In a discovery that’s shaking up what we thought we knew about one of nature’s most familiar rodents, a long-term study at Briones Regional Park in California has revealed that the usually seed-eating and nut-loving California ground squirrel (Otospermophilus beecheyi) is showing true predatory behaviour — chasing, killing and eating small rodents known as voles.
For over 12 years, a team of researchers from University of California, Davis (UC Davis) and University of Wisconsin–Eau Claire have been observing these squirrels in the park’s grasslands. In the twelfth year of the study, something unusual cropped up: the squirrels suddenly began hunting the much smaller California vole (Microtus californicus).
Over the course of just a few weeks, the scientists documented 74 separate events in which squirrels were seen either actively chasing voles, killing them or consuming their tiny bodies. In about 42 % of the interactions between squirrels and voles, a pursuit and kill was involved. The squirrels—both juveniles and adults, male and female—were involved.
Typically, ground squirrels are considered herbivores or near-herbivores. They eat the seeds, nuts, fruits and grasses of California’s grasslands. They are known to sometimes feast on insects or scavenged food, but active hunting of another small mammal is something new.
So what changed? The researchers point to a sudden and unexpected boom in vole numbers at the park during that time — essentially, an abundant and easy prey source appeared, and the squirrels took advantage. The study shows that dietary flexibility — the ability to shift eating habits when the environment changes — may be a key survival trait for species living in landscapes altered by human activity or shifting climate.
Some of the striking observations included squirrels chasing voles across open ground, biting the necks of their prey, and then dragging and tearing apart the vole’s body. There were also interactions where squirrels fought each other over carcasses — another behaviour previously undocumented in this species.
What does this mean? For one, it forces a rethink of how we define the “normal” diet of an animal we’ve watched for decades. The fact that ground squirrels can flip from a mostly vegetarian, seed-eating lifestyle to full-blown carnivory (or at least partial carnivory) under the right conditions is fascinating. It also raises questions about how these behaviours will affect ecosystem dynamics. The squirrels themselves are prey for many predators (snakes, birds of prey, mammals) and if their behaviour changes, that could have ripple effects. The researchers note potential implications for parasite and disease transmission, since closer contact with voles might increase shared pathogens.
Of course, there are still open questions. The current evidence comes from one specific site during a specific time of abundant voles. It’s not yet clear how widespread this behaviour is among squirrels in other regions, or whether it will persist if vole numbers decline. Will the hunting skill be passed on socially or genetically? Will squirrels use other prey in different contexts? The scientists plan to keep monitoring.
In the bigger picture, the study offers a powerful reminder: animals often have more behavioural flexibility than we assume. As habitats change, species that can adapt may fare better. The ground squirrels at Briones show that even common urban-adjacent rodents can surprise us — and perhaps teach us a bit more about survival in a changing world.
If you stroll through grasslands or parks and spot a ground squirrel, you might now imagine one carrying off a tiny rodent instead of just stuffing its cheeks with nuts. Nature still holds surprises.