Geographic Range 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. (Van Devender, 2002) Biogeographic Regions

nearctic native



Physical Description 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. (Arizona-Sonora Desert Museum's Tortoise Adoption Program, 2003; Averill-Murray, et al., 2002b) Other Physical Features

ectothermic

bilateral symmetry Sexual Dimorphism

male larger

sexes shaped differently Range mass 11 to 23 kg 24.23 to 50.66 lb

Range length 15 to 36 cm 5.91 to 14.17 in

Lifespan/Longevity 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. (Arizona-Sonora Desert Museum's Tortoise Adoption Program, 2003; Germano, et al., 2002) Range lifespan

Status: wild 50 to 80 years

Typical lifespan

Status: wild 0 to 20 years

Average lifespan

Status: wild <1 years

Economic Importance for Humans: Positive 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. (Arizona-Sonora Desert Museum's Tortoise Adoption Program, 2003; Jarchow, et al., 2002; Nabhan, 2002) Positive Impacts

pet trade

food

body parts are source of valuable material

source of medicine or drug

Economic Importance for Humans: Negative There are no known negative impacts of desert tortoises on humans.

Contributors Allison Poor (author), University of Michigan-Ann Arbor. Gregory Crozier (author), University of Michigan-Ann Arbor.

Glossary Nearctic living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico. acoustic uses sound to communicate bilateral symmetry having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria. chemical uses smells or other chemicals to communicate crepuscular active at dawn and dusk cryptic having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect. desert or dunes in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots. diurnal active during the day, 2. lasting for one day. dominance hierarchies ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates drug a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease ectothermic animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature folivore an animal that mainly eats leaves. food A substance that provides both nutrients and energy to a living thing. forest forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality. fossorial Referring to a burrowing life-style or behavior, specialized for digging or burrowing. frugivore an animal that mainly eats fruit herbivore An animal that eats mainly plants or parts of plants. hibernation the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals. iteroparous offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes). motile having the capacity to move from one place to another. mountains This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation. native range the area in which the animal is naturally found, the region in which it is endemic. oviparous reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body. pet trade the business of buying and selling animals for people to keep in their homes as pets. polygynandrous the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females. scent marks communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them scrub forest scrub forests develop in areas that experience dry seasons. seasonal breeding breeding is confined to a particular season sedentary remains in the same area sexual reproduction that includes combining the genetic contribution of two individuals, a male and a female solitary lives alone sperm-storing mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females. tactile uses touch to communicate temperate that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle). terrestrial Living on the ground. threatened The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU). visual uses sight to communicate