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Dressed for Winter?

Animals that turn white each year are struggling to adapt to life without snow

Shattil & Rozinski/NaturePL.com (Winter); Loic Poidevin/NaturePL.com (Summer)

Snowshoe hare

The winter air is chilly as a snowshoe hare hops through a Montana forest. Suddenly, it hears a rustle in the bushes, which might be a predator. The hare freezes in place and waits for the predator to go away.

Weeks ago, the hare shed its brown summer coat and thick white fur grew in for winter. It’s relying on this color to keep it hidden in the snow. But there’s one big problem: This winter has been warmer than usual, and there’s no snow on the ground. The hare is completely visible to any hungry animals nearby. 

As climate change raises the average temperature of the planet, snowshoe hares across North America are facing this problem more often. “It seems like they’re getting more and more mismatched,” says Scott Mills. He’s a biologist at the University of Montana who has studied hares for more than 20 years.

Scientists like Mills are investigating how climate change is affecting snowshoe hares and other color-changing animals. Their big question: As snow becomes scarcer in winter, can these animals adapt?

A snowshoe hare hops through a Montana forest. There’s a winter chill in the air. Suddenly, the hare hears a rustle in the bushes. The sound might be a predator. The hare freezes in place and waits for the predator to go away.

Weeks ago, the hare shed its brown summer coat. Thick white fur grew in for winter. The hare is counting on this color to keep it hidden in the snow. But there’s one big problem: This winter has been warmer than usual. There’s no snow on the ground. The hare is completely visible to any hungry animals nearby.

Climate change is raising the average temperature of the planet. That means snowshoe hares across North America are facing this problem more often. “It seems like they’re getting more and more mismatched,” says Scott Mills. He’s a biologist at the University of Montana. He’s studied hares for more than 20 years.

Scientists like Mills want to know how climate change is affecting snowshoe hares. They’re also studying other color-changing animals. Their big question: As snow becomes scarcer in winter, can these animals adapt?

CHANGING COLOR

Snowshoe hares live in forests across North America, from the mountains of Alaska to the eastern Canadian shore. They munch on plant leaves, twigs, and tree bark, and they raise their young among the underbrush. They’re a favorite food for many predators, such as owls, hawks, coyotes, and bobcats. “We like to call hares the candy bars of the forest,” says Mills.

For protection, snowshoe hares rely primarily on camouflage. In the summer, their brown coats make them difficult to spot on the forest floor. As winter approaches, the days get shorter. The changing amount of sunlight triggers the hares’ bodies to start molting, or changing coats. First the tips of a hare’s ears and nose turn white, followed by its back and shoulders. After about six weeks, the animal is almost completely white.

When the forest is snowy, the hares’ winter camouflage is nearly perfect. If they hear a predator, they stay motionless to blend in with the white snow. But as the climate warms, snow is falling less often and melting more quickly in many areas. That means the winter-white hares stand out on the dark, snowless ground. “It’s like a white light bulb sitting on a brown carpet,” says Mills. “They’re not at all camouflaged.”

Snowshoe hares live in forests across North America. They’re found from the mountains of Alaska to the east coast of Canada. They eat plant leaves, twigs, and tree bark. They raise their young on the forest floor. The hares are a favorite food for many predators, such as owls, hawks, coyotes, and bobcats. “We like to call hares the candy bars of the forest,” says Mills.

For protection, snowshoe hares rely mostly on camouflage. In the summer, their brown coats make them difficult to spot on the forest floor. As winter approaches, the days get shorter. That triggers the hares’ bodies to change coats. First the tips of a hare’s ears and nose turn white, followed by its back and shoulders. After about six weeks, the animal is almost all white.

When the forest is snowy, the hares’ winter camouflage is nearly perfect. If they hear a predator, they stay still to blend in. But as the climate warms, snow is falling less often in many areas. If it does fall, it melts more quickly. That means hares that have turned white stand out on the dark ground. “It’s like a white light bulb sitting on a brown carpet,” says Mills. “They’re not at all camouflaged.”

Kevin Morgan (Winter); Klein & Hubert/NaturePL.com (Summer)

Arctic fox

STICKING OUT

Snowshoe hares aren’t the only animals caught wearing the wrong winter colors because of climate change. Across the Northern Hemisphere, 21 different species turn from brown to white in winter. On the northern tundra, Arctic foxes grow white fur to hide in the snow from prey and predators. Birds called ptarmigans, which the foxes often hunt, turn white too. Several species of other hares, lemmings, and weasels also make the seasonal change.

But without snow, a white winter coat can have deadly consequences. Predators have a much easier time snatching prey that stand out against the ground. A mismatched hare, for example, is 7 percent less likely to survive each week than a hare that’s properly camouflaged, Mills’s team has found. In some areas affected by warming temperatures, such as around the Great Lakes in Wisconsin, the hares are beginning to disappear.

