Visualize your dream vacation.
Maybe you’re stretched out on a towel, listening to waves swell and crash on a sandy shore. Or taking the first bite of a still-warm, flaky croissant on a hotel balcony in Paris. Perhaps you’re shaking urine- and feces-stained cotton out of a metal trap on a cold morning in the Pyrenees Mountains, listening for the gentle patter of mouse, vole, or shrew footsteps against the plastic bag.
Not so sure about that last one? Let me explain.
In September 2023, I embarked on Earthwatch’s Wildlife in the Changing Andorran Pyrenees expedition in Ordino, Andorra. I was awarded funding for the trip by Harvard’s Alex G. Booth Fellowship, a scholarship intended to ease the financial burden of traveling for graduating seniors. As an early-career science communicator, the expedition presented the perfect opportunity to get hands-on fieldwork experience while learning about environmental phenomena that could inspire and inform my future storytelling projects.
On these expeditions through Andorra’s mountainous terrain, Earthwatch volunteers and research staff gather data to contribute to the region’s only long-term study on the responses of plants and animals to both climate change and human presence. Research tasks vary by season; ours included monitoring small mammal populations, recording tree growth, collecting wildlife cameras, and digging up teabags to measure soil microbial activity.
Our first day in the field was unforgettable. I’m accustomed to New England trails, which tend to shroud hikers in dense forest until they reach the summit—but the Pyrenees offer stunning, sweeping views of towering tree- and meadow-covered mountains before one even sets foot on a trail. We began in Sorteny National Park, where our trip leaders, biologists Jana Marco and Oriol Palau, had laid out two square plots of 36 live traps to humanely capture the site’s small mammals. Each trap contained a chunk of apple and a mixture of tuna and flour to attract the animals, as well as a bundle of hydrophobic cotton to keep the caught individuals warm, comfortable, and dry.
The group split in half to check each row of traps. If a trap was open and undisturbed, we could leave it be. If the door was closed, there was likely a critter waiting inside.
“Closed!” yelled Oriol from the first row. We gathered around him in giddy anticipation. He pushed the door open a crack and peered in.
“There’s definitely something in there,” he said, then emptied the contents of the trap into a large plastic bag. Out came an adorable, plump rodent with sandy brown fur that Jana quickly identified as a bank vole. Since bank voles are generally herbivorous, the apple had been munched on, while the ball of tuna and flour was left untouched.
Oriol weighed the bank vole in the plastic bag, then gently picked it up. This individual had not been captured before, so he secured a tiny tag to its ear with an identification number. Jana took measurements of its feet and tail and noted the sex and reproductive status before releasing it back into the environment.
The data we gathered would contribute to the SEMICE Project, a large-scale initiative established in 2008 that seeks to monitor changes in small mammal populations over time as they respond to various environmental influences in Spain and Andorra. Long-term monitoring provides valuable data on the status and distribution of species that can be used to inform ecosystem management and conservation decisions.
After the excitement of our first capture, we carried on. Our leaders prepared us to find one or two closed traps at each site, but in a surprising turn of events, we were greeted by a total of 20 captures including bank voles, common shrews, and wood mice. We’d repeat the same routine each morning for the rest of the trip, adding new species to the roster in the days to come, such as the edible dormouse and the common vole.
Small mammals may seem insignificant, but that couldn’t be farther from the truth. This expedition demonstrated their immense value. Small mammals play crucial roles in ecosystems, from seed dispersers to prey for many carnivores.[1] They are also excellent bioindicators, meaning that changes in their populations can reflect broader ecosystem health.[2] Even subtle shifts in their environment often yield a demographic response.
Researchers in the region are already noticing changes in the distribution of small mammal species, likely due to climate change. For instance, Oriol told us that bank voles are increasingly found in large masses at higher altitudes, and some shrew species that were previously absent from higher-altitude habitats can now be found at sites in the Pyrenees. This is consistent with one of the most widely predicted impacts of climate change on biodiversity: species are expected to shift their range toward higher latitudes and/or elevations in response to rising temperatures.[3]
Surrounded by the sublime Pyrenees landscape, it’s easy to overlook the petite creatures that run through the tree canopy, rest in hidden burrows, and scour the forest for fruits, nuts, and insects. Most recreational hikers in the region are unaware of their existence. But with Earthwatch, we were encouraged to notice the unnoticed. Our focus shifted away from the macro as we crouched to examine each live trap, carefully checked dendrometers (devices that measure changes in the diameter of a tree’s trunk), and searched for obscure wildlife cameras.
