View of an American porcupine (Erethizon dorsatum). These large rodents are native to North America, with the exception of the more southern and eastern areas. They prefer to live in forested areas. They are largely nocturnal, and remain in their nests during the day. These porcupines are good climbers, and usually nest in trees. They are generally solitary. American porcupines eat mainly tree bark in winter, although their diet expands in summer to include berries, flowers and leaves. Their barbed spines offer them protection from predators. They cannot be pulled out, and burrow inwards, often killing the victim.