A new study from researchers in California and Wisconsin shows that ground squirrels, thought to mainly eat nuts and seeds, catch and eat smaller rodents, too.

The study, published in the peer-reviewed Journal of Ethology on Wednesday, Dec. 18, was conducted by the University of California, Davis, and University of Wisconsin-Eau Claire.

Videos, photos and direct observations show 74 cases of California ground squirrels hunting, eating and fighting over voles, which are tiny rodents, between June 10 and July 30, the study said.

Researchers found that nearly all vole hunting attempts were solo endeavors, with 59% adult hunters and 50% juvenile hunters being successful. More widespread vole hunting was seen "at least in part, in response to a temporary increase in availability of prey."

"This was shocking," 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, said in a news release. "We had never seen this behavior before."

Students observing squirrels at Briones Regional Park in Contra Costa County in the 12th year of a long-term project first reported the behavior to professors, the release said.

New findings surprise researchers

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

While there have been documented cases of ground squirrels eating meat, mostly birds, they were thought to be mainly granivorous, dining on grains, the study said.

The new study suggests the species is "actually is an opportunistic omnivore and more flexible in its diet than previously assumed," the release said.

Voles are small rodents often mistaken for mice, but are actually related to lemmings, according to Britannica.com.

Numerous questions remain, including how common hunting behavior is and how squirrels pass it down to future generations, the release said. But researchers suggest it seems more likely the squirrels are "genetically predisposed" to hunt voles when available.

There was no correlation between the age and sex of a squirrel and whether they hunted voles, according to the study, but older members of the species tend to have more success "either by trial and error or through social learning from adults."

The research team also includes Joey Ingbretson, Mackenzie Miner, Ella Oestreicher, Mari Podas, Tia Ravara, Lupin Teles and Jada Wahl of UW-Eau Claire and Lucy Todd of UC Davis.