Desert Tortoise, Gopherus agassizii
TAXONOMY & NOMENCLATURE
(Bonin et al 2006) (Bramble 1982) (Crawford et al. 2012) (Crumly 1984) (Ernst & Lovich 2009) (ITIS 2010) (Le et al 2006) (McCord 2002)
(Murphy et al 2007) (Zylstra & Steidl 2009)
Describer (Date): Cooper 1863 Proc. Calif. Acad. Sci. Vol 2, p.120.
Class: Reptilia (see Collins and Taggart 2002 for suggesting to place turtles alone in a class - Chelonia)
Order: Testudines (turtles)
Family: Testudinidae (11 or 12 living genera of terrestrial turtles)
Genus: Gopherus (4 species of North American tortoises)
Species: Gopherus polyphemus (gopher tortoise)
Species: Gopherus berlandieri (Texas or Berlandier's tortoise)
Species: Gopherus flavomarginatus (Bolson tortoise)
Species: Gopherus agassizii (desert tortoise)
Taxonomic History and Nomenclature
- Differences exist in morphology, genetics, physiology, and behavior between Sonoran and Mojave populations (Zylstra & Steidl 2009)
- Two populations may be separate species (Murphy et al 2007) or subspecies, but classified as same species at present
- Some researchers have proposed dividing the four gopher tortoises into two separate genera, with G. agassizii in Scaptochelys (Bramble 1982) or Xerobates (Bour & Dubois 1984); others now prefer to use Gopherus for all four species, based on several unique morphologies of these tortoises (Crumly 1984, Ernst & Lovich 2009)
- Synonym/s: Xerobates agassizii Cooper 1863; Xerobates lepidocephalus Ottley & Valazquez-Solis 1989.
- Common name: desert tortoise
- Scientific name: Gopherus - from French "gaufre" meaning waffle; used for small mammals making waffle or honeycomb-like multi-chambered burrows (Harper 2010);
agassizii - in honor of naturalist Jean Louis Agassiz
- Turtles are the closest relatives of birds and crocodiles (the archosaurs); they are less closely related to snakes, lizards and the tuatara (Crawford et al. 2012)
- An early, fully shelled turtle: Proganocheles, 210 million years ago (Late Triassic)
(Bonin et al 2006)
- Turtle origins assumed to be earlier
- Early in turtle evolution, both terrestrial and semi aquatic freshwater forms present (Renous et al 2008)
- Fully marine turtle evolved somewhat later, by Jurassic times.
- Testudinidae family of turtles probably originated in Asia, according to fossil record. (Le et al 2006)
- By 34-37 million years ago (Late Eocene), the Testudinidae family had spread from Asia to Europe, North America and Africa.
- Earliest tortoises probably similar to modern Asian forest tortoises, (Manouria emys). (Stanford 2010)
- Gopherus fossils: 35-33 million year-old (late Eocene to early Oligocene) (McCord 2002)
(Reynoso et al 2004)
- Wyoming, Colorado, Nebraska, South Dakota
- Two groups of Gopherus tortoises:
(Ernst & Lovich 2009)
- Flavomarginatus-polyphemus group (Bolson tortoise-gopher tortoise)
- Agassizii-berlandieri group (desert tortoise-Texas tortoise or Berlandier's tortoise)
- Around 10.5 million years ago (mid Miocene) desert tortoises may have diverged from Texas tortoises (G. berlandieri) (McCord 2002)
- Lineages of Sonoran and Mojave tortoises diverged about 5 million years ago
(Lamb & McLuckie 2002)
- Probably after being separated by an early Colorado River drainage
- Van Devender (2002) suggests, rather, that different rainfall regimes more of a factor for separation
- Populations are now geographically, genetically, and behaviorally distinct (Murphy et al 2007)
- Many Gopherus agassizii fossils discovered in California, Arizona, New Mexico and Texas (Late Pleistocene) (McCord 2002)
- Oldest are no more than 34,000 years old but older records may exist (McCord 2002)
- By 8,000 years ago, modern distributions achieved (Van Devender & Moodie 1977)
- Mojave population adapted to winter-rainfall regime, a climate pattern that began at the end of the Pleistocene. (Van Devender 2002)
- Mojave populations may have been derived from Sonoran ones, once winter rains established at end of Pleistocene.
