A surprising discovery has overturned long-held assumptions about the dietary habits of California ground squirrels. Researchers from the University of Wisconsin-Eau Claire and University of California, Davis have documented these squirrels engaging in widespread carnivorous behavior, actively hunting and consuming voles. The findings, published in the Journal of Ethology, mark the first evidence of such behavior in this species, traditionally classified as granivorous.
New Insights Into Squirrel Behavior
The discovery emerged during the Long-term Behavioral Ecology of California Ground Squirrels Project, a 12-year study conducted in Briones Regional Park in Contra Costa County, California. From June 10 to July 30, 2024, researchers observed 74 interactions between ground squirrels and voles, 42% of which involved active hunting by the squirrels.
Lead author Jennifer E. Smith, a biology professor at UW-Eau Claire, expressed surprise at the findings. “This was shocking,” she said. “Squirrels are one of the most familiar animals to people. Yet here’s this never-before-encountered-in-science behavior that sheds light on the fact that there’s so much more to learn about the natural history of the world around us.”
The observations, corroborated by video evidence, showed ground squirrels stalking and capturing voles with notable precision. Postdoctoral researcher Sonja Wild of UC Davis described her initial disbelief when students reported these behaviors, which were later confirmed through video recordings. “From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere,” Wild explained.
Peak Hunting Activity and Ecological Context
The study identified a clear temporal pattern in the squirrels’ hunting behavior. Activity peaked during the first two weeks of July, coinciding with an explosion in vole numbers, as reported by citizen scientists on iNaturalist. This suggests that the hunting behavior was directly influenced by prey availability during this period.
The table below summarizes key details from the study:
| Aspect | Observation Details |
|---|---|
| Study duration | June 10–July 30, 2024 |
| Location | Briones Regional Park, Contra Costa County, California |
| Number of interactions | 74 |
| Hunting behavior rate | 42% of interactions involved active vole hunting |
| Peak activity | Early to mid-July 2024 |
| Prey species | Voles exclusively |
The observed hunting behavior underscores the behavioral flexibility of California ground squirrels, which may enhance their survival in rapidly changing environments shaped by human activity.
Implications of Behavioral Flexibility
California ground squirrels join a growing list of mammals demonstrating remarkable adaptability in response to ecological shifts. “The fact that California ground squirrels are behaviorally flexible and can respond to changes in food availability might help them persist in environments rapidly changing due to the presence of humans,” Wild said.
Lead author Smith highlighted the opportunistic nature of such behavior, likening it to the strategies employed by raccoons, coyotes, and spotted hyenas. The research team noted that the squirrels were not observed hunting other mammals, suggesting their dietary expansion was limited to voles during this study period.
Unanswered Questions and Future Research
Despite these groundbreaking findings, several questions remain unresolved. Key areas of inquiry include:
- The geographic extent of this hunting behavior among California ground squirrels
- Whether this behavior is learned and passed from adults to young
- Potential ecological consequences, such as impacts on vole populations and squirrel reproduction
The researchers plan to return to Briones Regional Park next summer to assess whether vole hunting affects reproductive success compared to previous years. They are particularly interested in exploring the behavioral mechanisms driving this dietary shift.
Collaborative Efforts and Funding
The study was a collaborative effort involving faculty, graduate students, and undergraduate researchers. Coauthors include Joey Ingbretson, Mackenzie Miner, Ella Oestreicher, Mari Podas, Tia Ravara, Lupin Teles, and Jada Wahl from UW-Eau Claire and Lucy Todd from UC Davis.
The project was funded by several organizations, including the Ronald E. McNair Postbaccalaureate Achievement Program, Diversity Mentoring Program, Summer Research Experience for Undergraduates, and the Swiss National Science Foundation.
The findings challenge conventional views on California ground squirrels, highlighting their role as dynamic participants in the ecosystems they inhabit. This revelation adds a new layer to the understanding of one of the world’s most familiar yet surprisingly complex animals.