Snowshoe hares aren’t the only animals with this problem. Other species are also getting caught wearing the wrong winter colors because of climate change. Across the Northern Hemisphere, 21 different species turn from brown to white in winter. Arctic foxes on the northern tundra grow white fur to hide from prey and predators. Birds called ptarmigans grow white winter feathers. Several species of lemmings and weasels also make the seasonal change.

But without snow, a white winter coat can have deadly consequences. Predators have a much easier time catching prey that stand out. Mills’s team compared mismatched hares with those that were properly camouflaged. They found that the mismatched hares were 7 percent less likely to survive each week. Around the Great Lakes in Wisconsin, the effects of warming temperatures are already noticeable. The hares there are beginning to disappear. 

JoÎl Fischer/Biosphoto (Summer); Dick Pasman/Buiten-Beeld/Minden Pictures (Winter)

Weasel

HOPE FOR HARES

In 2014, biologist Laura Gigliotti was tracking snowshoe hares in Pennsylvania. She weighed and measured the animals to learn more about the population’s health. But there was something weird about the hares she was finding.

“We noticed that there were some hares that were completely brown in January,” says Gigliotti, who now works at Clemson University in South Carolina. Other hares were still brown around their eyes or ears. That made them one of the only known populations of snowshoe hares that never turn completely white.

In 2014, biologist Laura Gigliotti was tracking snowshoe hares in Pennsylvania. She now works at Clemson University in South Carolina. She weighed and measured the animals to learn more about the population’s health. But there was something weird about the hares she was finding.

“We noticed that there were some hares that were completely brown in January,” says Gigliotti. Other hares she saw were still brown around their eyes or ears. The hares had never turned completely white. That made them one of the only known populations not to do so.

Christoffers/BIA/Minden Pictures (Summer); Rob Reijnen/NiS/Minden Pictures (Winter)

Ptarmigan

Scientists think these groups of hares evolved over thousands of years to live in areas with only patchy snow. Staying partly brown helps them blend in. That’s good news for the entire species, says Mills. These hares that stay brown in the winter can reproduce with the white hares. Over time, more brown hares might survive and spread into areas where white hares can no longer live. 

Over the past few years, Mills and his colleagues have traveled the world looking for similar populations that remain brown in winter. They found that many color-changing species, including arctic foxes, have some groups that don’t turn completely white. Mills hopes that by conserving the areas where these animals mix with their white counterparts, people can boost the odds that color-changing animals will adapt. “It’s a really hopeful part of this story,” he says.

Scientists think these groups of hares evolved to live in areas with only patchy snow. Staying partly brown helps them blend in. That’s good news for the entire species, says Mills. The hares that stay brown in the winter can reproduce with the white hares. Over time, more brown hares might survive. They could spread into areas where white hares can no longer live.

Over the past few years, Mills and his colleagues have traveled the world looking for similar brown populations. They found that arctic foxes have some groups that don’t turn completely white. So do many other color-changing species. Mills wants to conserve the areas where these animals mix with their white counterparts. That could boost the odds that color-changing animals will adapt. “It’s a really hopeful part of this story,” he says.

One way to understand the variability of your data is to find the mean absolute deviation (MAD). That’s the average distance between each data value and the mean, or average. Round answers to the nearest whole number. Record your work and answers on our answer sheet.

One way to understand the variability of your data is to find the mean absolute deviation (MAD). That’s the average distance between each data value and the mean, or average. Round answers to the nearest whole number. Record your work and answers on our answer sheet.

A. What is the mean of the daily snow depth estimates in Williamsport, Pennsylvania, as shown in the chart above?

A. What is the mean of the daily snow depth estimates in Williamsport, Pennsylvania, as shown in the chart above?

B. Determine the distance of each value in the data set from the mean to complete the distance from mean column in the chart. What is the mean absolute deviation (MAD)?

B. Determine the distance of each value in the data set from the mean to complete the distance from mean column in the chart. What is the mean absolute deviation (MAD)?

A. What is the mean of the daily snow depth estimates in Fairbanks, Alaska, as shown in the chart above?

A. What is the mean of the daily snow depth estimates in Fairbanks, Alaska, as shown in the chart above?

B. Find the distance of each value in the data set from the mean to complete the chart. What is the MAD?

B. Find the distance of each value in the data set from the mean to complete the chart. What is the MAD?

Based on the MADs, in which city did the depth of the snow vary more that week?

How many blue whales are equal to the total mass of an Atlas V rocket?

What other conclusions can you draw from the MADs? What factors might have affected the data for that week?

What other conclusions can you draw from the MADs? What factors might have affected the data for that week?

In which area would it be harder for a snowshoe hare with a white coat to survive the week? Explain your answer.

In which area would it be harder for a snowshoe hare with a white coat to survive the week? Explain your answer.

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