Tiny mammal a little loser during big climate shift

BOISE – Researcher Erik Beever has watched the effects of climate change play out in front of his eyes.

The U.S. Geological Survey research biologist from Bozeman studies American pikas, which are disappearing from the Great Basin that stretches from Idaho to California and where Beever and other researchers found them just a decade ago.

A new study published last week in the journal Ecology says less winter snowpack and summer rain are the major factors in the pika’s disappearance, even where good habitat is available.

The size of pika populations did not correlate with the extent of habitat, in either the 1990s or 2000s, according to the researchers who visited sites where pikas have been recorded in surveys going back more than a century. In other words, precipitation is the deciding factor in the health of the American pika in the Great Basin, no matter how much good habitat is available.

“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.

The results suggested that climate change may be creating a new factor in the suitability of habitat.

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 put them at higher risk for extinction.

“We were surprised to find that sites with higher extinction risk in 1999 had larger populations in 2003 to 2008,” Beever said.

The earth’s warming happened gradually for most of the period since the cooler Pleistocene era 10,000 years ago, Beever said. But in the past two decades, he and other scientists have seen Great Basin pika distribution reduced in terms of years and decades instead of centuries and millennia.

Most of the remaining habitat is in alpine areas, like Idaho’s Sawtooths and other mountain 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 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 on steep mountainsides or at the bases of cliffs. In these piles of scree, the little creatures with thick fur coats find refuge from the 77- to 85-degree temperatures that they can’t tolerate.

But Craters of the Moon National Preserve’s lava structures were filled with pikas when Beever surveyed the areas in 1995. The physical complexity of the lava structures was the key, he found. Throughout the lava, he said, there are thermal “microrefugia” – the cooler places that pikas like.

When Mackenzie Jeffress, a University of Idaho graduate student now with the Nevada Department of Wildlife, visited Craters in 2010 and 2011, the pika were still thriving in the lava structures.

But in Craters’ talus fields, where pikas were found as recently as the 1980s, they were gone.

“They remain in the lava flows that provide those suitable microrefugia from climatic stresses,” Beever said.

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, the pikas have been biologically connected all the way to British Columbia, the northern edge of their habitat today. Craters of the Moon is among the lowest-elevation sites where pikas survive today.