Desert Tortoise

## Distribution

The desert tortoise (Gopherus agassizii), is a species of tortoise in the family Testudinidae. The species is native to the Mojave and Sonoran Deserts of the southwestern United States and northwestern Mexico, and to the Sinaloan thornscrub of northwestern Mexico. G. agassizii is distributed in western Arizona, southeastern California, southern Nevada, and southwestern Utah. The specific name agassizii is in honor of Swiss-American zoologist Jean Louis Rodolphe Agassiz.

The desert tortoise lives about 50 to 80 years; it grows slowly and generally has a low reproductive rate. It spends most of its time in burrows, rock shelters, and pallets to regulate body temperature and reduce water loss. It is most active after seasonal rains and is inactive during most of the year. This inactivity helps reduce water loss during hot periods, whereas winter brumation facilitates survival during freezing temperatures and low food availability. Desert tortoises can tolerate water, salt, and energy imbalances on a daily basis, which increases their lifespans.

## Appearance

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.

## Behavior

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.

## Diet

Desert tortoises are herbivorous (folivorous, frugivorous) animals. Grasses form the bulk of their diet, but they also eat herbs, annual wildflowers, and new growth of cacti, as well as their fruit and flowers.

## Reproduction

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).

## Population

### Population threats

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.

### Population number

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.

### Ecological niche

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.

## Domesticaton

Edwards et al. reported that 35% of desert tortoises in the Phoenix area are hybrids between either Gopherus agassizii and G. morafkai, or G. morafkai and the Texas tortoise, G. berlandieri. The intentional or accidental release of these tortoises could have dire consequences for wild tortoises.

Before obtaining a desert tortoise as a pet, it is best to check the laws and regulations of the local area and/or state. Desert tortoises may not be captured from the wild. They may, however, be given as a gift from one private owner to another. Desert tortoises need to be kept outdoors in a large area of dry soil and with access to vegetation and water. An underground den and a balanced diet are crucial to the health of captive tortoises.

## Fun Facts

The Desert tortoise is the state reptile of California and Nevada.

Adult tortoises can survive a year or more without access to water. During the summer and dry seasons, they rely on the water contained within cactus fruits and mesquite grass. To maintain sufficient water, they reabsorb water in their bladders and move to humid underground burrows in the morning to prevent water loss by evaporation.

Emptying the bladder is one of the defense mechanisms of Desert tortoises. This can leave the tortoise in a very vulnerable condition in dry areas, and it should not be alarmed, handled, or picked up in the wild unless in imminent danger. If it must be handled, and its bladder is emptied, then water should be provided to restore the fluid in its body.

Desert tortoises can survive body temperatures from below freezing to over 104 °F (40 °C).

Desert tortoises are most active after seasonal rains and are inactive during most of the year. This inactivity helps reduce water loss during hot periods, whereas winter hibernation helps survival during freezing temperatures and low food availability.

Desert tortoises show very strong site fidelity and have well-established home ranges where they know where their food, water, and mineral resources are.