Gut microbes: The secret to squirrel hibernation

When winter sets in and food becomes scarce, some mammals hibernate, entering a state of deep rest that slashes their energy needs and allows them to fast for months. However, fasting deprives them of essential nutrients, including carbon. Carbon, the building block of all life, normally comes from food. But hibernating animals take in no carbon, while their bodies keep releasing it through respiration, mostly as carbon dioxide.