- Sonoran (and Sinaloan) tortoises are more like their tropical ancestors, adapted to two rainfall seasons - winter-spring and summer. (Van Devender 2002)
DISTRIBUTION & HABITAT
(Anderson et al 2000) (Berry 1990) (Curtin et al 2008) (Ernst & Lovich 2009) (Lamb & McLuckie 2002)
(Osorio & Bury 1982) (U.S. Fish and Wildlife Service 1994)
(Van Devender 2002)
(Zylstra & Steidl 2009)
Distribution: (Van Devender 2002)
Habitat: (Van Devender 2002)
- Western California
- Southern Nevada
- Far southwestern and western Arizona
- Far southwestern tip of Utah
- Sonora and Sinaloa, Mexico
- Including Tiburón Island, Gulf of California (Osorio & Bury 1982)
- Possibly Chihuahua
- Populations separated into Mojave and Sonoran deserts:
(Lamb & McLuckie 2002)
- Mojave tortoises north and west of Colorado River
- Sonoran desert population: south and east of Colorado River (Arizona and Mexico)
- IUCN Red List: no distribution information for this species
- Desert scrub
- Foothills thorn scrub
- Tropical deciduous forest/coastal thorn scrub
- Sea level to 2,225 m (7,300 ft); best habitats at 305-914 m (1,000-3,000 ft)
- Three population assemblages:
- North and west of Colorado River/Grand Canyon - valleys and alluvial fans in creosote bush/yucca communities with good soil for digging and adequate forage
- South and east of Colorado River/Grand Canyon - steep, rocky slopes of mountains in palo verde-cactus communities
- In Mexico - thorn scrub and oak woodland communities.
- Habitats occupied Sonoran Desert: usually steep and east-facing (Zylstra & Steidl 2009)
- Shelter-sites most often utilized in naturally exposed caliche along washes or rock fractures. (Zylstra & Steidl 2009)
- Lower alluvial slopes of desert mountain ranges, in valleys between ranges (Riedle et al 2008)
- Habitats occupied in Mojave Desert: (Zylstra & Steidl 2009) (U.S. Fish and Wildlife Service 1994)
- Traditionally described as occupying flats and bajadas; also slopes up to juniper woodlands
- Soils may be important aspect to habitat; loamy soil (suitable for digging) preferred (Anderson et al 2000)
- Suitable plant cover, especially creosote bush communities (Larrea tridentata), along with annual and perennial grasses and cacti. (Ernst & Lovich 2009)
- Elevations 1,500 to 1,600 m (4921 to 5,249 ft); on occasion up to 2,000 m (6,562ft) (Ernst & Lovich 2009)
- Habitats in Mojave Desert have more irregular rainfall, limited resources
(Curtin et al 2008)
- Plant communities dominated by creosote bushes (Larrea tridentata) and burro bushes (Ambrosia dumosa) (Ernst & Lovich 2009)
- Habitats in Sonoran Desert's rainfall is more predictable, resources more abundant. (Curtin et al 2008)
(Auffenberg 1974) (Bonin et al 2006) (Ernst & Lovich 2009) (Stebbins 2003)
Body Weight: 3.6-6.8 kg (8-15 lb)
Carapace Length: 20.3-38.1 cm (8-15 in)
Tail Length: Short
- Largest terrestrial turtle in the United States.
- High-domed shell allows large space for lungs and efficient thermoregulation.
- Front limbs shovel-like.
- Prominent growth lines on scutes (also called scales or shields)
- Carapace (top) brown or gray without a pattern, but often may be brown or orange in the center, especially in young.
