Female Squirrels' Promiscuity Explained

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Female red squirrels are so promiscuous that they sometimes mate with up to 14 males in a single day, new research finds.

(A female red squirrel rests on a branch during her mating chase; Credit for all images: Ryan Taylor)

The reason, according to a study in the latest Royal Society Journal Biology Letters, is simple: male red squirrels are usually willing and available.

(A male red squirrel rests on a branch during a female mating chase.)

Preveiously it was thought that genetics might drive female squirrels to mate like crazy on the single day each year that they go into heat. As it turns out, genes have nothing to do with it. When opportunity knocks, the not-so-picky females usually don’t refuse.

“Their behavior is overwhelmingly influenced by opportunity,” said Eryn McFarlane, a researcher at the University of Guelph.

While being a sex stud can have its perks, it can also lead to big, potentially deadly, problems.

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“Having multiple partners means more energy expended on mating, increased exposure to predators as well as increased potential for the spread of sexually transmitted diseases,” she said. “Promiscuity also encourages harassment from male squirrels trying to coerce them into having sex.”

Optimal mating strategies can only evolve if genetics come into play, keeping individuals in line. Even humans have evolved genes that help to control hormones and other biochemical factors involved in our sex drives. Outside of the limited heat period, female squirrels haven’t yet been able to evolve the ability to “say no” to suitors, according to McFarlane and her colleagues.

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“We found the more males in the area interested in participating in the mating chase, the more squirrels she will mate with,” she said. “There are no strong ties between mating behaviour and genetics in red squirrels. So even if the costs of mating with many males outweighs the benefits, there doesn’t seem to be much capacity for them to evolve lower levels of promiscuity.”

McFarlane and Guelph integrative biology professor Andrew McAdam analyzed data collected from 108 mating chases involving 85 female squirrels. Researchers Jeff Lane and Ryan Taylor compiled the data as part of the Kluane Red Squirrel Project, a long-term field experiment in the Yukon investigating the importance of food abundance to the ecology and evolution of red squirrels. Thus far, the project has monitored the behavior and reproduction of about 7,000 squirrels.

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They observed that a few days before a female squirrel goes into heat, she will leave behind her scent for males to find. On the big day, she’ll run around trying to seduce males and will mate with anywhere from one to 14 partners.

(A male red squirrel approaches a female during her mating chase.)

They also discovered that female promiscuity is not always passed down from mothers to their offspring.

“A female squirrel that only chose to mate with one male could have a daughter that mates with many males,” McAdam said.

“The reality is that organisms cannot always be well adapted to their environment,” she continued. “Sometimes organisms do things that detract from their survival because they aren’t able to evolve a better alternative.”