Mammals Feel the Heat

For red squirrels and pikas, two very different reactions to global warming

• Laura Tangley
• Jun 01, 2003

FOR MAMMALS confronting a warming world, scientists have discovered both good news and bad. One worrisome study, published in the Journal of Mammalogy, reports that global warming already may have contributed to local extinctions of the American pika, a smaller relative of hares and rabbits that inhabits high-elevation talus of western North America. Revisiting 25 pika populations known to exist in the U.S. Great Basin half a century ago, scientists discovered that seven populations are now extinct. Their statistical models suggest that global warming has contributed to the extinctions, interacting perhaps with habitat loss, roads and other stresses.

Lead author and ecologist Erik Beever of the U.S. Geological Survey’s Forest and Rangeland Ecosystem Science Center calls the study’s results "alarming, because scientists previously assumed that these alpine and subalpine ecosystems are relatively undisturbed due to their isolation." He adds that pikas, which cannot travel great distances, are particularly sensitive to higher temperatures and "may be an early signal" of the havoc global warming may wreak in high-elevation habitats.

Another mammal, the red squirrel, seems to be faring better. University of Alberta researchers found that squirrels in Canada’s southwest Yukon are evolving to cope with global warming, by breeding an average of 18 days earlier than they did a decade ago. They say the change—greater than what would be expected from behavioral plasticity—is most likely driven by shifts in springtime food availability.