The American pika, a tiny rabbit-like creature living in rocky mountain slopes in the American West, is disappearing from California, and climate change is to blame, a study suggests.

Rising temperatures appear to be causing some populations of the heat-sensitive creature to become extinct in low elevation sites in the Sierra Nevada Mountains, researchers say.

An analysis of historical data shows pikas have disappeared from 15 percent of their previous California range, the scientists report in the Journal of Biogeography.

A high metabolic rate and thick fur make pikas well adapted to cold temperatures at high elevations; in winter they do not hibernate, existing on food stores they've gathered at lower elevations during the summer.

"Backpackers and hikers often see pikas scurrying back and forth across the rocks, gathering little bouquets of wildflowers in their mouths," says study lead author Joseph Stewart, a graduate student at the University of California, Santa Cruz. "They are uniquely adapted to cold temperatures, but these same adaptations make the species vulnerable to global warming."

If summer temperatures get too hot, Stewart explains, pikas must remain underground to keep from overheating. This in turn gives them less time for food foraging, increasing the risk of local extinctions.

In the areas where pika populations have disappeared, average temperatures are 2.2 degrees warmer than in sites where they remain, the researchers say.

If temperatures continue to rise with global warming, pikas could disappear from 40 to 90 percent of their historical California range by 2070, they predict.

"It's troubling," Stewart says. "This sort of points the finger at climate change."

Moving to higher and colder elevations isn't an option for many pikas in California, the researchers say, because in parts of their range in the state the mountains just aren't high enough to provide refuge from rising temperatures.

"A bird just has to pick up and fly," Stewart says. "If a pika wants to get from one mountain peak that isn't cold enough to another one that is colder, oftentimes it's going to have to go down into hotter, lower-elevation areas. The problem is their habitat doesn't go high enough in California."

Pikas fill important ecological niches, the researchers say, as prey for many species such as stoats and owls, and they also alter soil composition and vegetation through their foraging activities.

The loss of pikas in California is one more example of the negative impacts global warming has on animal and plant species around the world, Stewart says.

"Pikas are a model organism for studying climate change, and their decline at low-elevation sites suggests that the future for other species is not great either," he says. "The problem is that the climate is changing faster than species can adapt or disperse to new sites."