It’s spring and over the wetlands of the Truckee River watershed the cries of killdeer fade into the warming dusk and Lake Tahoe’s only island has again become a babbling cacophony of nesting Canada geese. Far upslope in the high talus fields near the basin’s rim some of the most vocal mammals of the watershed are being just about as sociable as they can be. As summer passes and colder temperatures approach, the American pikas will become more territorial; but for now, it’s time to mate. The pikas rendezvous among the jumbled rocks of their homes in early spring and give birth by July. If the warm weather lasts long enough they’ll multiply a second time before the onset of winter.
American Pikas (Ochotona princeps) are diminutive members of the rabbit family who lack their relatives’ outsize ears. An adult might weigh only 100 grams and give birth to a newborn the size of a walnut, but pikas compensate for their small stature with their piercing bleat-like calls, which carry with an almost ventriloquist clarity through the thin air of their high elevation homes.
In the Sierra Nevada, pikas probably don’t live lower than 8,000 feet, though researchers conjecture that such heights haven’t always been their homes. Fossils dating back to the late Pleistocene indicate that pikas once inhabited the lowlands as well. As the climate gradually warmed over the last 10,000 years their populations moved higher and higher in search of the cool temperatures and snow cover they need to survive. Western North America has echoed with the voices of the pikas for so many centuries, but if human-induced climate change continues as predicted the mountain scree slopes the pikas currently call home could fall silent within two centuries.
Unlike the marmots and golden-mantled ground squirrels that often live nearby, pikas don’t hibernate in the winter. Mantled squirrels will feast their body fat as high as 45 percent to prepare for cold weather torpor, but pikas don’t put on weight. They rely upon their fur, the piles of grass they’ve dried and stored during the summer, and a layer of snow to protect them from the winter chill. Pikas stake their territories near the edges of talus fields and spend most of their time down in the tunnels and spaces between the rocks. There in the shadows the temperature stays almost constant throughout the year – provided enough snow falls to insulate the pikas from the worst of the winter chill.
In the summer, the cool spaces between the rocks become a refuge from the sun since the pika’s warm coat and lack of body fat make the tiny mammal especially susceptible to heat. Scientists have caged pikas on top of scree fields during midday and learned that in 80-degree weather they will die within six hours.
The experiment provided biting proof for the poet’s description of man’s intellect – it ‘murders to dissect’ – but also gave researchers insight into one of the dynamics driving American pikas to extinction. Don’t jump to any conclusions yet though; they aren’t just dying from the heat.
In 2003, a USGS geologist named Erik Beever surveyed pika populations in the Great Basin. After comparing his results to historic data he learned that six of 25 pika populations had winked out of existence in the course of 40 years. Since he published his paper three more have vanished. According to Chris Ray, a researcher from the University of Colorado at Boulder who has worked with Beever and has studied pika populations in the Rockies for more than a decade, maximum summer temperature is a strong predictor of pika extirpation, but isn’t the only one and by itself isn’t the strongest.
According to Ray, pika populations on peaks in the Great Basin persist in places that have seen the largest decline, over the last 60 years, in the annual number of cold days. In other words, the pikas are having trouble withstanding cold snaps. If Ray is correct that’s a result of declining precipitation. Without an insulating layer of snow, pikas are freezing in their homes. Ray defines ‘cold’ as 23 degrees Fahrenheit. Outright heat is less of a factor as well, though pikas are disappearing from the places with the highest summer temperatures.
At the same time, pikas are surviving where they have somewhere to run to. If a talus field extends far upslope its residents can move higher to find places where more snow falls in the winter and temperatures are cooler in the summer. This slightly improves the outlook for populations in the Sierra Nevada and Rocky Mountains where talus fields tend to be larger, but means little to populations in the Great Basin. There, most pikas have climbed as high as they can.
‘We might still have pikas in a few places a hundred years from now even with climate change,’ Ray said. ‘But we’re losing them real rapidly from a lot of places, we’re losing a lot of genetically unique populations and we don’t know what to do about it except stop global climate change. There’s really no other solution.’
Many thanks to LTBMU wildlife biologist Julie Roth, Jim Patton of the Berkeley Museum of Vertebrate Zoology, Chris Ray of the University of Colorado at Boulder, and Mary Peacock of UNR for their input.
Wondering where the wilds around you have gone, or just in a muddle over the mountain beaver? Email bioregionboy@moonshineink.com.
Tahoe survey yields baseline pika data…
The Lake Tahoe Basin Management Unit recently compiled the results of a three-summer plant and wildlife survey in the Tahoe basin. Pika were detected at 30 of the 253 sites sampled. They were most abundant from the Upper Truckee River down the west side of the basin toward Ward Canyon. As yet, it’s unknown if local populations are dwindling. The survey only provided baseline data for future comparisons.
