adapt quickly enough to changing snow and temperature patterns.
“It’s a picture that paints a thousand words,” Mills told NPR. “It’s a very clear connection to a single climate change stressor.”
Snowshoe hares aren’t the only species being affected by climate-induced mismatches. Birds, especially migratory ones, are especially vulnerable to changes in phenology, particularly the emergence of plant and insect life in spring. The red knot, which has one of the longest migrations of any bird, depends heavily on horseshoe crab eggs when it stops over in Delaware Bay on its way to its summer grounds in the Arctic. The birds rely primarily on day length to determine when to migrate, but the crabs’ cues to spawn are driven by multiple factors, including water temperatures and wave-generating storm frequency, so extreme weather or warmer temperatures could cause the red knot to miss the arrival of crab eggs in Delaware Bay, which could have a negative effect on the birds’ populations. Springs are starting earlier in some places and later in others, which means the timing of insect hatching and bud bursts is thrown off — a mismatch that means migratory birds could arrive to their spring grounds before or after peak amounts of food sources are available.