California squirrels turning into carnivorous killers: ‘Never seen before’

‘I could barely believe my eyes’: Scientists stunned by behavior captured on camera

DAVIS, Calif. — Evolution works in mysterious ways. Sometimes, it creates specialized carnivores with sharp teeth and claws; other times, it turns seemingly peaceful plant-eaters into opportunistic hunters. Scientists have just documented the latter in action, discovering that California ground squirrels – those supposedly harmless seed-gatherers – have developed a taste for meat and the skills to obtain it.

In the eye-opening study, researchers observed the squirrels actively hunting and eating other mammals, specifically California voles. It marks the first evidence that these supposedly vegetarian animals regularly engage in predatory behavior.

“This was shocking,” said lead author Jennifer E. Smith, an associate professor of biology at University of Wisconsin-Eau Claire, in a statement. Smith leads the long-term ground squirrels project with Sonja Wild of the University of California, Davis.

“We had never seen this behavior before,” Smith continues. “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.”

For over a decade, scientists had been studying a population of California ground squirrels at Briones Regional Park in California’s Contra Costa County. These squirrels were known primarily as peaceful vegetarians, munching on seeds, grasses, and occasional insects. However, in 2024 — the 12th year of their long-term study — something remarkable happened. The researchers observed 74 separate instances of the squirrels actively hunting, killing, and consuming adult voles.

Even the researchers were initially skeptical of what they were seeing. When undergraduate students first reported the hunting behavior, postdoctoral research fellow Sonja Wild from UC Davis’s Environmental Science and Policy department was dubious. “I could barely believe my eyes,” said Wild. “From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere.”

The sudden emergence of this hunting behavior coincided with an unprecedented surge in the local vole population. Analysis of data from the citizen science platform iNaturalist revealed that vole sightings in 2024 dramatically exceeded all records from the previous decade, reaching levels never before documented in the area. This remarkable abundance of potential prey appeared to trigger new foraging behaviors in the squirrel population.

The hunting tactics employed by the squirrels were predominantly opportunistic. Rather than using sophisticated stalking techniques, these new hunters typically chased their prey over short distances in open areas across dirt substrate. In three documented cases, squirrels were observed staying low to the ground and minimizing noise before attacking. When close enough, they would pounce on their prey, using their forepaws and teeth to subdue it. The kill typically involved bites targeting the neck area, though other body parts were also targeted.

What’s particularly fascinating is the success rate of these amateur hunters. Out of 31 observed hunting attempts, 17 resulted in successful kills – a 55% success rate that would make many natural predators envious. The squirrels showed a consistent pattern in consuming their prey: they would first remove the vole’s head before either pulling meat directly from the torso or methodically stripping away fur to access the meat, organs, and cartilage underneath.

The behavior, described in a paper published in the Journal of Ethology, wasn’t limited to a few specialized individuals either. Both adult and juvenile squirrels of both sexes participated in the hunting, with no significant differences in success rates between age groups. The researchers specifically identified 2 juvenile males, 3 juvenile females, 2 adult males, and 6 adult females among the traceable hunting events, with adult females accounting for nearly half of these observations.

The discovery has broader implications for understanding how wildlife adapts to human-modified environments. “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 noted. Smith added that many species, including the California ground squirrel, are “incredible opportunists.” From raccoons and coyotes to spotted hyenas and humans, the flexibility these mammals apply to their hunting strategies help them change and adapt with the human landscape.

Study authors point out fascinating social dynamics surrounding this new hunting behavior. While squirrels typically hunted alone, the presence of a fresh kill often led to competitive interactions, with some individuals attempting to take prey from successful hunters. Yet not all interactions were aggressive – in some cases, squirrels showed surprising tolerance around food sharing. Researchers documented rare instances of adults allowing juveniles to feed on their catches, suggesting complex social dynamics around this new food source.

This discovery opens up numerous avenues for future investigation. The research team plans to explore whether this hunting behavior exists in other squirrel populations, investigate potential mechanisms for passing these skills between generations, and study how this dietary shift might affect local ecosystems. Of particular interest is whether access to this high-protein food source might influence squirrel reproduction rates in future seasons.

“Through this collaboration and the data coming in, we’re able to document this widespread behavior that we had no idea was going on,” Smith said. “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.”

These findings force us to reconsider what we think we know about the animals sharing our urban and suburban spaces. Behind their cute, fuzzy appearances, ground squirrels harbor unexpected capabilities that have gone unnoticed despite decades of observation. What other secrets might our backyard wildlife be keeping? Sometimes, it seems, you just need to look at familiar things with fresh eyes.