 When the day length starts to decrease, the hibernating mammals start preparing for it. They store energy reserves to survive the periods of non-feeding. They build up heavy fat reserves, grow long winter paltz, they also increase brown fat deposits. These students, the time taken for an animal to the dormant state of hibernation is quite long. In comparison to it, the time taken for arousal is much less. For example, ground squirrels take 12-18 hours to hibernate. For example, we have to sleep. We say that it takes 5 minutes or half an hour to sleep. Because it is a process of daily life. But hibernation is a long process in which we have to sleep for weeks or months. So in this way, this process does not happen immediately. It will take a few months to hibernate. It takes 12-18 hours for ground squirrel to enter the dormant state of hibernation. Or arousal requires about 3 hours. This is the timing of squirrel. It varies in different animals. Some hibernators wake up periodically during the hibernation. For example, once a week or after every 4-6 weeks, this waking period is to empty their bladders to urinate or to defecate. After that, it continues in hibernation. For these students, the arousal from hibernation requires rapid heating by intensive oxidation of brown fat. When hibernation is to be finished, these processes occur. First of all, oxidation of brown fat, which is accompanied by shivering, so that shivering thermogenesis is produced. Search in metabolic rate and a rise in body temperature. These are the requirements to come out of the state of hibernation. Now we shall discuss winter sleep. Winter sleep is a state of prolonged inactivity in winter. It occurs in some larger mammals with large energy reserves. For example, badgers, beards, skunks, opposums or raccoons. During winter sleep, body temperatures do not drop substantially, but they drop for only few degrees centigrade. The sleeping animal can wake and become active for a long time. Now we shall discuss activation. Estivation is a period of inactivity in some animals to withstand the extended hot and dry periods. As the environment of the animal begins to dry, animal enters the burrow and stops eating the food. The animal begins to dry, animal enters the burrow and stops eating and drinking, drops its metabolic rate, becomes slow and becomes inactive. Animal emerges from activation when moisture returns in the environment. This period is usually seasonal, dry seasons and hot seasons. When it ends and rains, the animal becomes active again. Estivation process is usually observed in many invertebrates, especially in mollusks. Lungfishes are a very big example of activation, whereas some reptiles and some amphibians also undergo activation.