California ground squirrels have been observed hunting, killing, and consuming voles, according to a recent study that highlights this unexpected carnivorous behavior in the species.
Typically, we see ground squirrels maximizing their cheeks with nuts, seeds, or grains. However, a new study led by the University of Wisconsin-Eau Claire and the University of California, Davis provides the first documented evidence that California ground squirrels actively hunt, kill, and eat voles. This research marks a significant step in recognizing broader carnivorous behaviors in squirrels.
Published in the Journal of Ethology, this study significantly alters our perception of ground squirrels. It proposes that a species previously thought to be strictly granivorous is, in fact, an adaptable omnivore with a more varied diet than previously understood.
The research took place during 2024 as part of the Long-term Behavioral Ecology of California Ground Squirrels Project at Briones Regional Park in Contra Costa County. Over 74 recorded interactions with voles from June to July, 42% involved ground squirrels actively hunting these small rodents.
“This discovery was astounding,” stated Jennifer E. Smith, the lead author and an associate professor of biology at UW-Eau Claire, who conducts the long-term ground squirrel research alongside Sonja Wild from UC Davis. “We had never witnessed this behavior before. Ground squirrels are among the most visible animals in our everyday lives. We encounter them frequently, yet here we discovered a behavior that had not been documented before, underscoring that there is still much to learn about the natural world around us.”
Wild, who has observed numerous squirrels in their natural habitat, found it challenging to believe the reports from her undergraduate students when they first described what they had seen. However, after viewing video evidence, she was astounded.
“I could hardly believe what I was seeing,” said Wild, a postdoctoral research fellow at the UC Davis Environmental Science and Policy department. “Once we began to look for it, we noticed it almost daily. It was everywhere.”
Adapting to Change
The researchers captured videos, photographs, and direct observations of California ground squirrels of various ages and genders hunting, consuming, and competing over voles between June 10 and July 30. The activity peaked in the first two weeks of July, aligning with a surge in mole populations at the park reported by citizen scientists on iNaturalist. This indicates that the squirrels’ hunting behavior developed in response to the temporary increase in prey availability, according to the study. Notably, the researchers did not observe squirrels pursuing other mammals.
“The adaptability of California ground squirrels in changing food availability might enable them to survive in rapidly evolving environments influenced by human activity,” Wild noted.
Smith emphasized that many species, including the California ground squirrel, exhibit remarkable opportunistic behaviors. From raccoons and coyotes to spotted hyenas and humans, the ability to adapt their hunting strategies allows these mammals to thrive amidst human expansion.
“Through our collaboration and the incoming data, we’re uncovering this widespread behavior that we were previously unaware of,” Smith remarked. “While digital technology aids scientific discovery, nothing can replace firsthand observation of animal behavior, as it often surprises us.”
The researchers acknowledged that many questions remain, such as how prevalent this hunting behavior is among squirrels, whether it is passed from parent to offspring, and its potential ecological impact. They are eager to return to the field next summer to examine the possible effects of this year’s vole hunting on squirrel reproduction compared to the previous ten years.
Coauthors of the study include Joey Ingbretson, Mackenzie Miner, Ella Oestreicher, Mari Podas, Tia Ravara, Lupin Teles, and Jada Wahl from UW-Eau Claire, as well as Lucy Todd from UC Davis.
Several coauthors participated in fieldwork during their undergraduate studies. This research received partial funding from the Ronald E. McNair Postbaccalaureate Achievement Program, Diversity Mentoring Program, and the Summer Research Experience for Undergraduates. Additional funding sources comprised the Swiss National Science Foundation and the Vicki Lord Larson and James Larson Tenure-track Time Reassignment Collaborative Research Program.
