How do kangaroo rats and fennec foxes live without drinking?

Desert animals mostly avoid the problem rather than solve it: they hide from the heat, make water from their food, and waste almost none. Take the kangaroo rat, a small, mostly nocturnal rodent of the deserts of western North America. Merriam's kangaroo rats obtain enough water from the metabolic oxidation of the seeds they eat to survive, and they do not need to drink water at all. Burning food releases water, and burning fat gives the most: a gram of fat makes 1.07 grams of water.

They also lose very little. Kangaroo rats have a low metabolic rate, produce very concentrated urine, plug their burrow entrances with soil during the day to keep the air in cool and humid, and come out only at night. When one sleeps, it buries its nose in its fur to trap a small pocket of moist air.

Half a world away, the fennec fox of the Sahara plays the same game. The smallest fox species has unusually large ears, which dissipate heat and listen for prey underground. Its sand-coloured fur reflects sunlight by day and helps keep it warm at night. Mostly nocturnal, it avoids the heat and loses less water by panting less. Its dense kidneys help store water in times of scarcity, and it gets moisture from its prey, though it drinks when it can.

The fox and the rat are only distant cousins, yet they landed on similar habits. When separate lineages evolve similar solutions to the same problem, biologists call it convergent evolution, and deserts are full of it: kangaroo rats and jerboas are one listed example.