Out in the Cold

On a cold winter day, a snowshoe hare hops through a Montana forest. Suddenly, it hears a noise that sounds like a predator. The hare freezes. If it sits perfectly still, the predator might not see it and go away.

Weeks ago, the hare shed its brown summer coat and grew white fur. The color acts as camouflage, hiding the hare in the snow. But there’s a problem: Winter has been warmer than usual this year. There isn’t any snow on the ground, and the hare is perfectly visible.

A snowshoe hare hops through a Montana forest. It’s a cold winter day. Suddenly, the hare hears a noise. It sounds like a predator. The hare freezes. It sits perfectly still. The predator might not see the hare. Then it will go away.

Something happened to the hare a few weeks ago. It shed its brown summer coat and grew white fur. The color acts as camouflage. It hides the hare in the snow. But there’s a problem. Winter has been warmer than usual this year. There isn’t any snow on the ground. And the hare can be clearly seen.

Snowshoe hares are facing this problem more often. In recent years, the average global temperature has been increasing. Many areas receive less snow than they once did. As a result, more and more hares don’t match their surroundings, says Scott Mills, a biologist at the University of Montana. 

Mills is studying snowshoe hares and other northern animals that turn white in the winter. His big question: As the climate warms and snow becomes scarcer, can these animals survive?

Snowshoe hares are facing this problem more often. The average global temperature has been going up. A lot of places get less snow than they once did. More and more hares don’t match their surroundings as a result, says Scott Mills. He’s a biologist at the University of Montana.

Mills is studying snowshoe hares. He’s also looking at other northern animals that turn white in the winter. Mills wants to find out if these animals can survive as the climate changes.

Snowshoe hares live in forests across the northern U.S. and Canada (see Snowshoe Hare Range). They’re a food source for many animals, such as owls, coyotes, and bobcats. “We call them the candy bars of the forest,” says Mills.

In the summer, brown coats help the hares blend in with the forest floor. As winter approaches, the changing amount of sunlight triggers a process inside the hares’ bodies. They begin molting, or changing coats. First the tips of a hare’s ears and nose lose their color, followed by its back and shoulders. After about six weeks, the animal is all white.

Snowshoe hares live in forests. They are found across the northern U.S. and Canada (see Where Snowshoe Hares Live). Many animals eat hares. They include owls, coyotes, and bobcats. “We call them the candy bars of the forest,” says Mills.

Hares have brown coats in the summer. That helps them blend in with the forest floor. But as winter nears, there is less sunlight. Because of this, hares’ bodies change. They begin molting, or changing coats. First, the tips of a hare’s ears and nose lose their color. Then its back and shoulders do too. The animal is all white after about six weeks.

But snow is falling less often and melting more quickly in areas where hares live. That makes the animals easy to spot. “It’s like a white light bulb sitting on a brown carpet,” says Mills. 

Predators have a much easier time catching prey that stand out. Mills and other scientists recently tracked snowshoe hares in Montana. They found that hares that didn’t match their environments were less likely to survive the winter. In some areas, such as in parts of  Wisconsin, snowshoe hare populations are shrinking.

But snow is falling less often in places where hares live. And it’s melting more quickly. That makes the animals easy to spot. “It’s like a white light bulb sitting on a brown carpet,” says Mills.

Predators have an easier time catching prey that stand out. Mills and other scientists recently followed snowshoe hares in Montana. They found out something about hares that didn’t match their surroundings. They were less likely to survive the winter. It could be why some snowshoe hare populations are shrinking. That’s happening in parts of Wisconsin.

Snowshoe hares aren’t the only animals that turn white in the winter (see Color Changers). Arctic foxes grow white fur to hide from predators like golden eagles. The color also helps them sneak up on lemmings and other prey. Some species of lemmings, weasels, and caribou also make the seasonal switch.

In a world without snow, white winter coloring can have deadly consequences for all of these animals. And when one species disappears from an area, many others are affected. If prey animals become scarce, predators may go hungry. Without predators, prey populations can grow out of control.

Other animals also turn white in the winter (see Color Changers). Arctic foxes grow white fur. It helps them hide from predators like golden eagles. The color also helps them sneak up on prey like lemmings. Other creatures switch color each season too. They include some lemmings, weasels, and caribou.

But being white in winter can be bad in a world without snow. Many species could be affected if these animals die out in an area. Predators may go hungry if there’s less prey. Prey numbers can grow out of control without predators.

Despite the threats, scientists have hope for the color-changing animals. In January 2014, biologist Laura Gigliotti was tracking snowshoe hares in Pennsylvania. She expected the hares to have completely white coats. She was surprised to spot some hares that were partly or completely brown.  

Scientists think that skipping the color change is an adaptation. Over many generations, some hares have become browner to help them survive in areas with patchy snow.

Scientists have hope for color-changing animals though. Laura Gigliotti is a biologist. She tracked snowshoe hares in January 2014. The animals lived in Pennsylvania. She thought the hares would have all-white coats. But she was in for a surprise. Some hares were partly or totally brown. 

Scientists think skipping the color change is an adaptation. Becoming browner can help hares survive in areas with patchy snow. This change happens over a long time.

That’s good news for the entire species, says Mills. If the brown hares survive better than the white ones, they’ll pass genes for staying brown to their offspring. Over time, more and more hares will stay brown year-round. 

To make sure that happens, Mills wants to conserve areas where the brown and white hares mix. By protecting those places from human development, people can boost the odds that the color-changing animals will adapt to climate change. “It’s a hopeful part of the story,” says Mills.

That’s good news for the entire species, says Mills. Brown hares might survive better than white ones. Then they’ll pass genes for staying brown to their children. More and more hares will stay brown year-round over time.

Mills wants to make sure that happens. He wants to protect areas where brown and white hares mix. That can boost the chances color-changing animals will adapt to the effects of climate change. “It’s a hopeful part of the story,” says Mills.