From nuts to nightmares: California ground squirrels filmed actively hunting and eating voles

During the summer of 2024, researchers at Briones Regional Park in Contra Costa County, Northern California, documented unprecedented behavior in California ground squirrels: hunting and consuming voles. The observation challenges the long-held belief that these squirrels are primarily herbivorous, revealing their adaptability and opportunistic feeding habits.

The research, part of the Long-term Behavioral Ecology of California Ground Squirrels Project, was led by Jennifer E. Smith of the University of Wisconsin-Eau Claire and UC Davis. The team observed 74 interactions between ground squirrels and voles between June 10 and July 30, 2024, with 42% involving active hunting attempts and a 55% success rate.

"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," Jennifer E. Smith stated, according to Phys.org.

Initially skeptical of reports from undergraduate students, Dr. Sonja Wild, a postdoctoral researcher at UC Davis, reviewed video evidence of the squirrels' predatory behavior. "I could barely believe my eyes. From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere," she said, as reported by Popular Science.

Both adult and juvenile squirrels of both sexes participated in hunting voles, with at least 27 different individuals involved. Adult females accounted for nearly half of the traceable hunting events, indicating their particularly active role as hunters. There were no significant differences in success rates between age groups.

The researchers believe the sudden emergence of hunting behavior coincided with an unprecedented surge in the local vole population. Data from the citizen science platform iNaturalist revealed that vole sightings in 2024 dramatically exceeded all records from the previous decade. This abundance of prey likely triggered new foraging behaviors in the squirrels.

"It seems that these squirrels are just opportunistic," Smith noted, according to The Guardian. "The super abundance of voles during this particular summer really opened up the novel dietary niche for them."

While there have been isolated accounts of California ground squirrels scavenging carcasses or occasionally killing small animals, such behavior was considered rare. The documented predatory activity toward voles marks a significant shift in understanding their dietary habits. This finding suggests that California ground squirrels are more behaviorally flexible and opportunistically omnivorous than previously thought, which may provide them a survival advantage in rapidly changing environments.

"Digital technology can inform the science, but there's no replacement for going out there and witnessing the behavior because what animals are doing always surprises us," Smith added, as reported by studyfinds.org.

Many questions remain unanswered, such as whether this behavior is common among all squirrels, whether it is passed from parents to offspring, and how it affects ecosystems. The researchers plan to return to the field next summer to gauge the impact of vole predation on squirrel reproduction compared to previous years. They are particularly interested in whether access to this high-protein food source might influence reproduction rates in future seasons.

The study was published in the Journal of Ethology.

This article was written in collaboration with generative AI company Alchemiq