Scientists make ‘shocking’ predatory discovery about California’s ground squirrels

Ravenous California ground squirrels have been observed killing and eating small rodents, marking the first widespread carnivorous behavior documented among the species.

The squirrels, rodents themselves, are eating California voles. California vole subspecies are listed as species of special concern and one is endangered.

“This was shocking,” Jennifer Smith, an associate professor of biology at the University of Wisconsin-Eau Claire said in a statement. “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,” she said.

Smith was the lead author of a related study — led by the university and UC Davis — that was published in the Journal of Ethology.

The authors said this year’s observations fundamentally change our understanding of ground squirrels, with a more opportunistic diet than previously assumed.

Out of 74 interactions the Long-term Behavioral Ecology of California Ground Squirrels Project observed at Contra Costa County’s Briones Regional Park, 42 percent involved active hunting of the voles. And, the hunt included all ages and genders, according to evidence obtained between June and July.

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

The scary summer behavior peaked in the first two weeks of July when numbers of voles were reported to have exploded. The authors said this suggests their hunting behavior emerged alongside that temporary increase in the availability of prey. They didn’t see the squirrels hunting other mammals.

However, it remains unclear how widespread hunting behavior is among squirrels if it could affect the ecosystem, and how it could be passed down generationally.

“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.