A ground squirrel with cheeks stuffed with nuts, seeds or grains, is a common sight. But a new study provides the first evidence that California ground squirrels also hunt, kill and eat voles. The study, led by the University of Wisconsin-Eau Claire and the University of California, Davis, is the first to chronicle widespread carnivorous behavior among squirrels.
Published in the Journal of Ethology, fundamentally changes our understanding of ground squirrels. It suggests that what was considered a granivorous species actually is an opportunistic omnivore and more flexible in its diet than previously assumed.
The observations occurred in 2024 鈥 the 12th year of the conducted at Briones Regional Park in Contra Costa County. Out of 74 observed interactions with voles between June and July, 42% involved active hunting of these small rodents by ground squirrels.
鈥淭his was shocking,鈥 said lead author , an associate professor of biology at UW-Eau Claire who leads the long-term ground squirrels project with of 新澳门六合彩内幕信息 Davis. 鈥淲e 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鈥檚 this never-before-encountered-in-science behavior that sheds light on the fact that there鈥檚 so much more to learn about the natural history of the world around us.鈥
Wild has observed hundreds of squirrels in nature and yet, even for her, when the undergraduate students came in from field work and told her what they had witnessed, she said, 鈥淣o, I鈥檓 not sure what you鈥檙e referring to.鈥 Then she watched the video.
鈥淚 could barely believe my eyes,鈥 said Wild, a postdoctoral research fellow in the 新澳门六合彩内幕信息 Davis Environmental Science and Policy department. 鈥淔rom then, we saw that behavior almost every day. Once we started looking, we saw it everywhere.鈥
Opportunists amid rapid change
Through videos, photos and direct observations at the regional park, the authors documented California ground squirrels of all ages and genders hunting, eating and competing over vole prey between June 10 and July 30. The squirrels鈥 carnivorous summer behavior peaked during the first two weeks of July, coinciding with an explosion in vole numbers at the park reported by citizen scientists on iNaturalist. This suggests that the squirrels鈥 hunting behavior emerged alongside a temporary increase in the availability of prey, the study said. The scientists didn鈥檛 observe the squirrels hunting other mammals.
鈥淭he 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,鈥 Wild said.
Smith added that many species, including the California ground squirrel, are 鈥渋ncredible opportunists.鈥 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.
鈥淭hrough this collaboration and the data coming in, we鈥檙e able to document this widespread behavior that we had no idea was going on,鈥 Smith said. 鈥淒igital technology can inform the science, but there鈥檚 no replacement for going out there and witnessing the behavior because what animals are doing always surprises us.鈥
The researchers said many questions remain unanswered, including how widespread the hunting behavior is among squirrels, whether and how it is passed down from parent to pup, and how it effects ecological processes. The authors are also excited to return to the field next summer to see what impact, if any, this year鈥檚 vole hunting may have on squirrel reproduction compared to the past decade.
Co-authors include Joey Ingbretson, Mackenzie Miner, Ella Oestreicher, Mari Podas, Tia Ravara, Lupin Teles and Jada Wahl of UW-Eau Claire and Lucy Todd of 新澳门六合彩内幕信息 Davis.
Several co-authors conducted field work during their undergraduate studies. Their work was partly funded by the Ronald E. McNair Postbaccalaureate Achievement Program, Diversity Mentoring Program and Summer Research Experience for Undergraduates. Additional funding sources include the Swiss National Science Foundation and the Vicki Lord Larson and James Larson Tenure-track Time Reassignment Collaborative Research Program.
Media Resources
- Jennifer E. Smith, University of Wisconsin-Eau Claire, smitjenn@uwec.edu
- Sonja Wild, 新澳门六合彩内幕信息 Davis Environmental Science and Policy, swild@ucdavis.edu
- Kat Kerlin, 新澳门六合彩内幕信息 Davis News and Media Relations, 530-750-9195, kekerlin@ucdavis.edu
Download permitted with credit to Sonja Wild/新澳门六合彩内幕信息 Davis.