- Plastron (underside) yellowish or brownish and is not hinged.
- Like most turtles, on the shell have 5 vertebral scutes, 4 pairs of costal (rib) scutes, 22 scutes around the margins and a single nuchal scute.
- Like all turtles, good hearing, but no external ear; no teeth (have beak)
Other Physical Characteristics
- Adults sexually dimorphic with males larger than females
- Males have concave plastron (bottom shell), longer tail, and enlarged glands under chin
- Glands possibly exude protein-like substance during breeding season
- Female's plastron is flat, slightly expanded towards rear
- Limbs stocky, elephantine
- Forelimbs somewhat flattened, hindlimbs columnar
- The turtles in this family (Testudinidae) have no connecting web of skin between digits
- Large cone-shaped scales on limbs
- Light eye ring
- Iris of eye usually greenish yellow
- Head relatively narrow; ridges on upper jaw meeting at a sharp angle
- Forelimbs cover opening when drawn in
- Forelimbs have five digits; hindlimbs, four
- Claws on front limbs for digging burrows
- Females use claws for digging nest
- A spur present on the hind limb.
- Gular area (part of plastron lying beneath the extended head) slightly forked (Bonin et al 2006)
- A single scute underneath the armpits (axillary scute). (Ernst & Lovich 2009)
BEHAVIOR & ECOLOGY
(Berry 1986) (Burge 1977) (Ernst & Lovich 2009) (Luckenbach 1982)
(Woodbury & Hardy 1948) (Riedle et al 2008) (Ruby & NIblick 1994)
Use of Dens
(Woodbury & Hardy 1948)
- Rainfall and temperature control many activities (Ernst & Lovich 2009)
- Most active spring and early summer; also in fall before cold weather; after rain in summer.
- Hibernate in winter den; annual cycle of shifts from months of inactivity to utilizing summer burrows, with daily active periods.
- Nest in June or early July to Aug. in Sonoran Desert; May and June in Mojave
- Much behavior determined by fact that these tortoises live in hottest habitat of any tortoises on earth (Stanford 2010)
- During heat of day, between May-October temperatures may exceed 50 degrees C (130 degrees F)
- Seasonal activity patterns differ for Mojave and Sonoran populations
- Two seasons of rain in Sonoran Desert - summer and winter; tortoises most active July to September (Averill-Murray 2002)
- One main season of rain in Mojave Desert - winter;
- Western Mojave is winter-rainfall desert;usually has more rainfall than eastern
- Easter Mojave has two seasons - main winter and unpredictable summer rainfall
- In a 1974-1975 study of tortoises in southern Nevada, active season is spring, summer, early fall; inactive winter season
- Change from active to inactive begins late October
- Change from inactive to active in March-April
- Activity pattern controlled by temperature of environment and precipitation.
- After active foraging, often assume a limp, spread-eagle posture with limbs and neck extended.
- Perhaps is technique for increasing body temperature and aiding digestion
Territory Size/Behavior/Density of Occupation (Berry 1986)
- Occupy two types of underground shelters according to study of wild population in SW Utah.
