Global Warming and the American Pika
The tiny pika, a cousin of the rabbit that lives on mountain peaks in the western United States, is running out of options.
In fact, they have already disappeared from over one-third of their previously known habitat in Oregon and Nevada. Now, the situation is so dire that the U.S. Fish and Wildlife Service is considering the pika for protection under the Endangered Species Act.
Because these small mammals have adapted to cold alpine conditions, pikas are intolerant of high temperatures and can die from overheating when exposed for just a few hours.
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Adapted to Cold Weather
Pikas, which once lived across North America, have been retreating upslope over the past 12,000 years. The species is believed to have evolved from Siberian ancestors that crossed the former land bridge between Asia and Alaska. American pikas are found in Colorado, Oregon, Washington, Idaho, Montana, Wyoming, Nevada, California and New Mexico as well as western Canada. Their thick fur and round bodies conserve heat, and furry paws provide traction on snow.
Though most pikas in the Lower 48 inhabit alpine ecosystems exclusively, some survive at lower altitudes where deep, cool caves are available, such as the ice tubes in California's Lava Beds National Monument.
Why is the Pika in Trouble?
The pika has adapted to life in mountainous areas that rarely get above freezing and can die when exposed to temperatures as mild as 78 degrees F.
Once they move upslope to reach the top and find the temperatures still too warm, the pika has no place else to go.
With round bodies, prominent ears, no visible tail and weighing just 5 ounces, pikas are unmercifully cute. But despite their cuddly appearance, American pikas, the smallest members of the rabbit family, are among North America's toughest animals--and they have to be. Pikas are one of the few mammals in the lower 48 states that can survive their entire lives in alpine terrain, the windswept no-man's-land above tree line.
Nowhere to Go
Biologists now fear that these hearty creatures may not survive global warming. Unlike many wildlife species that are shifting their ranges north or to higher altitudes in response to changing climate, pikas and other alpine animals have nowhere else to go. In some locations, entire pika populations already have disappeared. Scientists say the animal's decline, like the proverbial canary in a coal mine, may presage problems for other species, from butterflies and birds to large mammals.
Windswept, treeless and frigid, the alpine zone, like frosting atop a cake, covers less than 5 percent of the planet's surface. Over the past century, the interior West, which includes the lion's share of the country's high-mountain habitats, has warmed about 1 degree F. Computer models show the region heating up an additional 4.5 to 14.4 degrees F during the next 100 years. As the alpine warms, scientists expect snowpack to shrink, a phenomenon already observed in the Pacific Northwest, the Southern Rockies and the Sierra Nevada.
Trapped at the top, alpine wildlife is vulnerable to several of global warming's damaging effects, including vegetation changes, the invasion of new predators and pests, reduced winter snowpack and increases in extreme weather events. For pikas, one serious problem is heat itself. To survive in summer, they must descend into the cool, moist talus--rock piles at the base of mountain slopes--on hot afternoons.
As temperatures rise, researchers say pikas will abandon lower-elevation talus slopes and migrate higher into the mountains until they can go no farther--much like living on the highest point of a sinking island.
Great Basin Pikas Gone from 8 of 25 Mountain Locations
In the Great Basin--the arid region between the Rocky Mountains and California's Sierra Nevada--pikas already are disappearing. According to National Park Service biologist Erik Beever, the mammals have recently disappeared from 8 of 25 mountainous locations where they were documented in the early 1900s. Beever, who published his discovery in the Journal of Mammalogy, says the die-off indicates that suitable habitat is shrinking. Notably, the most recent pika losses occurred at the warmer, southern end of the animals' range. This is what you would expect from rising temperatures--a loss at the margins of their distribution, says Beever. The finding represents one of the first contemporary examples of a North American mammal exhibiting a rapid shift in distribution due to climate.
According to biologist Chris Ray, pikas also have disappeared from some talus slopes in Montana's Bridger Range over the past 30 to 40 years. While fossils show that pikas have been lost from several western mountain ranges over the past 10,000 years "the speed at which they are disappearing now is more rapid than ever before," she says.
In future years, Ray plans to compare her data on population fluctuations with temperature changes in the region. She suspects decreasing snowpack is at least part of the problem. Snow that covers talus slopes in winter insulates pikas from subfreezing temperatures. "If they are shivering through winter, that certainly would affect their fitness," says Ray. Ironically, global warming could be causing some pikas to freeze.
In the past, pikas could disperse between mountain ranges. But warmer temperatures make that journey a death march now. "If an isolated population blinks out today," Ray says, "it's nearly impossible for that habitat to become recolonized."
Asked if pikas could be the first mammal to disappear from the Lower 48 because of climate change, Ray hesitates. "That's a reasonable hypothesis," she says. "When you see a systematic decline in pikas, that tells you dramatic changes are taking place in the alpine."
National Wildlife Magazine
No Room at the Top
High-mountain species are particularly susceptible to global warming--and North America's cold-loving pikas may be the most vulnerable of all.
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