The American pika is a rotund, mountain-dwelling relative of rabbits, famous for adorably darting around with mouthfuls of grass and wildflowers. It's well-adapted to alpine terrain, where its fur, girth and resourcefulness have helped it endure for millennia.
Yet despite its popularity and resilience, this pika has vanished from a large stretch of habitat in California's Sierra Nevada, a new study finds. The local extinction spans 64 square miles, the largest area of pika extinction reported in modern times.
The American pika is not listed as threatened or endangered, but its population is decreasing overall, according to the International Union for Conservation of Nature (IUCN). The problem is that pikas have adapted so well to cold mountain climates that warm weather — even temperatures as mild as 78 degrees Fahrenheit — can become deadly within a few hours. And while pikas can flee warmth by moving higher up mountains, that strategy only works until they reach the top. That's why, according to the IUCN, "the most pervasive threat affecting the American Pika appears to be contemporary climate change."
Pikas' round bodies and thick fur evolved to insulate them from high-elevation winters, and they also spend summer hoarding grass and wildflowers into winter food caches known as "haypiles." These adaptations help them stay in their harsh habitats all year without need for hibernation, but as those habitats heat up, a pika's superpowers can quickly backfire.
"A larger haypile acts as insurance policy against winter starvation," says lead author Joseph Stewart, a Ph.D. candidate at the University of California Santa Cruz, in a statement about the new study. "But the same adaptations that allow them to stay warm during winter make them vulnerable to overheating in the summer, and when summer temperatures are too hot, they can't gather enough food to survive and reproduce."
The area where pikas have vanished stretches from near Tahoe City to Truckee, more than 10 miles away, and includes the 8,600-foot-tall Mount Pluto. Stewart and his colleagues searched the 64 square miles over the course of six years, from 2011 to 2016. They looked for the animals' distinctive droppings, which can last a long time because boulders often protect them from sunlight and rain, and camped next to former pika habitats, listening for their squeaky bleats. "We found old pika fecal pellets buried in sediment in nearly every patch of habitat we searched," Stewart says. "But the animals themselves were conspicuously absent."
Pikas definitely once lived there, so to figure out when they disappeared, the researchers relied on radiocarbon dating.
"Above-ground nuclear arms testing, from before the 1963 Partial Nuclear Test Ban Treaty, resulted in an elevated concentration of radiocarbon in the atmosphere, and we used this signal to determine an age range for the relict pika scat," says co-author Katherine Heckman, a radiocarbon scientist with the U.S. Forest Service. Their findings suggest pikas vanished from many lower-elevation sites around Mount Pluto before 1955, but held out near the mountain's peak until as recently as 1991.
"The pattern is exactly what we expect with climate change," Stewart says. "As the hottest, lowest-elevation sites became too hot for pikas, they became restricted to just the mountain top, and then the mountain top became too hot as well."
Pikas have overcome natural climate changes in the past, Stewart notes, but those happened much less quickly. As with many species of wildlife, American pikas are struggling to keep up with the pace of modern, human-induced climate change.
"The loss of pikas from this large area of otherwise suitable habitat echoes prehistoric range collapses that happened when temperatures increased after the last ice age," Stewart says. "This time, however, we're seeing the effects of climate change unfold on a scale of decades as opposed to millennia."
It's not too late to see American pikas in mountains near this area of extinction, he adds, noting that "Mount Rose and Desolation Wilderness are still great places to see pikas." Time is running out, though, as the researchers forecast that, by 2050, climate change will lead to a 97 percent decline in suitable conditions for pikas in the Lake Tahoe area.
"Our hope is that simply getting the word out there that climate change is causing iconic wildlife to disappear will get people talking and contribute toward political will to reign in and reverse climate change," Stewart says. "There's still time to prevent the worst impacts of climate change. We need our leaders to take bold action now."
Related on MNN: 'Magic rabbit' photographed for first time in decades