Physiological - Porcupines have a dense coat that allows it sufficient protection from the cold (hibernation). Males can roost in trees for days, eating bark. Females and juveniles sit it out in dens and nearby areas, changing dens every three weeks or so. Several can share a den, but usually of the same sex.
Behavioral - When a porcupine is threatened, it extends its quills, making it difficult for another animal to attack it or eat it.
