It's not in the genes, but in the number of knocks at the door.

Researchers at the University of Guelph have found that something a lot more circumstantial than genetics is behind female squirrels' promiscuity.

"Their behaviour is overwhelmingly influenced by opportunity," said Erin McFarlane, a graduate student and member of the team that looked into this issue that has long baffled biologists.

The findings are published in the Royal Society journal Biology Letters.

Female squirrels are known to sometimes have as many mates as possible, behaviour that doesn't always make sense for females, McFarlane said.

The researchers found that the more males there were in the area interested in mating, the more squirrels a female would mate with, McFarlane said.

"A female squirrel that only chose to mate with one male could have a daughter that mates with many males," integrative biology professor Andrew McAdam said in a release. "It seems the tendency to mate with fewer males isn't something that is being passed down from generation to generation."

The discovery that the mating patterns of female squirrels aren't genetic means mating habits in the species are unlikely to evolve, the researchers found.

The researchers analyzed data from 108 mate chases involving 85 female squirrels. The female squirrels mated with anywhere from one to 14 partners.