Forget The Acorns: California Squirrels Have Developed Taste For Fellow Rodents

CALIFORNIA — Squirrels are known for their propensity for stuffing their cheeks with nuts and acorns. But a new study published this week revealed that California ground squirrels do, in fact, eat meat — researchers caught the animals on camera hunting, killing and consuming other rodents, marking the first evidence of such behavior.

The research, published Wednesday in the Journal of Ethology, is part of a long-term study of California ground squirrels — the kind common in backyards across the state — at Briones Regional Park in Contra Costa County. This year, the 12th year of the study, researchers documented 74 incidents of squirrels hunting, eating and/or competing over California voles, according to the paper.

“This research radically changes our perception of squirrels, one of the most familiar mammals in the world,” lead study author Jennifer Smith, associate professor of biology at the University of Wisconsin-Eau Claire, told CNN.

The diet of squirrels is made up of mainly acorns, seeds, nuts and fruit. Though they're understood to maintain a vegetarian diet, any deviation from that was believed to be rare and linked to eating insects or eating eggs or young hatchlings, according to the study.

Researchers discovered that the squirrels adapted to changes in their ecosystem: At the park, scientists noted a significantly higher number of voles than average over the past decade.

“In the face of human insults such as climate change and drought, these animals are resilient and have the potential to adapt to live in a changing world," Smith said.

Smith's co-lead on the project, Sonja Wild of UC Davis, said in a release said she was in disbelief when her colleagues told her what they witnessed.

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

The vole hunting peaked over the summer and coincided with an explosion in the rodents' numbers at the park reported by citizen scientists. That suggests the squirrels hunting behavior emerged alongside the increase in the availability of prey: The scientists didn't observe the squirrels hunting other mammals, according to the release.

“We already knew that (California ground squirrels) could live (in) a range of elevations and feed (on) a breadth of plants, but what is most striking and incredible is the speed at which they shifted their behavior to this local surge in vole abundance,” Smith told CNN.

The study suggests squirrels might best be classified as opportunistic omnivores based on their willingness to hunt and consume live prey, particularly when there is an abundant supply. If an animal doesn’t adapt to utilize an available resource, it’s likely another species will take advantage of it, John Koprowski, dean of the Haub School of Environment and Natural Resources at the University of Wyoming, told CNN.

Many species are opportunists, Smith said. From raccoons to coyotes, mammals commonly show flexibility in their hunting strategies that help them adapt to a human dominated landscape.

“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.

Many questions remain unanswered, researchers say, including how widespread the hunting behavior is, whether it's passed down from generation to generation and how it impacts ecological processes.