Active all winter but still quite slow, porcupines get by because they are living fortresses.

I have encountered only one at a time, but other observers have seen them in groups of up to five or six. Many times they are in trees, where they eat bark.

A porcupine has an estimated 30,000 quills, so it is not incapacitated by a single encounter when an enemy might dislodge several hundred quills. New ones will replace those lost. There are no quills on the muzzle, legs or underparts of a porcupine's body. Quills on the face are only about half an inch long; on the back they may be up to 5 inches. The hollow quills provide buoyancy, making porcupines good swimmers. A small muscle is attached to each quill, which pulls it upright in the fur when the animal bristles with alarm. Porcupines cannot throw their quills, contrary to popular belief. They can, however, swat an animal with their tail, filled with loose quills.

Minnesota's second largest rodent, the porcupine is exceeded in size only by the beaver, and can weigh more than 30 pounds. It is found throughout the upper two-thirds of the state. The more snow, the less tendency they have to travel. Also, they rarely move in below-zero weather. When sitting hunched in a tree, a porcupine can be mistaken for a squirrel's nest, but close to the ground it is easily recognized.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.