Porcupines are primarily nocturnal and often rest in trees during daylight hours.

The bulk of their diet consists of plants, leaves and inner tree bark. Porcupines can cause significant damage to personal and public property by feeding on trees. Porcupines are rodents that need to sharpen their teeth, so they may chew on wood in your backyard.

Porcupines feed on salt and salt residue, and have been known to chew on leather items and even the brake lines of vehicles.

More information:
Control of Porcupine Damage