- Winter dens dug horizontally 2.4 to 9.1 m (8 to 30 ft) into banks of dry washes
- Summer burrows dug down 0.9 to 1.2 m (3 to 4 ft) from level ground
- Winter dens re-used year after year, but same den not necessarily used each year
- Burrows less permanent and multiple holes may be dug
- May occupy temporary shelters several minutes or several weeks before moving to another shelter (Riedle et al 2008)
- Several tortoises may occupy a winter den at the same time
- One record of 17 tortoises in a single large den
- 3.1 is the average number/den
- Burrows used normally by single individual, or a male and female together
- Hibernating tortoises show much variation in the timing of their fall entrance and spring exits from dens
(Haines et al 1999)
- Environmental cues did not seem to play a large role in affecting the timing
Aggressive/Defensive behavior (Ruby & Niblick 1994) (Berry 1986)
- In general, yearly home range size estimates vary from 1 to 89 ha (220 acres) with high variability. (Duda et al 1999)
- Each tortoise occupied a home range: 11-53 ha (27-131 acres) in 5 study sites in California, Nevada, Arizona
- Range overlaps range of other tortoises
- May be a very conservative estimate of the actual home range
- May not account for excursions for denning, mating, mineral licks, water
- Tortoises traveled distances of 1.4-7.3 km (0.9-4.5 mi) over periods ranging from 16 days to 5 years
- Territory not defended by individual tortoises
- Density of tortoises: 300 individuals/1200 acres for a study site in SW Utah. (Woodbury & Hardy 1948)
- Choice of sites for relocation of tortoises needs to be based on
- Awareness of complex tortoise social systems
- Disease status of resident and imported tortoises
- Homing capacity of tortoises
- Whether new habitat is suitable
- Edible plants
- Shelter sites
- Mineral licks
- Low enough density of resident tortoises,
- Lack of ORV and road traffic, predators and toxins
Communication (Ruby & Niblick 1994)
- Male/male aggression common during breeding season
- Opponents attempt to overturn each other, may bite and ram opponents, face to face
- Male/female aggression not known
- When surprised by intrusion may lie down quickly (all legs withdraw and shell hits the ground)
- When handled by humans or excessively stressed, may void water stored in the bladder.
- Can be life-threatening to tortoise in times of drought
- Larger tortoises are usually dominant; males dominant over females but females decide mate choice.
- Female tortoises observed defending nest from Gila monsters (Heloderma suspectum)
- Defensive behavior (biting, nipping, hopping forward, hissing) by hatchlings in wild
Displays and Olfactory Signals
- Head bobs may be one factor allowing species recognition in Gopherus.
- Postures (and odors from trails, fecal pellets, urine) help maintain dominance hierarchies (Berry 1986)
- Secretions of chin glands used for sex and species identification (Alberts et al 1994) (Miller & Dinkelacker 2008)
- Glands not active until sexual maturity
- Males' glands are larger than females'
- Dominant males' chin glands larger and contain more testosterone; size varies seasonally (Alberts et al 1994)
- Enlarged chin glands serve as chemical but also a visual signal
- Sound production common in the testudinids (Auffenberg 1977), but not well studied. (Berry 1986)
- Hiss, grunt, moan. (Ruby & NIblick 1994)
- Male vocalizes during mating (Auffenburg 1977)
(Woodbury & Hardy 1948)
Interspecies Interaction (Woodbury & Hardy 1948)
- Have normal quadruped gait (forelimb, opposite hindlimb, other forelimb, other opposite hindlimb) (Williams 1981)
- Walking speed on land: rate of .5 to 12 hours per km (.3 to 7.3 hours per mile),
- Can't keep up such a pace due to danger of overheating
- Can climb inclines, sometimes at angles of 45 degrees to reach dens
- Poorly adapted for swimming; has difficulty placing nostrils up high enough to breath above surface
- Digging achieved with forelimbs; hindlimbs push soil out of burrow
- Females dig nest holes with hind feet
- Many animals make use of desert tortoise dens and holes:
- Pack rats (most common associated species); tortoises often found covered with pack rat 'rubbish'.
- Banded geckos
- Desert scaly lizards
- Spotted night snakes
- Sidewinder rattlesnakes
- Great Basin rattlesnakes
- Gopher snakes
- Burrowing owls
- Cactus wrens
- Horned larks
- Arizona cottontail rabbits
- Desert jackrabbits
- Kangaroo rats
- Mojave pocket mice
- Spotted skunks
- Black widow spiders
DIET & FEEDING
(Averill-Murray 2002) (Boarman 2002) (Bonin et al 2006) (Bury 1982) (Hansen et al 1976)
(Jarchow et al 2002)
(Marlow & Tollestrup 1982)
(Murray 1997) (Nagy et al 1998) (Nagy & Medica 1986) (Oftedal 2002, 2003)
(Walde et al 2006)
- Mostly grasses, leafy plants, flowers. (Bonin et al 2006).
