Small body, strong voice – the American pika under bioacoustic observation

Fig. 1: This tiny mammal shapes the alpine soundscape of the Rockies with its piercing calls (photo credit: David Kingham)

The majestic slopes of the Colorado Rocky Mountains may seem serene and quiet, but in fact, they are anything but! One of its inhabitants, a small furry rabbit-relative hardly bigger than a fist, shapes the soundscape of this mountain range during the summer months with sharp, loud squeals. The American pika (Ochotona princeps) inhabits rocky slopes and talus fields in high elevations, typically above the tree line. The animals are solitary and highly territorial. They spend the summer months foraging for and storing plant parts during the day, to sustain themselves throughout the winter months, as they do not hibernate. Using loud squeaks and calls, they stay in contact with each other, defend their territories, and warn of dangers.

Fig. 2: The characteristic pika call (source: Brian Henderson, Xeno-canto.org, 2024)

But all is not well in these small communities on idyllic slopes: over the past thirty years, scientists have recorded a significant decline in pika populations, and — in one long-studied population — far fewer juveniles than in decades past. Among those most avid pika researchers is Dr. Chris Ray, a Colorado resident who has been returning to the same pika community every year, over the course of three decades, to study its population dynamics.

A labour of love

Ray has devoted a large part of her professional life to researching the pika community near her home in Colorado. She has always loved the Rocky Mountains and studying the pikas - who call this environment their home - came naturally to her.

Fig. 3: Chris Ray has dedicated a large part of her life to studying the American pika (photo credit: Kristi Odom)

Although many are smitten with the pika, historically little money has been going into their research. This means that, although Ray’s research on the local pika populations has been partially financially supported by the Niwot Ridge Long Term Ecological Research since 2008, for much of her career she had to keep her work on these animals as a largely self-funded side project to survive.

Her main research for the past ten years has been revolving around modelling population trends of various bird species throughout western national parks for The Institute of Bird Populations. However, her long-term private occupation remains the local pika populations, which she has been monitoring consistently for over three decades, creating one of the most comprehensive datasets for this species. A lot of hard work and money has been going into obtaining this data, as the local population yields only a small sample size every year, and reaching their habitats is arduous and difficult. This private project is a true labour of love but has also been a teaching opportunity for graduate students. Apart from the research itself, this teaching experience is described as hugely rewarding by Ray.  Today, she reckons her work on the America pika is what she is most known for in the scientific community.

The mountains are going silent

Ray is one of the few people on earth who has been actively following the decline of the American pika population in real time. She began studying the species as an undergraduate. This early academic interest later led to a collaboration with a graduate student by the name of Eric Beever in her postdoc years. He brought to her attention an observation that he had made: by visiting mountain ranges that had been documented to hold pika populations a mere seventy years ago, he discovered that at about a third of the documented sites, the populations had since disappeared. This sparked Ray’s interest and concern, as the time frame for these disappearances seemed unusually short, and their sheer number made them unlikely to be coincidental.

Ray’s initial interest was in how habitat fragmentation affected animal populations, and the pikas lent themselves to this question due to their naturally fragmented, well-defined, and sparse habitats. It fascinated her that such a small creature with low dispersal mobility manages to exist in such adverse terrain. Back then, the regression of pika populations was already a known issue, so she intended to explain this through the habitat pattern, with the hypothesis being that the further patches of viable habitat are apart, the higher the extinction rate of pika populations would be.

However, within a few years of following this hypothesis, she realized that something else must be at play. It seemed increasingly likely that the effects of anthropogenic climate change were reaching up into the remote talus fields of the Rocky Mountains and making life for the pikas more difficult. By documenting the location of numerous populations throughout the years, Ray has been able to show that while pika populations remained present all the way up to the peaks of the Rocky Mountains at four kilometres above sea level, the lower limit of the distribution has been moving uphill at a very rapid rate.

Based on the study of Bristlecone Pine, a plant species that inhabits the same habitat as the pikas, Ray formulated the hypothesis that in cold, low snowpack years, both the trees and the pikas suffer without the insulating effect of a thick snow cover. Pika populations rely on snowpack as insulation to survive the winter; mortality rates in low snowpack years would therefore be much higher than in years with heavy snowfall. On top of that, as they do not hibernate, pikas have evolved to retain body heat extremely efficiently, making them better adapted to staying active during the icy mountain winters than their relatives who inhabit similar climates. But this also means, that they are more susceptible to high temperatures, as they overheat easily.

Fig. 4: The American pika spends all the summer collecting food for the winter, a behaviour called ‘haying’. While perfectly adapted to cold temperatures, pikas run risk of overheating at temperatures as low as 26*C. (photo credit: Chris Ray, 2024)

Mammal songbirds

For most of the duration of the pika project, Chris Ray has been heading out to the talus fields every summer to trap, weight and mark individual pika, while also collecting biological samples from them, to then feed this data into her ever growing database. It is slow and exhausting work that puts stress on the animals and requires the researchers to spend many days on the exposed rockfaces.

However, in addition to this hands-on method, pikas are a species very well suited for bioacoustic research. Chris Ray describes them as “the birds of the small mammal world”, due to their constant contact calls, but also the distinctive songs that male pikas sing during mating season. It is therefore possible to not only confirm their presence using bioacoustics, but also to locate and count individual animals, as well as to identify them by their voice profile. The bioacoustic methodology could thus be used to estimate abundance, but also to understand territorial boundaries, and even to gather data about the sex and age of each member of a population, as well as their intercommunal behaviour. Long-term acoustic monitoring is aided by the fact that once established, a pika territory generally occupies the same location for many generations; once a recorder is placed in an area with constant pika presence, it is sure to capture valuable data for many years.

