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Mojave River Valley Museum
Mojave Desert Wildlife -
Desert TortoiseGopherus agassizii
Like other reptiles, the desert tortoise is cold-blooded. To survive in the desert, the tortoise estivates (remains underground in its burrow) during the hottest times of the day in the summer and hibernates (sleeps underground in its burrow) through the winter. Tortoises come out in the spring to eat grasses and wildflowers and drink water from the spring rains (although they obtain most of their water from the plants they eat). They store water within themselves and use it through the dry months while water is not available. In the spring, they socialize and look for mates. At other times of the year they are less active above ground.
A Primitive RelicIn America, the term "tortoise" refers to all turtle species that live primarily on land. According to fossil records, the desert tortoise, Gopherus agassizii, is one of four species that have remained virtually unchanged since the Oligocene Epoch (27-37 million years ago).
Geographic RangeThe desert tortoise occurs today in the Mojave and Sonoran deserts of southwest Utah, southern Nevada, southeastern California, and western Arizona.
Their habitat occurs below 5,000 feet in elevation. Their habitat can range from sandy creosote bush scrub to bajadas, as well as alluvial fans, washes and canyons.
LongevityTortoises are homebodies, spending up to 98% of their time in burrows, hibernating in the winter and estivating (remaining inactive) in the summer.
Even when they emerge they never travel far from home, usually ranging less than one square mile in their lifetime. Sexual maturity is reached in 15-20 years and their lifespan can often exceed 80 years.
Tortoise BurrowsBurrows are cresent shaped tunnels. The tortoises dome-shaped shell works as a plug to keep temperature and moisture loss to a minimum.
A tortoise may excavate and use many burrows during the year. Most are located at the base of desert shrubs or in wash banks. Many species of mammals, birds, reptiles, and invertabrates have been known to share tortoise burrows.
The ClutchFrom March to late October, tortoises emerge from their burrows to bask in the sun, drink, feed and mate. After mating the female deposits her eggs in a hole she has dug with her hind legs. Clutches range from 1-15 eggs, which she arranges and covers with soil.
HatchlingsBaby tortoises hatch from their eggs in 80-130 days and are about one inch in diameter. The embryos developed into males or females depending on the incubation temperature of the nest. At approximately 79-87F males are produced and about 87-91F females are produced.
Juvenile PredationHatchlings resemble adults and are immediately independent. The number one cause of newborn mortality is vulnerability to predators due to soft shells, which remain pliable for the first five years of life. Hatchlings are preyed upon by coyotes, ravens, kit foxes, badgers, roadrunners, and hawks.
The number of predators decreases as the shell hardens. Hatchlings from only a few eggs out of every hundred actually survive the 7-8 years it takes to reach adulthood.
Tortoises and WaterTortoises are able to derive almost all of their water from consuming plants. In addition, they seek rainwater that collects in natural depressions or in ones tortoises dig themselves. Adult tortoises can survive a year or more without access to water.
These precious opportunities must last for months. The tortoises large urinary bladder allows them to store water constituting over 40% of their body weight. Tortoises can then reabsorb the water within their body as needed.
Tortoise DietThe Desert tortoise is an herbivore. Grasses form the bulk of its diet, but it also eats a wide variety of herbs, annual wildflowers, some shrubs, and new growth of cactuses, as well as their fruit and flowers.
Since droughts are common in the deserts that the tortoise inhabit, they rely on the erratic years of good rainfall and the ensuing growth of palatable foods.
Following are a few examples of food that could be included in the diet of the desert tortoise.
This species is common throughout the desert. Tortoises enjoy eating the juicy pads and the magenta-colored flowers of this species.
This slender, densely tufted grass is prevelant throughout all North American Deserts. In times of need, it is an important food source for tortoises because of its abundance.
The diet of the desert tortoise varies with the season. This tiny annual flowering plant is an important spring food source for the desert tortoise.
Also know as the "sore-eye" poppy, it was named for the belief that the hairs of the plant are irritating to the eye. Its bright orange-red blossom is a favorite food source for the desert tortoise.
This non-native weed introduced from Eurasia is widespread and abundant. Tortoises enjoy eating the entire plant.
Other AnimalsThe Mojave Desert, despite its sometimes barren and empty appearance, is actually home to over 360 species of animals. It is one of the most diverse ecosystems in North America.
Following is a partial list of other animals that may be seen in tortoise habitats.
This hummingbird is often seen in the spring taking nectar from wildflowers and occasionally eating small insects.
An attractive sparrow, with distictive white stripes on its head, can be seen in winter flocks of 5 to 20 foraging for food. They often remain in the same area for several weeks.
Desert Spiny Lizard
This distinctive lizard is appropriately named for its glittering sharp-pointed scale covering, which resembles medieval body armor.
The fastest snake in the Mojave, it moves about during the day in search of grasshoppers, lizards and small rodents. When threatened, it imitates a rattlesnake by curling into a striking position and vibrating its tail.
This lizard is aptly named for its whip-like tail which can detach to aid in its escape from danger. Several species of this lizard are all females whos eggs require no fertilization. The offspring are cloned genetic copies of their mothers.
White-tailed Antelope Squirrel
This bold small animal is often seen sitting upright flicking its expressive tail. While foraging for seeds and small insects, it makes its presence known by sounding off with a shrill bark resembling a bird's call in its clarity.
This rodent is commonly known as the "pack rat" or "trade rat" named for collecting any shiny or metallic object it fancies. Its burrow is easily recognized by the rubbish littered about the entrance.
These gentle giants are our deserts largest spiders, often having a leg span of 6 to 7 inches. Despite their fearsome reputation, they are not dangerous to humans.
Giant Desert Hairy Scorpion
The southwest's largest scorpion is a secretive, nocturnal animal that is seldom seen during the day. Its sting, though painful, is not life threatening.
North America's largest wren is often seen scratching around under ground litter searching for insects, spiders, small lizards and seeds.
This annual visitor to the Mojave spends much of its time skillfully flying about catching insects to eat and to feed its young.
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