- A study of foods of desert tortoises in California:
- Desert annuals are preferred food (flowers and vegetative portions)
- Can consume enough annuals at peak blooming time to survive summer and winter dormancy periods.
- In years of high rainfall, tortoises can afford to be more selective in food choices
- Observed choosing plant species that aren't common
- May choose many high-moisture plant
- Stay in burrows in drought years; rarely feed; emerge to drink and feed after rains. (Oftedal 2002)
- Winter rainfall of at least 26 mm (1.0 in) necessary for annual plants to germinate in Mojave and feed tortoises
- Seem to sense coming summer rains; move to low areas to secure drinking water. (Averill-Murray 2002)
- Major plant food consumed in Mojave and Sonoran Deserts:
- 43 plant species are important
- Only 8 species were major food item in both deserts
- Diversity of annual plants available varies markedly from year to year; an "average" tortoise diet hard to characterize. (Oftedal 2002)
- Non-native plants may pose a threat to tortoise's health (Boarman 2002)
- Split grass (Schismus barbatus) - may deplete nitrogen, phosphorus, and water, causing weight loss
- Russian thistle (Salsola tragus)
- Red brome (Bromus madritensis rubens) - sharp awns cause mechanical injury to tortoise nostrils
- Cheat grass (Bromus tectorum)
- Many introduced weed species are high in potassium, (in high concentrations, toxic to tortoises)
- Dry grasses often consumed in summer may be the least toxic food available, but these plants also dehydrate the tortoise. (Nagy et al 1998)
- Wild tortoise diet is a delicate balance between their need for protein and water and need to excrete excess toxic potassium.
(Oftedal 2002, 2003)
- Rains allow tortoises to drink and void potassium, then switch to a diet of dry grasses to gain weight. (Nagy & Medica 1986)
- Without rainwater to drink, tortoises need to get water and protein from plants with a high potassium excretion potential (PEP), to avoid buildup of too much potassium
- Oftedal suggests shortage of high PEP plants led to tortoise population crashes
- Digestive physiology similar to that of rabbit or horse: plant fiber is a crucial nutrient for all these hindgut fermeters
- Known to seek out sources of calcium, in soils, bone (Walde et al 2007)
- Hansen et al (1976) found bird feathers, mammal hairs, snake and lizard skins, and arthropods in tortoise fecal pellets
- Walde et al (2007) describe tortoises deliberately consuming bone from tortoise carcasses and skeletons
- Murray (1997) reports desert tortoise ingesting a vulture pellet; clumps of hair from the pellet noted on tortoise's beak
- Known to ingest calcium salts from desert soils by digging down to depths of 2-6 cm (0.8-2.4 in) where salts occur. (Marlow & Tollestrup 1982)
but other researchers caution that the tortoises might have been seeking associated minerals (Oftedal 2002)
- Walde et al (2006b) observed consumption of rabbit feces by desert tortoises and notes other records of eating scat of woodrats, lizards, peccaries and other tortoises; such behavior may add needed nutrients or beneficial gut microbes to the tortoise diet
REPRODUCTION & DEVELOPMENT
(Averill-Murray et al 2002) (Curtin et al 2009) (Ernst & Lovich 2009) (Germano et al 2002)
(Grover & DeFalco 1995) (Luckenbach 1982)
(Miller & Dinkelacker 2008) (Nowak et al 1999)
(Ruby & Niblick 1994) (Stebbins 2003) (Woodman & Juarez 1988)
(Ruby & Niblick 1994) (Miller & Dinkelacker 2008)
Egg Laying/Nesting (Averill-Murray et al 2002) (Curtin et al 2009) (Miller & Dinkelacker 2008 ) (Nowak et al 1999) (Wallis et al 1999)
- Courtship activity happens in any month of the tortoise's active season.
