California ground squirrels, long regarded as seed- and nut-loving herbivores, are now challenging that assumption. A new study, published in the Journal of Ethology, provides the first documented evidence that these familiar backyard rodents actively hunt, kill, and eat voles, showcasing a dietary flexibility that has gone previously undetected.
A Shift in Our Understanding of Ground Squirrels
Traditionally viewed as granivores subsisting mainly on nuts, seeds, and grains, California ground squirrels are now recognized as opportunistic omnivores. Led by researchers at the University of Wisconsin–Eau Claire and the University of California, Davis, the study observed an unprecedented pattern of carnivorous behavior. The findings not only reshape our understanding of these common mammals but highlight just how adaptive and resourceful wildlife can be in changing environments.
A Surprising Summer Discovery
The breakthrough observations occurred in 2024 during the 12th year of the Long-term Behavioral Ecology of California Ground Squirrels Project at Briones Regional Park in Contra Costa County, California. Between June and July, researchers documented 74 encounters between ground squirrels and voles, with an astonishing 42% involving active hunting of the small rodents. Prior to these findings, such behavior had never been reported, making it a groundbreaking moment in behavioral ecology.
“This was shocking,” said lead author Jennifer E. Smith, an associate professor of biology at UW–Eau Claire. “Squirrels are so familiar to us, yet here we’ve discovered a behavior that changes how we view their place in the ecosystem.” Smith’s colleague, UC Davis postdoctoral research fellow Sonja Wild, was equally astonished after reviewing video footage captured by undergraduate research assistants. “I could barely believe my eyes,” Wild said. “Once we knew what to look for, we saw this behavior almost daily.”
Opportunistic Omnivores in a Changing World
Why would a squirrel known for eating seeds and nuts suddenly develop a taste for meat? The researchers point to a temporary boom in vole populations documented by citizen scientists on iNaturalist during early July. With voles suddenly abundant, the squirrels adapted their diets to take advantage of this readily available protein source. While their carnivorous streak appears seasonal and opportunistic, it hints at a remarkable behavioral flexibility. Such adaptability may help California ground squirrels—and other wildlife—survive in rapidly changing landscapes dominated by human activity.
“The ability to pivot and exploit different food sources is likely a key factor helping these mammals persist in environments altered by human presence,” said Wild. Smith added that this opportunistic trait places ground squirrels in a category with many other adaptable species, from raccoons and coyotes to spotted hyenas and humans.
Unanswered Questions and Future Research
This surprising discovery opens the door to numerous questions. Are other squirrel species also hunting prey when the opportunity arises? How do squirrels learn this behavior—could it be passed down from parent to pup? What implications does this newfound carnivory have for local ecosystems?
The research team plans to return to the field next summer. They will examine whether this unusual dietary choice influences squirrel reproduction rates or has lasting effects on the population, prey species, and the broader ecological community. As Smith noted, “Digital technology can enhance our understanding, but nothing replaces direct observation. Animals always find new ways to surprise us.”
Collaborative Efforts and Support
Coauthors include students and researchers from UW–Eau Claire—Joey Ingbretson, Mackenzie Miner, Ella Oestreicher, Mari Podas, Tia Ravara, Lupin Teles, and Jada Wahl—and Lucy Todd of UC Davis. Many of the coauthors contributed during their undergraduate studies, supported in part by the Ronald E. McNair Postbaccalaureate Achievement Program, the Diversity Mentoring Program, and the Summer Research Experience for Undergraduates. Additional funding was provided by the Swiss National Science Foundation and the Vicki Lord Larson and James Larson Tenure-track Time Reassignment Collaborative Research Program.
A New Chapter in Squirrel Ecology
This groundbreaking study reminds us that even the most familiar creatures harbor secrets waiting to be discovered. The California ground squirrel’s unexpected carnivorous behavior challenges long-standing assumptions about wildlife diets and underscores the importance of sustained observation, new technologies, and the willingness to question what we think we know. As the world changes, so do its inhabitants—often in ways we are only beginning to understand.