The Kangaroo Rat is one of the most remarkable animals in the desert. Neither a rat, nor a kangaroo, the Kangaroo Rat is in the genus Dipodomys and is closely related to mice and gophers, with whom they share the characteristic of having external cheek pouches. They are much larger than pocket mice, however, and can be differentiated by their strong hind feet and small, weak forefeet. All kangaroo rats have exceptionally long tails with a conspicuous white hip stripe running the length of the tail. When in a hurry, kangaroo rats hop, and they can hop very fast indeed – up to 12 miles per hour.
Kangaroo rats are certainly “cute.” But what makes them extraordinary is that they do not need to drink water – they can get all the water they need from their food. This approach would not be adequate if kangaroo rats were as profligate with water as other mammals, but kangaroo rats are masters of water conservation. They have several physiological adaptations that serve this end, and they actively behave in ways that contribute to conservation.
Despite the high temperatures of their preferred habitats they have no sweat glands; instead they obtain all of their cooling through respiration. To do the cooling and keep as much water as possible, they have specially modified nasal cavities that act as condensers. As warm air leaves their lungs, it cools and the condensation that results is drawn back and readsorbed by their bodies.
Their high body temperatures allow them to radiate heat more effectively than most animals, and although they have few sweat glands, those they do have are in their feet. The evaporating moisture therefore condenses on the floor of their burrows, and increases the humidity inside.
Kangaroo rats have superb kidneys – probably the most advanced of any animal on earth. Their urine is between 4 and 5 times as concentrated as that of humans. It is almost solid when passed; salts and other metabolites may be concentrated as high as 24 percent, compared to 6 percent in humans.
Kangaroo rats build extensive burrows which they use both as home and granary. They cope with daytime desert heat by remaining underground, and foraging above ground only at the coolest times of the night. In periods of extreme cold or low food intake, they can become torpid to reduce energy consumption.
Kangaroo rats plug their burrows during the day and can maintain humidities near 50 percent or higher even while humidities outside may be as low as 5 to 15 percent. The moisture they exhale is then absorbed by the seeds they store, becoming available to them once again when eaten. They are selective in the seeds they gather and store, always taking the moistest seeds available – they are able to distinguish exceedingly small differences in water content.
Early researchers thought the kangaroo rat’s diet contained mostly dry seeds. More recent studies that analyzed both cheek and stomach contents have revealed that kangaroo rats consume as many insects as they can, and are also fond of green vegetables. This is particularly true during breeding. In fact, when available, insects and green vegetation make up most of their diets. They also consume large quantities of creosote bush seeds along with cactus, mesquite, and the seeds of many wildflowers. Creosote seeds may make up as much as 37 percent of the food they carry back for storage putting the lie to the notion that nothing eats creosote!
Though some researchers claim that kangaroo rats never drink water, that is not true. They can and do drink water when it’s needed and available. In captivity, kangaroo rats can be stressed to the point that they will even drink sea water – they are the only land animal known that can do that.
These animals are rarely seen, but it is not really that hard to get a glimpse of one. I’ve been able to observe them by waiting near a burrow entrance, after dark (preferably on a night with little or no moon), with a small kerosene lantern. I’ve used peanuts and popcorn to lure them out (I break up the peanuts into small pieces). You have to remain very still as they have superb hearing, and activity outside the burrow may discourage them from coming out. But it’s definitely worth the wait. They really are adorable little creatures!