It's not unusual to see squirrels eating acorns or other nuts, or seeds; they are considered herbivores though they sometimes eat insects as well. But researchers now have evidence that when presented with a good opportunity, ground squirrels will also hunt down voles, and kill and eat them. The observations were made in the summer of 2024 at the Briones Regional Park in Contra Costa County, California. There were 74 documented interactions between ground squirrels and voles, with 42 percent involving hunting.
The data, which is the first evidence of widespread, carnivorous ground squirrel behavior, suggests that ground squirrels have a more flexible diet than known and they are actually opportunistic omnivores. It was part of the Long-term Behavioral Ecology of California Ground Squirrels Project, which was in its twelfth year at the time. The work has been reported in the Journal of Ethology.
"This was shocking," said first study author Jennifer E. Smith, an associate professor of biology at he University of Wisconsin-Eau Claire. "We 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's this never-before-encountered-in-science behavior that sheds light on the fact that there's so much more to learn about the natural history of the world around us."
When corresponding study author Sonja Wild, a UC Davis postdoctoral research fellow was shown video of the ground squirrels hunting voles, she "could barely believe my eyes," she said. "From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere."
The researchers documented ground squirrels of various ages and genders hunting and competing for vole prey and consuming their kills.
This behavior occurred during June and July, with a peak in the first two weeks of July. This coincided with a dramatic increase in the vole population, as reported by citizen scientists. The researchers noted that the squirrels seemed to simply take advantage of this brief explosion in prey numbers. This seems to be confirmed by the observation that squirrels did not hit other mammals, only the readily available voles.
"The 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," noted Wild.
Smith noted that it's common for species to become opportunistic. Many are. quite flexible, and will readily adapt to changing conditions that are often brought on by humans.
There is still a lot more to learn about this novel behavior, such as what ecological influence it may have, how widespread it may be, what effects it could have on the squirrel population, and whether squirrel parents pass it down to pups.
Sources: University of California, Davis (UC Davis); Journal of Ethology