Kangaroo Rats

Sometimes research for The Emotional Calendar, the book we are working on with Dr. John Sharp, leads to some amazing—but totally irrelevant—discoveries that need to be shared.

The kangaroo rat is absurdly cute. But that’s not what makes it a fascinating creature. The kangaroo rat is almost perfectly adapted to its ultra-hot desert habitat in the southwest US. It does not drink water!

Here’s how it works. Kangaroo rats feed on seeds, which have an extremely low water content. For this reason, almost all of the water that the rat uses is what’s known as “metabolic water.” The oxidation of sugar during cellular respiration results in the release of water as a biproduct. Specifically, the oxidation of 1 gram of carbohydrate releases 0.56 grams of metabolic water.

Because kangaroo rats have so little water, they have amazing water conservation adaptations. Their kidneys have a unique design that allows them to produce urine which is 30x more concentrated than blood—the most hypotonic (electron-rich) urine known among animals. Furthermore, their respiratory system is designed to conserve water. The rats spend their days in burrows where the air temperature is cooler than their body temp. As the air is warmed in their nasal passages, it picks up water vapor, cooling the tissue. When the warm, moist air returns from the lungs, it cools as it flows through their extensive nasal passages. The moisture condenses as the air cools, so that most of the water lost during inhalation is conserved as they exhale.