“When we try to pick out anything by itself, we find it hitched to everything else in the universe.” —  John Muir 

Deserts conjure images of extreme aridity, searing heat, and for naturalists, an appreciation for the array of solutions that animals and plants have developed for not only surviving, but thriving under these otherwise cruel conditions. Lizard skin that reduces water evaporation, plants that open their stomata – leaf pores that allow carbon dioxide to enter and oxygen and water vapor to be emitted – only at night, are just a couple of the many adaptations for survival in an otherwise harsh environment. Another is simply only coming out at night when the extreme desert heat is not so extreme at all. Some lizards do this (geckos), and some birds (owls and nighthawks), but the desert night is ruled by mammals, snakes, and insects.

Years ago, as part of an effort to understand what was available for Coachella Valley fringe-toed lizards to eat and from that menu what they consumed, I surveyed the abundance and diversity of dune insects found here. The species diversity was truly amazing, especially in a single family of nocturnal beetles – darkling beetles (Tenebrionidae). Across the Coachella Valley dunes I recorded no less than 33 species and I suspect there are still more to be discovered. These beetles only come out at night (those that mistakenly venture into the light of day perish quickly) and are essentially the clean-up crew for the desert as they are classed as detritivores, consumers of dead plants and animals. The clean, sparkling sand dunes owe that character to the tireless efforts of darkling beetles. I conducted that study more than two decades ago and to my knowledge no one has found a greater level of species diversity within a single family in such a small area, anywhere. Imagine a lake with 33 species of ducks, a meadow with 33 species of sparrows, or 33 species of spiny lizards in a region just a fraction of the area of Joshua Tree National Park.

Except for three species of diurnal ground squirrels that call this desert home (antelope, round-tailed, and California ground squirrels), all other rodents living here are nocturnal. This includes a family of rodents (Heteromyidae) which are generally restricted to the arid lands of western North America. These consist of kangaroo rats (genus Dipodomys) and pocket mice (Perognathus and Chaetodipus). A common feature of species within these genera is that they have a fur-lined pocket on each side of their mouth where than can store more than 300 seeds in each pouch. Their closest relatives are pocket gophers, (which also have fur-lined pockets), and beavers, (which do not have such pockets). They are only distantly related to true mice and rats, so it is unfortunate that their common names include “rats” and “mice." There is an endangered kangaroo rat, Stephen’s kangaroo rat, restricted to open, flat, dry landscapes between the southern California cities of Riverside and Hemet. In the effort to set aside land to protect this species people complained bitterly about spending money and effort to protect a “rat." Perhaps if it had instead been named the “Stephen’s kangaroo-beaver” there might have been less resistance.

On desert lands within the Coachella Valley there are two species of kangaroo rats, the larger “desert kangaroo rat” (restricted to loose sandy areas such as sand dunes) and the smaller Merriam’s k-rat (shorthand for kangaroo rat) found just about everywhere. On the low elevation alluvial fans and sand dunes there are also two species of pocket mice, the much smaller Palm Springs’ pocket mouse found only in the western and central portions of the Coachella Valley, and the larger but still just half the size of a k-rat, desert pocket mouse. Another species, the long-tailed pocket mouse occurs in rocky slopes. Pocket mice and especially k-rats have exceptionally large auditory bullae, portions of their skulls that house their internal hearing apparatus. In k-rats these bullae comprise more than half their skull. Why so big? The better to hear approaching predators. It is almost as if the k-rats and one of their primary predators, owls, are in an evolutionary race, the owls with softened feathers that dampen the sound of their fluttering wings, and the k-rats with increasingly large auditory bullae to hear and then evade an approaching owl. The k-rat’s strategy is often to jump straight up just before the owl strikes, leaving the owl catching nothing but air.

Kangaroo rats and pocket mice live their entire lives never drinking water. Life on earth depends on water. Up to 60% of our body (and those of k-rats and pocket mice) is water. Yet these species do not drink; how can that be? Part of the answer lies in what they (do not) excrete; their urine is extremely concentrated, and their feces are dry. The other answer is in what they eat. They are seed eaters and prefer seeds with high water content. However, even when eating dry seeds, they gain water. As their digestive systems break down the carbohydrates and protein of the seeds, water is a metabolic by-product. That plus living in humid burrows during the day and only emerging with the higher humidity of night, having a nose that extracts water from exhaled air, and reducing water loss in their excretions allows them to be superbly adapted to desert life.

Those fur-lined, seed-storing pockets allows heteromyid rodents to collect enormous amounts of seeds in any foraging excursion, far more than they would need to survive for a day. This eliminates the wasted energy of multiple foraging excursions each night and reduces their risk of being eaten by predators who might clue into the extra activity of going back and forth from seed sources to their burrow throughout the night. K-rats then store their seed larder in chambers within their burrow system. Research has indicated that they then manage their larders to absorb humidity, but not too much to be spoiled by mold. The k-rats are regularly moving seeds from one chamber to another to maximize both water gain and food value. One study found that the k-rats prefer seeds with just a little mold, perhaps because the seeds have a maximum level of moisture, and perhaps there are then some added nutrients from the mold. Another study found that they prefer seeds that are on the verge of germinating, again maximizing water and food value. All this occurring deep within a burrow and the cover of night, enabling these rodents the ability to thrive in a landscape that would be inhospitable without such amazing adaptations.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.