The polar bear, Ursus maritimus, lives in one of the most extreme environments on Earth, an Arctic habitat dominated by sea ice and frozen ocean. This vast, icy landscape presents a paradox: water is everywhere, yet fresh water is exceedingly scarce. The challenge for a polar bear is finding liquid that will not dehydrate them. Understanding how these powerful carnivores sustain themselves requires examining their remarkable biological adaptations. The answer to what polar bears drink is a testament to the evolutionary pressures of life in the high Arctic.
Why Saltwater is Not an Option
Polar bears do not drink the saltwater that surrounds them, a behavior that would quickly lead to severe dehydration. Seawater contains a high concentration of dissolved salts, approximately 35 parts per thousand. If a mammal consumes this salty liquid, its kidneys must use fresh water to flush the excess salt from the bloodstream. Excreting this high salt load requires more water than the bear gains from drinking the seawater, creating a net water loss. This makes the Arctic Ocean a biological barrier to hydration rather than a source. Any mammal attempting to sustain itself on saltwater would rapidly exhaust its internal water reserves and succumb to poisoning from the buildup of electrolytes. This physiological constraint forces the polar bear to rely on other, specialized methods to meet its water needs.
The Role of Metabolic Water
The primary source of hydration for a polar bear is not liquid water, but metabolic water, a byproduct of their internal energy production. This water is chemically created within the bear’s body through the oxidation of stored fat reserves. Polar bears are highly specialized predators that consume a diet rich in lipids, primarily the blubber of seals, which has earned them the nickname lipovores, or “fat eaters.”
When the bear breaks down fat molecules for energy, oxygen is used in a chemical reaction that yields water and carbon dioxide. This process, known as fat oxidation, is efficient, producing a greater volume of water per gram compared to the metabolism of carbohydrates or protein. For every 100 grams of fat metabolized, a polar bear can generate approximately 107 grams of water. This internal water factory is crucial during long fasting periods, such as when waiting for the sea ice to form or when denning. The stored blubber supplies a continuous stream of fresh water for their system.
Managing Salt and Conserving Water
The polar bear’s survival depends on producing water, retaining it, and managing the salt load from their seal-rich diet. They possess highly efficient kidneys, a physiological adaptation that minimizes the loss of water. These specialized kidneys produce extremely concentrated urine, allowing them to excrete metabolic waste and excess salts with the least amount of fluid possible.
This ability to concentrate urine is comparable to that of desert-dwelling animals, reflecting the scarcity of accessible fresh water in both environments. Polar bears conserve water through low rates of water loss through respiration and feces. By recycling urea and minimizing evaporative loss, they maintain a precise water balance, ensuring that the metabolic water they produce is effectively retained and utilized.