Two Studies, One Lesson: How Citizen Science is Transforming Our View of Yellowstone
- Luis Diego Molina
- Sep 18
- 4 min read
It’s early morning in Yellowstone. A group of high school students is out on the snowy plains, following a herd of bison at a safe distance. When the animals move on, the students kneel down, gloves on, and carefully collect what the bison left behind. To most people, it’s just scat. But for science, it’s a treasure chest of information. Every sample is a window into what these animals are eating, how they’re moving, and how they’re shaping one of the most iconic ecosystems on Earth.
Recently, two groundbreaking studies, one led by Brown University and another by Yellowstone National Park, used these very samples to uncover surprising truths about Yellowstone’s large herbivores. Both studies prove something powerful: citizen science can drive discoveries that change how we understand and protect wildlife.
Rethinking Grazers and Browsers
The first study, The Apportionment of Dietary Diversity in Wildlife, was led by Hannah K. Hoff and colleagues at Brown University. This study analyzed 503 fecal samples collected between 2016 and 2021 from bison, elk, pronghorn, mule deer, and bighorn sheep. Using DNA metabarcoding, they found that animals don’t fit neatly into the classic categories of “grazers” (grass eaters) and “browsers” (woody plant eaters).
As the authors explain, "Clusters did not reflect traditional diet classification schemes such as the grazer–browser continuum... Instead, clusters in Yellowstone reflected seasonal dietary variation within species that often equaled or exceeded niche differences between species."
In plain terms, Yellowstone’s herbivores are more flexible than we thought. A mule deer might graze in summer and browse in winter. Even bison, long seen as strict grazers, showed a more varied diet.
"When we talk about grazers and browsers, and we define those categories, and then we lump whole species into those categories, we're not telling the whole story. This science is saying that's not the whole story", says Joe Loviska, Yellowstone Program Manager at Ecology Project International (EPI)
This matters for conservation. If we oversimplify what animals eat, we risk managing their habitats poorly. Joe reminds us:
"There are situations when individuals or whole populations act more like mixed feeders... So how does that contribute to a more nuanced, accurate understanding of what we're seeing in front of our eyes?"
Bison as Ecosystem Engineers
The second study, Yellowstone’s Free-Moving Large Bison Herds Provide a Glimpse of Their Past Ecosystem Function, was published in Science by Chris Geremia and colleagues. It zoomed in on Yellowstone’s free-roaming bison and revealed that these herds do much more than graze, they actually engineer the ecosystem.
The researchers tracked grazing patterns and nutrient cycling across the landscape between 2015 and 2022, documenting how bison migrations affect soil and plant communities.
They discovered that "Bison stabilized net aboveground production while accelerating nitrogen turnover, increasing aboveground nitrogen pools while carbon pools remained stable, which improved landscape nutritional quality."
In other words, bison boost the nutritional value of Yellowstone’s grasslands, creating fertile grazing lawns that benefit not only themselves but countless other species. As the authors put it, "Our findings suggest that the return of freely moving bison is actively stimulating and transforming Yellowstone grasslands."
For Joe, this makes the story even richer to share with students. "What they're showing here is essentially... bison don't do the same thing everywhere all the time. Instead, they're doing different things in different places at different times. So it makes this picture more whole."
The Power of Citizen Science
Here’s the amazing part: neither of these discoveries would have happened without years of fieldwork by students and citizen scientists. Volunteers from different programs, schools, and organizations all contributed to the collection of fecal samples and herd data that powered both studies.
"EPI students collect data that contributed to this study in two ways. One is the direct fecal samples that our students collect. The other type of data that we contribute is herd demographic data", Joe explains.
Those simple acts, picking up a sample, counting herd members, recording ages and sexes, allowed scientists to link GPS-collar data with actual diet information, revealing patterns that no one could see otherwise.
For students, the impact is deeply personal. One student from the University of Nebraska Omaha who joined EPI’s Yellowstone program reflected:
"I really enjoyed how EPI showed us how field research is collected and allowed us to get familiar with some of the equipment like telemetry. This trip also made going to a national park more accessible... EPI made me realize how fulfilling and accessible a career in ecology is. This trip helped me appreciate little details about nature and how to understand them. It reminded me that I need to ask questions every time I wonder about something."
Experiences like these show how citizen science not only fuels discoveries published in journals like PNAS and Science, but also inspires the next generation of conservationists.
Toward Smarter Conservation
Together, The Apportionment of Dietary Diversity in Wildlife and Yellowstone’s Free-Moving Large Bison Herds Provide a Glimpse of Their Past Ecosystem Function paint a picture of Yellowstone’s wildlife as adaptable, resilient, and deeply intertwined with the landscapes they roam. They challenge old categories, highlight bison as ecosystem engineers, and provide guidance for how we can better manage herds being restored across North America.
As Joe puts it, "If we know that bison can exist quite happily in a mixed forest that has some grassland habitat, but it's not all grassland habitat... They can adjust to that using this data."
At the heart of these discoveries are the citizen scientists, the students kneeling in the snow, carefully collecting samples that help unlock the secrets of Yellowstone. Their work shows that science isn’t just something that happens in labs, it’s alive in the field, and anyone can be part of it.
References:
Hoff, H.K., Littleford-Colquhoun, B.L., Kartzinel, R.Y., Anderson, H.M., Geremia, C., McGarvey, L.M., Segal, C., & Kartzinel, T.R. (2025). The apportionment of dietary diversity in wildlife. Proceedings of the National Academy of Sciences, 122(29), e2502691122. https://doi.org/10.1073/pnas.2502691122
Geremia, C., Hamilton, E.W., & Merkle, J.A. (2025). Yellowstone’s free-moving large bison herds provide a glimpse of their past ecosystem function. Science, 28 August 2025, 904–907. https://doi.org/10.1126/science.adu0703