The snowshoe hare, in other words, constantly changes its coat to match its seasonal habitat. Grange loved it. “What is important is the fact that there does seem to be a very definite correlation between the [coat] color and the average climatic conditions ... The success with which this average situation is met is often almost miraculous.”

Snowshoe hares are not the only animal to pull off such a divine feat. Twenty-one species—including Arctic foxes, long-tailed weasels, and mountain jackrabbits—shift their coat color through the year to match the changing seasons.

But where it was once extraordinary to catch snowy-hued animals during a snowless season, it is now far more common. As the world has warmed, snow has become a rarer sight across much of the Northern Hemisphere, and hares and foxes increasingly find themselves in “mismatch” with their environment.

For the last decade, the ecologist L. Scott Mills and his colleagues have been studying how coat-changing animals might be able to survive climate change. On Thursday, their team published a new study—the culmination of years of work combing through museum collections—that pinpoints the parts of the world where conservation work would be most likely to save coat-changing creatures.

Since the 1980s, ecologists have worried about how global warming will wreck the delicate seasonal timing of animals and plants. They fret about the decline of honeybees, about early flowerings and late frosts, about migratory birds arriving too early in the spring to help trees spread their seeds. But it can be hard to tell how much climate change is responsible for these ills, since so many of them can also be tied to pollution, deforestation, or overhunting.

A decade ago, Mills—a bearded, genial professor at the University of Montana who has worked with Arctic foxes in Sweden and snow leopards in the Himalayas—realized that the threat facing snowshoe hares and other color-changing animals wasn’t so complex. “The [success of the] trait is 100 percent determined by climate,” he told me.

But across the 21 species who can change their winter coat color, there are both “brown morphs” and “white morphs”—something determined totally by genetics. White morphs grow white fur in the winter, and brown morphs retain their summertime color year-round. For both morphs, hares are more likely to survive the winter if the color of their coat matches their local climate. As Ben Zuckerberg, a professor of ecology at the University of Wisconsin, puts it, winter coat color has huge “fitness consequences.”

In fact, hares often don’t even realize that they’re mismatched to their environment. In the 1990s, Mills realized this while doing field work near the Canadian border. “As I wandered around in the fall and spring, I started to see more and more of these white light bulbs hopping around the forest,” he told me.