Why squirrels masturbate

Since I mentioned in my last post that the amount of sperm produced by humans is literally astronomical, I've been thinking about which animals masturbate and why. For humans it seems to be a sexual outlet but is that the case for other mammals? How about non-mammals, do birds and bees masturbate? Well the motivating factor for male squirrels has been discovered, and it doesn't seem to be related to blue balls. Firstly, it appears that they are quite acrobatic:

“An oral masturbation was recorded when a male sat with head lowered and an erect penis in his mouth, being stimulated with both mouth (fellatio) and forepaws (masturbation), while the lower torso moved forward and backwards in thrusting motions, finally culminating in an apparent ejaculation, after which the male appeared to consume the ejaculate.”

Secondly, it seems to be motivated by cleanliness according to this paper:

"These results suggest that masturbation in this species was not a response to sperm competition nor a sexual outlet by subordinates that did not copulate. Instead masturbation could function as a form of genital grooming. Female Cape ground squirrels mate with up to 10 males in a 3-hr oestrus, and by masturbating after copulation males could reduce the chance of infection. Sexually transmitted infections (STIs) can profoundly affect fertility, and their consequences for mating strategies need to be examined more fully."

So who said masturbation was dirty?