Scientists have found California ground squirrels are evolving in a 'shocking' way - the animals have developed a taste for flesh.

A video captured dozens of them hunting, attacking and feasting on rodents for the first time ever.

The bizarre behavior was seen for two weeks at Briones Regional Park in Contra Costa County as cameras recorded squirrels pouncing on their prey, ripping them apart and consuming the lifeless animal.

On one occasion, scientists watched in horror as a squirrel 'vigorously' shook its prey while holding it in its mouth.

The observations have suggested that these nut foraging creatures are evolving into carnivorous predators. 

'This was shocking,' said Dr Jennifer E. Smith, an associate professor of biology at University of Wisconsin-Eau Claire, who led the study. 

'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.'

Scientists observed 74 interactions between squirrels and voles, which are similar to hamsters, from June 10 to July 30.

And more than 32 of those exchanges ended with the squirrel feasting on the small animal.

The predator typically restrained the rodent with its forepaws and teeth, then deliver one or several bites killing bites to the neck area.

In three of the recorded hunting attempts, squirrels stayed low to the ground and stalked their prey.  

Nineteen squirrels chased voles across the landscape, which was usually followed by a pounce to restrain the prey. 

Then, the squirrels would go for the kill. 

Though they primarily targeted bites to the neck, they sometimes went for other body parts, the researchers noted.

The squirrels successfully captured and killed a vole 55 percent of the time. 

These carnivorous eating habits coincided with an explosion of vole numbers in the park. 

According to the researchers, this suggests their hunting behavior emerged alongside a temporary increase in the availability of vole prey. 

This dietary flexibility may give the squirrels a survival advantage.

Sonja Wild, a behavioral ecologist at UC Davis and author of the study, said in a statement: '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.' 

While the researchers have been studying squirrels for years, even they were amazed at the findings. 

'I could barely believe my eyes,' Wild added.

'We saw that behavior almost every day. 

'Once we started looking, we saw it everywhere.'

'This research radically changes our perception of squirrels, one of the most familiar mammals in the world,' lead author Dr Smith told CNN via email. 

'In the face of human insults such as climate change and drought, these animals are resilient and have the potential to adapt to live in a changing world.' 

The researchers published their findings in the Journal of Ethology.

Though this is the first time California ground squirrels have been documented hunting rodents, previous research has found evidence of them eating bird eggs, invertebrates, and certain species of rabbits, gophers and rats.

But those studies did not find evidence of the squirrels hunting and killing these animals.

Other studies have reported California ground squirrels scavenging trapped fish, meat, woodrats, songbirds and in one case — another adult squirrel. 

A few studies have found evidence of this squirrel species hunting and killing other animals. 

Those reports identified captive side-blotched and western fence lizards, northern broad-footed moles and potentially a domestic chicken as prey.

What's more, infanticide — the direct killing of new young — has also been documented extensively in California ground squirrels.

'For example, 40 killings of post-emergent juvenile ground squirrels were documented over 4 years; juveniles were cannibalized in at least 22 of these cases,' Wild and co-authors wrote in their report.   

Several questions about the new eating behavior remain unanswered, according to the researchers.

This includes how widespread the behavior is among squirrels, how and if it is passed down from parent to pup, and how it affects ecological processes.

But the team is planning to return to the park next summer to see if there has been a long-term impact on either the voles or the squirrels themselves.