The American pika -- tiniest member of the bunny family -- once was voted "3rd Cutest Animal in North America" in an admittedly non-scientific survey by a global wildlife group.
Few would argue, though. The creator must have been in a 1950's Disney mood when designing this terminally cute rock-scrambler, beloved of mountain hikers in America's West whose treks are punctuated from time to time by pikas' high-pitched warning whistles -- and a glimpse, if they're quick, before the pikas vanish down a crevice in some jumbled pile of talus slope rocks.
But these bite-sized bunnies, beloved of weasels, which like to eat them, are starting to "fall off the tops of mountains," as field biologists put it -- as are many other mountain species -- because of global warming.
Dr. Chris Ray of the University of Colorado at Boulder told ABC News that of 25 pika colonies she's been surveying in mountains in the Great Basin between the Rockies and the Sierras over recent years, the furry creatures -- the size and shape of a tennis ball -- are now gone from 10 of them.
That's up from eight only two years ago.
And there's a pattern.
"They're disappearing from the lower elevations," she said, "especially from colony sites where there was no higher ground up slope from which they might come back down and recolonize."
Pikas need the cold, Ray and other pika experts have told ABC News; they are adapted to survive in high altitude cold with thick fur, in which -- if it gets relatively warm -- they can overheat and quickly die.
With global warming pushing more warm air up into the lower elevations of where pikas live, local pika extinctions in Dr. Ray's study area are increasing amid warmer summers and winters that don't get as cold as they used to.
Ray said it would be expensive and difficult -- perhaps impossible -- to relocate pika colonies to mountains further north on the continent where it still may be cool enough for them.
For one thing, she said, "pikas are incredibly sensitive. They sometimes die just from being handled."
Across America and the world, studies in hundreds of different local mountain ecosystems have found creatures, adapted to the average temperatures of specific elevations, struggling to find cooler ground upslope. Where their path is blocked, often by human development, they can die out.
One study in the California Sierras found many species relocating at elevations more than 2,000 feet above traditional sites.
Unless humanity manages to curb the current rapid rise in average global temperatures, said Ray, the American pika could disappear forever.
"If the current trends continue at the rate they're going right now," ecologist Ray said, it could well be that the American pika "will be extinct within the next 100 years."