The polar bear may be bigger (like, much bigger) and better-known, but there's another mammal native to harsh environments that folks concerned about climate change – and, oh yeah, that should be everybody – are paying close attention to.

We're talking here about that little roly-poly mountaineer the American pika, and some new research from the northern Sierra Nevada of California raises fresh concerns for its future on a warming planet.

Before we get into that story, let's take a page from the playbook of Sarah Gilman – who tempered a sobering 2011 High Country News report on pikas and climate change with cuteness – and convince you why you should be concerned about this diminutive rock-dweller.

First, pikas have a pretty adorable way of sounding the alarm: a high-pitched bleat familiar to many a hiker who's spent any time rambling the mountains of the American West. They're basically dog squeaky toys come to life:

Pikas are taxonomically sneaky, too: at first glance you'd assume they're some sort of alpine hamster, but actually they're lagomorphs, kin to rabbits and hares. (Pikas have been called "rock rabbit", "whistling hare" and "mouse-hare" – why not "hamster-hare?" – though probably the most widely used alternative name in North America is "cony".)

We can also admire pikas for their work ethic and all-around hardiness. Their favourite digs are those mountainside rockpiles called talus: jumbles of boulders often found at the foot of cliffs or beneath ridge crests. Here, the furballs seek refuge from temperature extremes and predators (eagles, coyotes, foxes, wolverines and the like) in the cool, dark crannies, which is also where they stash "haypiles" of grass and forbs for a cold-season larder. Pikas, you see, don't hibernate, so they rely on those haypiles – plus lichen and other under-snow forage – to get by during blizzardy mountain winters.

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Stocking up for the winter while the sun shines. Image: Stoil Ivanov/YouTube

All right, now to the research! A new study published in PLOS ONE documents the likely disappearance of pikas from a 165-square-kilometre swathe of the Sierra Nevada immediately northwest of Lake Tahoe. Defined by the lakeshore, a highway and the Truckee River (Lake Tahoe's outflow), the wedge of habitat – the researchers call it the Pluto triangle, after the 2,625-metre Mount Pluto roughly at its centre – made a stepping stone between pika populations along the main Sierra crest to the west and a high subsidiary uplift, the Carson Range, to the east.

The team identified likely talus outposts in the Pluto triangle and surveyed for pika presence there between 2011 and 2016. Sure enough, they found plenty of evidence in the form of the conies' distinctive faecal pellets – except they were all on the vintage end of the spectrum, nothing recent. Radiocarbon dating suggested pikas were disappearing from the area by the mid-twentieth century, and likely last inhabited the triangle in the early 1990s.

Data from a nearby weather station, meanwhile, showed average annual temperatures in the area rose by 1.9 degrees Celsius, and snowpack substantially declined between 1910 and 2015. Pikas are adapted for high-country cold: the brisk metabolism and thick pelt that serve them well in winter make them vulnerable to overheating in summer. Although they can seek refuge from high temperatures in talus nooks, too many hours spent holed up from the heat means less time out gathering for their winter pantry.

“In the face of climate change, pikas will retreat upslope as average temperatures rise, and in some mountain ranges, they'll eventually run out of higher elevations in which to seek refuge.”

And climate change doesn't just stress pikas with summer heat: a scantier high-country snowpack could make overwintering pikas more vulnerable to cold, given snow roofs insulate their talus colonies.

Other studies have shown that areas historically (but no longer) inhabited by pikas in California experience average summer temperatures above 14.2 degrees Celsius. Weather-station records analysed by the researchers show that such temperatures have become the norm in the Pluto triangle in recent decades, supporting the hunch that climatic shifts are the likeliest explanation for the disappearance of local conies.

That disappearance, the researchers note, has likely severed the genetic flow between pikas along the Sierra crest and those in the Carson Range.

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A pika in the High Sierra (National Park Service)

Pika distribution in North America has expanded and contracted across millennia, with periods of pika-friendly cooling and pika-unfriendly warming. (Indeed, the fossil record shows ice-age pikas inhabited lower-elevation steppes, as some Asian pika species still do today.) The warming trend following the most recent North American glacial period (the Wisconsin) drove the region's pikas upslope, scrunching their distribution mainly to loftier mountain ranges, and wiping out many isolated populations.

The disappearance of the "rock rabbits" in the Pluto triangle in the face of a warming climate seems to mirror this prehistoric pattern, as well as more recent documented pika losses in the semi-arid Great Basin of the western US. Pika habitat in the Great Basin is naturally fragmented because suitable mountain ranges are isolated by surrounding dry steppes (the ranges are therefore often called "sky islands"). But this new research suggests pika populations even in core and continuous habitat such as the Sierra Nevada may be vulnerable to climate warming, and also reveals the speed with which those populations may die out.

"Our results suggest that, at least in some areas, the timeframe of shrinking of pika distribution as a result of warming temperatures is likely to be on the scale of decades, not centuries," the authors of the study warn.

What's more, habitat modelling conducted by the team suggests that a warming climate could dramatically reduce pika distribution more broadly across the Lake Tahoe region by 2050. One general prediction is that, in the face of climate change, pikas will retreat upslope as average temperatures rise, and in some mountain ranges, they'll eventually run out of higher elevations in which to seek refuge.

We know, however, that certain US populations at lower-than-usual elevations appear capable of adjusting their lifestyles to deal with warmer conditions – exhibiting (to get technical about it) "behavioural plasticity". A prime example are the pikas of the Columbia River Gorge on the Oregon-Washington border, at home just a few hundred feet above sea level. These low-country pikas seem to beat the significant summer heat of the canyon (lately on fire) by foraging in the shady forest edging their rocklands. In the mild maritime winters of the region, they actively go out and about to feed on moss, a year-round food source.

This flexibility could make some pika communities resilient to hotter climates, at least to a point. But it's not at all clear how common such a response will be.

The Sierra Nevada research certainly hints at the potential of climate change to eliminate the dispersal corridors and "stepping stone" habitats that help maintain genetic diversity in formerly uninterrupted wildlife ranges, putting the viability of cut-off populations at risk even if the environment of an isolated climate refuge remains suitable.

As the authors of the study conclude, "We anticipate this study foreshadows an era in which accelerating climate warming will drive the extirpations not just of species' peripheral habitat, but cause fragmentation of core habitat for many species."



Top header image: llsproat/Flickr