Extensive high altitude habitat may serve as a climate refuge for tiny alpine mammals
By Bob Berwyn
SUMMIT COUNTY — Despite concerns about climate-change impacts, it appears that the high-alpine reaches of the southern Rockies still holds plenty of good habitat for American pikas, according to a University of Colorado Boulder study released this week.
The temperature-sensitive mammals have been singled out as a possible bellwether species for global warming impacts in mountain regions, but the extensive CU survey shows that populations appear to be holding their own. Localized population declines appear to be linked to the dryness rather than directly to temperature, according to CU doctoral student Liesl Erb, who led the study.
“The sites that had been abandoned by pikas in our study area all were drier on average than the occupied sites,” she said.
Erb’s team assessed 69 historical sites known to host pikas in a swath of the Southern Rockies ranging from southern Wyoming through Colorado and into northern New Mexico. The results showed that 65 of the 69 historical sites that had hosted pikas — some dating back more than a century — were still occupied by the round-eared, hamster-like mammals, Erb said.
The American pika lives in mountainous regions including British Columbia, Washington, Oregon, Idaho, Montana, Utah, Wyoming, Colorado, Nevada, California and New Mexico. Members of the rabbit family, the conspicuous pikas can be seen scurrying about rocky debris known as talus in alpine and subalpine regions of the Rockies, emitting their signature, high-pitched squeaks. Instead of hibernating, pikas cache huge amounts of plants and flowers known as hay piles under large rocks that sustain them through the long winters.
“There’s so much habitat here compared to the other areas where pikas have been studied,” Erb said, referring to recent surveys that suggested a significant decline of pika populations in the mountains of the Great Basin. Pikas most often live among the boulder fields on steep mountainsides, near meadows where they harvest hay to eat during the long, cold winters.
The Great Basin study found that some pika populations had moved uphill by 500 feet, signaling a possible response to global warming. Other findings suggest that losses of local pika populations in the region may be linked to cold weather, combined with a lack of snow, which provides winter insulation for the animals.
On the other end of the spectrum, pikas may reduce summer foraging activities to avoid heat stress caused by rising temperatures, leading to smaller winter food caches that can’t sustain them during extreme cold snaps, said Chris Ray, a CU-Boulder research associate who co-authored the study with Erb.
Erb said the study suggests that the Southern Rockies still have extensive areas of well-connected habitat for pikas, which don’t roam widely across the landscape, and don’t appear to be significantly affected by the relatively small-scale human impacts found in the alpine zone. It also appears as though there’s room for pikas to move up in elevation to suitable habitat, should lower-elevation sites become to warm or too dry for the animals, she added.
The lovable little critters might still be susceptible to future climate change impact, Erb said. While some studies show that marmots, for example, are growing larger, possibly because of longer growing seasons, pikas are very sensitive to temperatures.
“We don’t expect pikas to necessarily benefit … they are more temperature sensitive than marmots. If it’s too hot in the summer, they may not be able to hay enough in the summer to sustain them through the winter,” she explained.
Alpine species are among the plants and animals most threatened by climatic shifts because of their physiological and geographic constraints, Erb said. In 2010, the U.S. government denied endangered species listing for the American pika in part because there was insufficient data on its distribution and abundance across western North America.
“Many have assumed that warming temperatures would be the primary signal affecting North American pikas,” said co-author Robery Guralnick. “This study shows it is more complicated than that, and that drier conditions could affect the persistence of pikas across the West.”
The CU-Boulder study team initially looked at about 800 historical records of pika sightings in Colorado, New Mexico and Wyoming, but most locations were not specific enough for scientific use. The team eventually narrowed down the historical sites of pikas to 69 specific places known to have been occupied at some point before 1980, using tools like GPS to help pinpoint the geographical accuracy of each individual site.
The CU team used data from Oregon State University’s PRISM Climate Group to compile local climate information from 1908 to 2007 for the 69 historical pika sites in the Southern Rockies. The information produced estimates of monthly precipitation and minimum and maximum temperatures. The team confirmed the presence of pikas at each site either visually, by their distinctive squeaks, or by evidence of fresh pika hay piles cached under rocks in the study areas.
Sites visited early in the 2008 field season that lacked fresh pika signs were revisited in late October and early November for re-evaluation, Erb said. In places where pikas were still absent, researchers searched rock slopes up to two miles in all directions in an attempt to locate pika populations.
Volunteers have helped gather similar data on pikas through the PikaNET program, the Front Range Pika Project and the New Mexico Pika Monitoring Project. Such volunteer projects are organized through collaborations between CU-Boulder, the Colorado Division of Wildlife, the Denver Zoo, Rocky Mountain Wild, Colorado State University, the Mountain Studies Institute in Silverton, Colo., the San Juan Public Lands Center headquartered in Durango, Colo., and the Seventh Generation Institute in Santa Fe, N.M. Click here for more information on how to get involved with citizen monitoring.
“It is good news that pikas are doing better in the Southern Rocky Mountains than some other places,” said Erb. “It is likely that the geographic traits of the Rockies are a big reason why we are not seeing significant declines, at least not yet.”
A paper on the new CU-Boulder study by Erb is being published in the September issue of the journal Ecology.