Hibernation is when an animal sleeps for a long period of time during cold weather. Hibernation lasts anywhere from a few weeks to several months. The length of time an animal hibernates depends on the species, the time of year, ambient temperatures, and how healthy the animal is. [source] Animals such as rodents, reptiles, and insects all hibernate. Technically, a bear does not. Bears fall into a deep sleep called a torpor. [source]