The Desert Tortoise: A True Survivor

The desert tortoise is at home in the most dry and extreme areas of the desert.  Its unique body and survival ability make it able to move with ease in some of the most desolate areas, and to live as long as 80 years—some have lived to be more than 100 years old.

Their stumpy legs, which remind us of elephant legs, are round and designed for walking on land.  Their front legs are designed for digging, and earned them the genus name of Gopherus, or “gopher tortoises.”  The name is very appropriate because of the desert tortoise’s ability to use its powerful front legs to dig burrows, and to escape the high heat of the desert—they can survive in temperatures as high as 140 degrees F.  They also spend about 95% of their life in underground burrows, to escape freezing temperatures and extreme heat.  During the colder months, from November through February, tortoises are dormant.

In Spring, the tortoise comes out of hibernation. There are many plants in the desert that the tortoise can eat: cactus, annual forbs, grasses, and wildflowers.  A special treat is the fruit of the prickly pear cactus.  In fact, we came across one desert tortoise that we thought had been hit by a car—he was covered with “blood” that on closer inspection turned out to be the bright red juice from a feast of prickly pears.

From March to June, the tortoises forage to build up fat stores and water for the rest of the year.  In June, they go underground to escape the heat; in the fall when outside temperatures are cooler, they will emerge and eat dried grass and drink after a thunderstorm.  When no water is available, they are able to absorb water from their bladders, and may go as long as a year without drinking water, using only the water they have stored.  If they are frightened, for example, when a human comes too close, they may release their bladder and lose this vital water supply.  This is one reason that naturalists advise that we keep our distance from tortoises in the wild.

The tortoise is also an individual when it comes to his home, or burrow. A tortoise may make a small burrow just his own length, and snug, while other tortoises make burrows several feet long. Some tortoises have a dozen or more burrows over their home range, which can be up to 1.5 square miles. Adult males may travel even further to find food or water. 

Breeding can occur at any time the tortoises are above ground, but usually this happens in late summer or early fall, when the males have a testosterone peak. After breeding, the females store the sperm and lay eggs in May, June, and July. The number of eggs varies and usually depends upon the size of the female. A mature female might lay 4 to 8 white, hard-shelled eggs in a clutch, and produce 2 or 3 clutches in a season. Only a few of these eggs will result in adult tortoises—usually only a few eggs out of a hundred make it to adulthood. 

The females dig their nests near the opening of the burrow early in the season and further inside later in the season. After laying the eggs, the female leaves the nest and the warm temperature of the soil acts as the incubator—typically the eggs incubate from 3 months to 4 months.  Interesting experiments have shown that at cooler temperatures, such as 79 to 87° F, the hatchlings will all be males; at warmer temperatures, such as 88 to 91° F, all hatchlings will be females. As for size, a mature tortoise is usually 7 to 8 inches across; desert tortoises don’t reach sexual maturity for 15 to 20 years.

Though you might live a long time without hearing a sound from a tortoise, they aren’t silent.  Instead, they make a range of sounds, including hisses, pops, and “poinks,” and the mating song of a male tortoise is a grunting sound.

Predators: on the increase

Several mammals, reptiles and birds prey upon the tortoise’s eggs and young tortoises, which have soft shells. Gila monsters, badgers, kit foxes, roadrunners and coyotes are all predators of the desert tortoise. 

But, surprisingly, the most dangerous predator for tortoises is not the coyote  or fox, as you might expect, but the common raven (Corvus corvax). It’s believed that ravens are responsible for at least half of the deaths of young tortoises.  The increasing number of ravens can be traced directly to greater development, which has brought more sources of food to the desert in the form of roadkill, landfills, trash, garbage dumps, and agricultural development.  Civilization has even provided the raven with new perches and nests through fence posts, utility poles, signs, buildings, bridges, and freeway ramps.

Desert tortoise populations have been declining due to loss of their habitat through livestock grazing, off-road vehicles, and general development. Grazing by cattle or sheep can damage the topsoil, and livestock can trample the tortoises and their eggs. Sheep can bed down and destroy shrubs the tortoises use to shield themselves from the sun or to lay eggs under.  Estimates of the decline of individual desert tortoise populations have ranged from 3% to as high as 59%.  People also collect the tortoises as pets, for food, and to sell commercially.  Tortoises are also often struck and killed by cars near highways and roads.

But the good news is..
The good news is that the desert tortoise is protected by several Federal laws: it is against the law to touch, harm, harass, or collect a wild desert tortoise. And, a number of groups have formed to help protect the wild desert tortoise.  Their main purpose is to educate the public about these wonderful desert survivors, and how to help the desert tortoise stay around for at least another million years.

Other groups encourage the public to adopt tortoises that have wandered into populated areas or that have been injured by cars.  Also, since desert tortoises can live to be 100, they sometimes outlive their original owners!  Such an organization is the Arizona Sonora Desert Museum, just west of Tucson, Arizona. To find out what taking care of these easygoing animals entails, contact the Arizona-Sonora Desert Museum (an approved adoption agency: www.desertmuseum.org  or  call 520/883-3062). Local fish and wildlife bureaus can also provide information about adopting and caring for desert tortoises.