21 Aug 2025 5 min read

Layered Toxicity

Surviving in a harsh mountain environment takes ingenuity

A pika nibbling on a piece of grass. Photo by David Lukas

Pikas are best known as icons for climate change, but the story of how they survive harsh mountain conditions is more complicated than you realize.

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If you've hiked anywhere in the rocky landscapes of western mountains you've almost certainly heard the loud, sharp calls of pikas warning each other of your presence. Cryptically hidden and scampering amid rock crevices, these lovely little rabbit relatives that look like guinea pigs can be very hard to see.

pika running — A fleeting glimpse of a pika bounding through jumbles of rock. Photo by David Lukas

To my utter amazement, I had the great fortune this week of sitting within a few feet of two pikas (one larger male and one smaller female) who went about their business as if I wasn't there. I'm used to seeing pikas warily watching the world with big beady eyes and darting quickly into hiding places, so I was unprepared to discover how relaxed they can be.

sleepy pika — Stretched out and nodding off in the sun. Photo by David Lukas

Over the course of several hours, these two pikas spent long periods of time drowsing in the warm sun, grooming, eating their fecal pellets (a common rabbit behavior), yawning, and stretching.

grooming pika — A lazy grooming session. Photo by David Lukas

Such languid moments are rarely observed because a pika's life is otherwise a blur of frenetic energy as it spends its entire spring and summer squabbling over territories, seeking mates, and raising babies.

pika calling — Pikas are very vocal and have complex social interactions that include stealing food from each other. Photo by David Lukas

At the same time, pikas must gather enough surplus food to get them through the winter. Pika's don't hibernate and they don't accumulate fat, so they spend their summer harvesting, drying, and storing up to 50 pounds of food in a "haypile" that is literally the centerpiece of a pika's life.

A pika's haypile tucked under a rock out of the elements. Photo by David Lukas

Gathering this much surplus food in a rocky mountain landscape takes a tremendous amount of time and effort, and surpisingly, it also takes a lot of careful planning.

pika with a mouthful — At first I thought this was a muddy plant root, but then I read that pikas also collect nitrogen-rich marmot scat to eat over the winter, so now I'm not sure what this pika has in its mouth. Photo by David Lukas

While some plants grow quickly and don't protect themselves, other plants invest much of their energy into protecting themselves with toxic, hard-to-manufacture compounds like phenolics and sesquiterpenes. These compounds are an effective defense for plants because they inhibit digestion, so herbivores avoid these plants.

pika foraging — Leaving the security of rocky crevices to harvest nearby plants. Photo by David Lukas

Here's where things get interesting: Pikas spend the summer eating yummy (i.e. unprotected) plants, but when it comes time to harvest plants for the winter they gather both yummy and toxic plants, then carefully layer them in their haypiles.

pika illustration — In some areas, alpine avens (*Acomastylis rossii*) form 50-75% of a pika's winter diet because these plants are very high in phenolic compounds. ©Jane Maday, used with the artist's permission.

It turns out that toxic plants (by which I mean plants protected by secondary compounds) have two interesting properties that benefit pikas. One property is that toxicity breaks down over time, so that by mid-winter these toxic plants are as yummy and nutritious as summer (unprotected) plants. The other trait is that phenolics and other secondary compounds have anti-fungal and anti-bacterial properties, so they act as preservatives when layered generously throughout a slowly decomposing haypile.

pika carrying leaves — A pika collecting materials for a warm winter nest. Photo by Jack McLeod

One other fascinating part of this story is that a pika will typically store 350 days worth of food in its haypile but only eat 180 days worth of food over the course of a winter. It doesn't make sense that a pika would spend so much time gathering food it doesn't eat, but it turns out these unused haypiles decompose into patches of highly fertile soil, and plants that grow on these soils produce higher levels of nitrogen. This might benefit a pika in its lifetime, or it might benefit closely related offspring that take over a pika's territory after it dies, so it seems like a worthwhile payoff for all that effort.

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A short climate story. Because they have compact bodies, small ears, fur-clad feet, and the ability to close their nostrils to avoid heat loss, pikas are uniquely adapted to cold climates. But adaptations that protect them from the cold can work against them in a warming world. Pikas will die at higher temperatures, and some pika populations are being lost, so pikas have become poster animals for climate change. More recent studies, however, are finding that pikas are more adaptable than previously known, and many of their most important populations are thriving.