What causes some animal to hibernate?

Hibernation is the animal's way of adaptation in order to be able conserve energy by staying inactive and lowering its physical activity in preparation for future purposes say for example a bad weather.  Other animals also hibernate in preparation for a long drought or scarcity of food. They tend to consume a lot of food before the scarce and will use the accumulated energy during the drought when there will be no more food to eat. It is a way of recharging themselves.