Animals prepare for food shortage
Leaves have one further shortcoming as food. In temperate parts of the world (vizdeciduous forests), many disappear almost entirely for months at a time. The creatures dependent upon them must, therefore, make special preparations as winter approaches. Asiatic sheep (Ovis ammon) turn their food into fat and store it as cushions around the base of their tails. Other species not only feed and fatten themselves as much as they can, but reduce the demands of the next few months to a minimum by hibernating. The triggers to initiate hibernation have not all been precisely identified. It is certainly not simply a drop in the temperature since animals kept in a constantly warm environment will still hibernate. In some cases it appears to related to shortening of daylight hours. It may be that the stimulus comes from the fat reserves themselves. When the animal has accumulated sufficient fat biochemical processes initiate hibernation.