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Lifespan, longevity, and ageing

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Maximum longevity: 62.8 years (captivity) Observations: Their longevity has been reported to be between 50 and 100 years (http://www.fs.fed.us/database/feis/). Estimates of longevity in the wild suggest these animals may live over 50 years (Castanet 1994).
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Benefits

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In the past, desert tortoises were used by indigenous peoples of the American Southwest for food and medicine, and the shells were used to make bowls, ladles, and shovels. Desert tortoises were also central figures in the folklore of the region. Desert tortoises are occasionally still used for food in some parts of Mexico. In addition, many people in Arizona keep desert tortoises as pets, though the keeping of captive tortoises is strictly regulated: tortoises must not be collected from the wild, only one tortoise is allowed per family member.

Positive Impacts: pet trade ; food ; body parts are source of valuable material; source of medicine or drug

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Associations

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Desert tortoises are primary consumers, and they are prey for various mammalian, avian, and reptilian predators. Desert tortoises are also ecosystem engineers, digging burrows that are used as shelters by snakes (Serpentes), lizards (Sauria), birds (Aves), rodents (Rodentia), javelinas (Pecari tajacu), and insects (Insecta) and other invertebrates. Desert tortoises themselves take advantage of packrat (Neotoma albigula) houses for shelter. In one study, desert tortoises were found sheltering with large colonies of Africanized honeybees (Apis mellifera)--a very effective defense against predators! Finally, desert tortoises have few external parasites, but they are host to intestinal pinworms (Oxyurida).

Ecosystem Impact: creates habitat

Species Used as Host:

  • packrats (Neotoma albigula)

Commensal/Parasitic Species:

  • snakes (Serpentes)
  • lizards (Sauria)
  • birds (Aves)
  • rodents (Rodentia)
  • javelinas (Pecari tajacu)
  • insects (Insecta)
  • other invertebrates
  • pinworms (Oxyurida)
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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Trophic Strategy

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Desert tortoises are herbivorous, surviving on low-growing plants and freshly fallen leaves. The species of plants eaten vary widely by season and geographic region, but overall the desert tortoise diet consists of the leaves, bark, stems, fruits, and/or flowers of trees, shrubs, woody vines, succulents, perennial and annual grasses, herbaceous perennials, and annuals. During rainy seasons, desert tortoises drink large amounts of water from temporary pools.

Plant Foods: leaves; wood, bark, or stems; fruit; flowers

Primary Diet: herbivore (Folivore , Frugivore , Lignivore)

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Distribution

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Desert tortoises are found in the southwestern United States and northwestern Mexico. They range from northern Sinaloa up through Sonora and western Arizona to southeastern California, southern Nevada, and the southwestern tip of Utah.

Biogeographic Regions: nearctic (Native )

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Habitat

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Desert tortoises live in different habitats in different parts of their range. In the south, (northern Sinaloa and southern Sonora) they inhabit thornscrub and tropical deciduous forests, further north, this habitat gives way to foothills thornscrub and Sonoron desertscrub, and in the northenmost part of their range (California, Nevada, and Utah), Mohave desertscrub. There are three distinct populations of desert tortoises, which are adapted to these different habitat types. Sonoron desert tortoises inhabit the Sonoron desertscrub of western Arizona, where paloverdes, saguaros, and ironwoods are the most prominant plants. At about 1,100 to 1,400 meters in elevation, these plants give way to desert grassland communities, which mark the upper elevational limit of desert tortoises. Tortoises in the Sonoron desert inhabit mountain slopes strewn with large boulders at densities of about 40 tortoises per square kilometer, and occur at much lower densities in intermountain valleys. On the other hand, Mohave desert tortoises of southeastern California, southern Nevada, and southern Utah live primarily in valleys where large rocks are absent, and may occur in densities of more than 150 tortoises per square kilometer. The Mohave desertscrub that these tortoises call home is characterized by creosotebush, white bursage, and galleta grass. Finally, to the south, Sinaloan desert tortoises inhabit the thornscrub and tropical deciduous communities of southern Sonora and northern Sinaloa. The thornscrub habitat is dominated by plants such as desert feather tree, papelio, torotes, tree ocotillo, and organpipe cactus, and the tropical deciduous forests are dominated by mauto, amapa, brasil, torotes, kapok, and tree morning glory.

Range elevation: 1400 (high) m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune ; forest ; scrub forest ; mountains

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Life Expectancy

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Mortality for young desert tortoises is very high. For every 15 clutches of eggs that are laid, only one individual is likely to live to age 20. However, once a desert tortoise makes it to age 20, it has a very high chance of living at least 20 more years. Thus, the life expectancy of desert tortoises that live past age 20 is 50 to 80 years.

Range lifespan
Status: wild:
50 to 80 years.

Typical lifespan
Status: wild:
0 to 20 years.

Average lifespan
Status: wild:
<1 years.

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Benefits

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There are no known negative impacts of desert tortoises on humans.

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Morphology

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The head of a desert tortoise is scaly, and the body has thick skin. Desert tortoises also have extremely long nails, which are used in digging through the desert sand to find shelter. The upper shell of a desert tortoise ranges in length from 15 to 36 centimeters, and its color varies from dull brown to a dull yellow. Males are typically larger than females. An adult male desert tortoise averages around 20 kilograms in weight, and an adult female averages 13 kilograms. Males and females are also shaped differently. Male tortoises have long, curved, gular horns that are used for leverage in male-male combat, heavier claws, and longer tails that facilitate copulation. Each male tortoise also has a depression in the plastron that fits around the carapace of a female, and an inward curve at the rear portion of the carapace that allows him to achieve the upright postion needed for mating. Females, on the other hand, have carapaces that curve outward and flat plastrons.

Range mass: 11 to 23 kg.

Range length: 15 to 36 cm.

Sexual Dimorphism: male larger; sexes shaped differently

Other Physical Features: ectothermic ; bilateral symmetry

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Conservation Status

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Desert tortoises face many threats from humans, including habitat loss and fragmentation, road mortality, shooting, collection for food and the pet trade, trampling by livestock, and predation by feral dogs (Canis lupus familiaris) and ravens (Corvus corax), which thrive around human settlements. Desert tortoises have suffered enormous declines in population sizes in recent years--up to 55% in some areas. The Mohave Desert population, ravaged by upper respiratory tract disease, has fared the worst, and Mohave desert tortoises were listed as threatened by the U.S. Fish and Wildlife Service in 1990. Beginning in 1988, Arizona state law has recognized desert tortoises as a threatened species and strictly prohibited their capture. Possession of captive desert tortoises is strictly regulated, and it is illegal for anyone to release captive desert tortoises into the wild, so that released captives do not disturb wild populations. Desert tortoises have been listed as threatened in Mexico since 1994. In addition, desert tortoises appear in the CITES appendix II and as "vulnerable" on the IUCN's 2004 Red List of Threatened Species.

To preserve desert tortoises, the Federal Bureau of Land Management has established a 98 square kilometer sanctuary in California called the Desert Tortoise Natural Area. This preserve is closed to all vehicles, livestock grazing, and mining. In Arizona, the Arizona Interagency Desert Tortoise Team, established in 1985, has produced a management plan for desert tortoises calling for the establishment of management areas that would support healthy tortoise populations, continuous monitoring of tortoise populations, and measures such as tortoise-proof fencing and tortoise overpasses that would keep tortoises off of roads.

US Federal List: threatened

CITES: appendix ii

IUCN Red List of Threatened Species: vulnerable

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Associations

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Adult tortoises, with their hard shells, have few natural predators. Only mountain lions (Puma concolor) can crush their shells. Eggs, hatchlings and juveniles are more vulnerable, and are preyed upon by kit foxes (Vulpes velox), coyotes (Canis latrans), feral dogs (Canis lupus familiaris), gray foxes (Urocyon cinereoargenteus), bobcats (Lynx rufus), badgers (Taxidea taxus), golden eagles (Aquila chrysaetos), common ravens (Corvus corax), greater roadrunners (Geococcyx californianus), and Gila monsters (Heloderma suspectum). Female desert tortoises may deter egg predators by guarding their eggs for some time after laying, but hatchlings and juveniles must rely heavily on camouflage and the use of shelters to keep themselves safe. All desert tortoises, large and small, will urinate as a last resort when handled.

Known Predators:

  • mountain lions (Puma concolor)
  • kit foxes (Vulpes velox)
  • coyotes (Canis latrans)
  • feral dogs (Canis lupus familiaris)
  • gray foxes (Urocyon cinereoargenteus)
  • bobcats (Lynx rufus)
  • badgers (Taxidea taxus)
  • golden eagles (Aquila chrysaetos)
  • common ravens (Corvus corax)
  • greater roadrunners (Geococcyx californianus)
  • Gila monsters (Heloderma suspectum)

Anti-predator Adaptations: cryptic

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Behavior

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Desert tortoises perceive the world using visual, chemical, tactile, and auditory senses. They communicate with one another by vocalizing and posturing, and they may use feces and anal gland secretions to mark their burrows and home ranges.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: scent marks

Perception Channels: visual ; tactile ; acoustic ; chemical

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Reproduction

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Desert tortoises have multiple mates during their lifetime. During the breeding season, males fight one another for access to receptive females. During combat, males posture, bob their heads, ram into one another, and chase one another. Often, they attempt to flip one another over by using their large gular shields as levers. If one succeeds, the loser eventually rights himself and escapes. Meanwhile, the winner courts the female using behaviors similar to those used in male-male combat. He bites the female, hisses at her, and butts her in the flank until he is able to mount her. Mating ends when the female eventually wanders away.

Mating System: polygynandrous (promiscuous)

Desert tortoises breed from spring to fall. Females store sperm in their reproductive tracts, and stored sperm can remain viable for eighteen months after copulation. Thus, females often mate in late summer and hibernate before laying eggs in spring. Each female desert tortoise lays 1 to 14 (most commonly, 3 to 5) round, off-white eggs in a deep nest that is scooped out of the desert floor. Females in the Mohave desert often lay a second clutch in late summer, which may not hatch until the next spring. Usually, however, the incubation period is 90 to 135 days, and the eggs hatch in September or October. The length of the incubation period is determined by temperature (as is the sex of the offspring). The shell of a newly hatched tortoise is extremely soft and remains soft up during the first five years of life. It eventually hardens as the tortoise matures. Sexual maturity is reached at about 14 to 21 years.

Breeding interval: Most desert tortoises breed once per year; those in Mohave desert may lay up to three clutches per year

Breeding season: Desert tortoises breed spring to fall

Range number of offspring: 1 to 14.

Average number of offspring: 3-5.

Range gestation period: 90 to 135 days.

Range age at sexual or reproductive maturity (female): 14 to 21 years.

Range age at sexual or reproductive maturity (male): 14 to 21 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous ; sperm-storing

Average number of offspring: 8.

Female desert tortoises provide their young with yolk, which not only sustains them while the eggs incubate, but which provides the hatchlings with enough energy for six months--enough to sustain them in case they are not able to feed before hibernating. Before laying their eggs, females select nest sites in sheltered spots near their burrows or resting sites. Each female digs a hole with her hind legs in the spot she has chosen, urinating throughout the process--perhaps to ward off predators or provide the eggs with moisture. After deposting her eggs in the hole she has dug, each female covers the eggs with soil and urinates again. Females may guard their eggs for some time after laying, fending off predatory Gila monsters (Heloderma suspectum) and curious humans. Before long, however, females wander off and leave their young to fend for themselves.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female)

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Crozier, G. 1999. "Gopherus agassizii" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Gopherus_agassizii.html
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Gregory Crozier, University of Michigan-Ann Arbor
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Allison Poor, University of Michigan-Ann Arbor
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Biology

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Desert tortoises reach sexual maturity when they attain a size of roughly 20 centimetres, which may take up to 15 years (3). Mating begins in early spring; male courtship involves head bobbing and nipping the female's carapace and legs (2). Males also compete amongst each other at this time, using their gular horn they attempt to overturn their component or to chase them away (2). Females construct nests in the desert sand, burying their clutch of around 5 eggs (3). The temperature of the developing eggs determines the sex of the hatchlings; females develop at higher temperatures (3). Hatchlings emerge 90 – 135 days after laying, but the mortality rate of both eggs and hatchlings is very high (2). These tortoises graze on desert grasses, obtaining almost all of the water they require from their food (2). Rocks and soil are also ingested, possibly as a means of obtaining minerals (2). As cold-blooded animals, tortoises adopt behavioural means of regulating their temperature; they hibernate in burrows during the winter months and are also dormant through the hottest part of summer in a behaviour known as aestivation (2). In some areas, extensive burrow systems are constructed and these may be shared by a number of tortoises (2).
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Conservation

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The desert tortoise is listed as Threatened on the U.S. Endangered Species Act and is protected throughout its range. The U.S. Fish & Wildlife Service has published a Recovery Plan for the species that recommends managing areas of suitable habitat for tortoise conservation (7). The Desert Tortoise Council was established in 1976 and is working to promote the conservation of this rare tortoise (8).
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Description

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This medium-sized tortoise inhabits the deserts of the western USA. The carapace varies in colour from light brown to dark with orange or yellowish markings (3). The front of the under shell (or plastron) is extended in a projection known as the 'gular horn', which is particularly pronounced in adult males (3). Males are also distinguished by having longer tails and a raised area to the rear of the plastron (4).
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Habitat

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The desert tortoise occurs in a variety of different habitats within the Mohave and Sonoran Deserts, from sandy flats to rocky foothills, river valleys and canyons (2).
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Range

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Endemic to the southwestern United States and Mexico. This tortoise is recorded from southeastern California, southern Nevada, southwestern Utah and Arizona. In Mexico, it is found from Sonora to northern Sinaloa and the cape of Baja California (5).
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Status

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Classified as Vulnerable (VU – A1acde+2cde, E) on the IUCN Red List 2002 (1).
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Threats

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The population of desert tortoises has declined throughout their range, habitat has been degraded by development, mining and the grazing of livestock (4). In addition, these tortoises are collected for the illegal pet trade and are at risk from desert vehicles (6).
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Desert Tortoise

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The California Desert Tortoise finds its habitat throughout the desert region. They can have a 15 inch shell length, and they can weigh up to 20 pounds. The lifespan of a Desert Tortoise, on average, is 80-100 years, but some tortoises can live until 130 years old. Desert Tortoises are considered herbivores and rely on a diet of dry grasses, cacti, and flowers. The California Desert Tortoise digest its food in 20-30 days which allows for repopulation of dry grasses.

The Desert Tortoise mainly receives its water intake from the plants it eats. These tortoises can store about a quart of water in their bladder for necessary use. The adaptation of being able to store water aids in the Desert Tortoise’s survival in the arid climate. Not only does the bladder store water, but the tortoise’s scales keep moisture inside their bodies to eliminate dehydration. The California Desert Tortoise can go up to 1 year without drinking water!

