A California ground squirrel in Conta Costa County runs with a vole it hunted in its mouth. A study from UC Davis and University of Wisconsin-Eau Claire is the first to document widespread carnivorous feeding of voles by squirrels. Credit: Sonja Wild/ UC Davis. CC BY-NC-ND.
The first evidence of ground squirrels hunting and eating voles in Bay Area of the USA has been documented by researchers.
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 University of California, Davis, is the first to chronicle widespread carnivorous behaviour among squirrels.
The study 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 was assumed.
The observations occurred in 2024 — the 12th year of the Long-term Behavioral Ecology of California Ground Squirrels Project 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.
Lead author Jennifer E Smith, an associate professor of biology at UW-Eau Claire who leads the long-term ground squirrels project with Sonja Wild of UC Davis, said: “This was shocking. We had never seen this behaviour 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’s this never-before-encountered-in-science behaviour that sheds light on the fact that there’s so much more to learn about the natural history of the world around us.”
A California ground squirrel eats a vole it hunted in Briones Regional Park in Contra Costa County. Credit: Sonja Wild, UC Davis. CC BY-NC-ND.
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’ carnivorous summer behaviour peaked during the first two weeks of July, coinciding with an explosion of vole numbers at the park reported by citizen scientists on iNaturalist.
This suggests the squirrels’ hunting behaviour emerged alongside a temporary increase in the availability of prey, the study said.
The scientists didn’t observe the squirrels hunting other mammals.
Wild said: “The fact that California ground squirrels are behaviourally flexible and can respond to changes in food availability might help them persist in environments rapidly changing due to the presence of humans.”
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.
Smith said: “Through this collaboration and the data coming in, we’re able to document this widespread behaviour that we had no idea was going on.
“Digital technology can inform the science, but there’s no replacement for going out there and witnessing the behaviour because what animals are doing always surprises us.”
The researchers said many questions remain unanswered, including how widespread hunting behaviour is among squirrels, whether and how it is passed down from parent to pup, and how it effects ecological processes.
The study is published in the Journal of Ethology.
