Animals That Turn White in Winter Face a Climate Challenge

About 20,000 years ago, somewhere along the crease where the Cascade Mountains drop into the plains, black-tailed jackrabbits and snowshoe hares mated.

But as snowshoe hares, with their unique ability to seasonally change from brown to white, bounded away, they took with them a black-tailed jackrabbit gene, one that would serve them well millennia later: the black-tailed jackrabbit ability to stay brown all winter.

Fast forward to today, as the climate in the Cascades continues to warm and snowpack comes later and leaves earlier, more and more of those winter brown snowshoe hares are beginning to appear.

Their relatives in other parts of the country, however, continue to struggle with changing seasons, leaving them more vulnerable to predation with white fur on dry ground. The Cascade hares are a real-time readjustment to a very real and present danger.

This surprising example of adaptation, published 2018 in Science, offers some hope in the face of an uncertain future.

But it should not be used to lull us into a false sense of security that animals simply adapt to an ever-changing climate, says author and University of Montana professor Scott Mills. Instead, the example shows that many animals, even those as adapted to their surroundings as snowshoe hares, could potentially, if given the space and the time, adjust to survive an unknown future.

Color Changes and Climate

Most species evolved unique adaptations to their environments. Wood frogs freeze their bodies in winter only to thaw out again in spring. Axolotls can regrow limbs along with spinal cords and even hearts. Bears recycle their own urine during hibernation to heal wounds and prevent atrophy.

But few adaptations are quite as obvious, at least to the human eye, than creatures that change color twice a year.

Take the Arctic and snowshoe hares. Beginning in the fall, the lagomorph with dusty brown fur that perfectly matches its surroundings, begins to molt. The physiology of the coat change is similar to many other furry mammal winter coat swaps, from mule deer to Labrador retrievers. The thin, summer coat is shed and in grows a thicker winter coat.