Similar to other turtles and tortoises, the California Desert Tortoise moves at a slow pace; they travel at approximately 0.2 mph. By moving at a slow pace, the Desert Tortoise has to find other ways to escape predators. They have strong claws that allow for digging, and the tortoises make burrows that they share with other desert wildlife. Nevertheless, they are predatory threats to the desert tortoise that include: ravens, Gila monsters, kit foxes, badgers, roadrunners, and foxes. The predators mainly prey on juveniles because they are only 2-3 inches in length and have softer shells.

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New Distribution due to new taxonomy

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In 2011 the Desert Tortoise was recognized to actually be two species, Gopherus morafkai and Gopherus agassizii. The two species apparently do not overlap in range and are divided by the Colorado River. Gopherus agassizii ranges northwest of the Colorado River, in California and Nevada. It's sister species lives southeast of the Colorado River, in Arizona and Mexico.
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Activity and movement

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More info for the terms: aestivation, cover, hibernation

Activity and movement: Temperature strongly influences desert tortoise activity level. Although summaries note that desert tortoises can survive body temperatures from below freezing [7,107] to over 104 °F (40 °C) [5,38], most activity occurs at temperatures from 79 to 93 °F (26-34 °C) [95,107]. The influence of temperature is reflected in daily activity patterns, with desert tortoises 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 [5,55,60,73,112]. In the Picacho Mountains, most desert tortoises were active when temperatures were 79 to 86 °F (30 °C), and activity levels were higher at these temperatures than at temperatures from 97 to 104 °F (36-40 °C). Active desert tortoises were not observed when temperatures were below 52 °F (11 °C) or above 104 °F [107]. From 27 November to 23 January in the Mojave Desert of California, significantly (P≤0.004) higher percentages of juvenile desert tortoises were active on days with higher minimum temperatures than on days with lower minimum air temperatures [112]. Desert tortoises less than 2.4 inches (6.0 cm) in length were observed at significantly (P<0.05) lower temperatures than larger individuals at several California sites [13]. See Cover Requirements for details of shelter sites used to regulate body temperature and [55] for citations addressing the physiology of desert tortoise thermoregulation.

Desert tortoise activity generally coincides with rainfall. July thundershowers triggered desert tortoises in the eastern Mojave of Nevada to emerge from aestivation [83]. In the south-central Mojave Desert the proportion of locations outside burrows and distance traveled per day was significantly (P<0.001) lower in spring and summer of a dry year than in a year with above-average precipitation [37]. Greater spring foraging activity in the Sonoran Desert of Arizona occurred in years with high winter and spring rainfall than in years with low winter and spring rainfall [106]. However, in southern California the percent of juvenile Mojave desert tortoises active during winter was not correlated with amount of rainfall [112].

Although desert tortoises spend the majority of their time in shelter, movements of up to 660 feet (200 m) per day are common and long-distance movements do occur. The common, comparatively short-distance movements presumably represent foraging activity, traveling between burrows, and possibly mate-seeking or other social behaviors. Long-distance movements could potentially represent dispersal into new areas and/or use of peripheral portions of the home range. Desert tortoises in a southern Arizona plant community with several grass species, catclaw acacia, and velvet mesquite spent an average of 95.6% of the days they were observed in shelter sites [75]. In the eastern Mojave Desert of Nevada, movements less than 660 feet (200 m) were most common [86]. According to a technical report on the status of a relocation project (cited in [10]), desert tortoises commonly traveled 1,540 to 2,700 feet (470-823 m) per day. Berry [10] did not include information on the desert tortoises these estimates were based on, such as resident or reintroduced status or time since reintroduction. Long distance movements of 2 or more miles (≥ 3 km), including movements through atypical habitat, were noted by Averill-Murray and others [6] and Berry [10]. In at least one study area in southwestern Utah, desert tortoises migrate short distances between winter hibernation dens in washes and adjacent summer feeding grounds [116]. Other citations addressing desert tortoise movement are included in the locomotion section of Grover and DeFalco [55].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Annual cycle

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More info for the terms: cactus, hibernation, series

The activity peak of Mojave desert tortoises occurs in spring [73], while the activity of Sonoran desert tortoises peaks in late summer to fall [5,74]. Desert tortoises in creosotebush vegetation of the western Mojave Desert in California started eating daily from 24 March to 2 April and were aestivating by 21 June [64]. Mojave desert tortoises are most active in April and May, and the level of summer activity increases in eastern populations [5]. In contrast, food consumption by Sonoran desert tortoises in southern Arizona peaked from July to October [74]. Several populations exhibit 2 activity peaks, 1 in spring and another in late summer or fall [5,73,78,83,106]. A review discusses instances of increased winter precipitation preceding greater spring activity of Sonoran desert tortoises [106]. In Mojave Desert populations, summer precipitation is likely to influence the amount of activity in the summer and fall [73,83]. Desert tortoises in the western portion of the range likely spend more time aestivating during summer than those in eastern populations due to the lack of summer monsoon rains in the western regions [106]. See Activity and movement for more information on the impact of rainfall on desert tortoise activity.

Desert tortoises hibernate during the winter. In creosotebush scrub of the western Mojave in California, desert tortoises emerged from 24 March to 2 April in a year with greater than average rainfall [64]. On a site on the northern edge of the Mojave Desert in southwestern Nevada, 98% of individuals hibernated from 15 November to 15 February. Results of this study suggest that the timing of the start of hibernation may be more variable than emergence from hibernation in the Mojave Desert. Desert tortoises on the site emerged from hibernation from 15 February to 28 April, while the first individual to begin hibernating started on 18 August, and the last began on 7 December [90]. Desert tortoises in the Sonoran region generally begin hibernating from October to December and emerge from March to May [5,7,75,107]. Emergence dates are more variable than starting dates [5,75], with desert tortoises emerging from hibernation as early as 21 February in the Picacho Mountains of south-central Arizona [107] and as late as 16 August on another southern Arizona site. Average length of hibernation on the former site was 188.5 days but ranged from 88 to 315 days [75]. In the Picacho Mountains the average hibernation length was 125 days [107]. Hibernation length ranged from 118 to 154 days on a site dominated by yellow paloverde, saguaro, and creosotebush in the San Padro Valley of southeastern Arizona [7]. Female desert tortoises tend to emerge from hibernation earlier than males [5,7,75,90] and may begin hibernating later than males on some sites. In addition, juveniles may emerge earlier than adults [90]. In southern California, desert tortoises less than 4 years old fed mostly from 23 January to 18 February (22 of 30 feeding observations). The study period was 22 October to18 February [112].

Desert tortoises in the Mojave nest in May and June [5,101,103,110], while those in the Sonoran Desert nest from June or early July to August [4,5,81,107]. In the Ivanpah Valley, desert tortoises nested from 15 to 28 May, with some laying again from 12 to 25 June in 1980 [103]. In the eastern Mojave near Goffs, California, and the western Mojave Desert near California City, California, desert tortoises laid their first eggs in April or May, with 70% nesting again in May or June. Timing of the 1st nest did not differ between the 2 sites, and timing of the 2nd nest was later (P<0.01) in the western population [110]. Eggs hatched from September to October in the eastern Mojave Desert and August to September in the western Mojave Desert [5]. Eggs laid in southwestern Utah hatched from 21 August to 12 September, following an estimated incubation period of 89.7 days [78]. In paloverde-mixed cactus habitat series of the northeastern Sonoran Desert of Arizona, desert tortoises laid eggs from 27 June to 25 July over a 4-year period [4]. Averill-Murray and others [5] observed laying as late as 30 August in the Sonoran Desert. Sonoran desert tortoise eggs typically hatch from the end of summer to fall [4,5]. During a 4-year study on a paloverde-mixed cactus site, the latest a hatchling was observed emerging was 29 October [4]. The incubation period of desert tortoise eggs generally ranges from 90 to 120 days; some eggs may overwinter and hatch the following spring [4,38,55,73]. In a laboratory experiment, average incubation time decreased with increasing temperature, ranging from 124.7 days when incubated at 77°F to 78.2 days when incubated at 88 °F (31 °C) [69].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Associated Plant Communities

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More info for the terms: cacti, cactus, shrub, tree, woodland

Desert tortoises occupy a wide range of desert shrub communities of the southwestern United States, including creosotebush (Larrea tridentata) scrub, Joshua tree (Yucca brevifolia) woodland, shadscale (Atriplex confertifolia) scrub, saltbush (Atriplex spp.) scrub, alkali sink, cactus scrub, desert washes, and paloverde (Parkinsonia spp.)-mixed cactus scrub associations. In the southernmost reaches of their range, desert tortoises occupy Sinaloan thornscrub and Sinaloan deciduous woodland [27,43,49,55]. Ecotones between these communities are also used [9,38,55,72] and may be preferred in some areas [9] (see Plant species composition). A single desert tortoise was observed in a ponderosa pine (Pinus ponderosa) woodland in Saguaro National Park, Arizona [3].

The habitats used in Mojave and Sonoran deserts differ, with vegetation communities typical of valley bottoms used more often in the Mojave than in the Sonoran Desert [46,98,107]. Creosotebush associations are characteristic desert tortoise habitat in the Mojave Desert [9,49,55]. Some of the highest densities of desert tortoises occur in creosotebush and creosotebush-white bursage (Ambrosia dumosa) vegetation in the western Mojave Desert [55,73,99]. Paloverde- and saguaro (Carnegiea gigantea)-dominated associations are characteristic habitat in the Sonoran Desert [55,98,107]. For instance, in the Sonoran Desert of southeastern Arizona, desert tortoises occupied a paloverde-mixed cactus community but not adjacent, lower-elevation creosotebush habitat [107]. Near Tucson, Arizona, 82.8% of desert tortoise sign occurred in mixed paloverde-cactus habitat compared to 17.2% in creosote-white bursage habitat (Walchuk and Devos 1982, cited in [55]).

Plant communities occupied by Mojave desert tortoises include:
  • creosotebush associations [9,49,55]
  • Joshua tree woodland ([49,73,78], reviews by [25,55,98,99])
  • blackbrush (Coleogyne ramosissima) ([73], reviews by [25,27,55])
  • desert wash communities ([9], reviews by [99,117]). In the extreme southwestern Mojave Desert, the wash community where desert tortoise burrows were located included common Mediterranean grass (Schismus barbatus), big galleta (Pleuraphis rigida), Texas stork's-bill (Erodium texanum), white burrobrush (Hymenoclea salsola), creosotebush, and white bursage [9].
  • cactus scrub, which commonly includes teddybear cholla (Cylindropuntia bigelovii) and white bursage [73]
  • shadscale/saltbush/alkali scrub, which is comprised of one or more saltbushes (Atriplex spp.) and may include halophytic chenopods (Chenopodiaceae) ([73], reviews by [25,55]).
  • western honey mesquite (Prosopis glandulosa var. torreyana)-saltbush habitat near Koehn Dry Lake in the western Mojave Desert [73]
Plant communities occupied by Sonoran desert tortoises include:
  • paloverde and/or saguaro associations [7,8,55,98]
  • saguaro-ocotillo (Fouquieria splendens) communities (reviews by [55,98])
  • cactus scrub typically comprised of succulents such as cholla (Opuntia spp.) and other cacti (e.g., Echinocactus spp., Echinocereus spp.) [73]
  • Sonoran Desert washes [8,55,73,117]. The Colorado Desert of southeastern California and southwestern Arizona often supports woodland communities of honey mesquite, desert ironwood (Olneya tesota), blue paloverde (Parkinsonia floridum), and smoke tree (Psorothamnus spinosus) in large drainages [2,25,73]. Species in small drainages may include white burrobrush, Anderson wolfberry (Lycium andersonii), catclaw acacia (Acacia greggii) and desertbroom (Baccharis sarothroides) [25].
  • a community in southern Arizona comprised of several grama (Bouteloua spp.) and threeawn (Aristida spp.) grasses, catclaw acacia, velvet mesquite (Prosopis velutina), soaptree yucca (Yucca elata), and several cacti (e.g., Opuntia spp., Cylindropuntia spp., Ferocactus wislizenii, Mammillaria grahamii) [75]
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Common Names

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desert tortoise
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Conservation Status

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Information on state-level protection status of desert tortoises in the United States is available at NatureServe, although recent changes in status may not be included.
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Cover Requirements

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More info for the terms: association, cactus, caliche, cover, density, hibernation, shrubs, tree

Burrows and other shelter: Desert tortoises take shelter in burrows, rock shelter sites, and pallets to regulate body temperature and reduce water loss [38,55]. Burrows are tunnels dug into soil by desert tortoises or other animals [28], rock shelter sites are spaces or tunnels protected by rocks and/or boulders [75], and pallets are depressions in the soil [107]. Site characteristics, season, and region likely influence the type of shelter used. The number of burrows used, the extent of repetitive use, and the occurrence of burrow sharing are variable. Males tend to occupy deeper burrows than females. Seasonal trends in burrow use are influenced by desert tortoise gender and regional variation. Desert tortoise shelter sites are often associated with plant or rock cover. Desert tortoises often lay their eggs in nests located at the entrance of burrows. Information on burrow structure is available in these sources: [55,116].

Burrows are important for desert tortoise temperature and water regulation. Burrows and other shelter sites allow desert tortoises to slow their rate of heating on hot summer days [5] and provide protection from cold during the winter [7,73]. The humidity within burrows prevents desert tortoise dehydration [38,55]. In fenced enclosures on a site in southern California, long burrows were more humid than short burrows, and higher humidity contributed to reduced water loss in juvenile desert tortoises [113]. Burrows may also provide protection from predators [9]. The apparent association between certain soil characteristics (see Soil) and desert tortoise density in southern Nevada suggests that the availability of adequate burrow sites can influence desert tortoise densities [114]. In addition, a review reports a significant (P=0.0154) positive correlation between the number of burrows and population density in the Sonoran Desert, and suggests that a lack of adequate shelter sites could limit population density [6].

The use of the various types of shelter may be related to the soil [7,27,38], the abundance of rocks and boulders [75], and the temperature extremes that occur on a given site [38]. In the Mojave Desert of southern Nevada, burrows were used most in the hottest and coldest months, and pallets and sites with no cover were used most in April and May, months with moderate temperatures [91]. Deep burrows are used frequently in the northern portions of the desert tortoise's range, and burrows are used less often in the southernmost portions of the desert tortoise's range [27,49,55,73].

