More spruce cones more pups: Study says male squirrels leave wealthier estates

A squirrel’s survival, and the survival of its pups, could depend on the food storage habits of a dead squirrel it’s never met, according to new research from the Kluane Red Squirrel Project.

Red squirrels that inherit food stores from males increase pup production by 50 per cent, says study

An adult female red squirrel on a tree. Research from the Kluane Red Squirrel Project. If a squirrel inherits a food cache previously owned by an adult male squirrel, its lifetime pup production could increase by 50 per cent, according to a recent study. (Juliana Balluffi-Frye)

A squirrel's survival — and the survival of its pups — could depend on the food storage habits of a dead squirrel it's never met, according to new research from the Kluane Red Squirrel Project.

The study, published in this month's Ecology Letters, says young squirrels will take over abandoned middens — underground caches of food such as white spruce cones. If a squirrel inherits a midden previously owned by an adult male squirrel, its lifetime pup production could increase by 50 per cent. 

"It's a bit like a young couple moving in and finding a pile of money kind of hidden in a chest of drawers in their house or something like that. It gives them an enormous leg up," said David Fisher, the study's lead author, and a former postdoctoral researcher with the University of Guelph.

Fisher explained that this is because male squirrels store more food than females. Research showed that, on average, middens kept by male squirrels had 1,300 more cones than those kept by females. That's enough food to keep a squirrel alive for an additional 17 days.

Squirrels between three and four years of age also store more cones, Fisher added. 

David Fisher is the lead author on a study about squirrel middens. He was a postdoctural researcher with the University of Guelph at the time. (Submitted by David Fisher)

The study also found that females that inherit a midden from a male squirrel give birth earlier in the spring. This gives their pups a greater chance of surviving the winter. Fisher said they think this is because pups that are born earlier are more likely to inherit a midden.

"It shows the … amazing diversity of the natural world," Fisher said of the study.

"Even in something we think [of] as quite common [like a squirrel]. They're actually doing these really, really interesting things like inheriting territories from each other, and somehow one squirrel being dead can influence a current living squirrel."

Fisher said they don't know what determines which midden a particular squirrel will inherit. But, he said, they have seen cases where a female squirrel will bequeath her midden to one of her offspring and then take over another midden if there are vacant food stores in the area.

The findings come from data gathered from hundreds of squirrels through the Kluane Red Squirrel project — a partnership between five universities — between 1987 and 2017. Fisher said researchers also estimated the size of middens by taking samples from middens during the caching season in the autumn.

"We put them all back of course, we [didn't] want the poor little squirrels going hungry."

New white spruce cones stored in a midden. Researchers found that the average midden contains 20,000 cones. (Kluane Red Squirrel Project )

Fisher said the middens ranged in size from having almost no cones to 145,000 cones. The average midden contained around 20,000 cones. 

Stored cones can be edible up to four years, he said, and multiple squirrels will use the same midden at different periods over time. At least one midden they studied was active for 31 years and used by 13 different squirrels. 

"We tend to think of humans as being the only organisms that pass on like a material culture," said Fisher. "But it demonstrates that these kinds of physical resources can matter to organisms other than humans and make a huge difference to the lives of even tiny mammals living in the North."