Written by Soleil Gaylord

Miners brought canaries into coal mines for decades. More sensitive to colorless and odorless gases than humans, these small birds were the original carbon monoxide alarms. Carbon dioxide — another colorless, odorless gas — has now reached atmospheric concentrations over 400 parts per million, but instead of the canary, a small alpine lagomorph is our warning signal of what is to come for other species globally. 

The American pika, Ochotona princeps, has been dubbed an “indicator species” as an acutely climate-sensitive, alpine mammal. Climate change affects pikas in numerous ways by drying out vegetation and therefore pika forage, causing pikas to experience heat stress, reducing their ability to disperse from their mother’s territory once grown, and even by reducing already low rates of gene flow among populations. As average global temperatures have increased, climate change has extirpated pikas — or caused local extinctions — in lower, hotter sites. Remarkably, pikas can suffer from heatstroke and die at temperatures higher than 78 degrees Fahrenheit when prevented from the ability to retreat into the talus and broken rock interstices. These small, silvery members of the rabbit and hare order have a high resting metabolic rate, making even incremental increases in their body temperature a possible death sentence. 

Pikas have experienced a nearly five-fold increase in the rate of local extinction, as well as an 11-fold increase in the rate of migration upslope.

In one study, pikas moved upwards at an average rate of about 145m per decade as they attempted to escape warm temperatures in the Great Basin. Great Basin pikas have experienced “significant,” or greater than 28%, extirpation from historical habitat in the last half-century. They have disappeared from 7 of 25 sites in the Great Basin.

Peter Billman, a Ph.D. student at the University of Connecticut who studies pikas, said they are well adapted for cold with their thick fur coat, and their sensitivity to high temperatures makes them especially vulnerable to climate change. 

“Their resting body temperature is pretty close to lethal, so if they get just a little bit warmer, they can die of heat stress.” “We are seeing a lot of losses of pikas in lower, hotter, and drier regions,” Billman said, adding that this is a range-wide phenomenon. 

Billman said that because pikas are so sensitive to changing climate conditions, they serve as early indicators of broader shifting ecological conditions, often signaling how other species in the ecosystem might respond. 

Pikas leave hay piles, pellets, and urine stains in their wake, making it easier for scientists to determine if pikas previously occupied a site. According to Billman, this has allowed researchers to find robust correlations with where pikas are now — typically cooler, wetter areas — compared to where they used to be, often lower and increasingly hotter sites.

Due to their high metabolic rates, pikas cannot hibernate and remain active all winter by feeding on stored hay. Pikas must stay warm during frigid winter temperatures. Subnivium, the space between snowpack and ground, provides pikas with a vital refuge from cold winter temperatures. Counterintuitively, as the climate warms and snowpack declines, organisms like the pika that rely on insulation provided by snow will be negatively affected by freezing winter temperatures. 

According to one study, with climate change, “functionally” colder winters have increased, meaning that as snowpack declines, there is less snow to buffer pikas and other subnivium-dependent organisms from the extreme cold above. That means that to pikas, winters will be colder solely because of the reduced snowpack. Additionally, snowpack provides a steady and critical water source to plants and animals during melt-off. 

“We might expect to see greater extirpations and lower overwinter survival,” Billman said. 

Though pikas have been heralded as an indicator species in mountain ecosystems affected by climate change, making their decline more significant, pikas are also a keystone species. To lose the pika means to lose nutrient redistribution, important grazing and seed dispersal in alpine regions, and an important food source for predators. Pikas have shown us that climate change can cause species to decline even where suitable or protected habitat is intact. 

Jennifer Wilkening, a research ecologist who has studied pikas for 20 years, said climate-related pika population decline should be cause for alarm. 

“Species provide many benefits, emotionally, intellectually, and philosophically to humans everywhere,” Wilkening said. “Pikas are a very important indicator species; they give us a sense of what might be happening within alpine ecosystems and what might be happening at the larger scale in terms of climate change.”