The number of burrows used by desert tortoises varies spatially and temporally. During an approximately 18-month study in paloverde-cactus mixed scrub of the Picacho Mountains, desert tortoises used an average of 7.6 burrows or pallets [8]. In the Mojave Desert of southern Nevada, desert tortoises used an average of 11.7 burrows per year [91]. Desert tortoises used 12 to 25 shelter sites yearly on another Nevada site (Burge 1978, cited in [73]). Desert tortoises at Joshua Tree National Park used a mean of 11.6 to 13.8 burrows in a year with above-average precipitation, which was significantly (P<0.001) more than the average of 6.2 to 6.9 burrows used by desert tortoises at another location, the Marine Corps Air Ground Combat Center in California, during the same year. These values were significantly (P<0.001) greater than the number of burrows used on the same sites in a year with below-average precipitation [37]. In a community comprised of several grasses, catclaw acacia, and velvet mesquite in the Sonoran Desert of southern Arizona, significantly (P<0.0005) more shelter sites were used from winter to spring than from summer to fall [75].

Desert tortoises use some burrows repeatedly, although reuse of burrows is variable [6,55]. Fidelity to burrows was high in an area of the Sonoran Desert with little soil development and few shelter sites, with one burrow used for 6 consecutive years [6]. In southern Nevada 83% of burrows used in 1974 were reused in 1975 (Burge 1978, cited in [55]). In the Mojave Desert of southern Nevada, an average of 5 new burrows were used per year, which represented 39% to 52% of the total yearly burrow use. Approximately 80% of the new burrows were less than 3 feet (1 m) deep [91]. In contrast, on a site in extreme southwestern Utah, only 4 of 56 burrows used in 1973 were used again in 1974 (Coombs 1974, cited in [55]). Reuse of winter burrows in a southeastern Arizona was not observed during a 2-year study [7]. Reviews report that burrow collapse can be common [55,95], which may necessitate increased use of new burrows.

Desert tortoises share burrows with other desert tortoises and with several other animals including mammal, reptile, bird, and invertebrate species. According to a review, 23 desert tortoises were observed in one burrow in southwestern Utah [38], while in the Picacho Mountains, no winter shelter sites were shared [107]. Sharing of burrows is more common for desert tortoises of opposite sexes than for desert tortoises of the same sex [6,75]. Other animals that occur in desert tortoise burrows include white-tailed antelope squirrels (Ammospermophilus leucurus), woodrats (Neotoma spp), collared peccaries (Pecari tajacu), burrowing owls (Athene cunicularia), Gambel's quail (Callipepla gambelii), rattlesnakes (Crotalus spp.), Gila monsters (Heloderma suspectum), beetles (Coleoptera), spiders, and scorpions (Arachnida) [52,55,73,107].

Male desert tortoises tend to use deeper winter burrows (hibernacula) than females in the Sonoran and Mojave deserts [5]. In Sonoran desertscrub of southeastern Arizona, hibernacula used by females were shorter (P<0.02) and had significantly (P<0.01) larger differences between maximum and minimum temperatures than hibernacula used by males [7]. In the Mojave Desert of southern Nevada, male desert tortoises tended to use deep burrows more, and were generally located deeper in burrows, than females, although the average minimum depth of hibernacula used by male and female desert tortoises was similar (35 and 33 inches (89 and 85 cm), respectively) [91]. In the Picacho Mountains, time spent within winter burrows was positively associated with burrow depth [107], suggesting that short burrow depth may promote early emergence of females from hibernation [7] (also see Annual Cycle). The average length of juvenile desert tortoise burrows on a Mojave Desert site in southern California was 20.8 inches (52.7 cm), with active juveniles in significantly (P=0.017) shorter burrows than inactive juveniles [112].

Seasonal trends in burrow use may vary by gender and region. The use of more burrows by females in spring and by males in summer and fall on a site in southern Nevada reflects increased activity of females earlier in the year [91]. In the Sonoran Desert of southern Arizona, the average length of hibernacula was 43 inches (108 cm), significantly (P<0.05) shorter than the average length of summer burrows (64 inches (162 cm)). The author stated that this was opposite the trend observed in the Mojave Desert [107]. Burrows occurred on steep (>45%) slopes on Sonoran Desert sites in Arizona [7]. It has been suggested that desert tortoise use of steep slopes in the Sonoran Desert prevents exposure to thermal sinks, periodic flooding, and damp soil [7,107]. Winter burrows used by desert tortoises tend to occur on south-facing slopes in both the Mojave [73,107] and Sonoran deserts (see [7] and Topography).

Shelter sites are often associated with creosotebush, other shrubs, or rocks. A model based on data from a site in the north-central Mojave in California suggests that desert tortoises tend to avoid areas with very little plant cover [1]. On a site in the southwestern Mojave Desert, 97% of burrows were associated with shrubs, and 71% were partially or completely under a creosotebush. Most of the remaining burrows were associated with white bursage or big galleta [9]. In the Mojave of southern Nevada, most desert tortoise burrows greater than 3 feet (1 m) deep were under boulders (50.8%). Deep burrows were also under caliche (25.7%) or shrubs (13.3%). Most burrows less than 3 feet deep were under shrubs (51.4%) or boulders (26.3%) [91]. Throughout the desert tortoise's range, shrubs protect the majority of burrows and pallets, especially those of juvenile desert tortoises [13,95]. Juveniles in a southern California study site were only rarely observed in the open [112].

Nests: Desert tortoises often lay their eggs in nests dug in sufficiently deep soil at the entrance of burrows [6,6,38,55,81,107] or under shrubs [38,55]. In paloverde-mixed cactus vegetation in Arizona, nest burrows faced north and were on 20° to 30° slopes [81], and in the Picacho Mountains the few eggshells and hatchlings observed were in burrows in washes at the base of the mountains [107]. Nests are typically 3 to 10 inches (8-25 cm) deep [38]. For more information regarding nest construction and other egg laying behaviors, see Grover and DeFalco [55].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Cover Requirements: Soil

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More info for the terms: caliche, cover, density, tree

Soil: Due to the importance of burrows for shelter, reduction of water loss, and regulation of body temperature, soil characteristics may have a strong influence on desert tortoise density and distribution [9,114]. Burrow construction requires soil that crumbles easily during digging and is firm enough to resist collapse. Desert tortoises commonly use sites with sandy loam soils with varying amounts of gravel and clay, and tend to avoid sands [55,73,95]. One explanation for fewer desert tortoise burrows than expected in a big galleta-white bursage community in the southwestern Mojave Desert was that sandier soils (90% sand) in these areas may have inhibited burrow construction [9]. However, sands are used by desert tortoises in stabilized dunes in the Pinto Basin of Joshua Tree National Park [73]. A model based on data from the north-central Mojave suggests that desert tortoises avoid stony soils and tend to use sites with loamy soils [1]. Although hardpans (i.e., caliche layers) can limit desert tortoise burrowing [114], dens are sometimes constructed under exposed caliche layers in wash banks [55]. For more information on desert tortoise shelter sites, see Cover Requirements.

A comparison of soil maps and desert tortoise distribution and density in southern Nevada suggested that the following soil characteristics were negatively related to desert tortoise abundance: low available water-holding capacity, shallow (<40 inches (100 cm)) depth to a limiting layer, fragments larger than 3 inches (8 cm) on the surface, excess salts, soil temperatures below 59 °F (15 °C) at 20-inch (51 cm) depths, and soils prone to flooding. These factors may directly interfere with desert tortoise den construction and/or reduce cover and forage availability [114]. Because desert tortoises may consume soil to maintain adequate calcium levels (see Food Habits), they may prefer sites with high soil calcium content [9,55].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Cover Requirements: Topography

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Topography: Desert tortoises in the Mojave occur on valley bottoms much more frequently than desert tortoises in the Sonoran and Sinaloan regions ([7,8,46], reviews by [49,55,98]). Sites in the Mojave near Goffs, California and Las Vegas, Nevada, had slopes of 4% or less, while Sonoran Desert sites had slopes of over 40% [55]. In winter desert tortoises used 41% to 80% slopes of the Picacho Mountains more than expected and 0% to 20% slopes less than expected based on availability [8].

Desert tortoises tend to use south-facing slopes, although they also use other aspects. In a community of mixed grasses, catclaw acacia, and velvet mesquite in southern Arizona, aspect at Sonoran Desert tortoise burrows averaged 182 °S. Desert tortoises showed a significant (P<0.0005) preference for south-facing burrow entrances [75]. In paloverde-creosotebush-saguaro habitat in southeastern Arizona, most desert tortoises hibernated in burrows on south-facing slopes [7]. A model developed to predict important features of their habitat suggests that desert tortoises in the north-central Mojave Desert tend to use southwest-facing slopes and avoid north-facing slopes [1]. Although not significantly different from random locations, most desert tortoise burrows faced south on a site that transitioned from Mojave to Sonoran Desert vegetation [72]. Desert tortoises also used south-facing bajadas in southern California. However, use of northern and northwestern aspects in Pima County, Arizona, was also reported [55]. In the Picacho Mountains, desert tortoise used different aspects throughout the year and avoided (P<0.001) south-facing slopes in winter [107]. Most desert tortoise burrows on a site in Nevada occurred on north-, northeast-, and east-facing slopes (Burge 1978, cited in [72]).

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Density and home range

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Density and home range: Estimates of desert tortoise densities vary from less than 8 individuals/km&sup2 on sites in southern California [11] to over 500 individuals/km&sup2 in the western Mojave Desert (Marlow, personal communication cited in [73]), although most estimates are less than 150 individuals/km&sup2 [6,11,28,50,55,95,114]. Of 29 sites in California, 8 sites had densities less than 8 individuals/km&sup2, 6 sites had densities from 8 to 39 individuals/km&sup2, and 13 had densities from 42 to 184 individuals/km&sup2 [11]. Densities of desert tortoises at several locations are provided in the following reviews: [38,55]. For information on changes to population densities, see Status.

The often overlapping home ranges of desert tortoises generally average from 10 to 100 acres (4-40 ha) [5,8,10,37,38,44,75,86], although average home ranges as small as 2.2 acres (0.9 ha) [37] and as large as 131 acres (53 ha) (Berry 1974a, cited in [10]) have been observed. Variations in home range sizes are likely due to differences in gender, season, and the availability of resources.

Males may have larger home ranges than females in some areas. For example, during the second breeding season following translocation to a site in southern Nevada, the home range of male desert tortoises averaged 63 acres (25.5 ha), which was significantly (P=0.0315) larger than the female desert tortoise average home range size of 22 acres (8.9 ha) [44]. In a creosotebush-white bursage community of the south-central Mojave Desert, male home ranges were significantly (P<0.001) larger than those of females on 2 sites surveyed in a drought year and on 1 of the 2 sites surveyed in a year of above-average precipitation [37]. On 2 of 3 sites in the Mojave Desert, the home range size of male desert tortoises was significantly (P≤0.05) larger than the size of female home ranges [45]. When home range data from Nevada were combined with data collected from 2 other studies, one in the Mojave and the other in the Sonoran Desert, male home range size was significantly (P≥0.003) larger than female home range size [86]. Studies with small sample sizes found no differences in the size of male and female home range size in the Sonoran Desert [8,75]. In extreme southwestern Utah, reproductive female desert tortoises had home ranges that averaged 124 acres (50 ha), while home ranges of nonreproductive female desert tortoises averaged 33 acres (13.5 ha). However, this difference was not significant [78]. Home range size was not related to desert tortoise size in either the Picacho Mountains [8] or the Desert Tortoise Conservation Center in Nevada [86].

Home range size may vary in relation to rainfall and season, with home range size increasing with increasing resources. Desert tortoises on 2 creosotebush-white bursage sites in the south-central Mojave had significantly (P<0.001) smaller home ranges in a year with 25% of average precipitation compared to a year with 225% of average precipitation [37]. Females on a Mojave Desert site in California that received 4.8 inches (122 mm) of rain had significantly (P≤0.05) larger home ranges than those on the site that received 1.1 inch (29 mm) of rain. However, this relationship was not observed the following year when the sites received 7.6 inches (192 mm) and 4.2 inches (108 mm) of rain, respectively. Results suggest that home range size may be larger when resources are most abundant [45]. Areas used from summer to fall were larger than those used from winter to spring on a Sonoran Desert site (P=0.0002) [75]. A review notes similar trends on several other sites in Arizona [5].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Distribution

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Desert tortoises occur from extreme southwestern Utah and southern Nevada south through southeastern California, western and southern Arizona, and most of Sonora to northern Sinaloa, Mexico [12,38,43,46,49,55,73,95]. They may occur in extreme southwestern Chihuahua, Mexico, but are unlikely to occur in Baja California [28,46]. Due to several differences including variation in life history, habitat selection, and population status across their range, the desert tortoise's distribution is often split into subregions. Subregions typically include the Sonoran Desert, the eastern and western portions of the Mojave Desert, and the Sinaloa region ([27,49], reviews by [98,104]). In this review, populations from these regions are referred to as "Mohave desert tortoises", "Sonoran desert tortoises", and "Sinaloan desert tortoises". The term "Sonoran desert tortoise" includes tortoises from the Colorado subdivision of the Sonoran Desert (Colorado Desert) in southeastern California. A map of the desert tortoise's distribution can be found at the website for the conference Impacts of Climate Change and Land Use in the Southwest. Despite declines in population densities in many areas (see Status), information available as of 2008 suggests that desert tortoise's distributional area has not declined.
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Fire Management Considerations

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More info for the terms: fire regime, fire suppression, fuel, grassland, nonnative species, prescribed fire, shrub

Given the sensitivity of desert tortoises to the direct and indirect impacts of fire (see HABITAT RELATED FIRE EFFECTS), exclusion of fire from desert tortoise habitat is widely recommended [22,23,40,117]. To mitigate the potential negative impacts of fire suppression on desert tortoises and their habitat, the following practices have been recommended [36,53]:

  • determine sensitive areas that should be excluded from high-intensity uses such as fire camps
  • drive on the road whenever possible
  • have someone watch for desert tortoises when driving off-road
  • minimize ground disturbance
  • leave unburned vegetation intact whenever possible

The occurrence of fire in desert tortoise habitat can be minimized by reducing human ignitions [22,23] and preventing nonnative grasses from establishing and/or becoming dominant [21,23]. A review notes that public education and regulations help limit human-caused ignitions, but acknowledges that increasing human populations will make reductions difficult. Actions that can be taken to prevent the establishment and spread of nonnative species include reducing disturbance, monitoring areas where nonnative plant species are likely to establish, and controlling newly established populations while small. On sites where nonnative grasses have already established, options are more limited due to the likelihood that fuel reduction techniques, such as prescribed fire and grazing, will have negative effects on desert tortoises [22].

