The Desert tortoises are two species of tortoise native to the Mojave and Sonoran Deserts of the southwestern United States and northern parts of Mexico. They are Agassiz's desert tortoise and Morafka's desert tortoise. These are slow-growing and long-lived tortoises that have changed little during the past 200 million years. Males are slightly larger than females and have a longer gular horn; a male's plastron (lower shell) is concave compared to a female tortoise. Males have larger tails than females do. The shells of Desert tortoises are high-domed, and greenish-tan to dark brown in color. The front limbs have sharp, claw-like scales and are flattened for digging. Back legs are skinnier and very long. Desert tortoises can tolerate water, salt, and energy imbalances on a daily basis, which increases their lifespans.
Desert tortoises are native to the Mojave and Sonoran Deserts of the southwestern United States and northwestern Mexico and the Sinaloan thorn scrub of northwestern Mexico. They are distributed in western Arizona, southeastern California, southern Nevada, and southwestern Utah. Desert tortoises live in a different type of habitat, from sandy flats to rocky foothills. They prefer the Mojave Desert for alluvial fans, washes, and canyons where more suitable soils for den construction might be found. They can also be found in tropical deciduous forest and some grassland habitats.
Desert tortoises spend most of their lives in burrows, rock shelters, and pallets to regulate body temperature and reduce water loss. Burrows are tunnels dug into soil by Desert tortoises or other animals. Males tend to occupy deeper burrows than females. The number of burrows used by tortoises varies from about 5 to 25 per year. They share burrows with various mammals, reptiles, birds, and invertebrates. One burrow can host up to 23 Desert tortoises, usually of opposite sexes. The activity of these turtles depends on location, peaking in late spring for the Mojave Desert and in late summer to fall in the Sonoran Desert; some populations exhibit two activity peaks during one year. Desert tortoises hibernate during winters, roughly from November to February-April. Females begin hibernating later and emerge earlier than males; juveniles emerge from hibernation earlier than adults. Desert tortoises are often active late in the morning during spring and fall, early in the morning and late in the evening during the summer, and occasionally becoming active during relatively warm winter afternoons. Although Desert tortoises spend the majority of their time in the shelter, they may move up to 660 feet (200 m) per day. This time is spent foraging, traveling between burrows, and possibly mate-seeking or other social behaviors. Desert tortoises are generally solitary creatures. They may share a burrow to hibernate but rarely will congregate with other tortoises within the same area. They communicate with the help of head-bobs, grunts, hisses, pops and poink sounds.
Desert tortoises are polygynandrous (promiscuous); males and females both have multiple mates. They mate in the spring and autumn. Males grow two large white glands around the chin area, called chin glands, that signify the mating season. Months after mating, the female lays a clutch of 4-8 hard-shelled eggs, which have the size and shape of ping-pong balls, usually in June or July. The eggs hatch in August or September. Wild tortoises produce up to three clutches a year depending on the climate. Their eggs incubate from 90 to 135 days; some eggs may overwinter and hatch the following spring. The length of the incubation period depends on the temperature, the same as hatchling gender. After depositing her eggs females may guard their eggs for some time but then they leave and hatchlings will take care for themselves alone. Desert tortoises grow slowly, often taking 16 years or longer to reach about 8 in (20 cm) in length. They generally reach reproductive maturity at age 15-20 years, when they are longer than 7 in (18 cm).
The most significant threats to Desert tortoises include urbanization, disease, habitat destruction and fragmentation, illegal collection and vandalism by humans, and habitat conversion from invasive plant species. Ravens, Gila monsters, Kit foxes, badgers, roadrunners, coyotes, and Fire ants are all natural predators of Desert tortoises. They prey on eggs, juveniles, which are 2-3 inches long with a thin, delicate shell, or, in some cases, adults. Ravens are thought to cause significant levels of juvenile tortoise predation in some areas of the Mojave Desert - frequently near urbanized areas. Another potential threat to Desert tortoises' habitat is a series of proposed wind and solar farms. As a result of legislation, solar energy companies have been making plans for huge projects in the desert regions of Arizona, California, Colorado, New Mexico, Nevada, and Utah. Desert tortoise populations in some areas have declined by as much as 90% since the 1980s, and the Mojave population is listed as threatened. It is unlawful to touch, harm, harass, or collect wild Desert tortoises.
The IUCN Red List and other sources don’t provide the number of the Desert tortoise total population size. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List.
The Desert tortoise is the largest terrestrial turtle in the United States and is a very important species in the Mojave Desert ecosystem. Due to their burrowing habits, these turtles provide shelters for other animals. They also act as seed dispersers from eating various fruits, plants and grasses.