The Amicable Ageless Tortoise

FOCUS NATURE TORTOISES: SENIOR CITIZENS OF THE DESERT

"Slow and steady wins the race," wrote Aesop, celebrating the tortoise's victory over the hare. And, if longevity counts, the plodding desert tortoise is a clear winner in the evolutionary sweepstakes as well. During its lifetime, a wild desert tortoise may see a saguaro cactus grow from a tiny seedling to a towering 100-year-old giant. Even more impressive, though, is the 3-million-year span the tortoise has been around as a terrestrial species.

There are two subspecies of desert tortoises: the Mojave, which is found north and west of the Colorado River, and the Sonoran, which lives south and east of the river as I do.

Experts guess that up to 50 tortoises may live in a single square mile of prime Sonoran Desert habitat. But count yourself lucky if you've seen one. Tortoises hibernate about five months every year and during midsummer's intense heat retreat to their burrows, tunneling several feet into a cool arroyo bank. Roaming about only in the half-light of dawn or dusk, they seldom stray farther from their home burrows than the equivalent of two city blocks. I'm lucky. The first time I spotted a desert tortoise I saw double. I was working outdoors when I heard a knocking sound, like stones being tapped together. Peering over a low block wall at the back of my carport, I spied not one but two large tortoises clambering up the wash embankment beside my house, one leading, the other following closely. As they climbed, their carapaces bumped against rocks, producing the knocking sound.

The one behind bobbed its head vigorously, a kind of mating dance, I learned later, while the leader grazed placidly on clumps of tender grasses, tearing off mouthfuls, chewing loudly. Suddenly the head bobber stopped and lumbered off across the back lot, heading west.

After watching for a bit, I tiptoed closer to the grazer. Sensing my approach, it froze in its tracks. When I reached down, I heard a hissing sound, and the tortoise retracted halfway into its shell. The hissing sound is caused by the tortoise expelling air so it can draw into its shell. The hissing got louder when I touched its horn-brown carapace.

Tortoises make a variety of squeaky noises, but except for hissing - I heard nothing. Its leathery skin was dusty, and it had long claws on both front and hind feet. I measured it: 14 inches head to tail and about 10 inches across its carapace, clearly a mature specimen. Something about the way it slowly closed an eyelid over its yellow-green iris suggested the forbearance of great age.

There are some interesting bits of information about these antediluvian animals: adult tortoises breed between the ages of eight and 13, the females usually laying two clutches of six or seven eggs a year. Dietary staples include grasses, forbs, flowers, and ripe cactus fruits.

Not yet listed as endangered, the Sonoran Desert tortoises are in trouble nonetheless, and it is illegal to remove them from the wild. Gila monsters, coyotes, kit foxes, ringtails, and ravens prey on hatchlings, but destruction of their habitat by off-road vehicles and urban development is a primary cause of their decline. Perhaps more serious is sickness in wild tortoises. Upper respiratory tract disease has decnimated some populations in California's Mojave Desert. Elsewhere biologists have found osteoporosis porous, brittle bones, and thin carapaces in the bodies of dead tortoises, a malady that could result from a number of things, including inactivity, malnutrition, and old age.

I've had many close tortoise encounters in the prime habitat near my Tucson home. One even approached boldly while I was watering plants with a garden hose, its apparent thirst overcoming natural wariness. But since that first sighting, I've never seen more than one at a time. I keep an eye out, though, hoping to see another pair climbing "slow and steady" up the wash bank.