Tips for mitigating the impact of nonnative plants on the fire regime include restricting land uses that increase dominance of nonnative species and creating firebreaks to prevent the spread of fire into desert shrub vegetation [21]. Early season prescribed fire in conjunction with planting native species may help restore habitat and reduce fuel loads in areas already converted to nonnative grassland with a high probability of recurrent fire. However, Brooks and others [22] do not include details of implementing such fires, and these practices are not recommended for sites where desert tortoises still occur.
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Fire Regime Table

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Food Habits

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More info for the terms: forb, forbs, fresh, herbaceous, natural, nonnative species, phenology, selection, shrubs

The desert tortoise diet is variable. Reviews cited in this section provide helpful compilations of available information. Van Devender and others [106] review the diet of desert tortoises in the Sonoran Desert and northern Sinaloa, Mexico, including a list of plant species eaten by Sonoran desert tortoises with the site and year of observation. Oftedal [87] provides a list of major forage species including their seasonality, growth form, and regions of importance. Brief summaries of several diet studies are included in Grover and DeFalco [55]. Desert tortoise Foraging behaviors are described by Grover and DeFalco [55] and Vaughn [107].

Desert tortoises are herbivores with a varied diet of primarily grasses and forbs. Although nonnative species generally do not comprise a major portion of the desert tortoise's diet, some can be important components. Plant species composition of the desert tortoise's diet is likely influenced by plant community composition, plant phenology, rainfall, and nutritional quality.

Desert tortoises forage on the leaves, stems, flowers, fruits, and seeds of a variety of grass and forb species. Although the 5 most abundant species comprised over 60% of the diet in all cases, desert tortoises have been observed foraging on 32 plant species on a site in northwestern Arizona [39], 44 species on a site in the western Mojave Desert of California [64], 50 or more species on sites in the Sonoran Desert of Arizona [74,107], and 79 plant species in blackbrush-dominated habitats in Utah [39]. Most of these species are annuals and herbaceous perennials [39,59,64,74,107]. Several reviews note the importance of annuals in the diet of desert tortoises [38,55,73,106]. At the Desert Tortoise Research Natural Area in California, Mojave desert tortoises most often ate the leaves, stems, and flowers of annuals and herbaceous perennials, but occasionally selected seeds. Selection of plant parts varied with species [64]. The only vegetative portion of plants Luckenback [73] observed desert tortoises eating were the pads of beavertail prickly-pear (Opuntia basilaris). In a community comprised of several grasses, catclaw acacia, and velvet mesquite in southern Arizona, desert tortoises ate the fruits and seeds of a variety of plant species and browsed the leaves of a few species [74]. Cutleaf filaree (Erodium cicutarium) [39,64,88,107], plantains (Plantago spp.) [39,74,88], and milkvetches (Astragalus spp.) [64,73,74] comprised a substantial proportion of desert tortoise diets at sites in both the Sonoran and Mojave deserts. In the Sonoran Desert, lupines (Lupinus spp.) [74,107], threeawns (Aristida spp.), gramas (Bouteloua spp) [74,106], slender janusia (Janusia gracilis), and mallows (Hibiscus spp., Abutilon spp., and Sida spp.) [106] were important components of the diets of desert tortoises on more than one site. Evening primroses (Camissonia and Oenothera spp.) [64,73,88] and red brome [39,74] comprised a substantial portion of Mojave desert tortoise diets. Other species consumed on Mojave Desert sites included phacelia (Phacelia spp.) [64,73], desert dandelions (Malacothrix spp.) [73,88], and big galleta [9,73]. Desert tortoises also forage on spurges (Euphorbiaceae), including narrowleaf silverbush (Argythamnia lanceolata) [106,107] and Euphorbia spp. [74] in the Sonoran Desert and white-margin sandmat (Chamaesyce albomarginata) in the Mojave Desert [64]. Shrubs [107] and the pads and fruits of prickly-pears (Opuntia spp.) [55,73,74,103,106,117] are occasionally important components of the desert tortoise's diet.

Some nonnative species may be important components of desert tortoise diets. As noted above, cutleaf filaree was commonly used in both the Mojave and Sonoran deserts [39,88,107], and red brome commonly occurred in the diets of Mojave desert tortoises [39,56,73]. Common Mediterranean grass was an important species in the diet of desert tortoises near Goffs, California [59], and in extreme northwestern Arizona [39]. In contrast, in the central Mojave, desert tortoises consumed only 0.02% of the Mediterranean grass plants encountered [88]. As the diversity of annual species increased in the northeastern Mojave Desert, the prevalence of nonnative plants in the diet declined [39]. In a western Mojave Desert study area, 78% of the diet was comprised of 9 native species that occurred at very low densities. On this site cutleaf filaree was the only nonnative species eaten, and it accounted for 3.3% of observed bites taken by desert tortoises [64]. A nutrition experiment comparing native smooth desert dandelion (Malacothrix glabrata) and Indian ricegrass (Achnatherum hymenoides) with nonnative cutleaf filaree and common Mediterranean grass found that life form (forb or grass) and phenological stage were, in most cases, more strongly related to plant nutritional value than geographic origin, with the fresh forbs being more nutritious than dried grasses in several respects [82].

Phenology influences desert tortoise forage availability, through its influence on plant species availability and productivity. While annual plants are available during spring, they comprise a large portion of the desert tortoise's diet [39,64,107]. Annual forbs were a larger component of the diet in the early spring than late spring and summer in the northeastern Mojave Desert [39], and annual plants comprised more of the desert tortoise's diet in spring and summer than in fall in Sonoran desert scrub of southern Arizona [107]. Grasses were a larger component of the diet in late spring than in early spring in the northeastern Mojave Desert [39] and comprised a larger portion of the diet in the summer and fall than in spring in a Sonoran Desert community comprised of several grasses, catclaw acacia, and velvet mesquite [74]. In Sonoran desert scrub in southern Arizona, the proportion of forbs decreased during the course of the year and the use of shrubs increased, peaking in the fall at 78% of total dry weight [107].

Rainfall may also influence desert tortoise diet. In the Mojave Desert of California, fewer annuals were eaten in spring and more prickly-pear were eaten in the summer of a year when less than 1.6 inches (400 mm) of precipitation fell from September to March than in spring and summer of the previous year, when between 2.6 and 3.0 inches (670 and 750 mm) of precipitation fell in the same timeframe. Biomass production was much greater in the year with higher rainfall [103]. In the eastern Mojave Desert of southern Nevada, annual biomass production was positively correlated with rainfall on 2 sites [70]. On 2 sites in the eastern and western Mojave Desert, energy acquisition by desert tortoises was constrained by rainfall through its impact on food availability and the apparent requirement for free-standing water [89]. The number of plant species available was inversely related with consumption of nonnative plants in the northwestern Mojave Desert [39]. The impacts of the amount and timing of rainfall on species composition of forage plants are summarized by Oftedal [87]. Reduced plant biomass during drought years may at least partially explain instances of lower desert tortoise reproduction and survival in drought years.

The relative water, protein, and potassium content of plants may influence forage species selection due to desert tortoise's need to retain water and protein and excrete potassium [88]. Food items selected by desert tortoises in the western Mojave [64] had combinations of these nutrients that were more nutritious than those of the most abundant species [87]. Examples of species that have high nutritional value in this regard are primroses (Onagraceae), cutleaf filaree, legumes (Fabaceae), mustards (Brassicaceae), and spurges (Euphorbaceae) [87]. For mineral and nutrient content of desert tortoise forage species from the northeast Mojave Desert and a discussion of the importance of moisture content on these values, see McArthur and others [76]. Consumption of bones, feces, and soil by desert tortoises may provide supplemental calcium, water, and/or other nutrients [39,55,108]. Nagy and others [85] suggest that desert tortoises with a body mass to shell volume of 0.64 g/cm&sup3 are in good condition.

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Habitat-related Fire Effects

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More info for the terms: avoidance, cactus, cover, density, fire frequency, fire occurrence, fire regime, fire severity, forest, frequency, fuel, grass/fire cycle, grassland, long-term effects, nonnative species, severity, shrub, shrubland, shrubs, tree

Since most native shrubs in desert tortoise habitat are not fire-adapted, fire in desert tortoise habitat would likely result in reduction of plant cover and the diversity of forage species. Alterations to the fire regime, such as increased ignitions and the potential for conversion of habitat into nonnative grasslands, are major threats to desert tortoises.

Most shrubs that protect desert tortoises from temperature extremes and predators (see Cover Requirements) are killed or top-killed by fire [22,24,36,40,42]. The year following a fire in the Mojave Desert of southern California, cover in burned areas was about 3% of cover in unburned areas [68]. Fire-caused mortality rates of creosotebush are often over 60% [26,34,77]. White bursage experienced 89% mortality after a fire in the Coachella Valley in California [26]. Several other plant species in desert tortoise habitat are sensitive to fire, including saguaro, yellow paloverde, and blue paloverde [31,93,94]. High mortality of several desert shrub species was observed after prescribed fires in a buffelgrass community of central Sonora, Mexico [63]. For a review of this study, see its Research Project Summary. Many other plant species in desert tortoise habitat are at least moderately sensitive to fire, including Joshua tree, Mojave yucca, ocotillo, blackbrush, white burrobrush, catclaw acacia, Anderson wolfberry, barrel cactus, and big galleta. A review summarizes the effects of fire on plant species in the low-elevation desert shrubland zone of southern California [24].

Potential long-term effects of reduced cover include increased nonnative plant species (see Fire ecology), increased erosion, changes in species composition, and altered habitat structure [42].

Fire could also result in short-term declines in the availability of some forage species, potentially reducing diversity of high quality food species and/or the availability of forage species throughout the desert tortoise's active period [22]. Although increases in nonnative grasses following fire (See Fire ecology) could increase forage availability, the associated decline in forage species diversity is likely to detrimentally affect desert tortoises in the long term [40].

High-severity fires, repeated fires, and/or fires during the desert tortoise's active period will likely have greater indirect impacts on desert tortoises than low-severity, infrequent, and/or dormant-season fires. Similarly to direct fire effects, fires occurring while desert tortoises are active would probably have greater indirect impacts due to decreased cover and food availability. Fire severity is likely to influence the impacts on desert tortoise habitat, with greater shrub mortality and lower sprouting rates following more severe fires. Repeated burning would have greater negative impacts on plant species used by desert tortoises for cover and would likely increase nonnative species abundance [22] (see Fire ecology).

Fire ecology: Although data on historic FIRE REGIMES in the Mojave and Sonoran deserts are lacking [41,62], the light patchy fuels of the Mojave and Sonoran Deserts suggest long fire-return intervals (see the Fire regime table). Brooks and Minnich [24] summarize information on presettlement FIRE REGIMES in habitats where desert tortoises occur. The seasonality of historic fires in this area is largely unknown.

Contemporary fires in the Mojave and Sonoran deserts generally burn during the summer [22,40,54,96]. Based on southern California fire occurrence data from 1980 to 1995, the peak fire season is from May to August, with July and August having the highest occurrence of fire in the Mojave and May and June having the highest occurrence of fire in the Colorado Desert [22]. Most fires in south-central Arizona occurred in summer, with incidence of smaller (x= 37 acres (14.9 ha)) human-ignited fires peaking in May and larger (x= 111 acres (44.9 ha)) lightning-ignited fires peaking in July [96]. A review of the fire ecology of Sonoran desert tortoises [40] notes that fires generally occur in summer, and Gottfried and others [54] state that fires on their southeastern Arizona study area generally occur before the late summer monsoon rains.

Biomass accumulation due to high rainfall [31,62] increases the fire hazard. A review notes that perennials such as Rothrock's grama (Bouteloua rothrockii) could potentially support fire in desert shrubland after periods of high precipitation [40]. Red brome density appeared to increase following above-average precipitation in southern California from 1992 to 1994 [42]. High precipitation may result in peaks in desert tortoise reproduction. Given the possible importance of periods of high recruitment to long-term desert tortoise population persistence and the vulnerability of young individuals, a review suggests that these fires may have large impacts on desert tortoise populations [22].

Altered FIRE REGIMES: Although reviews note that lightning was the predominant ignition source historically [40,41], in recent decades human-caused ignitions account for the majority of fires in the desert Southwest. Human-ignited fires accounted for almost 66% of fires on the Tonto National Forest of Arizona from 1955 to 1983, with a significant (P<0.05) increase in number of human-started fires during the study period [96]. From 1980 to 1995, 75% of fires on Bureau of Land Management lands in southern California were started by humans [22]. Reviews note that the increase in human-ignited fires, such as those started by campfires, fireworks, and vehicle use, is a threat to desert tortoises [24,40,41] and likely increases the rate of conversion of desert tortoise habitat into nonnative grassland.

Establishment of nonnative grasses, primarily red brome, common Mediterranean grass, and buffelgrass, is altering FIRE REGIMES and habitats in the Mojave and Sonoran deserts. Nonnative grasses provide abundant and continuous fuels, resulting in increased fire frequency. Since these species can increase in dominance following fire, repeated burning can convert native-dominated desert tortoise habitat into nonnative grassland. These grasslands are, in turn, likely to burn repeatedly. Thus, a grass/fire cycle is established. Reviews of the impacts of nonnative grasses on FIRE REGIMES and community composition, including descriptions of the nonnative grass/fire cycle, are available in these sources: [20,21,33,41,92].

    Unburned desert tortoise habitat with high continuity of nonnative grass. Nearby site burned in the 2005 Goodsprings Fire in southwestern Nevada.

Photos by Greg Carttar, 3rd St. R & D Production Services.

Nonnative grasses provide continuous fuel with characteristics that often differ from those of native species. Dried nonnative annual grasses were the only species in the Mojave Desert of southern California to accumulate continuous fuels that persisted into the fire season [19] (also see the Research Project Summary of that study), a trend noted in several reviews [23,40,41,92].

More abundant and continuous fuels have contributed to increased fire frequencies in the desert Southwest. Fires in Joshua Tree National Park have become more frequent and larger since the introduction of nonnative grasses [53]. On the Tonto National Forest of Arizona the estimated amount of time for the entire desert area to burn based on data from 1970 to 1983 was 226 years, substantially lower than the 340-year estimate based on 1955 to 1969 data [96]. The number of fires per year below 4,200 feet (1,280) in the Mojave and Colorado deserts increased significantly from 1980 to 1995 [22]. On some sites in the Mojave Desert, average fire-return intervals have declined from over 30 years to 5 years [23]. However, increased precipitation toward the end of Schmid and Rogers' 1955 to 1983 study period [96], and more human-caused ignitions likely account for at least some of the increase in fire frequency [22,96].

Fire severity may also be altered. Nonnative grasses vary in their contribution to fire severity. Buffelgrass often fuels high-severity fires. A review describes a buffelgrass fire that scorched the soil and cracked bedrock [40]. Brooks [19] found that fire in predominantly Arabian schismus (Schismus arabicus) and common Mediterranean grass burned more slowly, had smaller flame lengths, and resulted in patchier burns than fire fueled by red brome, cheatgrass (Bromus tectorum), and/or Chilean chess (B. berteroanus).

