Just in case you haven’t noticed, southeast Arizona, the Sky Islands region, is in yet another drought. After spotty monsoon rains last summer, winter precipitation was at best paltry in most places, setting the stage for the even more parched ecological bottleneck of May and June.
Even after many decades of living here, I am still in awe of how native species weather the sort of exceedingly dry conditions we are now experiencing. Evolution has conjured up a slew of both physical and behavioral traits among various biota that—at least at a species level if not individually—afford them safe passage across our perilously sere months. So, while the alert is out—we urgently need rain—make no mistake, life will survive in the interim, returning with a vengeance once rain finally arrives.
Plants exhibit a wide range of structural and physiological traits evolved to survive prolonged dry periods. Perhaps the most evident adaptations are among our local succulents. Some, such as our cacti, are utterly devoid of leaves which would otherwise be conduits of potentially fatal moisture loss. Instead, they photosynthesize via their green stems, which are covered in a waxy coating, termed a cuticle, that further preserves their precious water supply. Dense spines—think teddy bear cholla—reduce evaporative loss in some succulents. Shallow roots also aid in the moisture hoarding process, as they soak up even relatively superficial soil moisture after storms.
Added to this set of highly adaptive traits is the fact that many succulents, including our cacti, photosynthesize via a CAM pathway. (CAM stands for “Crassularean Acid Metabolism,” named for the stonecrop family where it was first discovered.) CAM plants are able to gather up sunlight by day with their stomata or pores closed, yet exchange gases at night via open pores when temperatures are lower and humidity levels often higher. The end result is that CAM plants lose far less water than those utilizing the more “standard” form of photosynthesis.
Many local leguminous plants—such as palo verdes, mesquites and desert ironwoods—have highly reduced foliage that is often shed during the driest of times. Palo verdes, living up to their billing, can even thrive for long periods by photosynthesizing through their green stems. Add to all the above traits a very simple one: waiting for the rain to finally come. Many local native plants bide their time as seeds, roots, tubers, or dormant above-ground structures until moisture conditions are once again conducive to growth and, hopefully, reproduction. Our fungi are extreme in this regard, often being totally absent until they literally come out of the woodwork or ground upon the inauguration of monsoon rains.
Many animals likewise have evolved to wait for rains. Think various frogs and toads in their underground lairs, surrounded by a mostly impervious skin coating that they’ll shed upon eventual emergence. Our Sonoran Desert and Mexican spadefoot toads fit neatly into this paradigm. Think legions of various invertebrate species that ride out the dry times as eggs, larvae tucked into wood or soil, and adult insects that similarly hide in moister micro-environments out of sight. Come monsoon season a flurry of butterflies, flies, grasshoppers, beetles, bugs, etc… suddenly and collectively prowl the land, skies, and water as if magically produced from the dry dust itself.
Being at least seasonally nocturnal is another way for animal species to avoid debilitating or fatal dehydration. Collared peccaries often adjust their activities to night during our hot, dry months. So too do even highly drought-resistant rattlesnakes.
Other creatures slake their thirst whenever they can; some, like mourning doves, will travel many miles to do so. A diet full of relatively succulent plant material and/or animal matter can also help to keep the bodily moisture ledger balanced. Antelope jackrabbits can thrive without water—they can get it from the plants they consume—while turkey and black vultures mainly keep hydrated via their decidedly gory fare.
Perhaps the ultimate local animal adaptation to drought occurs in our kangaroo rats. Yes, they live underground. True, they are strictly crepuscular and nocturnal. Their granivorous diet, comprised of wild seeds, allows them to produce metabolic water from fat digestion. This nifty trick even precludes the need to drink water. To top it all off, K-rats are able to reabsorb a disproportionately large percentage of water from their kidneys. These mostly bipedal rodents possess the proportionately longest “loop of Henle”—a conduit found in kidneys that reabsorbs water otherwise targeted to be dispelled from the body—of any animal on the planet. Gila monsters can also “steal back” a fair amount of moisture from their renal system, including from its last stop: their urinary bladder.
As for us mostly naked apes, I can only urge you to follow my advice as a wilderness survival instructor: keep hydrated, cover as much of your skin from direct sun as possible, reduce your pace, wear a wet bandana on the back of your neck to avoid overheating, and, perhaps most important of all, plea with the rain gods to be kind this coming summer. If they are not, look for me underground or at night, as I send out my own May Day distress signals.
Vincent Pinto and his wife Claudia run RAVENS-WAY WILD JOURNEYS, a Nature Adventure & Conservation organization devoted to protecting and promoting the unique biodiversity of the Sky Islands region. RWWJ offers a wide variety of private, custom-made courses, birding & biodiversity tours. Visit ravensnatureschool.org