California ground squirrels of all ages and genders were observed actively hunting the small rodents
California ground squirrels of all ages and genders were observed actively hunting the small rodents
Flesh-eating squirrels that hunt down and devour voles have been spotted for the first time in the wild.
Until now, squirrels were thought to be primarily vegetarian, cramming their cheeks full of seeds and nuts, which they often bury in underground stores to get through the colder months.
But biologists were amazed to see California ground squirrels chasing and killing voles in predatory behaviour never before recorded in the animals.
Experts say it fundamentally changes their understanding of squirrels, which clearly have a more omnivorous and flexible diet than had been assumed.
“This was shocking,” said squirrel expert Dr Jennifer Smith, of the University of Wisconsin.
“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.”
Ground squirrels are known to eat insects, bird eggs and nestlings, but can ‘respond to changes in food availability’, say scientists
Researchers have been following squirrel populations at Briones Regional Park in Contra Costa County since 2010, but this is the first time they have observed the carnivorous behaviour.
Out of 74 observed interactions with voles between June and July, 42% involved active hunting of these small rodents by ground squirrels.
Dr Sonja Wild, who helped set up the California Ground Squirrels Project with Smith, said she was astonished when undergraduate students first came to her saying they had filmed the strange new behaviour.
“I could barely believe my eyes,” said Wild, of the University of California. “From then, we saw that behaviour almost every day. Once we started looking, we saw it everywhere.”
Ground squirrels generally live on the ground or in burrows, in contrast with British tree squirrels, such as the red and grey, which make their homes in trees.
Tree squirrels have large bushy tails, unlike ground squirrels, and measure between 12 and 20 inches long, compared with ground squirrels, which average about eight to 12 inches in length.
The term ground squirrels is most often used for medium-sized animals, with larger varieties being known as marmots or prairie dogs and larger ones known as chipmunks.
Ground squirrels are known for their burrowing behaviour, creating intricate tunnel systems which they use as escape routes from predators.
As well as nuts and seeds, the animals are also known to occasionally eat insects, bird eggs and nestlings.
In new research, published in the Journal of Ethology, the authors documented California ground squirrels of all ages and genders hunting, eating and competing over vole prey.
The squirrels’ carnivorous summer behaviour peaked during the first two weeks of July, coinciding with an explosion of vole numbers at the park.
This suggests the squirrels’ hunting behaviour emerged alongside a temporary increase in the availability of prey, the study said. The scientists did not observe the squirrels hunting other mammals.
“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 because of the presence of humans,” Wild added.
Smith added that many species, including the California ground squirrel, are “incredible opportunists”.
But they 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 affects the environment.
The authors are planning to return to the same spot next summer to see what impact, if any, this year’s vole hunting may have on squirrel reproduction compared with the past decade.