Nonnative grasses often increase in dominance following fires [22,40,41,63,92,94]. Red brome "appeared dominant" after fire on a site in the Sonoran Desert of south-central Arizona [94], and buffelgrass increased after prescribed fires in Sonora, Mexico [63]. See the Research Project Summary of this study for further information. Mediterranean grass (Schimus spp.) increased in biomass and cover following fire on Sonoran Desert sites [31]. See the FEIS reviews of red brome and buffelgrass for information on their responses to fire.

Given the effects of nonnative grasses on fuel loads and the impact fires have on the native and nonnative species in these communities, multiple fires can lead to conversion of desert tortoise habitat into nonnative grassland [22,33,40,41,92]. Ibarra documents the increase of buffelgrass and the decline in native species following prescribed fires on a site in Sonora, Mexico [63]. Although there is little research on the effect of increased cover of nonnative grasses on desert tortoises, a review states that conversion of thornscrub habitat to buffelgrass will "eliminate most desert tortoises" from a site in central Sonora, Mexico. Several factors may contribute to potential desert tortoise avoidance of or exclusion from these areas, including inhibited movement, increased fire-induced mortality, and reduced availability of shelter sites and diverse forage [40].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Life History

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More info for the terms: aestivation, density, hibernation

The desert tortoise is a long-lived species that is slow growing and generally has low reproductive rates. Desert tortoises are inactive during most of the year. Aestivation assists in reducing water loss and exposure to extremely high temperatures during hot, dry periods, and winter hibernation facilitates survival during freezing temperatures and low food availability. Desert tortoises are most active following seasonal rains, when they move through 10- to 100-acre (4-40 ha) home ranges. Individual home ranges often overlap [5,8,10,37,38,44,75].

Desert tortoises tolerate water, salt, and energy imbalances on a daily basis. This ability apparently allows them to use unpredictable and ephemeral resources to meet nutritional requirements over the course of a year [89]. For detailed information on desert tortoise physiology and energetics see these sources: [55,58,59,83,87,89,95,113].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Longevity and survivorship

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Longevity and survivorship: Desert tortoises can live over 30 years and may be able to live more than 50 years [6,38,47,55]. Conservative estimates of maximum life spans were 32 years for individuals in the western Mojave and Sinaloan regions, 35 years for individuals in the Sonoran Desert, and 48 to 53 years for individuals in the eastern Mojave Desert (Germano 1992, cited in [38,47]). There are several reports of wild desert tortoises living more than 50 years [55]. Causes of mortality include predation, disease, human-related factors (see Threats), and environmental factors such as drought, flooding, and fire [11,50,55].

Survivorship of adult desert tortoises is typically over 90%, with lower values generally occurring in western populations [6,70,73,95,103]. In the Ivanpah Valley of southeastern California, annual adult survivorship was 95.6% from 1980 to 1981 [103]. Estimates of annual adult survivorship in 3 Sonoran desert tortoise populations in Arizona were 94% or higher [6]. However, annual adult survivorship as low as 75% has been reported (Turner and Berry, unpublished data cited in [47]), and rates from 80% to 90% are not uncommon [11,47,50,103]. Adult survivorship is generally lower in the western Mojave than in the eastern Mojave or Sonoran deserts [47]. For instance, an estimated 29% of Sonoran, 11% of eastern Mojave, and about 5% of western Mojave desert tortoises live more than 25 years (Germano 1992, cited in [38]). Desert tortoise annual mortality rates in California ranged from 0% to 17.3%, with sites in the western Mojave exhibiting higher mortality rates than those in the eastern Mojave or Sonoran deserts [11].

Young desert tortoises have much lower survivorship than adults. Only 2% to 5% of hatchlings are estimated to reach maturity (Holing 1986, cited in [55]). According to reviews, adult and subadult desert tortoises typically comprise the majority of populations [55,73]. Estimates of survival from hatching to 1 year of age for Mojave desert tortoises range from 47% [51] to 51%. Survivorship of Mojave desert tortoises from 1 to 4 years of age ranges from 71% to 89% [47]. Estimates of survivorship for Sonoran desert tortoises less than 7.1 inches (18 cm) long ranges from 84% to 93%, but these estimates are biased to large individuals. The survival of desert tortoises less than 2 years old is likely lower [6]. In a laboratory experiment, hatchling survival was significantly (P<0.0005) associated with incubation temperature, with over 80% of hatchlings from clutches incubated at 82 °F (28 °C) or 84 °F (29 °C) surviving 277 days, and less than 35% of hatchlings from clutches incubated at 77 °F (25 °C) or 81 °F (27 °C) surviving 277 days [69].

Drought may increase mortality rates of juveniles and adults. Low rainfall and the associated lack of annual plant production were suggested as likely reasons for reduced adult survival on the less productive of 2 sites in the eastern Mojave Desert of southern Nevada [70]. Below-average rainfall and the related reduction in dry standing crop and biomass of grasses in 1981 were probably factors in reduced survival of adult desert tortoises in the Ivanpah Valley in 1981 compared to 1980 [103]. Juvenile desert tortoises are likely more vulnerable to drought than adults [84,113]. See Food Habits for a discussion of impacts of rainfall on forage availability, and Predators for citations that suggest a possible interaction between rainfall, forage production, and rates of predation on desert tortoises.

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Management Considerations

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More info for the terms: competition, cover, density, hibernation, natural, nonnative species, population index

Status: Population declines of 10% or more were reported during the 1980s in the western Mojave and in the Colorado Desert [12,98]. Some of the largest declines occurred at the Desert Tortoise Natural Area in the western Mojave, where densities dropped from an estimated 150 individuals/km&sup2 in 1979 to less than 25 individuals/km&sup2 1992. At Chuckwalla Bench in the eastern Colorado Desert, density declined from about 225 individuals/km&sup2 in 1979 to about 75 individuals/km&sup2 in 1992 [12]. A review of desert tortoise status is provided in Grover and DeFalco [55].

Threats: Desert tortoises are threatened by many, primarily human-caused, factors. These include direct human-caused mortality; increased predation; disease; and habitat degradation from the accumulation of trash [109]; overgrazing; off-road vehicle use; and nonnative grass invasion. Loss and fragmentation of habitat due to urbanization and other development also threaten desert tortoises [55,61,79,98,117]. In 1995, populations in areas of the Mojave and Colorado deserts with comparatively little human activity were generally stable or declining more slowly than populations in areas with high levels of human activity [12]. More detailed reviews of these threats are provided by Howland and others [61] and Grover and DeFalco [55].

Desert tortoise mortalities due directly to humans can be high near human populations. The high percentage of desert tortoise carcasses that had been shot in the western Mojave Desert (20.7%) was likely due to accessibility and proximity to cities [11]. Capture and/or human predation of desert tortoises occur in some regions of Mexico. Although human predation is typically infrequent and impeded by low desert tortoise densities and rough terrain, in a few areas human capture or consumption of desert tortoise may negatively affect desert tortoise populations [46].

Release of captive desert tortoises with upper respiratory disease syndrome, which is typically fatal, into the wild may have resulted in the infection of wild desert tortoises [95,100]. Sonoran desert tortoises have not been as greatly impacted by upper respiratory and other diseases as Mojave populations, possibly due to their relatively lower densities and because they are generally less water stressed [35]. However, disease has been suggested as a cause for drastic declines in some populations in the Colorado Desert [12].

Habitat degradation from overgrazing, vehicle use, and invasion by nonnative grasses may have substantial negative impacts on desert tortoises. Although data on the effects of livestock grazing on desert tortoises are lacking [18,27], the impacts of severe grazing on their habitat suggest that high levels of grazing likely have negative impacts on desert tortoises. Potential effects of intense grazing that could negatively impact desert tortoises include soil compaction, decreased cover of annual plants, introduction of nonnative species, competition for forage, and the potential for trampling desert tortoises and their burrows [55,111,117]. Instances of livestock trampling desert tortoises and/or their burrows are noted in these sources: [30,95,97].

Vehicles also have direct and indirect impacts on desert tortoises. In the western Mojave, desert tortoise sign occurred significantly (P<0.05) less often within 1,300 feet (400 m) of roads than farther from roads. Vehicle-caused mortality was suggested as a likely explanation for the trend [17]. According to reviews, use of off-road vehicles damages habitat [55,97], and the increase in access provided by roads and use of off-road vehicles can exacerbate other human-caused threats such as desert tortoise collection, introduction of weeds and disease, and shooting [55].

Invasion of nonnative grasses and the potential for a nonnative grass/fire cycle pose major threats to desert tortoises (reviews by [12,22,24]). This is further discussed in Fire Ecology.

Climate change may negatively affect the desert tortoise if droughts become more frequent or severe (reviews by [55,59]) or if precipitation increases and results in the spread of nonnative plant species [14].

Population Management: Relocating desert tortoises may augment populations and mitigate negative impacts of development, fragmentation, or other disturbances when implemented appropriately [44,61]. Consideration of the social structure of the resident population and the movements of relocated individuals may increase the likelihood of success [10]. Other considerations when relocating desert tortoises include disease transmission and the genetic relationships of the relocated and resident desert tortoises [61]. Bury and others [27] cite several sources that discuss the instances when relocation is appropriate. Raising young in captivity for release, known as head-starting, may assist in augmenting wild populations. Limitations of head-starting and methods for release are addressed in Germano and others [51]. For information on care of captive desert tortoises, see these reviews: [51,55,105].

Methods used to study desert tortoise populations include radio-tracking [70,75,107], passive intergraded transponder tags [16], and specially trained dogs [29]. Duda and others [37] recommend that monitoring efforts should address variability in desert tortoise activity levels due to season, precipitation level, site, and desert tortoise gender. Temporal and spatial variability in burrow use suggests that the use of burrows as a population index is limited [91].

It has been suggested that management actions that may disturb desert tortoises are best performed in the winter, as desert tortoises are least likely affected when inactive [37]. However, management actions during winter should minimize disturbance of individuals to prevent rousing them from hibernation [90].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Maturation

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More info for the term: cactus

Maturation: Although the desert tortoise is slow-growing, often taking 16 years or longer to reach about 8 inches (20 cm) in length [48], growth rate varies with age, location, gender, and precipitation. Desert tortoises grow comparatively fast when young [6,38,48]. Of growth rates observed in desert tortoises less than 20 years old, the fastest (12.3 mm/year) occurred in 4- to 8-year-old desert tortoises from the western Mojave Desert, and the slowest (6.0 mm/yr) occurred in 16- to 20-year old desert tortoises from the Sinaloan region. Desert tortoises in the western Mojave and Sinaloan deserts generally grow faster than those in the eastern Mojave and Sonoran deserts [48]. Males and females grow at similar rates, although females can grow slightly faster when young [51,102]. Desert tortoise males may grow larger than females (Laderle 1999, cited in [91]). Growth rate of desert tortoises may be related to precipitation. Growth of desert tortoises in Nevada was greatest following winters with high precipitation [102], (Medica and others 1975, cited in [73]). However, Germano [48] found a significant (P<0.001) inverse relationship between the average width of growth rings on the scales of desert tortoise shells and average annual precipitation.

Female desert tortoises in the western Mojave and Sinaloan regions reach reproductive maturity at smaller sizes and younger ages than females in the eastern Mojave and Sonoran deserts. Desert tortoises generally reach reproductive maturity from 15 to 20 years of age and when more than 7 inches (18 cm) in length. Reproductive females as small as 7 inches [28,47] and as young as 10 years old have been observed in the western Mojave Desert. However, reproductive maturity at 13 to 14 years is more common in this area. Estimates of age of reproductive maturity for the Sinaloan region of Mexico are also 13 to 14 years. Average age of reproductive maturity was 15.4 years for females from the eastern Mojave Desert and 15.7 years for females from the Sonoran Desert [48]. The smallest reproductive female in a study on Yucca Mountain, southern Nevada, was 8.2 inches (20.9 cm) [80], and a 7.4-inch (18.9 cm) reproductive female was observed in the eastern Mojave Desert [47]. The smallest reproductive female observed in paloverde-mixed cactus habitat in the Sonoran Desert was 8.7 inches (22.0 cm) long [4].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Predators

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More info for the term: cactus

Desert tortoise eggs and juveniles are more susceptible to predation than adults. Five of 8 desert tortoise nests were preyed upon in paloverde-mixed cactus vegetation of the northeastern Sonoran Desert in Arizona [4]. According to reviews, the smaller size and softer shells of desert tortoises less than about 5 years old make them more vulnerable to predation [55,73]. Known predators of desert tortoise eggs and juveniles include Gila monsters [52,55,73,107], coachwhip snakes (Mastiocophis flagellum) [55,73], and common ravens (Corvus corax) [11,15,38,55,73]. Reviews note predation on eggs and juveniles by kit foxes (Vulpes macrotis), bobcats (Lynx rufus), western spotted skunks (Spilogale gracilis) [55,73], coyotes (Canis latrans), American badgers (Taxidea taxus), ringtails (Bassariscus astutus), and domestic dogs (Canis familiaris) [55]. Potential predators include red-tailed hawks (Buteo jamaicensis), other hawks (Accipitrinae) [6,15,38,73], and greater roadrunners (Geococcyx californianus) [6,15,55]. Coyotes and kit foxes [6,38,55,73] are known predators of adult desert tortoises throughout the desert tortoise's range. Golden eagles (Aquila chrysaetos) may prey on juvenile and adult desert tortoises [11,15,38,55,73]. In the Sonoran Desert, grey foxes (Urocyon cinereoargenteus) and mountain lions (Puma concolor) prey on desert tortoises [6], and in some regions of Mexico jaguars (Panthera onca) prey on desert tortoises [28]. Bobcat, American badger [6,38,55,73], and feral dogs [6,10,38,55] are potential predators of adult desert tortoises.

Higher levels of predation may occur in years with poor plant production and in areas with heavy human use. In years with low rainfall, declines in forage production and associated small mammal populations may result in greater predation pressure on desert tortoises [55,95,103]. Predation rates by common ravens increase with increasing common raven abundance, such as near human development [65]. Desert tortoises close to developed areas are also more likely to encounter domestic dogs [46]. Other threats to desert tortoises near human populations are discussed in Threats.

