Information about Desert Tortoises
Prepared by Kristin H. Berry for the Desert Tortoise Preserve Committee and used with permission
1. What is the difference between a turtle and a tortoise?
In the United States the following distinction is made between the terms "turtle" and "tortoise":
• A "tortoise" is a land dwelling turtle with high-domed shell and columnar, elephant-shaped hind legs. Tortoises go to water only to drink or bathe.
2. How many different kinds of tortoises occur in North America?
3. What is the habitat of the desert tortoise in the southwestern U.S.?
Tortoises occupy a wide variety of habitats in the United States. Two generalizations can be made. Tortoises living north and west of the Colorado River-Grand Canyon complex (California, southern Nevada, southwestern Utah, and extreme northern Arizona) generally occur in valleys, flat areas, fans, bajadas and washes. These tortoises live in the Mojave and Colorado deserts and are generally found below 4,000 feet in tree yucca (Joshua tree and Mojave yucca) communities, creosote bush and saltbush scrub habitats, and in some ocotillo-creosote habitats. They occupy a wide variety of soil types, ranging from sand dunes to rocky hillsides, and from caliche caves in washes to sandy soils and desert pavements. Tortoises must have suitable soils and terrain for constructing a burrow and must have adequate annual and perennial plants in the spring and/or summer for forage. Tortoises are usually absent from or rare in the low, very hot, and dry areas, such as the Death Valley sink.
4. When can one see tortoises in the deserts? When are they active?
In general, tortoises hibernate from October through February and are underground in burrows during that time. On warm, sunny days an occasional animal may be found near the mouth of its burrow in late fall or winter.
In the Mojave and Colorado deserts, the prime activity period is late winter and spring, from mid to late March through May. In early spring, tortoises are out from mid-morning to mid-afternoon, during the warm part of the day. As air temperatures rise, tortoises emerge from burrows earlier and retreat earlier. By May, tortoises may be out by 6:00 a.m. and back in burrowsby 9:00 a.m. In late spring, tortoises may also be active in late afternoon.
After May, when daytime air and soil temperatures are over 90 degrees Fahrenheit and the food supplies of herbaceous plants and grasses have dried, a large percentage of tortoises become inactive and remain underground in burrows. Some will emerge a few times a week or once every two or three weeks, especially in early morning or late afternoon. Others will not come out of burrow until summer thundershowers trigger a brief flurry of above-ground activity. With summer rains, the tortoises will emerge from burrows to drink, travel, or eat. Adults engage in courtship behaviors during summer in the early morning, late afternoon, and evening.
6. What do tortoises eat in the wild?
Tortoises are selective in choice of foods. Food preferences depend on locality and availability of the food items. In general, tortoises feed on herbaceous perennial (perennial plants live for more than one year) and annual wildflowers, such as wishbone bushes, lotus, loco weeds, spurges, blazing stars, lupines, Indian wheat, forget-me-nots, desert dandelions, gilias, phacelias, coreopsis, and many other species. They also eat annual and perennial grasses and fresh pads and buds of some species of cactus. They do not eat shrubs such as creosote bush and burro bush.
7. Do tortoises drink water in the wild?
Yes. Tortoises drink free water where it collects in pools near rocks or in depressions. Tortoises will dig depressions to collect the water, and such depressions can often be seen on areas of desert pavement.
8. When do females lay eggs and where?
In the wild, females usually lay one or more clutches of 1 to 12 eggs between mid-April and mid-July. The size of the clutch depends on the size of the female, with small females producing smaller clutches than the larger females. Clutch size and numbers of clutches produced also can depend on the food supply-how much food the tortoise has been able to obtain during the year or two prior to the time the clutch is deposited. Females dig the nests with the hind legs and drop the eggs into the nest, placing them with their hind legs and covering them carefully. The location of an undisturbed nest cannot easily be detected by humans.
9. How much time is required for eggs to hatch?
10. How large is the largest known desert tortoise? How are tortoises measured?
The largest known captive desert tortoise in California was a male about 15 inches in length. Known as "Max", the tortoise became the property of the California Department of Fish and Wildlife in the 1970's. Max finally died and has been freeze-dried for exhibits. An even larger captive tortoise is a 17.3-inch male, who lives with his proud owners in Las Vegas.
Two wild desert tortoises vie for record sizes: a 14.5-inch male on the Desert Tortoise Research Natural Area, and a 15-inch female in Lucerne Valley.
11. What are tortoise burrows like?
Tortoise burrows vary considerably in length and type. The style of burrow appears to be dependent upon the region, geologic formations, soil type, and vegetation in which it is found. For example, burrows in the eastern Mojave Desert of Utah are of two basic types on the Beaver Dam Slope: deep winter dens in natural caves in washes, some of which are 30 feet in length; and shallower summer burrows three to six feet in length in the flat areas. In the western Mojave Desert, tortoises have a variety of burrows. They use burrows about 2.5 to 10 feet in length for summer estivation and winter hibernation. They may also use shallower burrows or pallets that just barely cover the shell in spring, summer, and fall. These temporary burrows or pallets can be fragile and may be used for shelter for a few days while a tortoise is foraging in a particular area. A temporary burrow usually lasts from a few weeks to a season and disintegrates.
In the Sonoran Desert, tortoises frequently use rocks and boulders as sites for burrows or shelter. They may excavate a space beneath a boulder or squeeze into rock crevices.
12. Why are tortoise burrows important?
The tortoise burrow provides protection from the extremes of heat, cold, lack of moisture, and too much moisture. The burrow is especially important because it provides a cool place for the tortoise during the dry hot days in late spring and summer when water and food are unavailable anda relatively "warm" site for winter hibernation. The tortoise spends most of its life in the burrow.
13. Do tortoises migrate?
Migration refers to movement to a particular place for a particular purpose, such as feeding or breeding, and then return to the former site. Migration is not an appropriate term to use for tortoise movements. Each tortoise has a home range or activity area. A home range is the area in which a tortoise travels, feeds, sleeps, courts, and has its burrows. This is the area with which the tortoise is familiar. In general, large tortoises have large home ranges and small tortoises have small home ranges. Females are more sedentary than males, so they probably have smaller home ranges. Large males are known to occupy home ranges over 0.75 square mile.
Tortoises appear to have a good sense of compass direction. They are also very familiar with local landmarks. They can travel to find their burrows in a straight line. They also know locations of other tortoises (e.g., males know the location of females), drinking depressions, mineral licks (sites with deposits of calcium, sodium, magnesium and other salts), and particular food sources.
Some people, upon seeing tortoises cross roads in spring, think that tortoises are "migrating". Actually the tortoises are merely living in close proximity to the highways and roads and will travel across them during the course of moving about the home range.
14. When do tortoises court and mate?
15. How does one distinguish a male from a female tortoise?
16. What predators eat tortoises?
The type of predator varies depending on the age and size of the tortoise. There are egg predators such as the gila monster, kit fox, coyote, and badger. Predators of juveniles include ravens, roadrunners, some snakes, kit foxes, bobcats, badgers, coyotes, and probably the spotted skunk.
The larger the tortoise the more likely it will be able to resist predation. Large tortoises may be eaten by kit foxes, badgers, bobcats, coyotes, and golden eagles. The large mammalian predators are not likely to eat adult tortoises unless other food sources, such as rabbits and rodents, are in short supply. Coyotes and kit foxes may dig tortoises out of their burrows to eat. These predators can eat the tortoise without breaking open the shell.