Climate Change Hurting Hares: White Snowshoe Hares Can't Hide On Brown Earth

On an unseasonably warm May afternoon, University of Montana wildlife biology Professor Scott Mills treks into the shadowy forests above the Seeley-Swan Valley in pursuit of his quarry. He skirts the rivulets of water melting from snow patches. In one hand he holds an antenna and in the other a receiver that’s picking up signals from a radio-collared snowshoe hare. The beeps increase in volume as he draws nearer. Mills picks his way over downed branches, steps out from behind a western larch and spots the white hare crouched on the bare brown earth.

“That’s just an embarrassing moment for a snowshoe hare to think that it’s invisible when it’s not,” said Mills with a grin, quickly adding that seeing such mismatched colors is becoming all too common and disturbing.

For the past decade, Mills has directed teams of biologists and students to investigate snowshoe hares on more than 35 study sites in Montana, Wyoming and Washington, including just outside UM’s back door near Seeley Lake. His findings have led to improved forest thinning practices that maintain patches of dense trees for hares. He’s delved into population dynamics and genetics of hares in their southern range. His research has turned directly to lynx, too, as a key predator of snowshoe hares and a threatened species.

Increasingly Mills and his students have noted an exceptional number of white hares on brown earth. Radio telemetry data revealed spring and fall to be the most deadly seasons for hares and a bonanza for predators.

“I’m speculating that the reason they are dying more in the spring and fall is because of the mismatch of colors,” Mills said.

That leads Mills to the “sexiest part” of snowshoe hare research – how they respond to climate change. While a warming planet affects all wildlife, a cute white hare has the makings of the next version of the polar bear as poster animal for global warming.

Will hares continue to shift coat colors on cue regardless of the presence or absence of snow? Will this drive them to extinction? Or will they be able to adjust their seasonal pattern in time to fit new conditions?

“Climate trends for mountainous areas clearly show that while snow levels may vary from year to year, the number of days with snow on the ground is decreasing,” Mills said.

Snowshoe hares evolved with plentiful winter snow in the boreal forests that form a swath across Alaska and Canada and dip down into the lower 48 states. In winter, they grow long white guard hairs to match the snow. In summer, they shed white for mostly rusty brown coats to blend with trees and soil. They depend on their cryptic coloration to hide from predators that include lynx, coyotes, foxes, wolves, pine martens and birds of prey. A hare that’s the wrong color stands out like the emperor in his new clothes.

The signal for a hare to shift coat color comes from the pineal gland in the brain that senses changes in daylight length. Shortening days of autumn trigger the coat color change from brown to white. (People also have pineal glands that produce melatonin, the hormone that affects our waking and sleeping patterns and responses to seasonal day lengths.)

Like most subjects in science, the deeper you delve, the more complexities you find. Mills points out that in the Cascades, some snowshoe hares stay a mottled brown and white year-round. In the Olympic Mountains of Washington, snowshoe hares never turn white. Does this suggest some ability to evolve in response to temperature changes? If so, how quickly?

To find out, Mills will add an intensive genetic component to his fieldwork, teaming with the University of Porto in Portugal, where scientists are sequencing the rabbit genome. Together they will analyze the genetic drivers of coat color change. Mills will start with his core research areas and then expand his studies to compare coat color genetics as well as synchrony of hare cycles in southern versus northern ranges.

Mills isn’t starting from scratch. He and his team have collected genetic samples from thousands of hares and several generations for the past eight years. On a typical field day, they rise before dawn to check the 80 “have-a-heart” live traps that they’ve baited with alfalfa and apple. The traps are placed in prime snowshoe habitat such as moist forests of larch, lodgepole and Douglas fir with dense brush and overhanging branches.

Finding a hare in a trap calls for prompt action. Mills describes the process that has become routine. First, you put a pillowcase over the entrance to the trap, so the hare will run in. You keep the hare in the pillowcase while you weigh it, add an ear tag and take a tiny plug of tissue from the ear. That tissue contains DNA and is placed in a special vial. You also check the sex and assess the hare’s general health. You might add a radio collar as well, depending on the project. The whole procedure takes a matter of minutes.

Snowshoe hares seemed like a natural choice for study soon after Mills arrived at UM from the University of Idaho in 1995. They’re a local species with excellent opportunities for delving into their ecology and introducing students and the public alike to fieldwork. Hares also are known for a classic predator-prey relationship with the lynx. The two species are so closely associated that they even share a key attribute for winter living – thick furry hind feet for bounding atop snow.

Across Canada, snowshoe hares follow a synchronized population cycle of 10-year highs and lows. Hare numbers in the Yukon can peak at 200 to 300 per square kilometer and then drop to about seven. Lynx follow a cycle that’s just slightly behind the hares. When lynx numbers are down, hares start to go up. The more hares, the better the lynx do until finally the lynx drive the hare populations down again. Mills’ work has proven that those cycles are dampened in the southern range because hares don’t have the same vast, dense boreal forest, thus hares never reach the high peak counts. As their numbers rise, they disperse into habitat openings, where they become easy dinners for waiting predators. In Montana and other parts of the southern range, forests tend to be patchier naturally, with added challenges for hares from logging and thinning.

Today, as a result of Mills’ studies comparing survival rates in experimentally thinned forests, Plum Creek Timber Co. now leaves patches of unthinned trees to benefit hares, and in turn lynx.

His research has translated directly into useful management, a result that Mills always aims for and advocates in his widely used 2006 textbook, “Conservation of Wildlife Populations, Demography, Genetics, and Management.”

Until now, the lynx-hare relationship has proved Mills’ most high-profile research. After the U.S. Fish and Wildlife Service added lynx as a threatened species in 2000, his phone rang with calls from the National Park Service and timber companies alike on how to manage forests for lynx health. Mills’ subsequent studies led to findings that lynx are highly mobile in their southern range. One cat might travel 1,000 km (620 miles) in a season.

“Conserving where lynx are now is important, but it’s also important to conserve the places in between because lynx may move into those places as well,” Mills said.

Taking the next leap to examine snowshoe hare response to climate change is both a natural progression and an exciting new phase in his long-term research.

“Wildlife will either move, adapt or die in response to climate change,” explains Mills. “The study becomes important because we need to know how much natural selection will help animals deal with climate change that is happening at a very fast rate.”

That knowledge in turn will help managers focus their efforts to save species through such actions as conserving movement corridors from south to north.

“Hares are important because they are prey for almost everything in the forest that eats meat,” Mills said. “Without hares, the ecosystem unravels.”