- Courtship encounters may last 1 or more hours
- Male trails female
- Nodding at female
- Repeated circling
- Biting of female
- Behavior similar to early stages of combat
- Females lack a distinct display to discourage male attentions.
- Such displays common in other reptiles such as lizards and snakes
- Females appear to be very selective in choosing a mate
- Females usually receptive only after repeated mating attempts
- Females may mate with several males and store sperm for many years until ready to lay eggs
- Most females in Mojave Desert produced eggs every year; two, even three, clutches occasionally if resources are plentiful (Wallis et al 1999)
(Curtin et al 2009)
- Large females laid more eggs and larger eggs
- Females dig shallow depressions near den entrances, using hind limbs
- Sonoran desert tortoises lay single clutch in June-July when rainy season begins
- Eggs are covered, using hind feet; front and hind limbs scrape debris over egg chamber
- In captivity males have been observed helping females dig nests. (Grover & DeFalco 1995)
- Clutch of 1-14; 4-7 normally (Ernst & Lovich 2009)
- Eggs laid May - July; sometimes into Aug. in Sonoran Desert. (Stebbins 2003)
- Eggs are elliptical to spherical and ping-pong ball in size. (Ernst & Lovich 2009)
- Yolk sac remains attached to hatchling's plastron for several hours or days - provides needed nutrients.
- Incubation period in wild: 90-120 days; if artificially incubated 82-92 days (Ernst & Lovich 2009)
- Emerge from eggs mid-August to October.(Ernst & Lovich 2009)
- Male size at hatchling: about 45 mm (1.8 in) carapace length (Germano et al 2002) or size of silver dollar.
- Female size at hatchling: 42 mm (1.7 in) carapace length (Germano et al 2002)
- Young wild hatchlings defensive and "pugnacious" when disturbed
- Lunge forward and hiss if touched near the head
- Found in young up to 4 - 6 years and less than 60 mm (2.4 in) carapace length
- In captivity, quickly lose this response if touched frequently
- Very few reach maturity in the wild
- Grow slowly at about 2.5 cm/yr (1 in/yr) (Nowak 1999)
- Until shell hardens at 5-8 years, vulnerable to ravens, roadrunners, snakes, bobcats, kit foxes, coyotes
- Age in wild at maturity (female): 15.7 years or 190 mm (7.5 in) for length of carapace
- Sexual maturity of females varies in wild:
(Curtin et al 2009)
- West Mojave tortoises - about 17-19 years
- Sonoran tortoises - about 22 to 26 years
- Western Mojave tortoises grow faster than Sonoran tortoises
- Live at least 35 years; may live 50 -100 years (Nowak 1999)
- Tortoises in Sonoran Desert live longer than those in Mojave Desert
(Curtin et al 2009)
- 43 years for females vs. only 27 years for females in Mojave
- More frequent droughts in Mojave Desert may add stress
- Females in both deserts have shorter life spans than males. (Curtin et al 2009)
- Expanding raven populations
(Woodman & Juarez 1988)
- USFWS estimates raven populations in desert areas increased due to garbage dumps and sewage ponds
- 250 tortoise shells found under a single raven nest (some of which had been recently seen alive and healthy)
- When tortoises younger than 5-6 years, shell isn't fully ossified and it is easy to rip open.
- Ravens may pose a threat to overall population numbers in this long-lived species that doesn't reproduce until 15 - 20 years.
- Carnivores, especially coyotes and bobcats prey on tortoises.
