They are nocturnal. When alarmed a porcupine may stamp its feet, click its teeth, and growl or hiss. Usually its quills lie flat against its body. When threatened, the porcupine raises and spreads its quills. Porcupines cannot shoot quills at an attacker, but they are loosely attached and may come off when it slaps its tail or brushes against an enemy.
New quills grow in to replace lost ones.
Reproduction Porcupines have evolved one of the slowest reproductive rates of all mammals. The female becomes sexually mature during her third year and bears only one young annually for the remainder of her 15 year life span. Mating takes place at night. The precocial newborn can see at birth. Hair and soft quills cover most of their bodies and within a few days, their quills harden.