Warming Creating Extinction Risks for Hibernators

Hope Hamashige
for National Geographic News
February 1, 2008
When researchers at the Rocky Mountain Biological Lab in Crested Butte, Colorado, started documenting marmot hibernation patterns in the 1970s, the animals rarely awoke before the third week of May.

But these days, the scientists say, marmots regularly end their winter naps a month beforehand—by the third week of April.

These abbreviated hibernations are part of a growing body of evidence suggesting that hibernating animals are waking up earlier—or not going to sleep at all—due to rising temperatures from global warming.

From chipmunks and squirrels in the Rocky Mountains to brown bears in Spain, these altered slumber patterns are putting animals at risk both of starvation and increased predation, researchers say—which could bring many species to the brink of extinction.

"With respect to the marmots, at least, the evidence is convincing that it is connected to warming temperatures," said David Inouye, a biology professor at the University of Maryland who collaborated with the Rocky Mountain Biological Lab researchers.

Average low temperatures in April in Gothic, Colorado, the site of the marmot study, have climbed 2.5 degrees Fahrenheit (1.4 degrees Celsius) since 1976, the first year researchers began recording marmot hibernation stats. (Get a global warming overview.)

(Related: "Warming Sign? Another Early Spring for Rocky Mountains" [April 9, 2007].)

Sending the Wrong Signals

Scientists say it's logical to believe that rising springtime temperatures explain why animals are awakening at times that they would normally be snoozing.

Hibernating animals survive on fat reserves during the winter months when food is scarce. During hibernation, their metabolisms slow and their body temperatures drop to levels close to ambient air temperature.

As long is the air is cold, the animals' bodies are too, consuming very little of the fat they accumulated in summer and fall.

But as air temperature increases, so does body temperature and metabolism. The animals begin to use their stored fat more quickly, sending the signal that it's time to wake up and look for something to eat.

"We know that metabolic rates vary by temperature," said Craig Frank, a biology professor at Fordham University in New York who is currently studying the effects of climate change on hibernation patterns in chipmunks in New York and ground squirrels in California.

"It is reasonable to think that once temps reach a certain level, it would be practically impossible to survive an entire period of food restriction."

Food Crisis

But in this case, at least, the early riser doesn't get the worm.

Cutting hibernations short by several weeks puts animals such as marmots, hedgehogs, squirrels, and chipmunks at risk in two significant ways, experts say.

While animals are rousing themselves several weeks earlier, the plants that they normally eat are not, creating the real possibility of starvation for some of these animals, Inouye pointed out.

"Wildflowers still rely on the snowmelt as their cue to come out of their hibernation," Inouye said. And that snowmelt is still happening much later than the marmots' April appearances, he noted.

The biological lab researchers, meanwhile, have documented marmots trying to eat trees in early spring. The scientists attribute the strange behavior to the animals finding no suitable meals upon their early emergence.

Animals that end their hibernations early may also end up as dinner for predators more often, experts say, although the evidence is mainly anecdotal at this point.

When there is snow on the ground, for example, marmots have only have one hole into which to escape, Inouye pointed out. If the creatures wander far from that hole, as they likely will if they are having difficulty finding food, they are very vulnerable to predators such as coyotes.

Once the snow disappears, however, marmots can rely on large systems of holes in the ground, giving them far more escape routes in the summer.

These effects will vary by region, experts add, since not all animal species are reacting to warmer temperatures in uniform ways.

In Spain's Cantabrian Mountains, brown bears did not hibernate a year ago, according to the country's Brown Bear Foundation, but they found enough food to survive.

In the northeastern United States, meanwhile, chipmunks also reacted to higher-than-normal fall temperatures by not hibernating at all. But most of them did not survive the winter, scientists say.

Magnified Effects

Terry Root is a professor at Stanford University's Center for Environmental Science and Policy.

One alarming fact gleaned from the research, she said, is how much animals have altered their behavior in response to a small change in temperature.

In Inouye's study, marmots shortened their hibernations by weeks based on a change in temperature of just over a degree, Root noted.

If temperatures continue to climb, she said, it is reasonable to expect animals that are already halting their winter slumbers will continue to cut them ever shorter.

Unless the animals learn to adapt to new circumstances, Root added, many of these animals will be driven to the brink of extinction by rising temperatures.

"I do think we need to start being very honest about what is going on," she said, adding that not just hibernators are changing their behavior in a time of rapid climate change.

Some species are also starting their migrations earlier or giving birth earlier.

"I do think what we will be facing is the extinction of many species."

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