They may have twitchy noses and a quizzical expression but ground squirrels are not as cuddly as they appear: researchers have found they repeatedly hunt and eat voles, decapitating their prey and pulling flesh from the torso.
The team say the discovery was a shock: while California ground squirrels have previously been observed eating insects, bird eggs, hatchlings and even – albeit rarely – scavenging small, juvenile mammals, they were primarily thought to be herbivorous, snacking on seeds, acorns, fruits and nuts.
“This is incredibly exciting, because this is the first time for this species that we’ve documented active hunting from start to finish,” said Dr Jennifer Smith, an associate professor of biology at University of Wisconsin, Eau Claire and first author of the research.
“Once we saw it happening, it continued to happen again and again throughout the summer,” she added.
However it isn’t the first time California ground squirrels have displayed a less than fluffy side. As Smith notes, the females are also known to commit infanticide, killing and eating the young of others.
Writing in the Journal of Ethology, Smith and colleagues report how they made their discovery during the twelfth year of a long-term study on the California ground squirrel population carried out at Briones Regional Park in Contra Costa County, California.
Every June and July the team live-trap, mark, tag and release ground squirrels, allowing them to be individually recognised.
Over the course of 18 days in the summer of 2024, the team recorded 74 events in which ground squirrels hunted or ate California voles, or both, with at least 27 different squirrels engaging in the behaviour. The team noted that adults and juveniles, both male and female, hunted the voles, and typically did so alone. Occasionally, squirrels attempted to steal dead voles from each other.
The team also recorded that the unexpected behaviour coincided with an unusual explosion in the numbers of California voles, as revealed by citizen science data, the cause of which remains unclear.
“It seems that these squirrels are just opportunistic,” said Smith, although she said it remains an open question whether they learn the behaviour socially from each other.
Smith said California ground squirrels are known to be inherently flexible in their foraging behaviour.
“The super abundance of voles during this particular summer really opened up the novel dietary niche for them,” she said.
The researchers said their discovery suggests California ground squirrels are more flexible in their diet than previously considered, and may be best thought of as an opportunistic omnivore.
Smith added such flexibility could help the creatures to survive in the face of challenges such as climate change and human presence.
“This is important, because they are a major prey source for California ecosystems, and they are a native species,” she said. “And if they’re doing well, there’s a lot more opportunities for other species that are threatened to be able to survive and do well.”
Cory Williams, an assistant professor in the Department of Biology at Colorado State University who was not involved in the work, said he was surprised by the research given that ground squirrels are strictly diurnal and voles are most active at night.
“This likely only occurs when you have a population outbreak of voles and densities become extremely high,” he said. “But I’m not surprised they are eating them when they are available, given how opportunistic these animals are.”