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Preferred Habitat

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Desert tortoise tend to occur on low- to midelevation sites with soil suitable for den construction and adequate rainfall, including hillsides, bajadas, washes, and valleys. They may also be associated with high plant diversity and/or ecotones [8,9,38,46,98,117].
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Preferred Habitat: Elevation

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Elevation: Desert tortoises are generally most common from around 1,000 to 3,500 feet (300-1,070 m), with higher elevations occupied primarily in the Mojave Desert and lower elevations used throughout the desert tortoise's range. Desert tortoises tend to occur below 2,600 feet (800 m) in the northern and eastern Sonoran Desert and around and below 1,000 feet (300 m) in southern Sonora and northern Sinaloa, Mexico. In the Sonoran Desert, elevations from 1,000 to 1,640 feet (300-500 m) may support more uniform and abundant populations than lower or higher elevations [46]. In the eastern Mojave the desert tortoise's distribution consistently extends up to the 3,940-foot (1,220 m) elevation contour [27]. Desert tortoises are uncommon above 3,000 feet (915 m) around the base of the Sierra Nevada and above 3,300 feet (1,000 m) in the western Mojave Desert [73]. High-elevation mountains also limit desert tortoise distribution in Utah. Desert tortoise apparently prefer elevations from about 980 to 3,500 feet (300-1,070 m) in California, 1,320 (400 m) to 3,500 feet in Nevada, and 2,500 (760 m) to 3,500 feet in Utah [55]. However, it has been suggested that increased search effort at higher elevations in the eastern Mojave Desert may uncover greater use of these areas than previously reported [27]. Reasons for less use of high-elevation areas in the southern than in northern portions of their range are unknown but may be related to aspect, soil [46], and/or the potential detrimental impacts of excessive moisture [28].

Despite typically being found at low- to midelevations, reviews note desert tortoises occurring from below sea level in Death Valley [55] and near sea level in Mexico [28] to elevations over 7,200 feet (2,200 m) in Death Valley National Monument ([55] and Sanchez, personal communication cited in [73]). In the eastern Mojave, desert tortoises were located at maximum elevations from 4,100 to 5,250 feet (1,250-1,600 m) [27]. Most desert tortoises on a Yucca Mountain study site were found at elevations from 3,300 to 4,270 feet (1,000-1,300 m) [91]. According to unpublished Arizona Game and Fish data (cited in [3]), desert tortoises occurred on sites as high as 5,300 feet (1,615 m) in Arizona. A single desert tortoise was observed at 7,640 feet (2,328 m) in ponderosa pine-dominated habitat of Saguaro National Park. It is possible, though unlikely, that this individual was transported to the remote location [3].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Preferred Habitat: Plant species composition

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Plant species composition: The plant species important to desert tortoises likely vary with location. Near Twentynine Palms, California, 71% of desert tortoise burrows were associated with creosotebush, and desert tortoises avoided the only community without creosotebush. Desert tortoises rarely used the interior portion of the creosotebush-white bursage community, possibly due to the lack of big galleta, a potentially important component of their diet [9]. Burrows on a site that transitioned from Mojave to Sonoran Desert vegetation were not significantly closer to creosotebush than random sites. Burrows were significantly (P=0.04) farther from yucca (Yucca spp.) than random sites [72]. In southern Nevada, however, burrows were frequently associated with Mojave yucca (Y. schidigera) and catclaw acacia despite the relative rarity of these species (Burge 1978, cited in [72]).

In the southwestern Mojave, desert tortoises selected communities with high plant species diversity and ecotones between communities [9]. Desert tortoises were captured in a diverse wash community significantly (P<0.005) more than expected based on a random distribution. Their burrows were also significantly (P<0.0005) closer to ecotones than a set of random points. Use of high-diversity areas and ecotones may be related to increased food availability and/or the importance of plant species that cooccur in ecotones between communities [9].

The nonnative grasses invading desert tortoise habitat, such as red brome (Bromus rubens), common Mediterranean grass (Schismus barbatus), and buffelgrass (Pennisetum ciliare), have the potential to reduce habitat availability. These species can alter fuel characteristics, primarily increasing the continuity of fuels ([19], reviews by [23,40,41,92]). Greater fuel continuity can increase fire frequency ([53,96], reviews by [22,23,92]) and, in the case of buffelgrass, the fuels have the potential to increase fire severity [40]. Since these grasses are more tolerant of fire than native plant species in desert tortoise habitats, they can increase in dominance following fire ([31,63,94], reviews by [22,40,41,92]). According to reviews, these grass/fire cycles [20] can lead to the eventual conversion of desert tortoise habitat to nonnative grassland [22,33,40,41,92]. For more detail on the effects of nonnative grasses on FIRE REGIMES in desert tortoise habitat and the impact of these changes on desert tortoises, see Altered FIRE REGIMES.

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Preferred Habitat: Water availability

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Water availability: The annual precipitation in desert tortoise habitat is extremely variable and averages 4.9 inches (125 mm). The creosotebush communities that provide typical Mojave desert tortoise habitat generally receive from 2 to 8 inches (50-200 mm) of rain each year. Most precipitation falls in winter in the western Mojave; summer precipitation is more common in the eastern Mojave and Sonoran deserts [55]. In the eastern Mojave Desert of southwestern Utah and northwestern Arizona, plant moisture content was highest in spring [76]. A review notes that summer rainfall is often localized in the eastern Mojave and Sonoran deserts [87].

Desert tortoises may be associated with washes on some sites. In the southwestern Mojave Desert near Twentynine Palms, California, a high level of desert tortoise activity was observed near washes. Burrows were generally associated with washes, although the relationship was not statistically significant. Use of washes as travel corridors and availability of diverse plant species (see Plant species composition) may explain this trend [9]. Winter burrows of desert tortoises in southwestern Utah tended to occur in the banks of washes [116]. Burge (1978, cited in [9]) found a high occurrence of burrows associated with desert washes in southern Nevada. Although only a few eggs and hatchlings were observed in the Picacho Mountains, they were all found in washes [107].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Reproduction

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More info for the terms: cactus, natural

Reproduction: Each year female desert tortoises in the Mojave Desert lay 0 to 3 clutches, and those in the Sonoran Desert lay 0 or 1 clutch, with clutches typically comprised of 4 to 6 eggs [4,6,78,80,81,101]. Both Mojave and Sonoran desert tortoise females may increase egg production in years of above-average rainfall [6,101]. Trends associated with Mojave desert tortoise egg production include more eggs in clutches when fewer clutches are laid [80,101,110] and large Mojave desert tortoise females laying more eggs per year, more clutches, and more eggs per clutch than small females [78,80,101,110]. Available information suggests that less than 75% of desert tortoise eggs typically hatch [47,73,78,101]. The sex ratio of desert tortoise populations is usually around 1:1 [6,11,55,103,107], but instances of female-biased and male-biased sex ratios have been reported [6,50].

Desert tortoises in the Mojave lay more clutches per year than those in the Sonoran Desert. Sonoran desert tortoises lay a maximum of 1 clutch each year [4,6,81]. In paloverde-mixed cactus habitat in the northeastern Sonoran Desert of Arizona, from 36% to 80% of females reproduced each year during a 4-year period [4]. In contrast, Mojave desert tortoises lay up to 3 clutches a year and typically average between 1 and 2 clutches per reproductive female per year [78,80,101,103]. Near Goffs, California, desert tortoises most often laid 1 or 2 clutches per year, although females laying 0 and 3 clutches were observed [101]. Reported average annual number of clutches per female in the Mojave Desert range from 1.1 [103] to 1.89 [101]. Females that laid 2 clutches on a Mojave Desert site in Nevada laid their first clutch significantly (P<0.001) earlier than females that laid only 1 clutch [80]. On 2 southern California sites greater annual egg production was associated (P<0.05) with early first clutches [110].

Desert tortoises's clutches typically average 4 to 6 eggs [4,6,78,81,101], although clutches of 1 to 15 eggs have been reported [6,38,47,55,73]. Average clutch sizes of desert tortoises in paloverde-mixed cactus habitat in the northeastern Sonoran Desert ranged from 3.8 to 5.7 eggs. The author suggests that this is smaller than typical clutches from the Mojave Desert [4]. Average clutch size of desert tortoises was 5.2 eggs on a site in extreme southwestern Utah [78] and 4.5 eggs near Goffs, California [101]. On 2 sites in southern California, larger desert tortoise clutches were comprised of smaller eggs [110].

Productivity may be greater in years with above-average rainfall than in years with little rainfall. In southeastern California, the annual average number of clutches per reproductive female was higher in years with above-average winter rainfall [101], and the percentage of reproductive desert tortoises was low following nearly 10 years of drought in the Maricopa Mountains in southern Arizona (Wirt and Holm 1997, cited in [6]). Averill-Murray and others [6] discuss the influence of rainfall on desert tortoise productivity and summarize preliminary data that suggest a greater proportion of smaller desert tortoises breed and clutches are larger in years with high rainfall.

Females in the Mojave Desert that lay fewer clutches tend to lay more eggs per clutch [80,101,110]. On 2 sites in southern California, females that laid one clutch had significantly (P<0.05) larger first clutches than females that laid more than one clutch [110]. On a site at Nevada's Yucca Mountain, single-clutch females laid an average of 0.9 egg more than 2-clutch females [80].

The size of female Mojave desert tortoises may influence the number of clutches laid, the size of clutches, and the number of eggs laid per year [78,80,101,110]. Large female body size was associated with increased number of eggs produced per year in southwestern Utah [78], Yucca Mountain [80], and southern California populations [110]. Larger females laid larger clutches at Yucca Mountain [80] and at 2 sites in southern California [101,110]. In contrast, the clutch size of Sonoran desert tortoises does not appear related to female body size [4,6,81]. Although large females on 2 sites in southern California tended to lay more clutches than small females [101,110], there was no relationship between female size and number of clutches laid by females on a Yucca Mountain site [80]. Egg size was positively associated with female size in paloverde-mixed cactus habitat in the Sonoran Desert of Arizona [4] and in the Desert Tortoise Natural Area of southern California [110].

Desert tortoise hatching rates of less than 75% are common [47,73,78,101]. Of 71 eggs protected from predators after being laid by wild desert tortoises on a southwestern Utah site, 52 hatched [78]. Of 57 eggs collected from southern California nests and moved to predator-proof locations, 26 hatched by 31 October and 17 "seemingly viable" eggs did not hatch by 3 May of the following year [101]. According to a review, estimates of the percentage of eggs that produce hatchlings in the eastern Mojave Desert ranged from 46% to 67% [47]. Luckenback [73] notes that hatching rates in captivity are often near 60% but can be over 80%. In a laboratory experiment, temperature influenced hatching rates and hatchling gender [69]. Incubation temperatures from 81 to 88 °F (27-31°C) resulted in hatching rates of 83% or more, while incubation at 77 °F (25 °C) resulted in a 53% hatching rate. Incubation temperatures less than 88 °F (31 °C) resulted in all male clutches [69].

For discussion of desert tortoise social behavior, including courtship, mating, dominance hierarchies, nest defense, and defensive behaviors of juveniles, see Vaughn [107] and the following reviews: [10,38,55].

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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Synonyms

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Xerobates agassizii (Cooper) [8,98]

Scaptochelys agassizii (Cooper) [103]
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Taxonomy

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Gopherus agassizii (Cooper) is the scientific name of the desert tortoise,
a member of the Testudinidae family [33]. According to a review, populations north
and west of the Colorado River are generally accepted as a taxonomic unit
separate from those south and east [20]. Two reviews [40,56] include
information on desert tortoise taxonomy and genetics.
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

U.S. Federal Legal Status

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The desert tortoise is generally listed as Threatened. Mexican populations, and those south and east of the Colorado River in Arizona, are listed as Similarity of Appearance (Threatened). The Mojave Desert population is Under Review for an emergency uplisting to Endangered [104].
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Meyer, Rachelle. 2008. Gopherus agassizii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis/animals/reptile/goag/all.html

Distribution

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Continent: Middle-America North-America
Distribution: USA (S Nevada, SW California, W Arizona), Mexico (N Baja California, W Sonora including Tiburon Island in the Gulf of California, NW Sinaloa) Xerobates lepidocephalus: Sierra San Vincente region, approx. 1.5 km north of the Buena Mujer Dam, 20 km (by air) south of La Paz, Baja California Sur, Mexico.
Type locality: mountains near Fort Mojave, California.
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Desert tortoise

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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.[4] G. agassizii is distributed in western Arizona, southeastern California, southern Nevada, and southwestern Utah.[4] The specific name agassizii is in honor of Swiss-American zoologist Jean Louis Rodolphe Agassiz.[5] The desert tortoise is the official state reptile in California and Nevada. [6]

The desert tortoise lives about 50 to 80 years;[7] 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.[8]

Taxonomy

In 2011, on the basis of DNA, geographic, and behavioral differences between desert tortoises east and west of the Colorado River, it was decided that two species of desert tortoises exist: Agassiz's desert tortoise (Gopherus agassizii) and Morafka's desert tortoise (Gopherus morafkai).[9] The new species name is in honor of the late Professor David Joseph Morafka of California State University, Dominguez Hills, in recognition of his many contributions to the study and conservation of Gopherus. G. morafkai occurs east of the Colorado River in Arizona, as well as in the states of Sonora and Sinaloa, Mexico. The acceptance of G. morafkai reduced the range of G. agassizii by about 70%[10] In 2016, based on a large-scale genetic analysis, ecological and morphological data, researchers proposed a split between the Sonoran and Sinaloan populations. This southernmost member of the Gopherus genus was named G. evgoodei, Goode's thornscrub tortoise.[11]

Description

These tortoises may attain a length of 25 to 36 cm (10 to 14 in),[12] with males being slightly larger than females. A male tortoise has a longer gular horn than a female, his plastron (lower shell) is concave compared to a female tortoise. Males have larger tails than females do. Their shells are high-domed, and greenish-tan to dark brown in color. The high domes of their shells allow for space for their lungs, which helps them maintain thermoregulation, also known as maintaining internal temperature.[13] Desert tortoises can grow to 10–15 cm (4–6 in) in height. They can range in weight from 8 to 15 pounds, or 3.5 kg to 7 kg.[14] The front limbs have sharp, claw-like scales and are flattened for digging. Back legs are skinnier and very long.

Habitat

Desert tortoises can live in areas with ground temperatures exceeding 60 °C (140 °F)[15] because of their ability to dig burrows and escape the heat. At least 95% of their lives are spent in burrows. There, they are also protected from freezing winter weather while dormant, from November through February or March. Within their burrows, these tortoises create a subterranean environment that can be beneficial to other reptiles, mammals, birds, and invertebrates.

Scientists have divided the desert tortoise into three species: Agassiz's and Morafka's desert tortoises,[16] with a third species, Goode's thornscrub tortoise, in northern Sinaloan and southern Sonora, Mexico.[11] An isolated population of Agassiz's desert tortoise occurs in the Black Mountains of northwestern Arizona.[16] They live in a different type of habitat, from sandy flats to rocky foothills. They have a strong proclivity in the Mojave Desert for alluvial fans, washes, and canyons where more suitable soils for den construction might be found.[17] They range from near sea level to around 1,050 m (3,500 ft) in elevation. Tortoises show very strong site fidelity, and have well-established home ranges where they know where their food, water, and mineral resources are.

