Imma Perfetto
Cosmos science journalist
Compilation of vole hunting by California ground squirrels. Credit: (c) Sonja Wild, UC Davis
Evidence of widespread carnivorous behaviour among squirrels has been documented for the first time in a new study published in the Journal of Ethology.
The California ground squirrels (Otospermophilus beecheyi) were spotted hunting, killing and eating voles.
“This was shocking,” says lead author of the paper Jennifer E. Smith, from the University of Wisconsin-Eau Claire in the US. “We had never seen this behaviour before.”
The species was previously thought to be granivorous – eating nuts, seeds or grains –until footage filmed by undergraduate students in the field turned this understanding on its head.
“I could barely believe my eyes,” says Sonja Wild of the University of California, Davis, who co-leads the long-term ground squirrels project with Smith.
“From then, we saw that behaviour almost every day. Once we started looking, we saw it everywhere.”
The authors of the paper documented California ground squirrels of all ages and genders hunting, eating and competing over vole prey between 10 June and 30 July 2024.
Because the peak in this opportunistic omnivorous behaviour coincided with an explosion of vole numbers – reported by citizen scientists on iNaturalist – it suggests that the hunting behaviour emerged alongside a temporary increase in prey availability.
“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,” Wild says.
They did not observe the squirrels hunting any mammals other than voles.
Many questions, such as how widespread hunting behaviour is among squirrels, whether and how it is passed down from parent to pup, and how it effects ecological processes, remain unanswered.
Next year, the researchers will assess whether 2024’s vole hunting bonanza has had any impact on squirrel reproduction compared to the past decade.
