Eleventh in a Series: Ambush near Drews Station

FOCUS on Nature The Harris' Ground Squirrel and Other Survivors

Text and Photographs by Willis Peterson The desert wash with its finely graded sand spreads a sparkling granular symmetry before me. It is morning, and there is a hush, an expectancy in the dry stream bed. Between granite boulders, paloverde, mesquite, and ironwood trees flank the riffled sand. Overhead, a phainopepla flicks lightly from its perch. Black crest and white and ebony wings glisten in the early sunlight. Pungent odors of catclaw, creosote bush, and mesquite—all unique to the Southwest deserts—well up about me. Since sunup, bees have been collecting nectar in near-frenzy, hoping to complete their chore ahead of the noonday heat. Shining through the filigree of branches, the ascending sun casts its warming rays, outlining in highlight and shadow a mute but telling record etched upon the sands of the wash. Everywhere there are tracks, trails, gouges—vivid vignettes describing excursions, scuffles, clandestine meetings, life-and-death struggles. For the visually acute, the wash becomes an endless tabloid reporting the desert society's procession of events. Suddenly a melodious, lilting warble shatters the silence. Then it comes again. I peer around a leafy canopy of mesquite and there, perched upon a throne of granite alongside the dry waterway, sits the diminutive whistler. His tail curls jauntily over his back. Sunlight accents the white body stripes and gleaming coat. He flips his tail in a rhythmic motion, punctuating the pristine morning. It is a territorial ritual. The whistle announces that he has picked out a personal boulder. From here this cocky little creature surveys his tenuous domain. And tenuous it is. Only careful surveillance will keep him from falling prey to hawk, owl, bobcat, or some other predator. I purse my lips and, by drawing in my Highly skilled in desert survival techniques, the Harris' antelope ground squirrel manages to escape much of summer's heat by the design and construction of its burrow. When temperatures exceed 110° F., the squirrel simply stays indoors and passes the time dozing.

breath, make a series of sharp little squeaks. He reacts instantly. Caught between fear and curiosity, he droops his tail like a semaphore while he seeks out danger in the brush. Suddenly he arches it up again in a series of quick jerks. He waves the banner back and forth, holds up a forefoot for a split second, then is off. Leaping to another boulder, tail aloft like a guidon, he scurries down and across the wash into the protective spiny embrace of a prickly pear cactus. I have met the Harris' antelope ground squirrel. (Beneath his tail he shows distinctive whitish underparts, similar in appearance to the white rump patch displayed by the pronghorn; hence the name "antelope.") One of about 30 species of ground squirrels found in North America, the Harris' squirrel thrives over a range extending from central Arizona well into Sonora, Mexico-a stern desert area where a well-calculated survival scheme is a prime requisite. The Harris' squirrel rates high in the survival-skills category. This is demonstrated in his engineering ability and the imaginative burrows he digs, usually at the base of rocks or of cacti or other spiny plants. Because underground root systems help to bind the soil, his home becomes relatively permanent. Heat buildup lags below ground. By the time the subsoil becomes warm, evening is at hand. Even a foot below the surface, searing summer heat is dissipated, but moisture is retained. By designing an extremely functional home, the squirrel is able to defeat some of the odds stacked against him. A network of tunnels serves to cool and ventilate his living quarters. The seeds he gathers are disgorged into special floodproof pantries lined with chewed plant material. Cooling dens and rearing nests are also part of the elaborate quarters. The latter are usually padded with grasses, milkweed filaments, thistledown, and cotton-like heads of desert broom. Here three to five young are born in April or May. In three to four weeks the newcomers emerge from the burrow to scamper about near the entrance. The family will stay together, more or less, throughout the rearing season. To keep the nursery area comfortable, the Harris' squirrel raises the burrow's humidity by plugging certain chambers and tunnels, thus minimizing body-fluid loss by evaporation. When the little creature is sleeping, the nose passages trap moisture so it can be returned and absorbed by the body. Under some circumstances, moisture recirculated in this fashion can mean the difference between life and death for the squirrel.

