This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
I need devote but little space to the fact that animals fast for shorter or longer periods in times of food scarcity when floods, droughts, storms, etc., destroy their food supplies, or when snow has covered their food and rendered it temporarily inaccessible. It often happens in the lives of animals that they are forced to go for days at a time without food for the reason that they cannot find it. They sometimes, though relatively rarely, perhaps, go so long without food that they die of starvation. Luckily, they possess sufficient reserves to enable them to go without food for prolonged periods and survive. Animals that enter the winter season with considerable fat, commonly emerge from winter rather thin due to the fact that they are forced to subsist on greatly reduced food supplies and often have to go for days at a time without food. Even at the height of the food season insects may so completely destroy the food supply that many animals are forced to go for considerable periods without food.