Scientists thought this species stuck to eating grains, but this summer's open season on voles suggests otherwise.

When you think of squirrels, you probably imagine cute, fluffy-tailed rodents stuffing their faces with nuts. This past summer, however, researchers photographed California ground squirrels viciously digging into rodent flesh.Â

Researchers from the University of Wisconsin-Eau Claire (UW-Eau Claire) and the University of California (UC), Davis, have recorded California ground squirrels hunting, killing, and eating small rodents called volesâ€"the first documented evidence of the animal consistently eating meat. Their findings, detailed in a December 18 study in the Journal of Ethology, remind us that our understanding of even commonly observed animals is far from complete.

“We had never seen this behavior before. Squirrels are one of the most familiar animals to people,†Jennifer E. Smith of UW-Eau Claire said in a UC Davis statement. “We see them right outside our windows; we interact with them regularly. 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.â€

Smith leads the Long-term Behavioral Ecology of California Ground Squirrels Project along with Sonja Wild of UC Davis, who also contributed to the study. Last summer, during the project’s 12th year, researchers observed ground squirrels actively hunting voles in 42% of their interactions with the smaller rodents.Â

“I could barely believe my eyes,†said Wild. “From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere.â€

The team, including undergraduate students, documented California ground squirrels hunting, eating, and competing over voles at Briones Regional Park in Contra Costa County in June and July of 2024. The carnivorous behavior peaked during the first two weeks of July, overlapping with a sudden increase in the vole population.Â

In fact, the squirrels may have started hunting voles because of the increase, according to the study. Scientists previously maintained that California ground squirrels were granivorous (grain eating), but now the researchers suggest that they may actually be opportunistic omnivores. Â

“The fact that California ground squirrels are behaviorally flexible and can respond to changes in food availability might help them persist in environments [that are] rapidly changing due to the presence of humans,†Wild explained.Â

“Through this collaboration and the data coming in, we’re able to document this widespread behavior that we had no idea was going on,†Smith added. “Digital technology can inform the science, but there’s no replacement for going out there and witnessing the behavior because what animals are doing always surprises us.â€Â

While the team still has many questionsâ€"including how widespread the behavior is, how or if it’s passed on to new generations, and how it impacts ecological processesâ€"the study has upended scientists’ understanding of one of the most recognizable animals to live in proximity to humans.