Scientists Discover Carnivorous Behavior in Some California Squirrels
Researchers have discovered the first evidence indicating that certain squirrels in a Northern California park are hunting rodents instead of adhering to their traditional vegetarian diets.
This summer, some California ground squirrels exhibited carnivorous behavior by hunting and consuming rodents instead of their typical fare of nuts and seeds, as revealed in a new study published on October 18.
Squirrels are among the most recognizable animals to people, typically associated with foraging for nuts and seeds rather than hunting for food. Their usual vegetarian diet consists mainly of acorns, seeds, nuts, and fruits.
On rare occasions, these squirrels have supplemented their diets with insects, eggs, or young hatchlings.
Sonja Wild, a postdoctoral research fellow at UC Davis and a co-author of the study, was initially incredulous about the researchers’ findings.
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“I could hardly believe my eyes,” said Wild. “As we began observing [the squirrels], we discovered this behavior everywhere.”
The findings, published in the Journal of Ethology, fundamentally alter the understanding of ground squirrel behavior, according to the researchers.
Between June 10 and July 30, the scientists studied the squirrels at Briones Regional Park in Contra Costa County, situated approximately 25 miles northeast of San Francisco. The park features open grasslands interspersed with walnut and oak trees.
This research marks the 12th year of a long-term behavioral study on California ground squirrels. Since 2013, researchers have live-trapped, marked, and released known squirrels during the months of June and July, when the animals are most active above ground.
Out of 74 observed interactions with voles, small rodent-like creatures similar to hamsters, 42 percent involved squirrels actively hunting these small mammals, the researchers found.
The study involved three groups of observers monitoring different parts of the squirrel population concurrently.
The squirrels engaged in hunting included both juvenile and adult ground squirrels of all sexes, who would chase, strike, leap, or bite each other while competing for voles.
The carnivorous behavior peaked during the initial two weeks of July, which corresponded with an increase in the vole population in the park.
This suggests that the squirrels’ hunting behavior developed alongside the rise in vole numbers, the study indicates.
Notably, the researchers did not observe any squirrels hunting other mammals.
Wild stated, “The adaptability shown by California ground squirrels in response to changing food availability may help them thrive in environments increasingly altered by humans.”
Many species, including the California ground squirrel, have proven to be “incredible opportunists,” she noted.
Researchers highlighted that other animals like raccoons, coyotes, and hyenas exhibit similar flexibility in their hunting strategies to adapt to their environments.
Unanswered questions about the squirrels’ behavior persist, including how widespread the carnivorous tendencies are and whether they are inherited from parents to offspring.
The research team plans to return to the field in the summer of 2025 to assess any impact this year’s vole hunting may have on the reproductive outcomes of squirrels, in comparison to previous studies conducted over the last decade.
Other contributors to the study included Joey Ingbretson, Mackenzie Miner, Ella Oestreicher, Mari Podas, Tia Ravara, Lupin Teles, and Jada Wahl from UW-Eau Claire; and Lucy Todd from the University of California–Davis.
This research received partial funding from the Ronald E. McNair Postbaccalaureate Achievement Program, Diversity Mentoring Program, and Summer Research Experience for Undergraduates. Additional funding was provided by the Swiss National Science Foundation, as well as the Vicki Lord Larson and James Larson Tenure-track Time Reassignment Collaborative Research Program.
