JACKSON, Wyo. — Pikas utilize body posture and talus (loose rock) surfaces as tools to thermoregulate, but the limitations of these behaviors might be critical to the species as extreme temperatures and low snowpack could become more common.
According to Erik Beever, who’s been performing research on American pikas across the western U.S. since 1994 in 14 different regions, pikas are endothermic and internally generate their body heat. Beever says this is true of all mammals, which differs from species that are ectothermic and have internal temperatures that are dependent on ambient air.
All mammals are also homeothermic, which Beever says means they maintain a constant body temperature. He emphasizes this is particularly relevant to understanding pikas.
“If their internal body temperature changes by just a little bit more than three degrees Celsius, they die.”
Erik Beever
“If their internal body temperature changes by just a little bit more than three degrees Celsius, they die,” Beever tells Buckrail. “The idea of keeping a constant body temperature is a big, big deal because they have this narrow window that their body temperature has to be in.”
A study published by Beever et al. in 2017 explores how pikas can regulate their body temperature by modifying their body shape. In the winters, pikas will squeeze into a ball-like shape to minimize heat loss by reducing their surface-area-to-volume ratio.
According to data from over 200 pika photos taken near Calgary, Canada, approximately three-quarters of the time pikas adopt a ball-like posture when in temperatures below five degrees Celsius, roughly 41 degrees Fahrenheit. Alternatively, less than one-eighth of the pika images reviewed, or about twelve percent, showed pikas that appeared squeezed into a ball when it was warm.
In those warmer months, Beever reports that pikas can stretch out to increase their surface area and cool down. However, he says that because their insulating hair is great at preventing heat from being lost, pikas are less effective at handling those high temperatures.
Activity restriction is another tool for staying cool in warmer months. Beever says in places like New Mexico, the Great Basin or lower elevations in other parts of their range, pikas are more crepuscular and most active at dawn and dusk; this increases predation stress on those populations since many predators are also crepuscular, or nocturnal.
While that’s not currently being observed frequently in the Tetons, local pikas are shuttling into talus to shelter in more constant temperatures that are buffered from the ambient weather conditions.
Beever says the deeper the talus, the better, and Grand Teton National Park has some notably deep talus areas that shield pikas from temperature extremes. But there are costs to remaining in this buffered environment for too long, Beever says, restricting the time pikas can spend foraging or looking for mates. In places with shallower talus, Beever highlights that even cold-adapted pikas struggle during snowless periods where there’s no insulation, and cold snaps can seriously threaten the population.
Weighing only 150 to 200 grams, pikas don’t have energy reserves like elk, mule deer or pronghorn to soak up temperature stress. While most mammals generate heat by shivering, pikas do something Beever calls “non-shivering thermogenesis,” metabolizing their adipose tissue known as “brown fat” to stay warm.
Beever notes that while these certain behaviors allow pikas to cope with some weather stresses, thermoregulation has hard biophysical limits that only allow them to accommodate up to a certain point.
“It is a double-edged sword,” Beever says. “Such flexibility is nice in the sense that it’s immediate. It allows them the ability [to thermoregulate] without a ton of investment to mediate different kinds of energy flows…but if pushed beyond certain realms of weather and climate, especially in the absence of a nearby refugium like subsurface ice, [pikas] just go away.”
The minimum and maximum critical temperatures for pika are still not fully known across all parts of the species’ range, or how temperature limits may change depending on individual pika populations and where they’re located. Regardless of the numbers, Beever says it’s clear that if temperatures get too hot or too cold without sufficient local refuge, pikas aren’t going to survive.
