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For Wisconsin’s snowshoe hares, climate change now ranks as an even bigger menace than the bulldozing, paving and other destructive things people have done to northern forests.
Habitat loss as humans reshape landscapes has loomed for decades as the main conservation problem for a lot of wildlife. It’s still important, says climate change ecologist Benjamin Zuckerberg of the University of Wisconsin‒Madison. But along the southern boundary of the snowshoe hares’ range, climate change bringing skimpy snow covers has surpassed direct habitat loss as a threat, Zuckerberg and his colleagues say March 30 in Proceedings of the Royal Society B.
North America’s Lepus americanus hares may be especially sensitive to climate change. “Almost everything about them screams adaptation to seasons of extensive snow cover,” says study coauthor Jonathan Pauli, also at Wisconsin‒Madison. The hares have outsized snowshoe feet, thick fur and an annual molt from brown to snow-white. Getting out of sync with the snow turns camouflage into a come-on for predators (SN Online: 1/26/16). In bad years, “there’s a lot of white hares on brown backgrounds,” Pauli says.
To see how the hares have fared, the researchers looked for signs of the animals at 199 sites during the winters of 2012‒2013 and 2013‒2014. Many of these locations were mentioned in a rather anecdotal 1945 study and in a more systematic one in 1979 to 1980. Satellite images showed not much change in the overall amount of hare-suitable forest since the 1980s, but snow cover averages have declined. When researchers put all their information into a computer simulation, the climate-related changes — particularly the length of the snow-cover season — did a better job of explaining the ups and downs of hare populations than just the forest changes did.
Snow cover has powerful effects on hares. For each 7.41 days that snow blankets the landscape, snowshoe hare populations become four times as likely to survive, the researchers found.
If the hares dwindle from a place, the loss may ripple through the ecosystem. “Snowshoe hares are central, really central, to prey species,” Pauli says. Lynx, great horned owls, coyotes and many more species dine on them. And regardless of any ecosystem role, hares are remarkable creatures in their own right. “It’s hard for me, a person living in Wisconsin, to imagine these northern conifer forests without snowshoe hares,” Pauli says.
To prevent such a loss, reducing greenhouse gases is important, but so is creating “climate-resilient landscapes,” Zuckerberg says. For snowshoe hares, that landscape might bristle and tangle with abundant, thick young growth, full of hiding places for too conspicuous, out-of-season-sync hares, he suggests.
White furry animals may not be the only ones that will have to cope with a shift in the balance of threats. “In a number of cold-associated butterflies, and also birds, it is becoming clear that climate change is beginning to surpass land use as the primary driver of extinction at the trailing edges of the species’ range,” says ecologist Tom Oliver of the University of Reading in England. And the threats of climate change and land-use upsets can intensify each other. “We appear to be entering a worrying time,” Oliver says.
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