On the most micro level—microbial, that is—we were taught a surprisingly simple method of measuring soil decomposition rates: the tea bag index. In July 2023, Earthwatch volunteers buried Lipton green and rooibos tea bags as deep as the string with their tags sticking out from the soil. A couple of months later, our group had to delicately dig up the bags, doing our best to keep them intact. The difference in weight between when the bags were buried and when they were unearthed can be used to calculate the rate of soil decomposition, another variable that sheds light on changes in the Pyrenees ecosystem. The tea bag index procedure is a superb example of making science accessible, because it can be replicated pretty much anywhere by anyone, not just on an expedition or in an academic setting.[4]
Decomposition is linked to several ecosystem services, such as the release of nitrogen, phosphorous, and other mineral nutrients essential for plant growth into the soil.[5] The rate of soil decomposition generally accelerates under increasing temperatures and moisture levels.[6] However, excessive decomposition can become problematic, releasing large amounts of carbon dioxide into the atmosphere, degrading soil structure, and creating nutrient imbalances in the soil.[7]
With the tea bag index, researchers are monitoring changes in this crucial process over time. Andorra’s Earthwatch team needs more data to confidently observe a pattern, but the trends will likely correspond with shifts in the region’s temperature and precipitation under climate change.
Unfortunately, the spread of COVID-19 among our group a few days into the journey brought a halt to many volunteers’ field research experience, including my own. Although I was disappointed to miss out on the rest of the trip, I still walked away from the expedition with expanded scientific knowledge and new friendships with my fellow volunteers. We spent hours bonding over research tasks, van rides, and shared meals. I’ll never forget the retired pediatric occupational therapist who shared “hot tips” about raising a child, the retired educator who spoke to the importance of critiquing widely accepted narratives that often misrepresent the experiences of historically marginalized communities, or the biologist who learned English to communicate her love of birds and science with an English-speaking friend.
Earthwatch believes in the value of creating meaningful connections as a solution to the environmental and social challenges we face. This expedition facilitated connections not only among volunteers and research staff, but also between us and the natural world. By narrowing in on the details, we came to appreciate the nuances of Andorra’s complex alpine ecosystem. Now back home in the United States, I have a deeper understanding of, and respect for, the interactions between plants, animals, microbes, and other elements in the ecosystem I inhabit, even if they are happening out of sight. So yes, working with urine- and feces-stained cotton, day-old clumps of tuna, and skittish small mammals turned out to be my dream holiday. It may not sound glamorous, but trust me—there’s a lot to learn from weighing voles on your vacation.
[1] Carolyn H. Sieg et al. “Small Mammals: Pests or Vital Components of the Ecosystem,” (paper presented at the Great Plains Wildlife Damage Control Workshop, Rapid City, SD, April 28-30, 1987), 88-92.
[2] “Small Mammals,” National Ecological Observatory Network, accessed December 2, 2024; Andrew G. Hope et al. “Small Mammals as Indicators of Climate, Biodiversity, and Ecosystem Change,” Alaska Park Science 16 (2017): 71-76.
[3] Jonathan Lenoir et al. “Latitudinal and Elevational Range Shifts Under Contemporary Climate Change,” Encyclopedia of Biodiversity (Third Edition) 3 (2024): 690-709.
[4] For a step-by-step breakdown of the tea bag index method, see “Stepwise protocol,” Tea Bag Index, accessed December 2, 2024.
[5] Teresa E. Middleton et al. “Assessing biological soil health through decomposition of inexpensive household items,” Applied Soil Ecology 168 (2021).
[6] Miko U.F. Kirschbaum. “The temperature dependence of soil organic matter decomposition, and the effect of global warming on soil organic C storage,” Soil Biology and Biochemistry 27, no. 6 (1995): 753-760.
[7] Todd A. Ontl and Lisa A. Schulte. “Soil Carbon Storage,” Nature Education Knowledge 10, no. 3 (2012): 35; United States Department of Agriculture, Soil Respiration, (USDA, 2014).
*Cover Image: Measuring Small Mammals (photograph by the author, Nina Foster)
[Cover Image Description: An Earthwatch trip leader holds a captured bank vole while his colleague uses an instrument to measure the vole’s tail.]
Edited by Trang Dang; reviewed by Josephine Goldman.