Fig. 5: A Solar BAR mounted in a talus field, ready to record pika calls. (photo credit: Chris Ray, 2022)

Ray sees many possible advantages in using bioacoustics in her research. By incorporating bioacoustics into her project, she hopes to be able to quantify her data, as well as to more accurately determine abundance within the populations, while also putting less stress on the animals, and less exhaustion on her team.  Ray is planning for this coming summer to be her last year of physically trapping pikas, and that from then onward, comparable – or better – quantity and quality of data will be yielded from bioacoustic monitoring alone.

Solar BARs to the rescue

In 2022, Ray purchased four Solar BAR units from Frontier Labs. Together with her small team, she carried them up the rocky slopes of the Niwot Ridge Long-term Ecology Research Site near her residence and permanently installed them on star pickets rammed between boulders in the talus fields. She positioned them to form a transect running east to west, from the lowest to the highest potential pika habitat in the area, at almost 4000 meters of elevation.

In the beginning, Ray used a continuous recording schedule but soon switched to a recurring recording of the first 15 minutes every hour to keep data volumes manageable. Throughout the higher activity summer months, she kept the continuous 24/7 recording schedule is in place though, so as not to miss any calls in those most active months.

Fig. 6: Four Solar BARs form a transect across the elevation of the mountain range, from the valley up to the ridge. (source: Chris Ray, 2022)

During maintenance visits, Ray and her students take hours out of their visit to add narration to the recordings, explaining which individual made which call in real time, to be able to later attribute those sounds to a specific pika. For this purpose, they supplement their stationary Solar BARs with handheld and temporary recorders. However, neither of these can withstand the weather conditions at Niwot Ridge during the winter months, which has one of the harshest climates in the world. As Ray puts it:

“But man, the Solar BARs have been fantastic because we can use them year-round. […] And I have been amazed at how well those solar-powered ARUs have withstood the tremendous conditions that they're in, month after month up there.”

Not only that; the solar-powered battery extends maintenance cycles far beyond the winter months, so none of her team had to schedule visits in the deep snow and freezing wind ever since installing the devices. In her three decades of study at Niwot Ridge, Ray has had a play with hardware from many brands but has found herself especially impressed by the Solar BAR. As she says: “I'm just very excited to have a piece of equipment that can withstand the conditions that I'm trying to use them in.”

Fig. 7: One of the permanently installed Solar BARs on a talus field, weathering icy winds and deep snows. (photo credit: Chris Ray, 2022)

Very happy with her experience, she purchased three more Solar BARs to install a second transit from north to south, in addition to the already existing east-west transect. She planned to use these transects to verify the presence or absence of pikas in areas that were deemed good habitat by the researchers, as well as to understand which local extinction patterns would form.

All in all, the Niwot Ridge Long-term Ecology Research Site turned out to be the perfect pick for a study site due to its variation in hydrology, geomorphology and geochemistry along this elevational gradient.  As Ray puts it: “We're just making the best of what we have available, but what we have available is the best.”

Who’s calling?

With all practical fieldwork needs covered, what the bioacoustic project really needed to progress was a tech savvy student who could create an identifier to make counting individuals by voice profile alone reality. Enter Rachel Billings: a graduate with a degree in electrical engineering, and a love for the outdoors. With her help, Ray was able to make advances in her research: an AI model has been trained on the acoustic data she collected over the course of several years, and although the data is still relatively sparse, patterns are starting to emerge. Together with another engineering student who Rachel is supervising, she has been able to develop an AI identifier running on the programming language R, while also spending much of her time in the field gathering and annotating more data since her introduction to the project three years prior.

Fig. 8: Rachel Billings in the field, performing a maintenance check on a Solar BAR. (photo credit: Chris Ray, 2022)

Endless Possibilities

First results have shown that locally along the transect, pika populations in lower elevation seemed to be faring better than in higher areas. Ray hypothesizes that this is due to more consistent and thicker snow cover during the winter in less exposed, lower areas, which seems to be outweighing the threat of overheating in recent summers.

The main aim of her studies is, and has been for the last fifteen years, to find out which mechanisms drive the pika extinction. Which factors change due to climate change, that make former habitats unviable for established populations? Is it the lack of snow cover after all, or rather the change in available forageable fodders?  Or could warmer climate make the pikas more susceptible to disease and ectoparasites? With milder winters, would competition from lower elevation habitats arrive in the form of rodents, forcing the pikas out of their ecological niche? How do young pikas even find new habitat to disperse into in the first place? Are adults in long-standing territories suffering more from the changing climate, or is it the juveniles, that have yet to disperse and establish a territory outside of their nursery sites? Will the added stresses make dispersion and the formation of bigger colonies less likely than before, and will this lead to more isolated, smaller populations and subsequent local extinction?

Decades of pika research have expanded Chris Ray’s growing list of questions, but she hopes bioacoustic monitoring will soon provide at least some answers.

The future of the loudest Rocky Mountains dweller

While the future for Chris Ray’s local pikas may not look particularly bright, the species as a whole may not be facing extinction any time soon. As the effects of climate change intensify, Ray’s projections indicate that about half of the viable pika habitat in North America will be lost. This would still leave millions of individuals out there, inhabiting a microclimate that is likely protected by the cooling properties of the talus structures. It is impossible to know what the future brings, but Dr. Chris Ray hopes that because of their unique adaptations, and the stable nature of the habitat patches they inhabit, the American pikas will preserve as a species. Their squeals and calls will likely be heard by future generations, if largely diminished. For a small animal like that, it does announce its presence unmistakably after all.