- Badgers, skunks, kit foxes prey on tortoises and eggs. (Luckenbach 1982)
- Fire ants
- Occasionally, fires
- Mortality in wild for juveniles more than 90%
- Gila monsters eat tortoise eggs (Nowak et al 1999)
(Edwards et al 2004) (Jarchow et al 2002)
- Captive Breeding
- Captive breeding discouraged out of concern for spread of disease from captive tortoises
- Management practices should be "compatible with the evolutionary history of gene flow" in widely separated desert tortoise populations (Edwards et al 2004)
- Human-made barriers now block tortoise movements
- Translocations to small isolated populations from nearby populations may aid in long term survival
- Potential hazards of translocations currently being assessed; may increase spread of disease, survival of translocated tortoises needs further study
- Desert tortoises from a captive source can be kept in Arizona, but only one tortoise per family.
- In Nevada, desert tortoises can be kept if were already in captivity prior to listing; can't buy, sell, or give them away.
- Sonoran Desert Museum established a Tortoise Adoption Program (sanctioned by AZ Game & Fish Department)
- Desert tortoises can be kept in California after obtaining a permit from the U.S. Bureau of Land Management. http://www.blm.gov/ca/st/en/fo/ridgecrest/tortoise.3.html
- Desert tortoises are hardy and are often given harmful care because the effects are not immediately obvious
- Conditions necessary for healthy desert tortoises:
- Outdoor living
- Diet as close to that in the wild as possible (be wary of advice in websites and popular literature)
- Living in the species natural geographical range
- A well-designed and secure habitat with sun and shade, a burrow, walls to prevent climbing out
- Protection from injury and extremes of climate
- Protection from ants, dogs, other turtle species, predatory birds, rodents, house cats
- Dietary items often offered but which should be avoided:
- Apples, avocado, bananas, cat and dog food, corn, dairy products, iceberg lettuce, melons, peaches, primate biscuits
- Any commercial diets marketed for turtles (they are tortoises, with different dietary requirements than that of other turtles)
- Forages can include:
- Alfalfa (Medicago sativa)
- Bermuda grass (Cynodon dactylon)
- Clover (Trifolium spp.)
- Dichondra (Dichondra sp.)
- Ryegrass (Lolium spp)
- Grape and mulberry leaves
- Tortoises need to graze freely in foraging areas
POPULATION AND CONSERVATION STATUS
(Berry 1991) (Boarman 2001) (California Fish and Game Website 2010)
(Corn 1994) (Federal Register Aug 28, 2009) (Rosmarino & Connor 2008)
(Tortoise and Freshwater Turtle Specialist Group 1996)
(USFWS 1991, 1994) (Van Devender 2002)
(Zylstra & Steidl 2009)
- ISIS captive population
- 1980s. Major declines (33-77% over 10 years)
- Documented at several western and one eastern Mojave Desert site in California.
- 1987- 2006:Decline of 3.5 % per year for a 51% reduction in adults and subadults since 1987
- Monitored populations of Sonoran Desert tortoises
Threats to survival (Berry 1991) (Boarman 2001)
- IUCN Status: Vulnerable (Tortoise and Freshwater Turtle Specialist Group 1996.
- CITES Status: CITES II Listed 1975 - not threatened with extinction, but trade controlled
- U.S. Fish and Wildlife Service (USFWS): Mojave population listed: Threatened
- 1972: State Reptile of California
- 1961: Illegal under California State law to collect desert tortoises.
- 1973. Desert tortoise listed as Threatened by federal government
- 1980: Beaver Dam Slope, Utah population of desert tortoises first to have federal protection
- 1980: Desert Tortoise Research Natural Area (DTNA) set aside as sq km ( 39.4 sq mi) of natural habitat in Kern Co., California.
- 1989: Emergency listing as Endangered for Mojave population; collecting is a federal offense.
- 1989: Listed in California as Threatened
- 1989: State Reptile of Nevada
- 1990: Mojave population listed as threatened by USFWS
- 1991: USFWS rules population south and east of Colorado River (Sonoran) "not warranted".
- 2008: Petition filed to list Sonoran Desert tortoise under U.S. Endangered Species Act.
