U. COLORADO (US) — American pikas, whose numbers have been on the decline, are holding their own in the Southern Rocky Mountains, a new survey finds.
Researchers at the University of Colorado at Boulder 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 show 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, says doctoral student Liesl Erb, who led the study.
The new report, published in the September issue of the journal Ecology, stands in contrast to a 2011 study in Nevada’s Great Basin that showed local extinction rates of pika populations there have increased nearly five-fold in the past decade.
That study, by a separate research group, also showed that local Great Basin pika populations had moved up in elevation nearly 500 feet in the past 10 years, a migration believed to be triggered by warming temperatures.
Despite the low number of extirpations, or local population extinctions, in the Southern Rockies, the CU-Boulder team found that the pattern of pika disappearance at particular sites was not random, says Erb.
“The sites that had been abandoned by pikas in our study area all were drier on average than the occupied sites,” she adds.
One likely reason for the relative success of pikas in the Southern Rocky Mountains study is that available habitats are higher in elevation and are more contiguous than habitats in Nevada’s Great Basin, says Erb. But some climate models are predicting drier conditions in parts of the Southern Rockies in the coming decades as the climate warms, she notes
Alpine species are among the plants and animals most threatened by climatic shifts because of their physiological and geographicconstraints, explains Erb.
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. The American pika lives in mountainous regions including British Columbia, Washington, Oregon, Idaho, Montana, Utah, Wyoming, Colorado, Nevada, California, and New Mexico.
Surprisingly, most of the pikas that have disappeared from Great Basin sites under study in recent years were from sites that experienced extremely cold temperatures and may be related to a lack of winter snowpack insulation, says study co-author and research associate Chris Ray, who has participated in several GreatBasin pika studies including the 2011 study.
Ray suspects 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.
Study co-author Robert Guralnick, associate professor in the ecology and evolutionary biology department, says pikas are becoming a “bellwether” species for mountain ecosystems, primarily due to their recent Great Basin declines. Prior to the new survey, population trends of pikas in the Rockies were relatively unknown, he says.
“Many have assumed that warming temperatures would be the primary signal affecting North American pikas,” says Guralnick. “This study shows it is more complicated than that, and that drier conditions could affect the persistence of pikas across the West.”
The 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 researchers 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.
They 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 says. 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.
“It is good news that pikas are doing better in the Southern Rocky Mountains than some other places,” says 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.”
The study was funded primarily by the National Geographic Society.
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