Yukon red squirrels are randy.
Especially the females.
For more than two decades, scientists have been studying the horny rodents in Kluane Park.
Called the Kluane Red Squirrel Project, the long-term field study was set up to examine the importance of food to the ecology and evolution of red squirrels.
But over the past few years, one University of Guelph grad student threw sex into the mix.
Eryn McFarlane initially wanted to look at how often birds have sex and why.
But her professor, who was involved in the Yukon red squirrel project steered her to rodents instead.
“In the field of promiscuity, in other species, it’s thought females shouldn’t have a lot of mates,” said McFarlane.
Too much sex uses up energy, increases exposure to predators and can lead to sexually transmitted diseases, she said.
But female red squirrels don’t seem to care.
For three years, students tracked 85 squirrels during 108 mating chases.
The squirrels have different coloured pipe cleaners tucked in their ears, to identify them, so researchers could tell who was mating and how often.
What they learned turned animal promiscuity on its head.
Some of the female squirrels had sex with up to 14 partners in one day.
“They’re pretty busy,” said McFarlane.
The research didn’t stop there.
McFarlane wanted to determine if this behaviour was genetic or environmental.
Tramping through the Yukon bush in February and March, when the females go into heat, McFarlane used transmissions from the squirrels’ radio collars to listen for females in heat.
They only go into heat for one day, she said.
Some mating chases only resulted in sex with a couple males, while others saw more than a dozen suitors succeed.
Using the detailed family tree built up from decades of studying the Kluane squirrels, McFarlane discovered that some daughters would have sex with only one or two partners, while their mom really spread the love around.
Others would be born to a very selective mother and end up with more partners than you can count on both hands.
“So it has nothing to do with genetics,” said McFarlane.
It’s environmental influences that are “overwhelmingly responsible” for a squirrel’s sex life, she said.
Basically, the more males that show up, the more sex a female squirrel has.
“That doesn’t mean she’ll necessarily mate with all the males,” said McFarlane.
But a well-courted squirrel will definitely have more sex.
By eliminating the genetic influence, McFarlane’s findings have added a new angle to the study of animal promiscuity.
Next, she plans to study why some of Kluane’s female squirrels get more suitors than others.
She hopes to come north in March, “when there are no bugs and bears.”
This time, instead of observing squirrel sex, she will be trying to catch the females in the few days before they go into heat to see if some are better at spreading their scent than others.
After this, McFarlane isn’t sure if she’s going to pursue her squirrel-sex studies.
“Some people think it’s pretty funny,” she said.
Contact Genesee Keevil at