FOCUS on Nature

To offset the sun's wrath when gather-ing food, the Harris' squirrel may lower body temperature a few degrees by licking his forepaws and rubbing his face and head with the damp fur. But this is usually a maneuver of last resort, since it could result in a nonretrievable moisture loss. A more common practice is to flatten the body against the ground in a densely shaded area, allowing body heat to transfer to the soil.

Even the handsome pelage is a plus in the survival ledger. The tiny animal's gleaming, finely textured fur reflects rather than absorbs heat. And his thick skin resists heat penetration.

Aside from drinking what water may remain from scanty showers, he obtains moisture by eating greens, leaflets of mesquite, paloverde, and ironwood, cactus fruits, and hackberries in season. In the spring, new grass and a host of lush annuals offer a succulent addition to his standard fare of dried seeds. Insects and small lizards augment the diet.

The desert ground squirrels have adapted well to a dry climate. For example, the round-tailed ground squirrel and the Mohave ground squirrel solve the heat problem simply by staying in their bur-rows. Each species has its own heat tolerance level.

When summer temperatures rise above 110°F., many ground squirrels resort to one of the stranger adaptations to desert life, a process called estivation. Remaining underground, they escape the scorching days in a torpid sleep.

During these periods of relative inactivity, the animal's metabolism slows down, and the body temperature drops to a few degrees above that of the ambient air in the den. An extra store of body fat, gained earlier, provides nourishment through this cycle.

In winter, many ground squirrels hiber-nate. Then their torpor is triggered by cold and dwindling food supplies, rather than by heat or drought. In either state, the animal may rouse occasionally to eat.

Do Harris' ground squirrels estivate and hibernate? Scientists say they do not. But they do spend the hottest hours dozing in their burrows; I have photographed them (see pages 18 and 19). At our home at the base of Black Mountain north of Phoenix, we might not see the cheerful creatures above ground for several days during intolerable hot spells. When temperatures dropped a bit, they were at our back door again, looking for handouts.

At higher elevations of the Harris' squirrel's range, I personally have observed behavior that resembles hibernation. At our ranch overlooking Thomp-son Valley, southwest of Prescott, I have rarely seen the squirrels outdoors in December. Then, about the first of March, I would hear their cheerful whistles coming again from the woodpile, rock walls, and other lookouts.

Another desert animal with a remarkable method of coping with the heat is the jackrabbit or desert hare. The ears of the jack act as a specialized heat pump. The thin-skinned membranes cool his body by pumping blood through a lace-work of veins that radiate heat back into the atmosphere.

There are times, though, when daytime temperatures rise above the hare's heat tolerance. Then he must seek shade. To reduce further his body temperature, he will scratch away hot surface soil and Other desert denizens include (ABOVE, FROM LEFT) round-tailed ground squirrels, the jackrabbit, and the kangaroo rat. All have special survival characteristics. The squirrels exploit cool underground quarters. The rabbit throws off excess beat by means of its oversized ears. But the most remarkable is the rat, who requires no drinking water at all.

Hunker down in the cool depression.

But of all the desert creatures, the tiny kangaroo rat certainly numbers among the most perfectly adapted to an arid environment. He no longer requires drinking water, thanks to a physiological process that enables him to subsist on tiny amounts of water produced during the metabolic process. The kangaroo rat combines this astonishing characteristic with super-efficient kidneys and an extremely low level of moisture loss. He also conserves water by plugging burrow entrances during daytime and venturing out only at night.

The animals discussed here aren't the only desert dwellers adept at survival, of course. Other warm-blooded creatures as well as reptiles, insects, and even plants have developed an equally fascinating array of adaptation techniques to allay summer's heat and conserve precious moisture-techniques which for count-less years have meant a continuous regeneration of this very special natural world of our desert Southwest.

Willis Peterson recently retired from a long career as a photography instructor at Glendale Community College.