A Pika’s Life at the Alpine Salad Bar

Imagine if your house were high up in the mountains and you spent your summers gathering your favorite foods. That is similar to the life of one animal species, called the American pika (Figure 1). Pikas are small mammals related to rabbits. They usually live high in the mountains, in rocky areas called talus. The talus provides a pika with shelter from the weather and a place to feel safe. But living in the mountains is not easy for pikas. Their homes can be covered in snow for 9 months of the year. Pikas live under the snow in their talus homes all winter long: they do not hibernate or sleep all winter like other animals. Instead, during the short alpine summer when mountain meadows are full of plants to eat, they work hard to stock up enough food to last the entire winter. Imagine if you had to grocery shop for the entire school year all at once!

Stocking Up for Winter

Pikas are herbivores, which means they eat only plants. Pikas eat grasses and flowers from meadows near their rocky homes. During the summer, pikas must collect food for the winter. Pikas spend their summers collecting huge amounts of plants to store in a haypile [1]. This haypile is all that they have to eat during the winter when their whole neighborhood is deep under snow, so it is important for them to collect enough plants. Just like people, pikas in Colorado (USA) have a favorite snack to put in their haypiles: a plant called alpine avens. Alpine avens makes up most of the pika’s winter diet. They are the most common plant in a haypile, making up over half of everything stored in the pika’s pantry.

Pikas have different diets in the summer and winter because of what is in the plants they eat. The foods they eat in the summer are high in nutrients and easy to digest. But winter food is a bit more complicated. Foods that pikas store for the winter must last many months before they are eaten. Most normal plants would go bad long before winter is over. Can you imagine leaving a salad in your room all winter? It would not be very tasty by springtime! This is why alpine avens are special: they contain natural chemicals called phenolics, which act like preservatives [2]. Phenolics keep the alpine avens in a haypile fresh, so that a pika can eat them all winter long. But eating preservatives comes with a cost—phenolics are also toxic, which means that a pika cannot eat too many alpine avens without getting very sick or spending a lot of energy on digestion. Luckily, pikas know that, over time, the toxic phenolics break down and the plants become edible. Since the phenolics also preserve the alpine avens, the plants stay fresh until they are not toxic anymore. This means pikas can eat lots of stored alpine avens later in the winter, without getting sick.

Learning More About Pika Snacks

Climate change has already affected many species of plants and animals, as you can learn about in this Frontiers for Young Minds article. But the ways that changes in temperature and precipitation affect the daily lives of mountain species are not always obvious. We wanted to know more about how climate change might be affecting the pika’s main winter food source in Colorado. We expected that alpine avens may have become more toxic because plants could use the extra carbon dioxide in the atmosphere to make more phenolics.

We compared the phenolics in alpine avens now to alpine avens in the 1990s, to see if there were any differences over time. We started by returning to a site on Niwot Ridge, the same place where another scientist named Denise Dearing studied pikas in 1992 [1, 2]. Niwot Ridge is located high in the mountains of Colorado at an elevation of about 11,000 ft. We collected alpine avens each year from 2010 to 2018, just like Dr. Dearing did about 25 years earlier.

We took some of those plants back to the lab to measure the amount of phenolics they contained (Figure 2). We ground up the plant samples in a liquid that dissolved the phenolics. Then, we measured the phenolic levels using a chemical reaction in which the liquid changes color depending on the amount of phenolics present. So, the samples from plants with a lot of phenolics turned dark green, and the samples from plants with only a little bit of phenolics stayed yellow. Finally, a machine measured how yellow or green each sample was and translated the color into an amount of phenolics.

We also wanted to know how changes in phenolics might change plant preservation in pika haypiles. So, in September 2017, we put some plants in wire cages and placed them in the talus like a pika haypile (Figure 3). The cages kept the plants safe from curious pikas or other animals but let the plants break down, just like they would in a real haypile. These experimental haypiles spent the winter under the snow at Niwot Ridge, until we collected them in July 2018. Then, we dried and weighed what was left in the cages to see how well the plants preserved.

Finally, we compared our results to Dr. Dearing’s 1992 study, to see if there were any differences in the amount of phenolics in alpine avens or in how well the plants preserved in pika haypiles.

Changes at a Pika’s Dinner Table

It turned out that alpine avens has been changing a lot! First, this plant had more than twice the amount of phenolics at the time of our study than it had in 1992 (Figure 2). In fact, in 1 year of our experiment (2013), the alpine avens was almost three times more toxic than it used to be! The extra phenolics also made the plants preserve better. In our experimental haypiles, there was about 10% more food left at the end of winter compared to 25 years ago.

This is both good news and bad news for pikas. The fact that their favorite snack is more toxic now might make it less tasty to eat fresh. But on the other hand, alpine avens also stays fresh longer. So, pikas might have to wait longer to be able to eat alpine avens with more phenolics, but having more phenolics can help preserve alpine avens and maybe even other snacks in the haypile. This means that, even if they do not store as much food, pikas could still have more to eat in late winter. We also know that alpine avens has become less common in the meadows at Niwot Ridge, which are becoming drier due to climate change [3]. Instead, the meadows have more grasses, which pikas like to eat fresh. So, while pikas today may not be able to find as many alpine avens as the pikas that lived 25 years ago, they might not need to store as much food, either.

What Does It All Mean?

The way climate change affects pikas’ favorite foods is like a tricky puzzle. In some ways, climate change could make life harder for these cute creatures as they change what they eat. But on the other hand, the foods they collect might last longer in storage, which could make life easier. In the future, the changing climate might even change the food choices pikas have. Warmer temperatures are already changing mountain meadows to have more grasses and fewer flowers like alpine avens. Imagine if you had to eat only one thing forever, like pandas that eat bamboo or koalas that eat eucalyptus. That might happen to pikas!

As we keep studying pikas and their snacks over a long period of time, we can learn how climate change is making things different for these animals. It is like reading a history book about pikas and discovering that the foods they eat now are different than what they used to eat. Just like we compared our results to Dr. Dearing’s, maybe in 25 years YOU will be studying how pika snacks have changed compared to now!

So, the next time you are having dinner, think about how climate change might be changing the foods on your plate. Just like for pikas, climate change can change our favorite foods, too. It is a reminder that we all share this planet, and taking care of it is important—both for us and the animals!

Glossary

Talus: ↑ Rock piles that collect at the base of a cliff or along the edge of a glacier. Pikas in North America like to live in rock piles instead of burrows.

Alpine: ↑ Relating to high mountains. Alpine plants and animals are well-adapted to living at high elevations, in habitats with short, cool summers, and long winters.

Haypile: ↑ A collection of plants (mostly wildflowers) stored by a pika. A pika will eat this “food cache” throughout the winter when it is hard to find other food.

Phenolics: ↑ Chemicals that some wildflowers make naturally, which protect the plant’s tissue from the harsh environment and from herbivores; they also help preserve plants stored in pika haypiles.

Toxic: ↑ Harmful when eaten. Toxic plants can cause a range of problems for herbivores, from being difficult to digest (by requiring too much energy), to causing illness or even death.

Acknowledgments

The grant DEB-1637686 was awarded by the National Science Foundation to the Niwot Ridge Long-Term Ecological Research program (NWT LTER) to support NWT LTER research, including the portion of this work that was led by CR. The University of Colorado Mountain Research Station provided key resources and permissions for this research. JV was supported in this study through a Faculty Professional Development Grant from Colorado Mesa University and a Natural History Research Grant from the Western North American Naturalist. The preparation of this article was also made possible with support from IF/THEN and Lyda Hill Philanthropies.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.