- 2009: Sonoran Desert population of tortoises may warrant listing by USFWS as a distinct population with a critical habitat (Federal Register Aug 28, 2009)
- 2009: 250-acre Desert Tortoise Conservation Center (DTCC) inLas Vegas, Nevada (established 1990); now operated by San Diego Zoo in partnership with US Fish and Wildlife Service, Bureau of Land Management, Nevada Department of Wildlife, and Association of Zoos and Aquariums Conservation Centers for Species Survival. (San Diego Zoo Website 2010)
- Establishing science-based methods to select sites for release in wild and conduct follow-up monitoring
- Training professionals, teachers, community leaders on tortoise recovery issues
- Conducting research on-site, including health research
- Cultivating community support for tortoises in the wild
- San Diego Zoo maintains pet tortoise pick-up service for stray or unwanted pet tortoises and tortoises found in urban areas of Clark Co., Nevada
- 2010: Around 1,000 desert tortoises brought to DTCC yearly
- Many suffer effects of improper diet and care
- After assessment, healthy tortoises are released into a 104 km sq (40 mi sq) protected habitat and monitored
- Tortoises with metabolic bone diseases from lack of sunlight, and many other disease conditions are rehabilitated
- Off road vehicle traffic
- Human collection and removal
- Cattle and wild burro grazing
- Roads, highways, railroads
- Military activity
- Habitat destruction
- Toxic waste disposal
- Global climate change and long term drought (USFWS 2009)
- Invasive non-native plants (Boarman 2001)
- Natural gas pipeline construction and maintenance (Olson et al 1996)
- Wild predators
Important Web Resources:
- California Turtle & Tortoise Club. Website includes information on how get a desert tortoise permit in California.
- Utah Division of Wildlife.Website includes Utah's Desert Tortoise Adoption Program On-Line Booklet (Updated 2010).
- Nevada Tortoise Group
- Arizona Game & Fish. Gives info regarding what to do if you find a desert tortoise.
- CaliforniaHerps.com. Desert tortoise factsheet, includes lots of photos.
- World Chelonian Trust. Non-profit founded in 1992 for "production, publication, and support of worldwide turtle and tortoise research, with an emphasis on the scientific basis of chelonian diversity and conservation biology".
- U.S. Fish and Wildlife Service Spotlight Species 5-Year Action Plan
- U.S. Forest Service Fire Effects Information System: Reviews in detail knoweldge about fire and ecology of desert tortoises and other North American species of plants and animals.
- Wild Tortoise Assistance and Pet Tortoise Pick Up - Clark Co. Nevada. Provides guidelines and phone numbers to call for citizens who discover a tortoise in Clark Co., Nevada (where desert tortoises are native).
- IUCN Red List - Summary of key information. No distribution map available for this species.
- IUCN Tortoise & Freshwater Turtle Specialist Group.
- US Bureau of Land Managment - Ridgecrest, CA Field Office. Tips for how to protect wild tortoises and how to obtain permit for keeping a tortoise from a captive source.
- US Geological Survey Website. Newly revised (2010) website has extensive list of desert tortoise publications; search for "desert tortoise" in the search box.
- US Geological Survey. Threats to Desert Tortoise Populations: A Critical Review of the Literature. Extensive summary of scientific studies on desert tortoises, with comments on methodologies, implications of results, needs for additional data.
- Desert Tortoise Council. Organization for persons working for "the continued survival of viable populations of the desert tortoise throughout its range." Includes on-line newletter, list of current laws protecting tortoises, and a newly revised (2010) Answering Questions About Desert Tortoises: Guide for People Who Work With the Public by K. Berry and T. Duck.
- Arizona-Sonoran Desert Museum Desert Tortoise Adoption Program: Includes how to prepare a place for private individuals to keep a desert tortoise.
- US Food and Drug Administration - Salmonella and Turtle Safety. Website with information about risk for humans of salmonella infections from captive turtles.
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