These are some pictures of the leg of one of my fox squirrels. He was busy eating out of the bird feeder so I had an opportunity to zoom in and get some detailed shots. It freaked me out at first because the way he was gripping the feeder it looked like exposed muscle, very stringy and spaghetti-like. Thus, we have given him the name Spaghetti.

Incidentally, he also has a similar patch of hairlessness on his back that has been there for at least 4 months. The leg patch is a relatively recent occurrence. He's not one of my regulars, but I do see him every couple of months at the feeders. The leg does not seem to bother him at all and he walks, climbs, jumps, and runs without any apparent discomfort or limp.

It looks like mange to me, although I can't rule out an old hawk wound as there is a Cooper's Hawk hunts around my bird feeders every now and then. The main thing I'm worried about is exposure since the temperature has been so low recently. Other than their own winter stores and any foraging, when they come to my feeders they get a mix of corn, black oil sunflower seed, a few peanuts (too many can be bad for digestion) and shelled walnuts. If it is mange, and it persists or spreads, I'll probably get some medicine from the vet and put it in their food.