A North American porcupine (Erethizon dorsatum). These large rodents 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.