- Desert Tortoise
Taxobox
name = Desert Tortoise
status = VU
status_system = iucn2.3
image_caption = Desert Tortoise, "G. agassizii"
regnum =Animal ia
phylum =Chordata
classis = Sauropsida
ordo =Testudines
subordo =Cryptodira
superfamilia =Testudinoidea
familia =Testudinidae
genus = "Gopherus "
species = "G. agassizii"
binomial = "Gopherus agassizii"
binomial_authority = Cooper,1863 The desert tortoise ("Gopherus agassizii") is a
species oftortoise native to theMojave desert andSonoran desert of the southwesternUnited States and northernMexico . The epithet "agassizii" is in honor of Swiss-American zoologist Jean Louis Rodolphe Agassiz.Description
This tortoise may attain a length of 10 to 14 (25 to 36 cm)cite book |last=Kindersley |first= Dorling |year=2001,2005 |title=Animal |location=New York City |publisher=DK Publishing |isbn=0-7894-7764-5] , with males being slightly larger than females. Male tortoises have a longer gular horn than females, their plastron (lower shell) is concave compared to female tortoises. Their shells are high-domed, and greenish-tan to dark brown in color. Desert tortoises can grow from 4–6" in height and weigh 8–15 lb (4–7 kg) when fully grown. The front limbs have heavy, claw-like scales and are flattened for digging. Back legs are more stumpy and elephantine.
Habitat
The tortoise is able to live where ground temperature may exceed 140 degrees Fahrenheit (60 degrees Celsius) because of its ability to dig underground burrows and escape the heat. At least 95% of its life is spent in burrows. There, it is also protected from freezing winter weather while dormant, from November through February or March. With its burrow, this tortoise creates a subterranean environment that can be beneficial to other
reptile s,mammal s,bird s andinvertebrate s.Scientists have divided the desert tortoise into two types: the Mojave and Sonoran Desert tortoises, with a possible third type in the Black Mountains of northwestern
Arizona . They live in a different type of habitat, from sandy flats to rocky foothills. They have a strong proclivity in the Mojave desert foralluvial fans , washes andcanyon s where more suitablesoil s for den construction might be found. They range from near sea level to around 3,500 feet in elevation. It is believed that, in their entire lives, these tortoises rarely move more than two miles from their natal nest. They also live to be 80-100 years old.Diet
The desert tortoise is a
herbivore . Grasses form the bulk of its diet, but it also eatsherb s, annualwildflower s,and hibiscus someshrub s, and new growth ofcacti , as well as theirfruit andflower s. Rocks andsoil are also ingested, perhaps as a means of maintaining intestinal digestivebacteria and/or as a source of supplementarycalcium or other minerals. As withbird s, stones may also function asgastrolith s, enabling more efficient digestion of plant material in thestomach .Much of the tortoise’s water intake comes from moisture in the grasses and wildflowers they consume in the spring. A large
urinary bladder can store over forty percent of the tortoise's body weight in water,urea ,uric acid andnitrogen ous wastes. During very dry times they may give off waste as a white paste rather than a wateryurine . During periods of adequate rainfall, they drink copiously from any pools they find, and eliminate solid urates. Adult tortoises can survive a year or more without access to water.One defense mechanism the tortoise has when it is handled or molested is to empty its bladder. This can leave the tortoise in a very vulnerable condition in dry areas, and they should never be alarmed, handled or picked up in the wild.
Tortoises may also be vulnerable to diseases and viruses. Coming into contact may cause them to catch unfamiliar strains.
Reproduction
The mating season for the desert tortoise is lengthy. It occurs from spring to fall, with a peak in late summer/early fall (September). They typically lay 4-8 eggs per clutch, with 1-2 clutches per year. The eggs are hard, chalky and elliptical or spherical and buried in a funnel-shaped nest. They are incubated for 90-120 days. Hatchlings from only a few eggs out of every hundred actually survive the 7-15 years it takes to reach full adulthood.
Predators and conservation status
Raven s,gila monster s, kit foxes,badger s, roadrunners,coyote s, andfire ants are all natural predators of the desert tortoise. They prey on eggs, juveniles, which are 2-3 inches long with a thin, delicate shell, or in some cases adults. Ravens are hypothesized to cause significant levels of juvenile tortoise predation in some areas of the Mojave Desert - frequently near urbanized areas. The most significant threats to tortoises includeurbanization , habitat destruction and fragmentation, illegal collection andvandalism by humans, and competition with cattle for forage plants. The eggs they lay can get so shiny that they can look like they've been hard boiled.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. It is, however, possible to adopt captive tortoises through the Tortoise Adoption Program (TAP) in
Arizona , or through the Bureau of Land Management inNevada . When adopted in Nevada, they will have a computer chip embedded on their back for reference. Under Arizona law, one tortoise per family member may be possessed if the tortoises are obtained from a captive source which is properly documented. Captive sources include urban foundlings, unwanted captives, and their progeny.References
* Listed as Vulnerable (VU A1acde+2cde, E v2.3)
*ITIS|ID=173856|taxon=Gopherus agassizii|year=2006|date=6 February
* [http://www.desertusa.com/june96/du_tort.html The Desert Tortoise]
* [http://bss.sfsu.edu/geog/bholzman/courses/Fall00Projects/tortoise.htm The Biogeography of The Desert Tortoise, by Kerrie Bathel]
* [http://www.desertmuseum.org/programs/tap_tortnathistory.html The Arizona-Sonora Desert Museum]
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