By Steve Stampfli. Feb. 28, 2018. Many folks are aware that a small rabbit-related species, called the American pika, inhabits some low-elevation talus slopes in the western Columbia River Gorge. It is an unusual occurrence because pikas usually inhabit mountainous regions above 4,000 feet in our section of the Cascade Range. How and why populations occur near sea-level in the Gorge has remained largely unknown.
Most pikas are found dwelling on rocky slopes at elevations of 4,000 feet or more, which makes the population on the western edge of the Gorge an anomaly of sorts. Photo courtesy of NPS.
Pikas have very narrow physiological tolerances to both high and low temperatures. If unable to find some sheltering component in their natural habitat, they cannot survive more than a few hours in direct summer heat exceeding 78 degrees F. Likewise, they struggle during winter in places that are very cold and/or wet, and usually rely on sheltering in dens below snow packs in their typical high-elevation haunts.
After continued study, scientists now believe that the Gorge pika population represents the species’ lowest elevation occurrence in North America (excluding the coasts of British Columbia). And, as with any study, a number of theories have surfaced in an attempt to explain the seemingly out-of-place population. Some reports in the popular and scientific press suggest that the population evolved physical or behavioral adaptations that allow survival at our near sea-level elevations. At the same time, some of these reports conclude that these adaptations might not be enough, and that the population might perish as a result of the species’ direct exposure to a warming climate in an already warm elevation and latitude.
But is our current knowledge of the Gorge population, and more importantly its habitat, extensive enough to make such conclusions? Is the Gorge population unique in its ability to manage extreme temperatures? Or, is it possible that pikas, wherever they exist in North America, are linked to some little-understood habitat mechanisms that partially ‘decouples’ their temperature tolerances from the ambient environment, and facilitate survival in what appear extreme climates?
Researchers observed one such possible habitat mechanism during the summer of 2017 at a low-elevation pika colony at the base of Shellrock Mountain in the western Columbia River Gorge. On July 5, they discovered a patch of talus that displayed sub-freezing temperatures one foot below the surface. The patch was later determined to be a ‘periglacial’ feature occurring at an exceedingly low elevation. Historical evidence confirmed that the feature was noted by Gorge pioneers at least 103 years ago, but has been largely forgotten since then.
Researchers discovered “periglacial” features on Shellrock Mountain, which helps explain how pikas can survive at such a low elevation. Photo: Jurgen Hess
Linked to this unique geologic finding are discoveries made by a team of US Forest Service scientists (working under the leadership of Connie Millar) in the Great Basin and Sierra Nevada regions of California and Nevada. This team discovered a critical link between anomalously cold hillside zones and pika populations. During examination of hundreds of rocky pika occupations in the Sierra Nevada and Great Basin (at altitudes ranging from 5,593 to 12,752 feet), the team concluded that most (82%) were in close proximity to frozen talus, rock glaciers, or similar rock/ice (i.e., periglacial) features.
Last year’s work indicates that largely unexpected geologic and atmospheric processes led to periglacial activity at extremely low elevations in the western Columbia River Gorge. Combining this observation with the USFS team’s findings, it seems increasingly likely that the presence of our low-elevation pika population can be credited to this largely hidden and unrecognized aspect of its habitat in the western Gorge.
Does evidence of Columbia Gorge pika dependence on localized periglacial activity indicate that the species is completely decoupled from the impacts of climate warming?
Some would say no.
It is increasingly clear that the species has evolved an underground lifestyle, made possible by an unusual geologic and atmospheric-driven cooling mechanism, which buffers it from daily and seasonal temperature extremes. But even if Columbia Gorge pika populations are partially decoupled from short-term heat and cold extremes, the hidden and little-understood physical processes that maintain the stable talus environment may be changing.
Scientists currently have little idea of how broad changes in the earth’s climate will impact the western Gorge, let alone thermal processes within talus slope environments. This is why further work to explore the atmospheric, geographic and geologic processes responsible for the anomalous ‘cold talus’ effect at Shellrock Mountain (and throughout the Gorge’s 20 mile long ‘pika belt’) would be beneficial—not only for the pikas, but for the people that inhabit this dynamic region.
For the full version of this article, visit: https://gorgescienceshare.wordpress.com/
We purchased the property that Jurgen Hess is standing in Jan 2017 and posted it “Private Property No Trespassing” on trees and in the middle of the trail that you would literally have to step over to gain access to the rivers edge where Jurgen Hess took the photo.
It should be noted that Jurgen Hess is a trespasser.