Mountain hares are built for snow. That may become a problem.

The Scottish Highlands are a smooth, glaciated landscape scoured by ice and rock over millions of years. Mountains lift their rounded backs. Bowl-shaped hollows known as corries nestle within curving ridgelines. The land has two faces.

In late summer the terrain is shrouded in heather, threaded with the royal purple of its tiny blooms, along with delicate leaves of creeping willow and bog myrtle, soft beads of blaeberries, and red-glowing lingonberries. But within a few short weeks these same uplands might be swathed in snow: drifts banked high, gales whipping through the wind-carved ice at a hundred miles an hour.

This is the domain of the mountain hare. These little mammals are also found in tundra, alpine, and boreal regions across Eurasia. An estimated 99 percent of mountain hares in the United Kingdom live in Scotland, their heartland the rugged Grampian Mountains of the northeast.

Last winter I hiked in the Cairngorm Mountains. Staggering through deep snow, I set off a clatter of wings as a ptarmigan, a bird with downy bloomers, materialized, grunting at being disturbed from its bed. Sensing my footsteps on the high ground, white-coated hares flushed into the corrie below—fleet of foot, tumbling over the sides like the very first crumbs of an avalanche—before turning and gliding effortlessly up and over the ridge. 

(See the beautiful landscape of Cairngorms National Park, Scotland.)

The mountain hares will seek out shelter within nests—“forms”—in dense vegetation or in shallow depressions—“scrapes”—on the hillside, where they wait out snowstorms: hunched low inside their fur coats, black-tipped ears flattened to their necks. They might rest for days at a time, breaking only every hour or so to stretch or perhaps to briefly graze on hardy heather before returning to their refuge.

This behavior is one of many adaptations that allow this animal—the only hare or rabbit species native to the U.K.—to eke out an existence in such harsh conditions. Perhaps most striking is its seasonal change, when the smooth summer coat of mousy brown gives way to a thicker, better-insulated pelt of brilliant white or dove gray. Each year a combination of waning sunlight and falling temperatures triggers the hares’ winter molting process—the dense, pale new growth spreading upward from their feet, along their thighs and across their shoulders, mottling their bodies.

These creatures have evolved to fit their surroundings. But as climate change ushers in varying weather, mountain hares are increasingly out of step with the place they call home.

When camouflage backfires

Mountain hares are among a group of just 21 bird and mammal species with turncoat capabilities, almost all of which live in cold, snowy regions, says Marketa Zimova, assistant professor of biology at Appalachian State University in North Carolina. In Scotland the only other species that change color in this way are the stoat, also known as the short-tailed weasel—a slender, skilled hunter—and the ptarmigan.

For mountain hares, this luxuriant winter coat also offers valuable camouflage, keeping them safer from predators such as red foxes, stoats, and golden eagles that soar overhead. But in conditions as changeable as these, it may be a curse as well as a blessing.

In the Scottish hills it’s not unusual for temperatures to rise and fall dramatically on a daily basis. On the mildest days, when the peatland is black, sodden, and marbled with ice, the hares find themselves limelighted: gleaming figures against a stage of dark heather.

This has always been a danger, but recent research led by Zimova found that Scottish mountain hares have been out of sync with local conditions as climate change has brought a steep decline in days of snow cover—the first autumn snow blanketing the ground, on average, four days later in the 2010s than it did in the 1960s. Average temperatures in the region have risen by more than 0.1 degree Celsius per decade, leading to longer periods without snow cover. In all, the records reveal the hares spend an additional 35 days a year mismatched with the landscape.

The consequences of this discrepancy are not entirely clear, says Scott Newey, a population biologist who studies mountain hares at Scotland’s Game & Wildlife Conservation Trust. They are a “very challenging” species to monitor, he says. For instance, mountain hares experience population cycles, in which a scientist might find only a few hares in a square kilometer one year and more than a hundred in that same area several years later, or vice versa. These cycles, possibly linked to food availability and the prevalence of certain parasites, vary so much that untangling the impact of factors such as climate change can be extremely difficult.

However, analyses of snowshoe hare populations in North America offer some insight into possible long-term trends. It’s known “exactly how costly” such camouflage mismatch is for that species, says Zimova: The probability that a snowshoe hare will be hunted and killed by a predator in any given week increases by between 7 and 14 percent when the hare is wearing its white winter coat on a snowless background. “It’s something that doesn’t sound like a lot,” she says, but when you extrapolate it across the entire year, “it can have really profound consequences.” (Can snowshoe hares evolve to cope with climate change?)

As with so many of the issues facing wildlife on this warming planet, the challenge seems to be: Adapt or die. And for the mountain hares of Scotland, there’s no evidence they’re adapting at all.

(Watch a female hare battle male suitors.)

In the crosshairs

Oddly enough, it may well be that the increased risk of predation by foxes, birds of prey, and stoats has been far less worrisome, at least until recently, than the impact of humans.

For many decades, landowners had managed large swaths of mountain regions for the recreational shooting of wild red grouse. Controlled burning renders the hills a mosaic of different conditions—some patches blackened and scorched, some budding with fresh new shoots, some swaddled in thick vegetation—a mix of ecosystems that likely benefits the hares as much as the game birds. (Scotland could become first ‘rewilded’ nation—what does that mean?)

Mountain hares have long been killed purely for sport, but around the turn of the century some private estate managers began targeting the hares in large numbers on the basis that it would prevent the spread of a tick-borne disease to the grouse—something that scientists have disputed. (More than 33,500 hares were killed in total over the 2016-17 season.) The debate around hare culls, which were always controversial, took on a new tenor when a 2018 analysis by Adam Watson, an independent ecologist and mountaineer, argued that mountain hare populations on grouse-hunting grounds in the hilly northeast had dwindled to less than one percent of the levels seen in the mid-1950s. The Scottish mountain hare population is estimated at 135,000, although scientists stress the uncertainty baked into any such calculations; the true figure might fall anywhere between 81,000 and 526,000. (Badger culls are dividing England’s rural communities.)

Fearing the animal’s decline, the Scottish Parliament banned unlicensed killing of mountain hares in March 2021. It’s still too early to know the impact of this rule, says Newey, who’s been working for 20 years to identify the best way of monitoring numbers of this enigmatic animal.

That’s not surprising, considering a hiker might easily pass right by one, concealed in the heather. During a summer hike a few years ago, I witnessed a lithe hare jumping from the thicket, lifting onto its haunches before loping off with long, deliberate strides: a tawny silhouette against a tawny landscape. The hare paused, then dissolved away once more, merging into the brush a short distance away. One minute it was there; the next, gone again. It was as if it had never been there at all.