Red squirrels may be cute, but they’re also vicious cannibals

red-squirrel-on-a-tree Photo by seawhisper/Shutterstock

After what you’re about to read, you may never look at squirrels the same way.

A study published in Scientific Naturalist has found that male squirrels will commit infanticide and cannibalism of squirrel pups who aren’t their own.

The paper explains how red squirrels in the Yukon often have larger litters right before “mast years,” when white spruce produce more cones than usual, indicating that squirrels are able to predict years when there will be an abundance of food. It’s all very interesting, but nothing that would change a person’s perception of squirrels. However, things take a turn when the study describes another behaviour that was observed during these mast years: cannibalism.

“On 25 May 2014 . . . J. A. Haines observed a male intruding on a neighboring female’s territory […], The study reads. “The male killed one of the female’s pups with repeated bites to its chest and upper abdomen. On 1 June 2014, another pup from the same litter was found dead within 5 m of the nest tree with chest punctures and a partially consumed head.”

Eventually, the study explains, the female squirrel’s entire litter was killed, and the male who had committed the infanticide became the sire of the female squirrel’s next litter.

Squirrel in tree eating a pine cone
Red squirrels seem to be able to detect when there will be a mast year, when white spruce will produce more cones. These same years see an increase in infanticide and infanticide. [Credit: Jessica Haines]
While it’s hard for many of us to imagine the fuzzy, acorn-hoarding animals we see outside our windows committing bloody acts of cannibalism, Jessica A. Haines, an ecologist with the University of Alberta and the study’s primary author, says that squirrels aren’t always as cute and innocent as we imagine.

“Squirrels also eat things like baby bunnies, baby birds, and birds’ eggs,” she told National Geographic.

So why do male squirrels kill squirrel pups on these food-abundant mast-years? Haines believes it’s all about making sure their genes get passed on.

While on typical years, squirrels only have one litter, these mast years often mean female squirrels will have two. The study believes that since squirrels know which years will be more abundant in food, these mast years “[give] the male committing infanticide on an earlier litter a chance to sire later litters with the mother.” In other words, a male who kills an earlier litter gets to ensure that he alone will sire the next one, passing his genes on to the next generation.

Infant squirrel with wound on back
This infant squirrel has similar bite marks to those killed by adult males. [Credit: Jessica Haines]
John Kropowski, a conservation biologist at the University of Arizona, doesn’t think the behaviour is exclusive to Yukon squirrels. “Infanticide likely has a much more important influence on the evolution of behavior of animals than we currently appreciate,” he says.

For Haines, this discovery is less horrifying than exciting, as it opens up further questions about squirrel behaviour, including: How do squirrels know when there will be a mast year?

It’s a question she will continue to study with the Kluane Red Squirrel Project, a field experiment examining the importance of food abundance to red squirrels. The project has been running in the Yukon for 30 years, but Haines still believes there is plenty left for it to discover.

“Even after all that time, we’re still learning things about squirrels.”

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