Desert tortoises inhabit elevations from below mean sea level in Death Valley to 1,600 m (5,300 ft) in Arizona, though they are most common from around 300 to 1,050 m (1,000 to 3,500 ft). Estimates of densities vary from less than 8/km2 (21/sq mi) on sites in southern California to over 500/km2 (1,300/sq mi) in the western Mojave Desert, although most estimates are less than 150/km2 (390/sq mi). The home range generally consists of 4 to 40 hectares (10 to 100 acres). In general, males have larger home ranges than females, and home range size increases with increasing resources and rainfall.[8]

Desert tortoises are sensitive to the soil type, owing to their reliance on burrows for shelter, reduction of water loss, and regulation of body temperature. The soil should crumble easily during digging and be firm enough to resist collapse. Desert tortoises prefer sandy loam soils with varying amounts of gravel and clay, and tend to avoid sands or soils with low water-holding capacity, excess salts, or low resistance to flooding. They may consume soil to maintain adequate calcium levels, and may prefer sites with higher calcium content.[8]

With the creation of off-road vehicles more humans are making their way in and out of the desert tortoises' home environment.[18]

Shelters

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, rock shelters are spaces protected by rocks and/or boulders, and pallets are depressions in the soil. The use of the various shelter types is related to their availability and climate. The number of burrows used, the extent of repetitive use, and the occurrence of burrow sharing are variable. Males tend to occupy deeper burrows than females. Seasonal trends in burrow use are influenced by desert tortoise sex and regional variation. Desert tortoise shelter sites are often associated with plant or rock cover. Desert tortoises often lay their eggs in nests dug in sufficiently deep soil at the entrance of burrows or under shrubs. Nests are typically 8 to 25 centimetres (3 to 10 inches) deep.[8]

Shelters are important for controlling body temperature and water regulation, as they allow desert tortoises to slow their rate of heating in summer and provide protection from cold during the winter. The humidity within burrows prevents dehydration. Burrows also provide protection from predators. The availability of adequate burrow sites influences desert tortoise densities.[8]

Each desert tortoise uses about 5 to 25 burrows per year. Some burrows are used repeatedly, sometimes for several consecutive years. Desert tortoises share burrows with various mammals, reptiles, birds, and invertebrates, such as white-tailed antelope squirrels (Ammospermophilus leucurus), woodrats (Neotoma), collared peccaries (Dicolytes tajacu), burrowing owls (Athene cunicularia), Gambel's quail (Callipepla gambelii ), rattlesnakes (Crotalus spp.), Gila monsters (Heloderma suspectum), beetles, spiders, and scorpions. One burrow can host up to 23 desert tortoises – such sharing is more common for desert tortoises of opposite sexes than for desert tortoises of the same sex.[8]

Lifecycle

Reproduction

Tortoises mate in the spring and autumn. Male desert tortoises grow two large white glands around the chin area, called chin glands, that signify mating season. A male circles around female, biting her shell in the process. He then climbs upon the female and insert his penis (a white organ, usually only seen upon careful inspection during mating, as it is hidden inside the male and can only be coaxed out with sexual implication) into the cloaca of a female, which is located around the tail. The male may make grunting noises once atop a female, and may move his front legs up and down in a constant motion, as if playing a drum.[19]

Hatching baby desert tortoise

Months later, the female lays a clutch of four to eight hard-shelled eggs,[20] which have the size and shape of ping-pong balls, usually in June or July. The eggs hatch in August or September. Wild female tortoises produce up to three clutches a year depending on the climate. Their eggs incubate from 90 to 135 days;[4] some eggs may overwinter and hatch the following spring. In a laboratory experiment, temperature influenced hatching rates and hatchling sex. Incubation temperatures from 27 to 31 °C (81 to 88 °F) resulted in hatching rates exceeding 83%, while incubation at 25 °C (77 °F) resulted in a 53% hatching rate. Incubation temperatures less than 31 °C (88 °F) resulted in all-male clutches. Average incubation time decreased from 124.7 days at 25 °C (77 °F) to 78.2 days at 31 °C (88 °F).[21]

The desert tortoise is one of the few known tortoises in existence that has been observed engaging in homosexual intercourse[22] Same-sex intercourse happens in many species, There is no one answer as to why this occurs. One possible explanation for this could be the social component of gaining and establishing dominance.[23]

Maturation

The desert tortoise grows slowly, often taking 16 years or longer to reach about 20 cm (8 in) in length. The growth rate varies with age, location, gender and precipitation. It can slow down from 12 mm/year for ages 4–8 years to about 6.0 mm/year for ages 16 to 20 years. Males and females grow at similar rates; females can grow slightly faster when young, but males grow larger than females.[8]

Desert tortoises reach their reproductive maturity at ages 15 to 20, when they become longer than 18 cm (7 in). However, it is possible for them to mature faster as 10-year-old females that are able to reproduce have been observed.[8]

Activity

Their activity depends on location, peaking in late spring for the Mojave Desert and in late summer to fall in Sonoran Desert; some populations exhibit two activity peaks during one year. Desert tortoises brumate during winters, roughly from November to February–April. Females begin brumating later and emerge earlier than males; juveniles emerge from brumation earlier than adults.[8][24]

Temperature strongly influences desert tortoise activity level. Although desert tortoises can survive body temperatures from below freezing to over 40 °C (104 °F), most activity occurs at temperatures from 26 to 34 °C (79 to 93 °F). The influence of temperature is reflected in daily activity patterns, with desert tortoises 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. The activity generally increases after rainfall.[8]

Although desert tortoises spend the majority of their time in shelter, movements of up to 200 m (660 ft) per day are common. The common, comparatively short-distance movements presumably represent foraging activity, traveling between burrows, and possibly mate-seeking or other social behaviors. Long-distance movements could potentially represent dispersal into new areas and/or use of peripheral portions of the home range.[8]

Lifespan

The lifespan of a desert tortoise can vary from 50 to 80 years.[7] The main causes of mortality in desert tortoises include predators, human-related causes, diseases, and environmental factors such as drought, flooding, and fire.[8]

Desert tortoise with an estimated age of 63 years. Red Rock Canyon National Conservation Area, NV

The annual death rate of adults is typically a few percent, but is much higher for young desert tortoises. Only 2–5% of hatchlings are estimated to reach maturity. Estimates of survival from hatching to 1 year of age for Mojave Desert tortoises range from 47 to 51%. Survival of Mojave Desert tortoises from 1 to 4 years of age is 71–89%.[8]

Diet

Desert tortoise tds.jpg
Desert tortoise.jpg
A young desert tortoise

The desert tortoise is an herbivore. Grasses form the bulk of its diet, but it also eats herbs, annual wildflowers, and new growth of cacti, as well as their fruit and flowers. Rocks and soil are also ingested, perhaps as a means of maintaining intestinal digestive bacteria as a source of supplementary calcium or other minerals. As with birds, stones may also function as gastroliths, enabling more efficient digestion of plant material in the stomach.[8]

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 40% of the tortoise's body weight in water, urea, uric acid, and nitrogenous wastes. During very dry times, they may give off waste as a white paste rather than a watery urine. During periods of adequate rainfall, they drink copiously from any pools they find, and eliminate solid urates. The tortoises can increase their body weight by up to 40% after copious drinking.[25] Adult tortoises can survive a year or more without access to water.[8] 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 burrows in the morning to prevent water loss by evaporation.[25]

A desert tortoise can empty its bladder as one of its defense mechanisms.[26] This can leave the tortoise in a very vulnerable condition in dry areas, since the tortoise will no longer have a backup water supply. If a tortoise is seen in the wild, you should not handle, or pick them up unless they are in imminent danger. Handling of tortoises may have consequences for the animal, such as the development of upper respiratory tract infections.[26]

Predation and conservation status

Ravens, Gila monsters, kit foxes, badgers, roadrunners, coyotes, and fire ants are all natural predators of the desert tortoise. They prey on eggs, juveniles, which are 50–75 mm (2–3 in) 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.[27] The most significant threats to tortoises include urbanization, disease, habitat destruction and fragmentation, illegal collection and vandalism by humans, and habitat conversion from invasive plant species (Brassica tournefortii, Bromus rubens and Erodium spp.).

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 in Arizona, Utah Division of Wildlife Resources Desert Tortoise Adoption Program in Utah, Joshua Tree Tortoise Rescue Project in California, or through Bureau of Land Management in Nevada. When adopted in Nevada, they will have a computer chip embedded on their backs for reference. According to Arizona Game and Fish Commission Rule R12-4-407 A.1, they may be possessed if the tortoises are obtained from a captive source which is properly documented. Commission Order 43: Reptile Notes 3: one tortoise per family member.

The Fort Irwin National Training Center of the US Army expanded into an area that was habitat for about 2,000 desert tortoises, and contained critical desert tortoise habitat (a designation by the US Fish and Wildlife Service). In March 2008, about 650 tortoises were moved by helicopter and vehicle, up to 35 km away.[28] The Desert Tortoise Preserve Committee protects roughly 2,000 hectares (5,000 acres) of desert tortoise habitat from human activity. This area includes 1,760 hectares (4,340 acres) in Kern County, 290 hectares (710 acres) in San Bernardino County, and 32 hectares (80 acres) in Riverside County.[29]

Another potential threat to the desert tortoise's habitat is a series of proposed wind and solar farms.[30] 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. The requests submitted to the Bureau of Land Management total nearly 7,300 km2 (1,800,000 acres).[31]

While tortoises are made to withstand tough conditions and high temperatures, they are unable to cope with the dangers of human development, such as the use of off-roading vehicles. These vehicles that come along at high speeds have the potential to crush and kill tortoises, running over their eggs and burrows and significantly impacting their population. [32]

Human development

Ivanpah solar power project

Concerns about the impacts of the Ivanpah Solar thermal project led the developers to hire some 100 biologists and spend US$22 million caring for the tortoises on or near the site during construction.[33][34] Despite this, in a 2011 Revised Biological Assessment for the Ivanpah Solar Electric Generating System, the Bureau of Land Management anticipated the loss or significant degradation of 1,420 hectares (3,520 acres) of tortoise habitat and the harm of 57–274 adult tortoises, 608 juveniles, and 236 eggs inside the work area, and 203 adult tortoises and 1,541 juvenile tortoises outside the work area. The BLM expects that most of the juvenile tortoises on the project will be killed.[35][36]

Lawsuits

In the summer of 2010, Public Employees for Environmental Responsibility filed a lawsuit against the National Park Service for not having taken measures to manage tortoise shooting in the Mojave National Preserve of California. Biologists discovered numerous gunshot wounds (holes) on dead tortoise shells which could likely have been caused long after natural death as these shells can take five years to disintegrate and make useful targets for well intentioned target shooters. These shells left behind by nature, droughts, roadkill, or vandals may have attracted ravens and threatened the healthy tortoises as any predator bird need only feed once on a small tortoise to remember it as a viable food source.[37] The National Park Service did not take the measures they were urged to. They responded with "We simply do not believe that such regulations are warranted at this time." and no further action has been taken.[38]

Diseases

Reptiles are known to become infected by a wide range of pathogens, which includes viruses, bacteria, fungi, and parasites. More specifically, the G. agassizii population has been negatively affected by upper respiratory tract disease, cutaneous dyskeratosis, herpes virus, shell necrosis, urolithiasis (bladder stones), and parasites.[39][40][41]

Upper respiratory tract disease

Upper respiratory tract disease (URTD) is a chronic, infectious disease responsible for population declines across the entire range of the desert tortoise. It was identified in the early 1970s in captive desert tortoise populations, and later identified in the wild population.[39] URTD is caused by the infectious agents Mycoplasma agassizii and Mycoplasma testudineum, which are bacteria in the class Mollicutes and characterized by having no cell wall and a small genome.[42][43][44]

Mycoplasmae appear to be highly virulent (infectious) in some populations, while chronic, or even dormant in others.[45] The mechanism (whether environmental or genetic) responsible for this diversity is not understood. Infection is characterized by both physiological and behavioral changes: nasal and ocular discharge, palpebral edema (swelling of the upper and/or lower palpebra, or eyelid, the fleshy portion that is in contact with the tortoises eye globe) and conjunctivitis, weight loss, changes in color and elasticity of the integument, and lethargic or erratic behavior.[39][46][47][48] These pathogens are likely transmitted by contact with an infected individual. Epidemiological studies of wild desert tortoises in the western Mojave Desert from 1992 to 1995 showed a 37% increase in M. agassizii.[44] Tests were conducted on blood samples, and a positive test was determined by the presence of antibodies in the blood, defined as being seropositive.

Cutaneous dyskeratosis

Cutaneous dyskeratosis (CD) is a shell disease of unknown origin and has unknown implications on desert tortoise populations. Observationally, it is typified by shell lesions on the scutes. Areas infected with CD appear discolored, dry, rough and flakey, with peeling, pitting, and chipping through multiple cornified layers.[49] Lesions are usually first located on the plastron (underside) of the tortoises, although lesions on the carapace (upper side) and fore limbs are not uncommon. In advanced cases, exposed areas become infected with bacteria, fungi, and exposed tissue and bone may become necrotic.[47][49] CD was evident as early as 1979 and was initially identified on the Chuckwalla Bench Area of Critical Environmental Concern in Riverside County, California.[50] Currently, the means of transmission are unknown, although hypotheses include autoimmune diseases, exposure to toxic chemicals (possibly from mines, or air pollution), or a deficiency disease (possibly resulting from tortoises consuming low-quality invasive plant species instead of high-nutrient native plants).[40][45]

Impacts of disease

Two case studies outlined the spread of disease in desert tortoises. The Daggett Epidemiology of Upper Respiratory Tract Disease project, which provides supporting disease research for the Fort Irwin translocation project, lends an example of the spread of disease. In 2008, 197 health evaluations were conducted, revealing 25.0–45.2% exposure to M. agassizii and M. testudineum, respectively, in a core area adjacent to Interstate 15. The spread of disease was tracked over two years, and clinical signs of URTD spread from the core area to adjacent, outlying locations during this time. Overlaying home ranges and the social nature of these animals, suggests that disease-free individuals may be vulnerable to spread of disease, and that transmission can occur rapidly.[51] Thus, wild tortoises that are close to the urban-wildlife interface may be vulnerable to spread of disease as a direct result of human influence.

The second study indicated that captive tortoises can be a source of disease to wild Agassiz's desert tortoise populations. Johnson et al. (2006) tested blood samples for URTD (n = 179) and herpesvirus (n = 109) from captive tortoises found near Barstow, CA and Hesperia, CA. Demographic and health data were collected from the tortoises, as well from other reptiles housed in the same facility. Of these, 45.3% showed signs of mild disease, 16.2% of moderate disease, and 4.5% of severe disease, and blood tests revealed that 82.7% of tortoises had antibodies to mycoplasma, and 26.6% had antibodies to herpesvirus (which means the tortoises were seropositive for these two diseases, and indicate previous exposure to the causative agents). With an estimated 200,000 captive desert tortoises in California, their escape or release into the wild is a real threat to uninfected wild populations of tortoises. Projections from this study suggest that about 4400 tortoises could escape from captivity in a given year, and with an 82% exposure rate to URTD, the wild population may be at greater risk than previously thought.[52]

Domestic pets

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.[53]

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.

