A shy, flower-gathering mammal and longtime icon of the West's high peaks may be the first animal in North America to fall victim to global warming.
Pikas -- tennis ball-sized critters that whistle at passing hikers and scamper over loose, rocky slopes of the High Sierra and the Rocky Mountains -- have disappeared from nearly 30% of the areas where they were common in the early parts of the 20th century, according to a study released Tuesday.
The comprehensive survey found the sites that lost pikas were on average drier and warmer and at lower latitudes than sites where the animals remain, said Erik Beever, a U.S. Geological Survey biologist based in Corvallis, Ore., and the study's lead author.
A close analysis, Beever said, indicated that such factors as cattle grazing and proximity to roads had some effect on the animals, but that warmer and drier conditions in recent decades have been a major factor in their rapid disappearance.
The finding is supported by earlier surveys in the United States that found the animals missing from much of their previous range, and from work on pikas in the Yukon, where 80% of the animals have recently died out in some areas after extremely warm winters.
Many of the far north's ice-loving animals, such as polar bears, walrus and caribou, have declined in number or suffered lower reproduction rates in recent years as their sea ice and tundra habitats have been radically reshaped by warming in the Arctic.
But the current study is the first to link warming to the widespread dying out of entire populations of animals. It found that the pikas no longer existed in seven of 25 sites where they once were plentiful.
The animals are not in danger of becoming extinct, scientists said, but they could soon disappear from vast stretches of the American West and could be radically reduced in number.
Beever said he was most surprised to find groups of animals disappearing over decades, rather than in centuries or millenniums, as they have during climatic swings of the distant past.
His study, in the current issue of the Journal of Mammalogy, may be an "early signal" of what alpine and subalpine environments throughout the world will face if temperatures continue to rise as predicted, Beever said.
Globally, temperatures have risen about one degree in the last 100 years, and by several degrees in some parts of the Arctic -- a rise attributed to both natural cycles and the human production of greenhouse gases. The warming has melted glaciers around the world and has altered the behavior of many animals.
Pikas, relatives of rabbits despite their hamster-like appearance, are exquisitely adapted for ferocious cold, but they cannot withstand the heat. They typically live at altitudes above 7,000 feet and have been found as high as 19,000 feet in Asia.
The animals are active year-round, surviving the winter by subsisting on small haystacks of grass and wildflowers they collect and cure in the sun during the short alpine growing season.
The animals are well-known to mountain hikers for their whistles and their haystacks and are often photographed with mouthfuls of flowers, looking for all the world like they are about to deliver a tiny bouquet.
The almost unbearably cute animals -- also found through the mountains and steppes of Asia -- are thought by some fans to be the inspiration for Pikachu, the popular Japanese Pokemon character.
With a normal body temperature of 104 degrees and thick, furry pelts that keep them from shedding heat, the animals can die in minutes from overheating if their body temperatures rise just a few degrees, said David Hik, an ecologist and expert on Arctic and alpine animals at the University of Alberta.
Hik, who studies a cousin of the American pika -- the collared pika -- in the central Yukon, saw pika populations plummet during the warm winters from 1998 to 2000.
"We see these populations blink out, just like that," he said. "These little guys are very sensitive to warm climate conditions."
With recent colder winters, the pikas in the Yukon have started to recover, he said.
He suspects that the American pikas will have a harder time, however, because the populations are more isolated from each other atop distant mountaintops and because they face higher temperatures.
"Sadly, I'm not surprised," he said of Beever's findings.
In California, Utah and Nevada, the animals are marooned on isolated mountaintops that are separated by large -- and much warmer -- valleys that serve as a kind of pika no man's-land.
If temperatures rise in their home territory, the animals can't migrate to higher mountains or colder latitudes without facing a trek through warmer areas that would likely prove lethal, Beever said.
Pikas are severely constrained in their choice of where to homestead. They require loose, rocky slopes, which offer a somewhat cooler refuge during midday heat and a place to hide from predators. But they also need meadows nearby to collect plants.