California squirrels are eating another rodent for the first time, new study finds

Scientists have found unprecedented evidence of another type of squirrel exhibiting carnivorous behaviours, including hunting, killing and eating voles, according to a new study.

Traditionally known for stuffing their cheeks with nuts, squirrels can be carnivorous — though recorded instances of the rodents hunting and killing other live vertebrates are rare, with few species known to have done so. Now, scientists have found unprecedented evidence of another type of squirrel exhibiting carnivorous behaviours, including hunting, killing and eating voles, according to a new study.

The research, published Wednesday in the Journal of Ethology, is part of the Long-Term Behavioral Ecology of California Ground Squirrels Project at Briones Regional Park in Contra Costa County. The project examines how California ground squirrels — native to the state’s grasslands — adapt their behaviour in response to environmental changes, in this case an increase in the local vole population.

In parts of Northern California, vole infestations have been observed. At the research site, the study’s authors noted a significantly higher number of voles than average over the past decade. California ground squirrels have typically been considered herbivores or granivores, eating mostly plants and seeds. The new findings offer the first documentation of the species actively preying on other live vertebrates — underscoring its ability to respond to changes in the ecosystem.

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

Squirrels are an important part of California ecosystems, and understanding whether food discovery is a socially transmitted trait in these populations could provide key insights into how other species will adjust to shifting environments, Smith said.

Smith and her colleagues observed the squirrels’ meat-eating behaviour during a study period from June 10 to July 30. During that time, the scientists used live traps to capture, mark and release California ground squirrels on a biweekly basis.