Earlier this fall, we explored the ways our water-dwelling friends survive icy winters. But what about all the other creatures that walk the earth, climb the trees and fly at other times of the year? Every winter, hundreds of species undergo some form of hibernation to get through the cold and emerge ready for spring. In simple terms, they “go to sleep,” not waking up at all until temperatures climb to a safe level of warmth, or perhaps engaging in very limited, occasional activity. Either way, hibernating animals don’t maintain normal water-drinking activity to stay hydrated like they do the rest of the year. So, how do these hibernators do it and stay hydrated without water intake?
The answer demonstrates just how incredible nature really is and how fascinatingly adaptive the bodily functions of these animals can be! But before we dive in, please note that our discussion will be general terms—different animals have varying needs depending on size, species, surroundings and so forth; consequently, their hydration method is specific to their species.
First, we must understand what happens to an animal during hibernation. Everything slows down, considerably. Metabolism drops significantly. Breathing and all bodily functions slow—and in some species, believe it or not, stop altogether. Activity ceases completely or is extremely limited. Body temperature decreases to the animal’s natural “set point”—the minimum temperature its body can reach and still regain normal function come spring. All these changes allow the hibernating animal to expend little to no energy.
So now, with energy needs and activity at their lowest levels, the animal ceases to defecate and urinate—two of the three main ways the body loses water. The third contributor to water loss, breathing, is also minimized. Without activity, animals don’t “sweat out” bodily fluids either.
Hibernators don’t require water for energy, and they don’t expel much water at all. Still, we know that to survive, an animal’s cells need water—muscles, brain function and the like must maintain some level of health so that they can warm up the body and bounce back in the spring. So, where does that water come from? Fat reserves. During hibernation, an animal burns fat reserves in order to stay above its natural set point and “feed” itself. This fat-burning process produces what is called metabolic water, which is enough to sustain cells and other bodily needs. Many species can also convert elements of the urine that they do not expel into energy and water, thus adding to the hibernation hydration cycle.
Lastly, and adding to just how fascinating nature and animal adaptability is, species that dwell in sustained arctic temperatures produce a type of natural antifreeze that prevents water in their cells from freezing during hydration.
In conclusion, I say hats off to the hibernators, because, in a way, these animals just may be some of the best water conservationists that exist! They reduce, reuse and recycle—limiting their water use and producing only what they need!