Snowpack and precipitation play a larger role in the abundance of American pikas in the Great Basin, no matter how much good habitat is available.
That’s what scientists for the U.S. Geological Survey, University of Montana and Montana State University report in a new journal article in Ecology.
Pikas, a cousin to the rabbit that looks like a hamster and lives among broken rocks mostly in high-elevation mountains, is disappearing from much of its former habitat. The size of pika populations did not correlate with the extent of habitat present in either the 1990s or 2000s, according to the researchers, who revisited sites where pikas were first recorded in historical surveys going back more than a century.
The results suggested that climate change may be adding another filter for suitability of habitats. The amount of rain from June to September and the size of the snowpack appears to be the best predictors of pika density today, US Geological Survey research ecologist Erik Beever, lead author of the study said.
“Precipitation appears to be important because it can influence the amount of food available for pikas in the summer, and an insulating snowpack can minimize exposure of pikas to extreme cold-stress,” Beever said.
Snowpacks have been declining since the 1930s across the West at the same time that temperatures have been rising, the U.S. Geological Survey said.
Most surprising to the researchers was that smaller pika populations didn’t necessarily mean a higher risk for extinction.
“ We were surprised to find that sites with higher extinction risk in 1999 had larger populations in 2003-2008,” Beever said.
Studying these herbivorous mammals helps scientists measure the effects of climate change on the ecosystems that millions of living things, including humans, depend on.
“Pikas may be the early sentinels of biological response to global climate change, ” Beever told me in 2006.
The earth’s warming process happened gradually for most of the period since the cooler Pleistocene era 10,000 years ago, Beever said. But in the last two decades, he and other scientists have seen pika distribution reduced at rates of years and decades instead of centuries and millennia in the Great Basin.
Most of the remaining habitat is in alpine areas like Idaho’s Sawtooth Mountains and other ranges. But Beever found in the late 1990s that pikas were thriving in Craters of the Moon, the high desert Snake River Plain near Arco that’s dominated by 2,000- to 15,000-year-old lava flows, caves and fissures.
In most of the rest of their range, pikas live only in talus, broken rock that lies on a steep mountainside or at the base of a cliff. In these piles of scree, creatures with thick fur coats find refuge from the warm temperatures — 77 to 85 degrees — they can’t tolerate.
In earlier times, pika populations waxed and waned with the gradual climactic changes, Beever said. They were able to expand their range in cooler times, migrating from rock pile to rock pile down to lower elevations like the 5,900-foot Craters of the Moon.
But now the change is happening faster, scientists say. Rising temperatures are forcing pika colonies out of low elevations. Roads, housing developments and even livestock are standing in the way of traditional routes upward.
Craters of the Moon has a high desert climate, with average high temperatures during the summer around 80 degrees and average low temperatures in the winter in the teens. Its relatively flat lava flows connect to the Pioneer Mountains, the southern edge of the northern Rockies.
From there, historically, the pikas were biologically connected all the way north into British Columbia, the northern edge of their habitat today. Craters of the Moon is among the lowest elevation sites where pikas survive today.
Pikas remain there because of the physical complexity of the lava structures, Beever found in the 1990s. Throughout the lava, there are thermal “micro-refugia,” cooler places, where pikas can go.
When Mackenzie Jeffress, a University of Idaho grad student and now with the Nevada Department of Wildlife visited Craters in 2010 and 2011, the pika were still in the lava structures. But in pika’s traditional habitat in traditional talus fields, where pikas were found as recently as the 1980s, they no longer occur there.
“They remain in the lava flows that provide those suitable microrefugia from climatic stresses, Beever said.