Ed Yong reports on a new hypothesis by Jane Waterman on why Cape ground squirrels masturbate so much:
The final explanation is that masturbation is actually a form of self-medication. By cleaning their genitals, males reduce their odds of contracting a sexually transmitted infection. It’s a new hypothesis that Waterman herself put forward, but it’s the only one that actually fits with all of her data. If it’s true, you’d expect males to masturbate more frequently after sex than before it, which they do. You’d expect them to masturbate more frequently during the time of month when females are ready to mate, which they do. And finally, you’d expect their tendency to masturbate to increase as they get more sex, which it does.
Just don't tell Christine O'Donnell, ok? This is between you, me and the Internet.