Mosey On with the Mojave Desert Tortoise
Also known as the California desert tortoise, or more simply the desert tortoise, Gopherus agassizii is one of the few tortoise species native to North America. As its name implies, it is found only in the Mojave and Sonoroan deserts, from northern Mexico into the southwestern United States; there it is the state reptile of California and Nevada. Their habitat consists mainly of of desert scrub, where temperatures can reach over 60 °C (140 °F); however, in the southern reaches of its range, the desert tortoise can also be found in tropical deciduous forests.
To beat the heat, G. agassizii digs burrows where they can rest when its too hot or too cold to forage, and where they can aestivate during the hottest months of the summer and hibernate in the winter. These burrows can be quite extensive, reaching 10 m (32 ft) long, and up to 25 tortoises may share the same burrow. Individuals will often dig out several burrows in their territory, which can range anywhere from 3 to 25 hectares (7 to 61 acres). Many of these burrows will also become homes for other animals, including rattlesnakes, gila monsters, squirrels, burrowing owls, and quail.
Like all tortoises, the Mojave desert tortoise is herbivorous. Most of its food is grass, but due to the limited choice in the desert they may also consume wildflowers, shrubs, and cacti-- both fruits and new growth. Due to their hard shells, this species has few predators as adults, but hatchlings are vulnerable to foxes, coyotes, birds of prey, and gila monsters.
Very little rain falls in the desert, and so the desert tortoise is well adapted to do without; the species stores up to 40% of its body weight in water in its bladder, to be absorbed later. Individuals will also dig shallow 'watering holes' in the ground, to be visited after rainfall. G. agassizii also gets much of its water content from its diet, and can go up to a year without drinking.
Desert tortoises typically mate in the spring, from March to May, though mating can continue until autumn. Males seek out and fight each other for access to females, typically by ramming each other or attempting to flip each other over. However, this species is also one of the few known to engage in homosexual activity, particularly between males. Because this is not a species that mates for life, or maintains strict social hierarchies, the purposes of this intercourse is unknown.
Females can store sperm for up to eighteen months, and typically lay their eggs in the following year from May to July in clutches of 3 to 8. These eggs are laid in a deep nest dug into the ground, and take 90 to 135 days to hatch. Young emerge in the fall, and receive no parental care. If they survive, individuals may take between 10 to 16 years to become fully mature, and can live to be 80 years old.
Desert tortoises are well adapted to blend into their environments. The shell is typically a brown or dull yellow, while the body is tan or dusty grey. There is little difference between males and females, save that males are slightly bigger and have a concave plastron (lower shell) to accommodate mounting onto a female. The species is medium sized, ranging between 11 to 23 kg (24.23 to 50.66 lb) in weight and 25 to 36 cm (10 to 14 in) in length.
Conservation status: The IUCN has ranked the Mojave desert tortoise as Critically Endangered. Their primary threats include habitat fragmentation and loss, predation by feral dogs, and road mortality. The population is estimated to have declined by 90% since the 1980s. However, conservation programs are being implemented to preserve critical habitat, and several zoos and conservancies have captive breeding programs for the species.
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