Management activities and spread of disease

Tortoise Monitoring and Research at Joshua Tree National Park

Research

Wild populations of tortoises must be managed effectively to minimize the spread of diseases, which includes research and education. Despite significant research being conducted on desert tortoises and disease, a considerable knowledge gap still exists in understanding how disease affects desert tortoise population dynamics. It is not known if the population would still decline if disease were completely absent from the system; are tortoises more susceptible to disease during drought conditions? How does a non-native diet impact a tortoise's ability to ward off pathogens? What are the causes of immunity exhibited by some desert tortoises? The 2008 USFWS draft recovery plan suggests that populations of tortoises that are uninfected, or only recently infected, should likely be considered research and management priorities. Tortoises are known to show resistance to disease in some areas, an effort to identify and maintain these individuals in the populations is essential. Furthermore, increasing research on the social behavior of these animals, and garnering a greater understanding of how behavior facilitates disease transmission would be advantageous in understanding rates of transmission. Finally, translocation of tortoises should be done with extreme caution; disease is typically furtive and moving individuals or populations of tortoises across a landscape can have unforeseen consequences.[45]

Education

As a corollary to research, education may help prevent captive tortoises from coming into contact with wild populations.[52] Education campaigns through veterinarians, government agencies, schools, museums, and community centers throughout the range of the desert tortoise could limit the spread of tortoise diseases into wild populations. Strategies may include encouraging people to not breed their captive tortoises, ensure that different species of turtles and tortoises are not housed in the same facility (which would help to prevent the spread of novel diseases into the desert tortoise population), ensure captive tortoises are adequately housed to prevent them from escaping into the wild, and to ensure that captive turtles and tortoises are never released into the wild.

Desert tortoises have been severely affected by disease. Both upper respiratory tract disease and cutaneous dyskeratosis have caused precipitous population declines and die-offs across the entire range of this charismatic species. Both of these diseases are extremely likely to be caused by people, and URTD is easily linked with people releasing captive tortoises into the wild. The combination of scientific research and public education is imperative to curb the spread of disease and aid the tortoise in recovery.

State reptile

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

References

Public Domain This article incorporates public domain material from Gopherus agassizii . United States Forest Service.

  1. ^ Berry, K.H.; Allison, L.J.; McLuckie, A.M.; Vaughn, M.; Murphy, R.W. (2021). "Gopherus agassizii". IUCN Red List of Threatened Species. 2021: e.T97246272A3150871. doi:10.2305/IUCN.UK.2021-2.RLTS.T97246272A3150871.en. Retrieved February 19, 2022.
  2. ^ "Appendices". CITES. Convention on International Trade in Endangered Species of Wild Fauna and Flora. May 4, 2023. Retrieved May 11, 2023. Note: Protected as a member of the Testudinidae.
  3. ^ Fritz, Uwe; Havaš, Peter (2007). "Checklist of Chelonians of the World" (PDF). Vertebrate Zoology. 57 (2): 280. doi:10.3897/vz.57.e30895. S2CID 87809001. Archived from the original (PDF) on May 1, 2011. Retrieved May 29, 2012.
  4. ^ a b c Jones, Mike. Gopherus agassizii Cooper 1863 [sic] (California) Desert Tortoise. Encyclopedia of Life.
  5. ^ Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN 978-1-4214-0135-5. (Gopherus agassizii, p. 2).
  6. ^ "Gale - Product Login". galeapps.gale.com. Retrieved December 10, 2022.
  7. ^ a b "Desert Tortoise Life History".
  8. ^ a b c d e f g h i j k l m n o Gopherus agassizii. United States Forest Service. fs.fed.us
  9. ^ Genetic Analysis Splits Desert Tortoise into Two Species Archived January 2, 2017, at the Wayback Machine. US Geological Survey (2011-06-28). Retrieved on 2019-08-22.
  10. ^ Murphy, Robert; Berry, Kristin; Edwards, Taylor; Leviton, Alan; Lathrop, Amy; Riedle, J. Daren (June 28, 2011). "The dazed and confused identity of Agassiz's land tortoise, Gopherus agassizii (Testudines: Testudinidae) with the description of a new species and its consequences for conservation". ZooKeys (113): 39–71. doi:10.3897/zookeys.113.1353. ISSN 1313-2970. PMC 3187627. PMID 21976992.
  11. ^ a b Edwards T, Karl AE, Vaughn M, Rosen PC, Torres CM, Murphy RW (2016). "The desert tortoise trichotomy: Mexico hosts a third, new sister-species of tortoise in the Gopherus morafkaiG. agassizii group". ZooKeys (562): 131–158. doi:10.3897/zookeys.562.6124. PMC 4768471. PMID 27006625.
  12. ^ Wilson, Don E.; Burnie, David (2005). Animal: The Definitive Visual Guide to the World's Wildlife. New York City: DK [Dorling Kindersley] Publishing. 624 pp. ISBN 978-0-7894-7764-4.
  13. ^ Jirik, Kate. "LibGuides: Desert Tortoises (Gopherus agassizii) Fact Sheet: Physical Characteristics". ielc.libguides.com. Retrieved December 10, 2022.
  14. ^ "Desert Tortoise". The Nature Conservancy. Retrieved December 10, 2022.
  15. ^ "DROUGHT: Lack of water threatens desert tortoise". March 21, 2014.
  16. ^ a b Murphy, Robert; Berry, Kristin; Edwards, Taylor; Leviton, Alan; Lathrop, Amy; Riedle, J. Daren (2011). "The dazed and confused identity of Agassiz's land tortoise, Gopherus agassizii (Testudines: Testudinidae) with the description of a new species and its consequences for conservation". ZooKeys (113): 39–71. doi:10.3897/zookeys.113.1353. PMC 3187627. PMID 21976992.
  17. ^ "Federal agencies partner to conserve Mojave desert tortoises". VVNG. Victor Valley News Group. December 28, 2021. Retrieved December 29, 2021.{{cite news}}: CS1 maint: url-status (link)
  18. ^ Glass-Godwin, Lenela (April 2002). "Desert Survivor?". Ranger Rick. p. 16.
  19. ^ Tortoise Adoption Program – Care and Husbandry. Desertmuseum.org. Retrieved on 2013-01-06.
  20. ^ Desert Tortoise wildlife information. DesertUSA. Retrieved on 2013-01-06.
  21. ^ Lewis-Winokur, Vanessa; Winokur, Robert M. (1995). "Incubation temperature affects sexual differentiation, incubation time, and posthatching survival in desert tortoises (Gopherus agassizii )". Canadian Journal of Zoology. 73 (11): 2091–2097. doi:10.1139/z95-246.
  22. ^ Biol. Exuberance: Desert Tortoise - Bagemihl (1999 AD), pages 232, 664
  23. ^ Rodrigues, João Fabrício Mota; Liu, Yuxiang (May 1, 2016). "An overview of same-sex mounting in turtles and tortoises". Journal of Ethology. 34 (2): 133–137. doi:10.1007/s10164-015-0456-2. ISSN 1439-5444. S2CID 254145807.
  24. ^ Deane K. (2018). "The 'hibernation' process and post 'hibernation' care of tortoises". Veterinary Nursing Journal. 33 (7): 197–200. doi:10.1080/17415349.2018.1466670. S2CID 59535431.
  25. ^ a b Auffenberg, Walter (1969). Tortoise Behavior and Survival. Chicago: Rand McNally. OCLC 2583084.
  26. ^ a b "Desert Tortoise (Gopherus agassizii)". Mojave National Preserve California. National Park Service. March 21, 2022. Retrieved May 11, 2023.
  27. ^ Sahagun, Louis (June 10, 2019). "These tortoise-killing ravens are so smart, scientists must use drones to stop them". Los Angeles Times. Retrieved June 10, 2019.
  28. ^ Sahagun, Louis (2008-10-11) "Army suspends relocation of Ft. Irwin tortoises". Los Angeles Times
  29. ^ Connor, Michael J., and Mark Massar, "Megadump Initiative Threat to DTNA" and "2005 Annual Report Desert Tortoise Preserve Committee Accomplishments & Activities", "Tortoise Tracks." April 2006
  30. ^ Simon, Richard (2009-03-25) Feinstein wants desert swath off-limits to solar, wind projects, Los Angeles Times
  31. ^ Woody, Todd (2009-07-13) A Solar Land Rush, The New York Times
  32. ^ Glass-Godwin (April 2002). "DESERT SURVIVOR?". Science Reference Center.
  33. ^ Dini, Jack (2010-10-31) Desert Tortoises Get Trumped by California's Solar Plants. Hawaii Reporter
  34. ^ Desert Tortoise Care at the Ivanpah Solar Project Archived 2012-06-09 at the Wayback Machine. ivanpahsolar.com (2012-03-06)
  35. ^ Bureau of Land Management (2011-4-19) Revised Biological Assessment for the Ivanpah Solar Electric Generating System (Ivanpah SEGS) Project Archived 2013-10-21 at the Wayback Machine. U.S. Department of the Interior
  36. ^ Ertz, Brian (2011-4-29) Ivanpah solar project would disturb thousands of desert tortoises. The Wildlife News
  37. ^ Stade, Kristen (2010-07-28) Lawsuit to protect varmints in Mojave National Preserve Archived October 21, 2013, at the Wayback Machine, Peer
  38. ^ Jarvis Mojave letter 2011
  39. ^ a b c Jacobson, E. R., J. M. Gaskin, M. B. Brown, R. K. Harris, C. H. Gardiner, J. L. Lapointe, H. P. Adams, and C. Reggiardo (1991). "Chronic upper respiratory tract disease of free ranging desert tortoises (Xerobates agassizii )". Journal of Wildlife Diseases. 27 (2): 296–316. doi:10.7589/0090-3558-27.2.296. PMID 2067052. S2CID 42473017.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  40. ^ a b Jacobson, E. R.; T. J. Wronski; J. Schumacher; C. Reggiardo & K. H. Berry (1994). "Cutaneous dyskeratosis in free ranging desert tortoises, Gopherus agassizii, in the Colorado Desert of Southern California". Journal of Zoo and Wildlife Medicine. 25 (1): 68–81. JSTOR 20095336.
  41. ^ Berry, K. H., E. K. Spangenberg, B. L. Homer, and E. R. Jacobson (2002). "Deaths of desert tortoises following periods of drought and research manipulation" (PDF). Chelonian Conservation and Biology. 4: 436–448.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  42. ^ Brown, M. B., I. M. Schumacher, P. A. Klein, K. Harris, T. Correll, and E. R. Jacobson (1994). "Mycoplasma agassizii causes upper respiratory tract disease in the desert tortoise". Infection and Immunity. 62 (10): 4580–4586. doi:10.1128/iai.62.10.4580-4586.1994. PMC 303146. PMID 7927724.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  43. ^ Berry, K. H. and J. Van Abbema. 1997. Demographic consequences of disease in two desert tortoise populations in California, USA. Proceedings: conservation, restoration, and management of tortoises and turtles – an international conference 11–16 July 1993, State University of New York, Purchase, New York, USA.: 91–99
  44. ^ a b Brown, M. B., K. H. Berry, I. M. Schumacher, K. A. Nagy, M. M. Christopher, and P. A. Klein (1999). "Seroepidemiology of upper respiratory tract disease in the desert tortoise in the western Mojave Desert of California". Journal of Wildlife Diseases. 35 (4): 716–727. doi:10.7589/0090-3558-35.4.716. PMID 10574531. S2CID 22509874.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  45. ^ a b c Draft revised recovery plan for the Mojave population of the desert tortoise (Gopherus agassizii ). U.S. Fish and Wildlife Service, California and Nevada Region, Sacramento, California (2008).
  46. ^ Schumacher, I. M.; M. B. Brown; E. R. Jacobson; B. R. Collins & P. A. Klein (1993). "Detection of antibodies to a pathogenic mycoplasma in desert tortoises (Gopherus agassizii ) with upper respiratory tract disease". Journal of Clinical Microbiology. 31 (6): 1454–1460. doi:10.1128/jcm.31.6.1454-1460.1993. PMC 265561. PMID 8314986.
  47. ^ a b Homer, B. L.; K. H. Berry; M. B. Brown & G. Ellis, E. R. Jacobson (1998). "Pathology of diseases in wild desert tortoises from California". Journal of Wildlife Diseases. 34 (3): 508–523. doi:10.7589/0090-3558-34.3.508. PMID 9706560. S2CID 2657867.
  48. ^ Berry, K. H.; M. M. Christopher (2001). "Guidelines for the field evaluation of desert tortoise health and disease". Journal of Wildlife Diseases. 37 (3): 427–450. doi:10.7589/0090-3558-37.3.427. PMID 11504217. S2CID 6952651.
  49. ^ a b Homer, B. L.; C. Li; K. H. Berry; N. D. Denslow; E. R. Jacobson; R. H. Sawyer & J. E. Williams (2001). "Soluble scute proteins of healthy and ill desert tortoises (Gopherus agassizii )". American Journal of Veterinary Research. 62 (1): 104–110. doi:10.2460/ajvr.2001.62.104. PMID 11197546.
  50. ^ Jacobson, E. R. (1994). "Causes of mortality and diseases in tortoises – A review". Journal of Zoo and Wildlife Medicine. 25 (1): 2–17. JSTOR 20095329.
  51. ^ Mack, J. and K. H. Berry. 2009. Development of an epidemiological model of upper respiratory tract disease (Mysoplasmosis) in desert tortoises using the Daggett study area: Year 2, 2008. Proceedings of the thirty-fourth annual meeting and symposium. The desert tortoise council
  52. ^ a b Johnson, A. J.; D. J. Morafka & E. R. Jacobson (2006). "Seroprevalence of Mycoplasma agassizii and tortoise herpesvirus in captive desert tortoises (Gopherus agassizii ) from the Greater Barstow Area, Mojave Desert, California" (PDF). Journal of Arid Environments. 67: 192–201. Bibcode:2006JArEn..67..192J. doi:10.1016/j.jaridenv.2006.09.025. Archived from the original (PDF) on May 16, 2013. Retrieved January 6, 2013.
  53. ^ Edwards, T., C. J. Jarchow, C. A. Jones, and K. E. Bonine (2010). "Tracing Genetic Lineages of Captive Desert Tortoises in Arizona". Journal of Wildlife Management. 74 (4): 801–807. doi:10.2193/2009-199. S2CID 86409153.{{cite journal}}: CS1 maint: multiple names: authors list (link)

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Desert tortoise: Brief Summary

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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 is the official state reptile in California and Nevada.

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.

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