Carnivorous squirrels documented in California

We’ve all seen ground squirrels with their cheeks stuffed with nuts, seeds, or grains, but a new study has found evidence that California’s ground squirrels also prey on voles. The study led by the University of Wisconsin-Eau Claire and University of California and published in the Journal of Ethology, is the first to document widespread carnivorous behaviour among the rodents.

This fundamentally changes our understanding of them, suggesting that what was once considered a granivorous animal, may be an opportunistic omnivore with a more varied diet than was previously believed.

The team observed the animals in 2024, the 12^th year of the Long-term Behavioral Ecology of California Ground Squirrels Project that was conducted at Briones Regional Park in Contra Costa County. Of the 74 observed interactions with voles in June and July, 42% involved active-hunting by the ground squirrels.

“This was shocking,” said lead author Jennifer E. Smith, an associate professor of biology at UW-Eau Claire who leads the long-term ground squirrels project with Sonja Wild of UC Davis. “We had never seen this behavior before. Squirrels are one of the most familiar animals to people. 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.”

Wild has observed hundreds of squirrels in their natural habitats. When her undergraduate students came back from field work and reported what they saw, she didn’t believe them until she was shown the video.

“I could barely believe my eyes,” said Wild, a postdoctoral research fellow in the UC Davis Environmental Science and Policy department. “From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere.”

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